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Speaker 1: Welcome to Stuff to Blow Your Mind production of iHeartRadio.

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Speaker 2: Hey A, you welcome to Stuff to Blow your Mind.

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Speaker 2: My name is Robert Lamb.

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Speaker 3: And I am Joe McCormick. And we're back with Part

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Speaker 3: two in our series on the nineteenth century British naturalist

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Speaker 3: Alfred Russell Wallace and on the Wallace Line, the faunal

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Speaker 3: boundary in the Malay Archipelago that bears his name. If

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Speaker 3: you haven't heard part one yet, I would recommend you

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Speaker 3: go back and listen to that one first. But in

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Speaker 3: part one we started off with a general character sketch

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Speaker 3: of Wallace. He's a man of many adventurers and many opinions,

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Speaker 3: best known today for being the other guy who discovered

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Speaker 3: evolution by natural selection. He came up with a slightly

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Speaker 3: different version of the theory of natural selection around the

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Speaker 3: same time Darwin did, just some sort of differences of emphasis. Basically,

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Speaker 3: Zarwin's writings ultimately proved more influential in convincing his peers

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Speaker 3: on the reality of common descent and on articulating the

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Speaker 3: mechanisms by which species evolved. Wallace was also something of

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Speaker 3: a celebrity at his time. It's not like one of

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Speaker 3: those tragic cases of somebody, you know, somebody else who

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Speaker 3: also came across a great idea but was just like

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Speaker 3: totally forgotten. Wallace was kind of a celebrity, especially because

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Speaker 3: of the quality of his writing, and that would be

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Speaker 3: in books like The Malay Archipelago, published in eighteen sixty nine,

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Speaker 3: in which he vividly described his earlier travels in that

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Speaker 3: region of the world, including lots of very well observed

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Speaker 3: biological and cultural detail. And we read a bunch of

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Speaker 3: selections from that book in the last episode, and they

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Speaker 3: are kind of it's somewhat magical to read.

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Speaker 2: Yeah. Absolutely, again, you can see why this book was

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Speaker 2: such a success, and it was read by other naturalists,

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Speaker 2: but also just members of the general public who are

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Speaker 2: interested in the topic, interested in far away lands and

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Speaker 2: in the net.

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Speaker 3: Yeah. So we read some selections from the chapters where

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Speaker 3: he goes exploring, initially against his will, by the way,

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Speaker 3: on the islands of Bali and Lombach. And this included

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Speaker 3: everything from these evocative descriptions of the land itself, talking

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Speaker 3: about the terrorist agriculture and the way the fields are

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Speaker 3: irrigated and all that, two discussions about the geographic distribution

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Speaker 3: of ghosts to complaints about how hard it is to

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Speaker 3: do science when everything smells putrid and discovered in ants.

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Speaker 2: Right now, To be clear, it was putrid smelling because

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Speaker 2: of all the birds skinning gsty This is not a

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Speaker 2: general comment on the region or the people's there. This

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Speaker 2: was his nest.

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Speaker 3: No, no, it was not like Lombox smells bad. It

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Speaker 3: was my room smells bad. Yea yeah. Also we talked

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Speaker 3: about the concept of biogeography, the study of what lives,

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Speaker 3: where and why. Wallace is considered a very important founding

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Speaker 3: figure in biogeography, with one of his most enduring observations

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Speaker 3: being what is now called in his honor, the Wallas Line,

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Speaker 3: an invisible boundary passing in the ocean between the islands

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Speaker 3: of originally Borneo and Sulawesi, and even more astonishingly in

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Speaker 3: the tiny narrow strait between Bali and Lombach, which marks

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Speaker 3: the westernmost boundary of a lot of characteristic Australasian fauna marsupials,

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Speaker 3: cockatoos and things like that. So we are back today

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Speaker 3: to talk more about Wallace and the Wallas Line. Now,

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Speaker 3: one thing I think we've got to do before we

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Speaker 3: move on any further is just a bit of clean up, because,

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Speaker 3: as I mentioned in the last episode, our model of

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Speaker 3: the Wallas line has undergone some major revisions since Wallace

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Speaker 3: first proposed it in the mid nineteenth century. I'm not

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Speaker 3: going to do a whole detailed play by play of

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Speaker 3: the shifting history of the line, but for a brief

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Speaker 3: summary of developments, I was just looking at the abstract

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Speaker 3: of a paper called Wallace's Line WALLACEI and Associated Divides

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Speaker 3: and Areas History of a tortuous tangle of ideas and labels.

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Speaker 3: This is by Ali and Heene, published in the journal

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Speaker 3: Biological Reviews in twenty twenty one. So the authors go

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Speaker 3: through the concept which we discussed in the last episode,

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Speaker 3: the idea of a faunnel boundary being basically a place

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Speaker 3: where you find animals mainly of one sort on one

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Speaker 3: side of the line and animals mainly of a different

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Speaker 3: sort on the other side of the line. And this

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Speaker 3: raises questions how did it end up like that? The

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Speaker 3: authors write that the earliest dividing lines in this region

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Speaker 3: were considered quite sharp, especially the line Wallace drew in

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Speaker 3: eighteen sixty three, and this was based on looking at

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Speaker 3: the distribution of land mammals and some birds. This is

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Speaker 3: the line we've been talking about so far, passing between

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Speaker 3: Bali and Lombach, with Asian animals found west from the

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Speaker 3: west coast or from the eastern coast of Bali and

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Speaker 3: Australasian animals running east from Lombak. This particular theoretical boundary

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Speaker 3: proved very influential and it got you know, reproduced in

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Speaker 3: a lot of texts. It was baked into maps and

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Speaker 3: plates and stuff all over so like it had a

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Speaker 3: big cultural footprint, and within the discipline of biogeography it

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Speaker 3: came to be seen as something of a fixed marker

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Speaker 3: in nature, maybe like the tree line on a mountain.

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Speaker 3: But over time it also became obvious to experts in

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Speaker 3: the field that there were a lot of exceptions to

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Speaker 3: the Wallace line, especially a lot of Asian fauna found

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Speaker 3: east of the so called line. And this would not

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Speaker 3: have been very surprising to Wallace himself, I think, who

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Speaker 3: argued that biogeographic boundaries were all to some extent permeable,

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Speaker 3: But it might have been more surprising to people who

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Speaker 3: got a you know, a map printed with a line

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Speaker 3: on it that says animals do not cross this line. Yeah.

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Speaker 3: By later in the nineteenth century, many biogeographers had started

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Speaker 3: to think about zones instead of life. For example, there

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Speaker 3: is now a biogeographic region known as Wallace Sea. I've

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Speaker 3: also heard it pronounced to Wallasia, so Wallasia or Wallacea

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Speaker 3: named after again Alfred Russell Wallace. This region was sort

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Speaker 3: of proposed in the nineteen twenties, which is a faunal

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Speaker 3: transition zone where you essentially have Australasian fauna to the

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Speaker 3: east of the zone, Asian fauna to the west of

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Speaker 3: the zone, and more of a mix within. Though the

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Speaker 3: western boundary of Wallacea is still basically Wallace's line, passing

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Speaker 3: between Bali and Lombach and in between Borneo and Sulawesi.

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Speaker 3: So we're actually here creeping a bit back toward that

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Speaker 3: gradual transition idea of animal ranges that we talked about

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Speaker 3: in part one. Though some of the divisions you see,

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Speaker 3: especially between Bali and Lombach, are still actually quite striking,

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Speaker 3: So Rabbi included for you to look at in our outline.

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Speaker 3: Here an illustration from one of the papers I was

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Speaker 3: looking at, the region highlighted in red, and all the

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Speaker 3: islands within that is what is generally considered Wallacea today.

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Speaker 2: Yeah, and on this map here it looks like a

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Speaker 2: big old heart, like a big old Valentine. They even

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Speaker 2: colored it.

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Speaker 3: Red Happy Valentine's Day. You get some marsupials.

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Speaker 2: Yeah, and I was in the eastern part of this

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Speaker 2: very region.

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Speaker 3: Okay. So Ali and Heeney write that in the last

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Speaker 3: decade before their paper, even more new regions and boundary

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Speaker 3: modifications have been proposed, and the authors paint a truly

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Speaker 3: headache inducing picture of the historical understanding of all this.

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Speaker 3: As they say in their title, it is a tortuous

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Speaker 3: tangle of ideas and labels. For example, I'm just going

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Speaker 3: to read one section of their abstract to give you

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Speaker 3: an idea quote. Wallace's eighteen sixty three line is not

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Speaker 3: the one he finally settled upon in nineteen ten. Its

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Speaker 3: path around Sulawesi was transferred from the west to the

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Speaker 3: east of the island, ideally Huxley's divide, And that's referring

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Speaker 3: to Thomas Henry Huxley, who proposed a modification to this

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Speaker 3: to the where the line goes. Hucks divide eighteen sixty

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Speaker 3: eight should carry his name rather than Wallace's. The latter

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Speaker 3: never accepted the proposition. Lydacer's line of eighteen ninety six

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Speaker 3: ought to be labeled the hil Prin Lydacer line in

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Speaker 3: recognition of Angelo Hilprin's eighteen eighty seven contribution concerning transition zones. Ideally,

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Speaker 3: Wallacea should correspond to its original nineteen twenty four description,

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Speaker 3: which incorporated the Philippine Islands bar the Palawan group. Notably,

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Speaker 3: though a smaller form introduced by Darlington in nineteen fifty

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Speaker 3: seven used frequently from nineteen ninety eight onwards, in which

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Speaker 3: all of the Philippine Islands are excluded, is entrenched within

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Speaker 3: the recent literature, but this is often without evident justification.

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Speaker 3: It should also be recognized that the reduced meaning southern

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Speaker 3: Wallacea area was effectively defined by hilprint in eighteen eighty seven,

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Speaker 3: but was then labeled the Austro Malaysian transition zone. So

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Speaker 3: it's a mess. This is one reason why I've really

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Speaker 3: enjoyed researching for the episodes. But like when I was

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Speaker 3: reading all this stuff for the last episode, I was

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Speaker 3: just like, ah, I can't.

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Speaker 2: Yeah, I mean it's again, It's it's not like if

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Speaker 2: you take a kangaroo and have it walk over the

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Speaker 2: Wallas line, it will explode. Like, so, there's no it

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Speaker 2: becomes very difficult to actually test out some of these things.

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Speaker 2: It's based on a number of observations and factors.

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Speaker 3: Well, these modifications absolutely are based on empirical observations. I mean,

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Speaker 3: it's not just people kind of jousting around about absolutely nothing.

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Speaker 3: Like there are reasons based on the different kinds of

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Speaker 3: fauna that have been observed and the underlying theory about

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Speaker 3: like the geologic causes and so forth. But unfortunately, the

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Speaker 3: theoretical definition of the Wallace line and Wallace are kind

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Speaker 3: of a mess. There have been a few details that

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Speaker 3: have persisted, but there has not been clear or consistent

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Speaker 3: agreement across time on where to place the boundaries, whether

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Speaker 3: it's a line or a zone, to call those lines

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Speaker 3: and zones, and what exactly they mean. So you might

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Speaker 3: be wondering based on that, like, well, if you know,

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Speaker 3: if we can't agree on what we're talking about, is

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Speaker 3: the idea of a faunal boundary here just useless or

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Speaker 3: is it nonsense? I think the answer is no. I mean,

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Speaker 3: for one thing, some of this confusion is historical, Like

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Speaker 3: there have been general trends in how the idea is

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Speaker 3: getting refined over time. So there's nothing wrong with that.

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Speaker 3: I mean, obviously ideas get updated. But some of the

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Speaker 3: confusion is also because we're trying to figure out what

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Speaker 3: exactly is being proposed here, and so like you have

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Speaker 3: gotten away from the idea of a simple boundary line

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Speaker 3: on a map that you know, where you have one

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Speaker 3: thing on one side and one on another and more

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Speaker 3: into say the idea of a transition zone. And it

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Speaker 3: is absolutely still safe to say that there is something

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Speaker 3: very interesting with reference to biogeography that's happening in the

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Speaker 3: islands between Borneo and Bali to the west and Papa

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Speaker 3: New Guinea to the east, let's say, and this, this

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Speaker 3: boundary line or transition zone can tell us a lot

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Speaker 3: about the history of life on the surrounding continents in

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Speaker 3: the history of the Earth itself.

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Speaker 2: Yeah, and this is what they were trying to figure

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Speaker 2: out obviously in the late nineteenth century. But so we'll

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Speaker 2: be discussing here they didn't have all the information they

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Speaker 2: needed in order to really understand and to make what

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Speaker 2: we would think of as a modern theory as to

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Speaker 2: why it was like this.

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Speaker 3: That's right, and so that brings us to the question

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Speaker 3: of what causes the boundary. We raised this in the

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Speaker 3: last episode, but didn't really have time to answer it.

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Speaker 3: What causes the faunal boundary between the islands of say

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Speaker 3: Bali and Lombok. Why do you get mostly one set

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Speaker 3: of animals on Lombach and a fairly different set on Bali.

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Speaker 3: Even though the strait between these two islands is just

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Speaker 3: a few dozen kilometers wide, it's like it's barely any

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Speaker 3: ocean at all. And also the environment on the two

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Speaker 3: islands is very similar, so it seems like you would

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Speaker 3: expect that the animals find on one to be the

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Speaker 3: same as the ones you'd find on the other, right, right,

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Speaker 3: So to summarize sort of the original mainstream explanation, and

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Speaker 3: there will be some additions to this as we move on.

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Speaker 3: In this episode, Wallace understood the cause of the apparent

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Speaker 3: faunnel boundary between Bali and Lombach to be a result

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Speaker 3: of geological history. This is a core insight of biogeography.

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Speaker 3: Studying where animals live can tell us not only about

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Speaker 3: the animals, but also about the land, and there are

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Speaker 3: actually really awesome examples of this. If you get into

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Speaker 3: the way paleontology has helped interact with the geohistory of

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Speaker 3: Earth like fossil organisms from hundreds of millions of years

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Speaker 3: ago that appeared to live only in Africa and South America. Huh.

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Speaker 3: One example of this, there's this early Permian reptile called Mesosaurus,

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Speaker 3: the sort of shaped like a little crocodile. It lived

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Speaker 3: exclusively in freshwater lakes and rivers almost three hundred million

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Speaker 3: years ago, and its remains have only been found in

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Speaker 3: southern South America and southern Africa. Wait a minute, If

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Speaker 3: it only lived in fresh water like lakes and rivers,

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Speaker 3: how did it give from Africa to South America and

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Speaker 3: as far as we can tell nowhere in between. And

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Speaker 3: then you've got other examples like this, like there's a

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Speaker 3: Triassic land based therapsid called Syno Nathas, also found in

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Speaker 3: the fossil record of South America and Africa, among a

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Speaker 3: few other equally baffling locations like Antarctica. These examples showed,

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Speaker 3: along with lots of other evidence that we have now,

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Speaker 3: that these two land masses used to be one. That

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Speaker 3: you know, the range was one continuous range hundreds of

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Speaker 3: millions of years ago, and these animals died, their remains

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Speaker 3: were posited, they were quickly buried, they became fossilized, and

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Speaker 3: then the land split apart and the Atlantic Ocean in

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Speaker 3: between was formed. So that's one example of how biogeography

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Speaker 3: can tell us not just about the animals, but also

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Speaker 3: about the land. Coming back to Wallace. At the time

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Speaker 3: Wallace lived, plate tectonics was not yet an accepted theory.

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Speaker 3: In fact, it wasn't even really proposed in a form

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Speaker 3: that would be recognizable to us until I think, like

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Speaker 3: the nineteen tens around them, and it wouldn't be widely

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Speaker 3: accepted by geologists until the nineteen sixties. So Wallace in

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Speaker 3: his contemporaries did not know that the continents and land

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Speaker 3: masses of the Earth moved around, splitting and rejoining on

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Speaker 3: the timescale of tens or hundreds of millions of years.

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Speaker 3: But Wallace did know that the the surface of the

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Speaker 3: Earth could change drastically due to other factors, and one

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Speaker 3: of those was climate. Climate patterns determine Earth's average temperature

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Speaker 3: and weather, and in instances long ago, when Earth's surface

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Speaker 3: was colder and more of Earth's water was locked up

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Speaker 3: in polar ice caps, sea levels were lower much lower.

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Speaker 3: As a result, many areas that are now ocean were

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Speaker 3: once dry land, and many parts of the world that

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Speaker 3: are now islands surrounded by shallow seas were once continuous

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Speaker 3: land masses, allowing land animals to cross freely between them,

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Speaker 3: which is how you end up with large land mammals

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Speaker 3: like tigers and elephants living on what appeared to be

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Speaker 3: remote islands. In most cases, they didn't swim there, certainly

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Speaker 3: not in stable breeding populations. They crossed on land at

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Speaker 3: a time when there was a land bridge, and for

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Speaker 3: the most part, Wallace correctly identified that many islands east

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Speaker 3: of the line of the Wallas line were once joined

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Speaker 3: as a single land mass with Australia, this land mass

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Speaker 3: now known as the paleocontinent Sahul, with islands west of

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Speaker 3: the line once being part of a more continuous land

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Speaker 3: mass with Asia, now known as Sunda. However, just because

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Speaker 3: islands are close to each other does not mean a

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Speaker 3: land bridge always forms between them when sea levels drop.

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Speaker 3: What Wallace did not know for sure, but what later

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Speaker 3: proved perfectly consistent with his observation of the faunal boundary,

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Speaker 3: is that between Bali and Lombach there is a deep

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Speaker 3: ocean trench. The Strait of Lombach is not wide again,

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Speaker 3: it's just a few kilometers wide at the narrowest point,

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Speaker 3: but it is very deep, meaning that even when sea

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Speaker 3: levels were at their lowest, a land bridge between the

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Speaker 3: two islands never formed, and thus there was much less

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Speaker 3: opportunity for land based animals to colonize one island from

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Speaker 3: the other. The reason for the existence of this deep

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Speaker 3: ocean trench, by the way, brings us back once again

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Speaker 3: to plate tectonics. This trench is the meeting point between

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Speaker 3: two plates where one is undergoing subduction, meaning it's being

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Speaker 3: driven down underneath the other plate at the meeting point.

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Speaker 3: Subduction zones tend to create deep ocean trenches along with

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Speaker 3: other geologic activity like earthquakes and volcanic eruptions, so plate

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Speaker 3: tectonics also it explains that the deep ocean trench that

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Speaker 3: keeps the islands apart and never forming a land bridge,

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Speaker 3: but it Plate tectonics also helps explain why there were

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Speaker 3: such different collections of animals on Sunda and so Whul.

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Speaker 3: To begin with, they were once separated by much more

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Speaker 3: ocean than they are now Sahul And again, this is

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Speaker 3: modern day Australia and New Guinea and some other associated islands.

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Speaker 3: This was one part of the same land mass as

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Speaker 3: what is now Antarctica, and over tens of millions of

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Speaker 3: years in isolation from the Afro Eurasian and American land masses,

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Speaker 3: this ancient continent experienced its own distinct branch of evolution,

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Speaker 3: giving us, for example, marsupials instead of the placental mammals

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Speaker 3: that you would find on the rest of the globe.

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Speaker 3: It was only a little more than thirty million years

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Speaker 3: ago that sa who will actually broke away from the

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Speaker 3: land mass that would become Antarctica, and so who will?

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Speaker 3: After that, slowly drifted north and then collided with the

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Speaker 3: continental plates of Southeast Asia, giving us the arrangement of

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Speaker 3: islands that we see today in Indonesia and the Malay Archipelago.

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Speaker 3: And some of the islands we see in that archipelago

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Speaker 3: were created by the collision. They were raised up. But

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Speaker 3: again at the place where the plates collide we get

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Speaker 3: a subduction zone and a deep ocean trench, which means

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Speaker 3: even though the islands are now close, land bridge is

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Speaker 3: never formed between Bali and Lombach, So even though they

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Speaker 3: have been close, now for millions of years. There is

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Speaker 3: relatively little interchange of large land animals back and forth. However,

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Speaker 3: there is some interchange, and as we've discussed already, all

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Speaker 3: faunnel boundaries are to some extent permeable, and studying those

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Speaker 3: crossover examples can tell us even more about how this

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Speaker 3: boundary works. I'm going to come back to that in

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Speaker 3: a bit, but Rob, I think you also had some

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Speaker 3: good stuff about how this interacts with plate tectonics.

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Speaker 2: Yeah, and just getting a little bit into a little

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Speaker 2: more into just sort of the history of Wallace and

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Speaker 2: Darwin in trying to figure out why the Wallace line

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Speaker 2: seemed to be a thing, how this boundary worked, and

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Speaker 2: what were the factors behind it. Again, as you mentioned,

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Speaker 2: you know, we didn't have continental drift in a sort

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Speaker 2: of crystallized form until nineteen twelve, and we didn't have

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Speaker 2: plate tectonics until the nineteen sixties, again in its more

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Speaker 2: crystallized accepted form. At the time, a leading approach to

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Speaker 2: understanding all this was a theory of continental extensionism, which

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Speaker 2: Radical by Nature author James T. Costa describes as land

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Speaker 2: bridges on steroids. So you know, we've been talking here

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Speaker 2: about the concept of land bridges and how they work,

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Speaker 2: and again they're certainly real. The Isthmus of Panama is

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Speaker 2: a current land bridge, lost land bridges once connected India

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Speaker 2: and Sri Lanka, and a land mass known as the

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Speaker 2: Basian Plaine once connected Tasmania to mainland Australia. And of

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Speaker 2: course we've also talked about the now submerged north Sea

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Speaker 2: land mass of Doggerland.

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Speaker 3: Ah. Yeah, we did a couple of episodes on that.

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Speaker 3: Go back and look them up. Yeah, sometime last year.

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Speaker 2: So land bridges as an explanation for certain regional slash

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Speaker 2: local examples of geological distribution, that's all good. The problem

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Speaker 2: with continental extensionism as it was used at the time

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Speaker 2: was it leaned heavily on this as the prime, or

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Speaker 2: even the only way that many forms of fauna had spread,

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Speaker 2: employing actual and likely examples of land bridges, you know,

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Speaker 2: sunken land masses and shallow seas, but then adding in

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Speaker 2: other necessary lost land masses and land bridges as required

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Speaker 2: to fill in the gaps, often with little or no

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Speaker 2: actual evidence, and even dipping into lost continent myth making

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Speaker 2: and pseudoscience in order to get the job done.

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Speaker 3: God love a lost continent.

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Speaker 2: I mean, we all do. It's a it's a wonderful

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Speaker 2: concept in myth and in fiction and science fiction. But yeah,

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Speaker 2: this was especially the case when trying to connect the

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Speaker 2: dots across like Abystle Seas, so you'd have respected naturalists

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Speaker 2: of the days suddenly leaning into well, you know, the

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Speaker 2: idea of Lemuria, but even Atlantis.

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Speaker 3: We may have also talked about them in a series

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Speaker 3: of episodes we did, I think starting with the Eltannan Antenna,

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Speaker 3: where we were talking about how people take anomalous underwater

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Speaker 3: imagery that kind of looks interesting and then kind of

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Speaker 3: run wild with it, deciding that oh, this thing under

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Speaker 3: water has got to be an alien antenna, and actually

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Speaker 3: it's probably a sponge, and this other thing has got

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Speaker 3: to be evidence of Atlantis, when actually it's probably a rock.

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Speaker 2: That's right. And we definitely talked about Lemurria. This was

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Speaker 2: This one's a little different compared to Atlantis. It was

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Speaker 2: proposed in eighteen sixty four by zoologists Phillip Sklater to

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Speaker 2: explain the presence of lemur fossils, thus Lmuria on Madagascar

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Speaker 2: and in India, but not in Africa or the Middle East.

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Speaker 2: So you can you can see how Lumurria is very

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Speaker 2: much about filling in that gap, saying, these creatures had

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Speaker 2: to get from one side of the world as we

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Speaker 2: know it to another. How did they do it? There

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Speaker 2: had to be a land bridge, but not just any

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Speaker 2: land bridge. There had to be a lost continent right

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Speaker 2: there in the middle.

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Speaker 3: That's funny because it would be trying to explain, actually,

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Speaker 3: what is evidence for continental drift or plate tectonics.

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Speaker 2: Right right, So initially it's just it was an idea

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Speaker 2: to Lemuria was just a way to hypothetically fill in

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Speaker 2: the blanks here continental extensionism to explain everything into other

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Speaker 2: Individuals like biologist Ernst Haekel, considered the idea that human

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Speaker 2: origins might tie to this lost continent as well. But

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Speaker 2: then in the late nineteenth century, occultists began to appropriate

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Speaker 2: the concept, and Lumiria of course dies as a scientific

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Speaker 2: hypothesis in the nineteen sixties, but refuses to die in occultism,

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Speaker 2: conspiracy theory, and of course fiction. You can look to

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Speaker 2: various examples such as the fiction of Roberty Howard the

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Speaker 2: fiction of Lynn Carter. You'll find Lumiria showing up as

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Speaker 2: a location for various fantastic magical adventures.

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Speaker 3: It's a great place to have a leather diaper, barbarian face,

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Speaker 3: some psychic monsters.

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Speaker 2: Yes, so continental extensionism. This was a concept that Wallace

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Speaker 2: himself was rather taken with early on. Again, it seemed

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Speaker 2: a possible way to explain geological distribution of fauna and

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Speaker 2: explain some of what he was seeing. Though obviously, as

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Speaker 2: we've also discussed, he clearly wasn't opposed to viewpoints outside

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Speaker 2: of the scientific mainstream. Again, he was very interested in

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Speaker 2: spiritualism and defended spiritualism and so forth, So it's not

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Speaker 2: a stretch to imagine that he, you know, wouldn't have

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Speaker 2: strong objections to some of these concepts, which again at

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Speaker 2: the time were not like firmly wrapped up in a

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Speaker 2: lot of occultist dreaming, and was more firmly within the

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Speaker 2: realm of possible scientific explanations for the world.

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Speaker 3: That's right, And again to clarify we talked about this

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Speaker 3: last time, but spiritualism is different than what people mean

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Speaker 3: when they say like I'm spiritual today. Spiritualism then meant

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Speaker 3: the belief that you could make contact with and communicate

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Speaker 3: with the dead or with spirits other than living humans,

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Speaker 3: and that kind of contact was exciting to a lot

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Speaker 3: of people who were in the sciences. They were like, hey,

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Speaker 3: look here's something we can study empirically. Let's you know,

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Speaker 3: let's study it, let's take notes.

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Speaker 2: And this is another place where we kind of get

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Speaker 2: into the the butting heads of Darwin and Wallace, who again,

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Speaker 2: these two were not enemies. They rode to each other,

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Speaker 2: they seemed, you know, friendly with each other, and Wallace

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Speaker 2: looked up to Darwin. But Darwin really hated all of this.

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Speaker 2: He hated that naturalists would even flirt with the idea

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Speaker 2: of atlantis, and Darwin believed that over the course of

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Speaker 2: life's history on Earth, wind wing flotation, these were sufficient

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Speaker 2: to explain everything that we saw. In fact, Darwin favored

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Speaker 2: the permanence of ocean basins and continents in his calculations,

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Speaker 2: so not to say he thought everything was set in stone.

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Speaker 2: You know, he recognized that there would be regional uplift

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Speaker 2: and subsidence, for example. This was a part of a

431
00:25:41,320 --> 00:25:44,479
Speaker 2: key part of his understanding how reefs and atolls formed.

432
00:25:44,680 --> 00:25:48,600
Speaker 2: We've talked about that on the show before. But you know,

433
00:25:48,640 --> 00:25:53,440
Speaker 2: he was not keen on the idea that there were

434
00:25:53,920 --> 00:25:57,760
Speaker 2: lost continents that would have connected one land mass to

435
00:25:57,800 --> 00:26:00,560
Speaker 2: another and didn't think they were necessary. More the point,

436
00:26:02,600 --> 00:26:06,120
Speaker 2: and this is all interesting because everyone here had some

437
00:26:06,240 --> 00:26:10,280
Speaker 2: really good ideas going on, but those ideas had to

438
00:26:10,359 --> 00:26:12,920
Speaker 2: ultimately be overclocked to make up for what we had

439
00:26:12,960 --> 00:26:16,359
Speaker 2: yet to settle on regarding continental drift and plate tectonics.

440
00:26:17,480 --> 00:26:21,920
Speaker 2: So again, land bridges are a local slash regional reality,

441
00:26:22,280 --> 00:26:25,879
Speaker 2: but you can't apply them globally. It's not a solution

442
00:26:25,920 --> 00:26:29,080
Speaker 2: to every problem in the distribution of fauna.

443
00:26:29,200 --> 00:26:31,760
Speaker 3: Right, Land bridges explain a lot, but they don't explain

444
00:26:31,800 --> 00:26:34,920
Speaker 3: how life forms got to Easter Island, or to Hawaii

445
00:26:34,960 --> 00:26:35,600
Speaker 3: for that matter.

446
00:26:36,000 --> 00:26:40,040
Speaker 2: Right, right and wing, wind and flotation can get the

447
00:26:40,119 --> 00:26:44,000
Speaker 2: job done over the fullness of time, sometimes in remarkable ways.

448
00:26:44,320 --> 00:26:47,280
Speaker 2: But there are limitations to that as well. But there

449
00:26:47,280 --> 00:26:50,280
Speaker 2: are also some pretty amazing examples. I'm reminded of my

450
00:26:50,440 --> 00:26:53,160
Speaker 2: recent interview with Tom Lathan about his book Lost Wonders

451
00:26:53,320 --> 00:26:55,560
Speaker 2: regarding a number of species that wind up in rare,

452
00:26:55,680 --> 00:27:00,320
Speaker 2: far flung places, including both the Galapagos tortoise, which that's,

453
00:27:00,560 --> 00:27:02,560
Speaker 2: as we've discussed on the show before, that's an example

454
00:27:02,640 --> 00:27:06,000
Speaker 2: of floatation in action. But then you have the now

455
00:27:06,280 --> 00:27:10,040
Speaker 2: extinct Saint Helena Olive of Saint Helena Island in the

456
00:27:10,080 --> 00:27:15,440
Speaker 2: South Atlantic. The olive, as listeners might remember, possibly became

457
00:27:15,560 --> 00:27:19,160
Speaker 2: established there by dropping off of an albatross. So it's

458
00:27:19,160 --> 00:27:21,959
Speaker 2: one of these things that was extremely unlikely to occur,

459
00:27:22,520 --> 00:27:26,720
Speaker 2: but unlikely rare events do occur over the course of

460
00:27:26,840 --> 00:27:27,880
Speaker 2: geological time.

461
00:27:28,320 --> 00:27:28,520
Speaker 3: Yeah.

462
00:27:28,880 --> 00:27:32,080
Speaker 2: So Wallace did eventually come around to a different understanding

463
00:27:32,520 --> 00:27:36,200
Speaker 2: and wrote the eighteen eighty book Island Life, in which

464
00:27:36,240 --> 00:27:39,679
Speaker 2: he sets aside really any thought of lost continence in

465
00:27:39,720 --> 00:27:42,680
Speaker 2: favor of kind of a combo of both land bridges

466
00:27:42,760 --> 00:27:47,280
Speaker 2: and long distance dispersal via wind wing and floatation. And

467
00:27:47,320 --> 00:27:49,880
Speaker 2: so in this it brought his line of thinking closer

468
00:27:49,920 --> 00:27:53,960
Speaker 2: to Darwin's own, but ultimately leaning on a combination of factors.

469
00:27:54,600 --> 00:27:57,040
Speaker 3: And again he was aware of the idea of past

470
00:27:57,160 --> 00:28:00,240
Speaker 3: sea level changes due to changes in how much of

471
00:28:00,520 --> 00:28:02,159
Speaker 3: Earth's water is locked up in ice.

472
00:28:02,480 --> 00:28:06,359
Speaker 2: Absolutely and again those deep ocean trenches, though, would have

473
00:28:06,480 --> 00:28:09,080
Speaker 2: just been too deep to have been impacted by these

474
00:28:09,080 --> 00:28:11,600
Speaker 2: sea level drops, you know, I mean, sea level can

475
00:28:11,600 --> 00:28:13,560
Speaker 2: only drop so much and you're still going to have

476
00:28:13,560 --> 00:28:23,760
Speaker 2: to contend with trenches at that point.

477
00:28:25,119 --> 00:28:28,200
Speaker 3: So I was looking for some more recent papers on

478
00:28:28,240 --> 00:28:30,719
Speaker 3: the Wallace line, and I came across one that I

479
00:28:30,800 --> 00:28:33,600
Speaker 3: thought was pretty interesting. This was a twenty twenty three

480
00:28:33,640 --> 00:28:37,040
Speaker 3: study published in the journal Science by Skills at All

481
00:28:37,160 --> 00:28:42,520
Speaker 3: called paleo Environments Shaped by Exchange of terrestrial vertebrates across

482
00:28:42,520 --> 00:28:46,840
Speaker 3: Wallace's Line. The authors in this paper start off by

483
00:28:46,960 --> 00:28:52,320
Speaker 3: establishing a concept called biotic interchange. This is what happens

484
00:28:52,360 --> 00:28:57,680
Speaker 3: when the flora and fauna of two previously separate regions

485
00:28:58,080 --> 00:29:01,480
Speaker 3: are suddenly allowed to move into each other. They're allowed

486
00:29:01,520 --> 00:29:05,880
Speaker 3: to freely colonize one another's regions. Examples of this usually

487
00:29:05,880 --> 00:29:09,480
Speaker 3: occur when a barrier to travel between two places is

488
00:29:09,520 --> 00:29:13,840
Speaker 3: suddenly removed, and suddenly here would be a relative modifier

489
00:29:13,920 --> 00:29:17,520
Speaker 3: suddenly on geologic time. One example of this is the

490
00:29:17,600 --> 00:29:21,760
Speaker 3: American interchange, where land and freshwater animals from North and

491
00:29:21,840 --> 00:29:25,960
Speaker 3: South America were suddenly able to migrate across into each

492
00:29:26,000 --> 00:29:29,520
Speaker 3: other's territory. After Rob you mitched this earlier. The idea

493
00:29:29,600 --> 00:29:32,560
Speaker 3: of the Panama is isthmus. Oh Man, that word is

494
00:29:32,600 --> 00:29:36,040
Speaker 3: so hard to say isthemus for me, It's difficult. After

495
00:29:36,160 --> 00:29:41,200
Speaker 3: the Panama Isthmus was raised by volcanic activity, so that

496
00:29:41,240 --> 00:29:43,840
Speaker 3: came up from the seafloor. And previously there had been

497
00:29:43,880 --> 00:29:47,160
Speaker 3: a saltwater barrier between North and South America for some time.

498
00:29:47,840 --> 00:29:50,360
Speaker 3: But you have this volcanic activity. Now there's a land

499
00:29:50,400 --> 00:29:53,960
Speaker 3: bridge in Central America that happens between two and three

500
00:29:53,960 --> 00:29:57,280
Speaker 3: million years ago, and now there's all this exchange of

501
00:29:57,320 --> 00:30:01,000
Speaker 3: life forms across the barrier or across the former barrier.

502
00:30:01,920 --> 00:30:05,520
Speaker 3: Another one of these great biotic mingling events is the

503
00:30:05,560 --> 00:30:11,040
Speaker 3: Indo Australian Interchange, which arose when the Australian and Eurasian

504
00:30:11,080 --> 00:30:15,680
Speaker 3: techtonic plates smashed together, forming some islands in between within

505
00:30:15,720 --> 00:30:18,600
Speaker 3: the region we were talking about earlier known as Wallacea.

506
00:30:19,440 --> 00:30:22,600
Speaker 3: Now we've already talked about how there are some barriers

507
00:30:22,640 --> 00:30:26,239
Speaker 3: to exchange along this connection point. The extent of that

508
00:30:26,280 --> 00:30:29,880
Speaker 3: barrier to cross colonization was the original observation of the

509
00:30:29,880 --> 00:30:32,640
Speaker 3: Wallace line. It's like what Wallace observed is, hey, there's

510
00:30:32,720 --> 00:30:36,200
Speaker 3: not a lot of animal species going across here. Unlike

511
00:30:36,240 --> 00:30:40,239
Speaker 3: the American Interchange. There is not and was never a

512
00:30:40,320 --> 00:30:45,040
Speaker 3: full land bridge between Sunda and Sahul. But as Wallace

513
00:30:45,080 --> 00:30:48,440
Speaker 3: also observed, all boundaries are permeable, and we now know

514
00:30:48,640 --> 00:30:52,880
Speaker 3: a good bit of exchange does happen across this line,

515
00:30:53,240 --> 00:30:57,800
Speaker 3: and there are some more faunally mixed transition zones in

516
00:30:57,920 --> 00:31:01,960
Speaker 3: between in the islands of Wallacea. But the authors of

517
00:31:02,000 --> 00:31:08,000
Speaker 3: this paper point out something interesting. Biotic interchanges are rarely symmetrical.

518
00:31:08,320 --> 00:31:12,200
Speaker 3: They're rarely totally even. Usually you have more life flowing

519
00:31:12,280 --> 00:31:15,480
Speaker 3: in one direction across the new corridor than flowing in

520
00:31:15,520 --> 00:31:19,280
Speaker 3: the other direction. Why would that be? Why the asymmetry.

521
00:31:20,160 --> 00:31:24,640
Speaker 3: Some answers lie in characteristics of the organisms. Maybe some

522
00:31:24,920 --> 00:31:28,560
Speaker 3: organisms are just more adaptable, they're better at dispersing into

523
00:31:28,640 --> 00:31:31,840
Speaker 3: new environments. Maybe they're better at evolving more quickly and

524
00:31:31,920 --> 00:31:35,160
Speaker 3: changing what they're adapted to. But some answers, on the

525
00:31:35,160 --> 00:31:38,680
Speaker 3: other hand, might lie in characteristics of the land and

526
00:31:39,000 --> 00:31:42,800
Speaker 3: environment on either side of the new corridor, or within

527
00:31:42,960 --> 00:31:47,800
Speaker 3: the corridor itself. What if something about the geography favors

528
00:31:47,840 --> 00:31:51,800
Speaker 3: dispersal one way but not the other. And to be

529
00:31:51,840 --> 00:31:54,840
Speaker 3: clear here, the authors do not argue that Wallace was

530
00:31:54,880 --> 00:31:57,680
Speaker 3: wrong about the deep ocean trench in the Lombock Strait

531
00:31:57,720 --> 00:32:00,640
Speaker 3: being a barrier to dispersal. It is, as it does

532
00:32:00,680 --> 00:32:03,480
Speaker 3: stop a lot of exchange, and they note that the

533
00:32:03,520 --> 00:32:06,760
Speaker 3: only mammals which seem to have successfully crossed that boundary.

534
00:32:06,880 --> 00:32:11,720
Speaker 3: Naturally are bats and rodents. Big mammals seemingly do not cross.

535
00:32:12,520 --> 00:32:15,600
Speaker 3: But of the animals that have crossed, one thing that

536
00:32:15,760 --> 00:32:20,080
Speaker 3: is clear is which way the asymmetry goes. Over the

537
00:32:20,160 --> 00:32:24,160
Speaker 3: last twenty million years, way more animals from Asia have

538
00:32:24,320 --> 00:32:28,520
Speaker 3: successfully crossed the barrier and made their way into New

539
00:32:28,560 --> 00:32:33,000
Speaker 3: Guinea and onto the Australian continent. Relatively little dispersal has

540
00:32:33,040 --> 00:32:36,640
Speaker 3: gone the other direction, from Australia and New Guinea to

541
00:32:36,720 --> 00:32:40,720
Speaker 3: the west into Asia. Why would that be well, The

542
00:32:40,720 --> 00:32:44,440
Speaker 3: authors argue, based on analysis of a huge data set

543
00:32:44,520 --> 00:32:48,080
Speaker 3: and a sophisticated computer model, that the answer has to

544
00:32:48,160 --> 00:32:52,920
Speaker 3: do with the climate of the islands within and on

545
00:32:53,080 --> 00:32:57,880
Speaker 3: either side of Wallacea, especially how wet or dry those

546
00:32:57,920 --> 00:33:01,280
Speaker 3: islands are, and the precipitation tolerance of the animals that

547
00:33:01,320 --> 00:33:05,600
Speaker 3: evolved on either side. So to quote the authors quote here,

548
00:33:05,720 --> 00:33:09,000
Speaker 3: analysis of more than twenty thousand vertebrate species with a

549
00:33:09,080 --> 00:33:14,160
Speaker 3: model of geoclimate and biological diversification shows that broad precipitation

550
00:33:14,320 --> 00:33:18,400
Speaker 3: tolerance and dispersal ability were key for exchange across the

551
00:33:18,520 --> 00:33:24,120
Speaker 3: deep time precipitation gradients spanning the region Sundanian meaning Southeast

552
00:33:24,160 --> 00:33:28,320
Speaker 3: Asian lineages evolved in a climate similar to the humid

553
00:33:28,480 --> 00:33:34,240
Speaker 3: quote stepping stones of Wallacea, facilitating colonization of the Sahulian

554
00:33:34,400 --> 00:33:41,440
Speaker 3: meaning Australian continental shelf. By contrast, Sahulian lineages predominantly evolved

555
00:33:41,480 --> 00:33:48,120
Speaker 3: in drier conditions, hampering establishment in sunda and shaping faunal distinctiveness. So,

556
00:33:48,440 --> 00:33:52,240
Speaker 3: in other words, the islands in the transition zone here

557
00:33:52,360 --> 00:33:56,400
Speaker 3: are typically full of tropical rainforests like you would find

558
00:33:56,520 --> 00:34:00,320
Speaker 3: further up on the Malay Peninsula and the Asian Maine land.

559
00:34:01,040 --> 00:34:04,760
Speaker 3: New Guinea, on the same tectonic plate with Australia, is

560
00:34:04,840 --> 00:34:09,880
Speaker 3: also dominated with tropical rainforest. So animals adapted to Asian

561
00:34:09,920 --> 00:34:15,480
Speaker 3: tropical rainforests would find generally familiar and tolerably wet climates

562
00:34:15,520 --> 00:34:19,200
Speaker 3: throughout most of the islands that formed these stepping stones

563
00:34:19,719 --> 00:34:23,280
Speaker 3: leading to Australia and New Guinea, and once they reached

564
00:34:23,320 --> 00:34:27,160
Speaker 3: Australia there would be different conditions. The continent would be

565
00:34:27,200 --> 00:34:30,799
Speaker 3: much drier, but they could have more evolutionary time to

566
00:34:31,000 --> 00:34:35,239
Speaker 3: adapt by colonizing the islands along the way or by

567
00:34:35,320 --> 00:34:39,400
Speaker 3: landing in the friendly climate of New Guinea. Meanwhile, animals

568
00:34:39,400 --> 00:34:42,200
Speaker 3: adapted to the dry climate of Australia would have a

569
00:34:42,400 --> 00:34:48,000
Speaker 3: quite difficult time finding hospitable conditions along the humid stepping stones,

570
00:34:48,400 --> 00:34:50,960
Speaker 3: and once you get to the Asian mainland, it's still

571
00:34:51,040 --> 00:34:55,319
Speaker 3: just humid and dominated by tropical rainforest. So because the

572
00:34:55,440 --> 00:34:59,239
Speaker 3: transitional islands in between were more easily tolerated by the

573
00:34:59,280 --> 00:35:03,560
Speaker 3: Asian animal, more Asian animals flowed into the land masses

574
00:35:03,600 --> 00:35:06,759
Speaker 3: of the Australian Plate than the other way around. And

575
00:35:06,800 --> 00:35:09,959
Speaker 3: I thought that was really interesting because it I don't

576
00:35:10,000 --> 00:35:12,960
Speaker 3: know if it often occurs to us to think when

577
00:35:12,960 --> 00:35:17,800
Speaker 3: we think about like animals dispersing from one region into another,

578
00:35:17,920 --> 00:35:20,759
Speaker 3: we think about the sort of end stage reach, like

579
00:35:20,840 --> 00:35:23,600
Speaker 3: they start here and then they end up here, But

580
00:35:23,840 --> 00:35:27,479
Speaker 3: the place that they're having to move through as they

581
00:35:27,520 --> 00:35:30,920
Speaker 3: migrate also plays a big role in whether that migration

582
00:35:31,120 --> 00:35:32,319
Speaker 3: can take place at all.

583
00:35:32,960 --> 00:35:34,520
Speaker 2: Hmm. Yeah, that's a great point.

584
00:35:34,800 --> 00:35:36,360
Speaker 3: I was trying to think of a good analogy, and

585
00:35:36,600 --> 00:35:40,239
Speaker 3: this doesn't exactly work, but to grossly oversimplify. What if

586
00:35:40,280 --> 00:35:44,880
Speaker 3: there were a highway suddenly opened across the Atlantic Ocean

587
00:35:45,120 --> 00:35:48,919
Speaker 3: between Great Britain and the United States and you could

588
00:35:48,920 --> 00:35:52,040
Speaker 3: cross it by car, do you think you'd have more

589
00:35:52,120 --> 00:35:55,600
Speaker 3: people crossing one way or another. I mean, in reality,

590
00:35:55,640 --> 00:35:57,880
Speaker 3: there would be a lot of things influencing this, but

591
00:35:58,400 --> 00:36:01,160
Speaker 3: you could imagine that which side of the highway you

592
00:36:01,239 --> 00:36:04,320
Speaker 3: have to drive on on the highway going in between

593
00:36:04,880 --> 00:36:07,239
Speaker 3: might determine a lot about who decides to make the

594
00:36:07,320 --> 00:36:09,759
Speaker 3: journey more often, like if you got to be if

595
00:36:09,760 --> 00:36:11,200
Speaker 3: you got to be on the left side of the road,

596
00:36:11,239 --> 00:36:13,319
Speaker 3: I can imagine a lot of Americans saying, I'm not

597
00:36:13,400 --> 00:36:14,960
Speaker 3: driving that far on the left side. I don't know

598
00:36:15,080 --> 00:36:17,160
Speaker 3: how to do that. So if we were driving on

599
00:36:17,200 --> 00:36:18,880
Speaker 3: the left side, maybe it would be a motorway and

600
00:36:18,960 --> 00:36:20,160
Speaker 3: not a highway. I'm not sure.

601
00:36:20,239 --> 00:36:22,319
Speaker 2: Yeah, yeah, but I see what you're going for here,

602
00:36:22,400 --> 00:36:25,799
Speaker 2: Like the side of the car that you drive upon

603
00:36:25,920 --> 00:36:29,880
Speaker 2: is kind of like the environmental conditions of the passage. Yeah. Yeah.

604
00:36:29,920 --> 00:36:33,680
Speaker 2: And how conducive drivers on either side or going to

605
00:36:33,760 --> 00:36:34,800
Speaker 2: be to that passage.

606
00:36:34,960 --> 00:36:37,520
Speaker 3: Yeah. It's not just how well adapted you already are

607
00:36:37,600 --> 00:36:40,440
Speaker 3: to the end point. It's like how well adapted you

608
00:36:40,440 --> 00:36:42,279
Speaker 3: are to each little step along the way.

609
00:36:42,719 --> 00:36:43,399
Speaker 2: Yeah.

610
00:36:43,440 --> 00:36:46,680
Speaker 3: And in the case of Wallacea, it proved easier for

611
00:36:46,960 --> 00:36:51,560
Speaker 3: the humid adapted Asian mainland fauna to to make the

612
00:36:51,640 --> 00:36:54,120
Speaker 3: journey into especially into New Guinea.

613
00:36:55,840 --> 00:36:59,560
Speaker 2: Now, as we begin to reach the end of this episode,

614
00:37:00,040 --> 00:37:01,920
Speaker 2: I want to bring it back a little bit to

615
00:37:02,640 --> 00:37:06,359
Speaker 2: my travel experience in Indonesia where I actually visited these

616
00:37:06,400 --> 00:37:08,520
Speaker 2: stepping stones or some of these stepping stones we've been

617
00:37:08,520 --> 00:37:11,920
Speaker 2: talking about. So again, I was east of the wallace

618
00:37:12,040 --> 00:37:16,160
Speaker 2: line in Raja Ampat, which situated is also in an

619
00:37:16,200 --> 00:37:20,759
Speaker 2: area that is often called the coral triangle. Joe, I've

620
00:37:20,800 --> 00:37:23,359
Speaker 2: included a map of the coral triangle for you here.

621
00:37:24,040 --> 00:37:27,000
Speaker 2: This one isn't heart shaped and it's also not really

622
00:37:27,040 --> 00:37:30,680
Speaker 2: triangle shaped. It's located between the Pacific and Indian Oceans

623
00:37:30,719 --> 00:37:36,080
Speaker 2: and encompasses portions of two biogeographic regions, so the Indonesian

624
00:37:36,080 --> 00:37:41,000
Speaker 2: Philippines region and the Far Southwestern Pacific region. If it

625
00:37:41,040 --> 00:37:43,400
Speaker 2: looks like anything, it looks more like a rough sketch

626
00:37:43,400 --> 00:37:44,279
Speaker 2: of a fish.

627
00:37:44,600 --> 00:37:47,080
Speaker 3: Yeah, I guess see, it's a psilocybin triangle.

628
00:37:49,040 --> 00:37:51,880
Speaker 2: Yeah yeah. And so why do we call it the

629
00:37:51,920 --> 00:37:56,200
Speaker 2: coral triangle? Well, because it is super rich in coral.

630
00:37:56,520 --> 00:37:59,640
Speaker 2: According to the Coral Reef Alliance, this region contains over

631
00:37:59,719 --> 00:38:03,080
Speaker 2: seven twenty six percent of the world's coral species and

632
00:38:03,160 --> 00:38:07,240
Speaker 2: thirty seven percent of reef fish species. So we're talking

633
00:38:07,239 --> 00:38:11,480
Speaker 2: about somewhere around five hundred of the eight hundred and

634
00:38:11,480 --> 00:38:14,680
Speaker 2: forty coral species that we know of. So just a

635
00:38:14,920 --> 00:38:18,800
Speaker 2: rich hot bed of marine biodiversity, and there's a reason

636
00:38:18,840 --> 00:38:21,640
Speaker 2: that snorkelers and divers from around the world seek it out.

637
00:38:21,960 --> 00:38:26,160
Speaker 2: There's just breathtaking abundance there. I've never experienced snorkeling like

638
00:38:26,200 --> 00:38:28,839
Speaker 2: this before, and you know, unless I go back there,

639
00:38:28,880 --> 00:38:30,000
Speaker 2: I'm not sure I will again.

640
00:38:30,520 --> 00:38:33,400
Speaker 3: Well, as as I've said, I have no experience snorkeling myself,

641
00:38:33,440 --> 00:38:36,080
Speaker 3: but I'm still envious of what you got to see there.

642
00:38:37,239 --> 00:38:40,960
Speaker 3: But this does raise the question does the Wallis line

643
00:38:41,120 --> 00:38:44,960
Speaker 3: hold at all for underwater fauna. We know that it

644
00:38:45,040 --> 00:38:50,120
Speaker 3: holds to some extent for like land mammals. But you

645
00:38:50,239 --> 00:38:52,960
Speaker 3: might think intuitively, well, surely there would be no way

646
00:38:53,040 --> 00:38:55,560
Speaker 3: that the Wallas line would have any impact on say,

647
00:38:55,719 --> 00:38:57,920
Speaker 3: fish or other things that I can swim through. They

648
00:38:57,960 --> 00:38:59,719
Speaker 3: can just swim right across the strait.

649
00:38:59,480 --> 00:39:01,719
Speaker 2: Right, you would think of the fish or just have

650
00:39:01,760 --> 00:39:03,520
Speaker 2: a free for all, and so they don't have to

651
00:39:03,560 --> 00:39:06,239
Speaker 2: obey the rules of the Wall's line, and neither do

652
00:39:06,280 --> 00:39:11,319
Speaker 2: the birds. But this is not the case. Despite the

653
00:39:11,320 --> 00:39:14,560
Speaker 2: fact that we're under the water here, we're still subject

654
00:39:14,760 --> 00:39:17,440
Speaker 2: to some of the boundary effects of deep ocean channels.

655
00:39:18,000 --> 00:39:22,279
Speaker 2: So these deep trenches seem to act as persistent barriers

656
00:39:22,320 --> 00:39:26,839
Speaker 2: that prevent the widespread migration of many coral larvae and

657
00:39:27,080 --> 00:39:31,480
Speaker 2: many other marine invertebrates as well. Additionally, there's the Indonesian

658
00:39:31,640 --> 00:39:35,680
Speaker 2: through flow, which moves massive amounts of water from the

659
00:39:35,680 --> 00:39:38,799
Speaker 2: Pacific to the Indian Ocean, and so it plays a

660
00:39:38,800 --> 00:39:42,400
Speaker 2: crucial role here as well. It'll transport some larvae, but

661
00:39:42,560 --> 00:39:46,280
Speaker 2: also acts as a barrier to others, influencing the genetic

662
00:39:46,360 --> 00:39:49,360
Speaker 2: flow between populations of coral on either side of the line.

663
00:39:49,440 --> 00:39:52,960
Speaker 2: So some coral species have wide Indo Pacific ranges and

664
00:39:53,000 --> 00:39:57,000
Speaker 2: can be found on both sides, but others follow distribution

665
00:39:57,120 --> 00:39:59,319
Speaker 2: patterns that are more in line with some of the

666
00:39:59,400 --> 00:40:03,360
Speaker 2: terrestrial animals that are impacted by the Wallas line. And

667
00:40:03,440 --> 00:40:07,400
Speaker 2: we also see this play into distinct species. For instance,

668
00:40:07,400 --> 00:40:11,480
Speaker 2: there are two distinct subpopulations of the Indo Pacific leopard shark,

669
00:40:11,840 --> 00:40:14,360
Speaker 2: and they are separated by the Indonesian through flow current,

670
00:40:14,600 --> 00:40:19,640
Speaker 2: which again coincides roughly with the Wallas line. Here. For instance,

671
00:40:19,680 --> 00:40:23,480
Speaker 2: the Missoul Foundation, which runs the Missoul resort in raja Ampat.

672
00:40:24,160 --> 00:40:27,640
Speaker 2: There's they are part of a Star Project Reshark program

673
00:40:27,680 --> 00:40:31,440
Speaker 2: to help re establish the eastern subpopulation of the species

674
00:40:31,520 --> 00:40:35,800
Speaker 2: in raja Ampat. Meanwhile, there's another program Star Project Thailand

675
00:40:36,080 --> 00:40:41,840
Speaker 2: focused on the western variety. So one variety of Indo

676
00:40:41,880 --> 00:40:45,280
Speaker 2: Pacific leopard shark on one side and then another variety

677
00:40:45,320 --> 00:40:46,120
Speaker 2: on the other side.

678
00:40:46,239 --> 00:40:48,800
Speaker 3: Wow, I mean, even though we've established that the line

679
00:40:48,880 --> 00:40:54,200
Speaker 3: is not impermeable and sometimes animals do cross, I don't know,

680
00:40:54,239 --> 00:40:58,240
Speaker 3: it's fascinating how just like how much of a barrier

681
00:40:58,280 --> 00:41:01,160
Speaker 3: there could be that's just totally invisible to us and

682
00:41:01,160 --> 00:41:04,600
Speaker 3: and even even affects creatures. You would think that it

683
00:41:04,760 --> 00:41:06,840
Speaker 3: that it couldn't like many underwater creatures.

684
00:41:06,880 --> 00:41:08,920
Speaker 2: Yeah, that we can read it in the coral, we

685
00:41:08,960 --> 00:41:12,440
Speaker 2: can read it in the leopard sharks, and yeah, it's

686
00:41:12,480 --> 00:41:16,640
Speaker 2: it's fascinating. Yeah, just the power the powerful interplay of

687
00:41:16,680 --> 00:41:21,960
Speaker 2: division and mixing between rich ecosystems. Here. Another interesting thing

688
00:41:22,000 --> 00:41:25,400
Speaker 2: about the leopard shark program there is that they uh,

689
00:41:26,040 --> 00:41:27,719
Speaker 2: they were having to get you know, you wanted to

690
00:41:27,719 --> 00:41:30,440
Speaker 2: make sure that you were using the right variety of

691
00:41:30,520 --> 00:41:34,799
Speaker 2: into Pacific leopard shark to repopulate the region. There in

692
00:41:34,880 --> 00:41:37,440
Speaker 2: raja Ampat. So they had to reach out to various

693
00:41:37,440 --> 00:41:42,840
Speaker 2: aquariums to get surplus eggs from into Pacific leopard sharks

694
00:41:42,880 --> 00:41:45,920
Speaker 2: of the right variety, and one of the aquariums is

695
00:41:45,960 --> 00:41:51,319
Speaker 2: actually the Georgia Aquarium here in Atlanta. Uh So it

696
00:41:51,400 --> 00:41:53,040
Speaker 2: was entirely I don't know for certain, but it was

697
00:41:53,160 --> 00:41:56,720
Speaker 2: entirely possible that some of the the the baby leopard

698
00:41:56,719 --> 00:41:58,440
Speaker 2: sharks that I that I saw in the tanks that

699
00:41:58,440 --> 00:42:01,000
Speaker 2: were then going to be gradually re produced into the wild.

700
00:42:02,120 --> 00:42:06,279
Speaker 2: Perhaps we're descendants of eggs that were produced all the

701
00:42:06,280 --> 00:42:10,360
Speaker 2: way back home in Atlanta. The circle of life, Yeah,

702
00:42:10,680 --> 00:42:15,240
Speaker 2: circle of life with leopard shark eggs, you know, taking

703
00:42:16,080 --> 00:42:20,600
Speaker 2: international flights for days across the Earth, which in a

704
00:42:20,600 --> 00:42:22,520
Speaker 2: way is entering because it brings it back into the

705
00:42:22,600 --> 00:42:25,040
Speaker 2: like the vast way that humans end up moving around.

706
00:42:25,680 --> 00:42:27,520
Speaker 2: And of course we've talked before in the show about

707
00:42:27,560 --> 00:42:30,200
Speaker 2: how the movements of humans has of course been another

708
00:42:30,280 --> 00:42:34,560
Speaker 2: huge factor in the way other organisms are intentionally and

709
00:42:34,640 --> 00:42:39,080
Speaker 2: unintentionally spread around the world. Yeah, of course, but occasionally

710
00:42:39,120 --> 00:42:42,520
Speaker 2: we get strategic about it. We attempt to fix things

711
00:42:42,560 --> 00:42:45,480
Speaker 2: that we had broken before, because you know, there's a

712
00:42:45,520 --> 00:42:49,200
Speaker 2: reason that sharks are missing, as we've discussed before, or

713
00:42:49,400 --> 00:42:54,040
Speaker 2: shark populations are greatly decreased in various areas, and it's

714
00:42:54,040 --> 00:42:56,719
Speaker 2: because we have hunted them, we fish for them, we

715
00:42:56,800 --> 00:42:59,359
Speaker 2: have feared them, and so forth, and in doing so,

716
00:42:59,440 --> 00:43:02,440
Speaker 2: you know, we end up damaging the ecosystem that they

717
00:43:02,440 --> 00:43:06,760
Speaker 2: were a part of, because those apex predators are essential

718
00:43:06,880 --> 00:43:10,279
Speaker 2: to the overall structure of things. And also, as we've

719
00:43:10,320 --> 00:43:13,120
Speaker 2: discussed in the show, their place is fragile.

720
00:43:12,640 --> 00:43:13,080
Speaker 1: At the top.

721
00:43:13,480 --> 00:43:16,319
Speaker 3: Yeah, all right, Well, I have enjoyed this journey with

722
00:43:16,360 --> 00:43:17,440
Speaker 3: Alfred Russell Wallace.

723
00:43:18,000 --> 00:43:20,960
Speaker 2: Yeah, like I said, a fascinating individual. If you want

724
00:43:21,000 --> 00:43:24,120
Speaker 2: to read more about him, that book Radical by Nature

725
00:43:24,520 --> 00:43:27,040
Speaker 2: by James T. Costa is quite good, and there are

726
00:43:27,040 --> 00:43:28,719
Speaker 2: a number of other books as well that have come

727
00:43:28,760 --> 00:43:32,160
Speaker 2: out in over the recent decades about his work. There's

728
00:43:32,239 --> 00:43:36,360
Speaker 2: kind of been a resurgence of interest in Alfred Russell Wallace.

729
00:43:36,920 --> 00:43:39,560
Speaker 3: I enjoyed so much just reading Wallace's own writing in

730
00:43:39,600 --> 00:43:41,680
Speaker 3: the Malay Archipelago that I may want to come back

731
00:43:41,880 --> 00:43:45,080
Speaker 3: and plug that plum that maybe for some future topics.

732
00:43:45,320 --> 00:43:48,400
Speaker 2: Yeah, yeah, Plus, yeah, he wrote many, many books on

733
00:43:48,440 --> 00:43:51,359
Speaker 2: a number of topics, so yeah, he may pop up

734
00:43:51,360 --> 00:43:53,439
Speaker 2: again in a future episode of Stuff Blear Your Mind.

735
00:43:54,200 --> 00:43:55,799
Speaker 2: All right, we're going to go ahead and close it

736
00:43:55,880 --> 00:43:57,920
Speaker 2: up there, but we'd love to hear from everyone out

737
00:43:57,920 --> 00:44:00,440
Speaker 2: there if you have thoughts about the Wallace line, about

738
00:44:00,480 --> 00:44:03,560
Speaker 2: some of the organisms that we've discussed here. Just a

739
00:44:03,560 --> 00:44:05,279
Speaker 2: reminder of Stuff to Blow Your Mind is primarily a

740
00:44:05,320 --> 00:44:08,080
Speaker 2: science and culture podcast, with core episodes on Tuesdays and Thursday,

741
00:44:08,080 --> 00:44:10,600
Speaker 2: short form episode on Wednesdays and on Fridays. We set

742
00:44:10,600 --> 00:44:12,759
Speaker 2: aside most serious concerns to just talk about a weird

743
00:44:12,800 --> 00:44:14,800
Speaker 2: film on Weird House Cinema.

744
00:44:15,200 --> 00:44:18,960
Speaker 3: Huge thanks as always to our excellent audio producer JJ Posway.

745
00:44:19,239 --> 00:44:20,839
Speaker 3: If you would like to get in touch with us

746
00:44:20,840 --> 00:44:23,240
Speaker 3: with feedback on this episode or any other, to suggest

747
00:44:23,280 --> 00:44:25,239
Speaker 3: a topic for the future, or just to say hello,

748
00:44:25,560 --> 00:44:28,200
Speaker 3: you can email us at contact, stuff to Blow your

749
00:44:28,200 --> 00:44:36,120
Speaker 3: Mind dot com.

750
00:44:36,239 --> 00:44:39,160
Speaker 1: Stuff to Blow Your Mind is production of iHeartRadio. For

751
00:44:39,239 --> 00:44:42,040
Speaker 1: more podcasts from My Heart Radio, visit the iHeartRadio app,

752
00:44:42,200 --> 00:44:59,600
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.

753
00:45:00,800 --> 00:45:02,439
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