1 00:00:06,360 --> 00:00:09,160 Speaker 1: Hey, welcome to Stuff to Blow Your Mind. My name 2 00:00:09,220 --> 00:00:12,760 Speaker 1: is Robert Lamb. It is a buffer week here on 3 00:00:12,800 --> 00:00:16,020 Speaker 1: Stuff to Blow Your Mind. We're gaining strength for our 4 00:00:16,160 --> 00:00:19,860 Speaker 1: October Halloween episodes ahead. So today is an episode for 5 00:00:19,900 --> 00:00:21,840 Speaker 1: you that originally aired 8-21-2025. It is The Wallace Line 6 00:00:21,890 --> 00:00:28,030 Speaker 1: Part 2. Please enjoy. The Wallace Line Part 2. 7 00:00:29,520 --> 00:00:32,600 Speaker 2: Welcome to Stuff to Blow Your Mind, a production of iHeartRadio. 8 00:00:39,520 --> 00:00:41,400 Speaker 1: Hey, welcome to Stuff to Blow Your Mind. My name 9 00:00:41,440 --> 00:00:42,059 Speaker 1: is Robert Lamb. 10 00:00:42,680 --> 00:00:45,060 Speaker 2: And I am Joe McCormick. And we're back with part 11 00:00:45,120 --> 00:00:49,050 Speaker 2: two in our series on the 19th century British naturalist 12 00:00:49,250 --> 00:00:53,630 Speaker 2: Alfred Russell Wallace and on the Wallace Line, the faunal 13 00:00:53,690 --> 00:00:57,980 Speaker 2: boundary in the Malay archipelago that bears his name. If 14 00:00:58,000 --> 00:00:59,900 Speaker 2: you haven't heard part one yet, I would recommend you 15 00:00:59,920 --> 00:01:01,980 Speaker 2: go back and listen to that one first. But in 16 00:01:02,260 --> 00:01:05,440 Speaker 2: part one, we started off with a general character sketch 17 00:01:05,500 --> 00:01:09,390 Speaker 2: of Wallace. He's a man of many adventures and many opinions, 18 00:01:10,150 --> 00:01:13,149 Speaker 2: best known today for being the other guy who discovered 19 00:01:13,209 --> 00:01:16,589 Speaker 2: evolution by natural selection. He came up with a slightly 20 00:01:16,650 --> 00:01:20,110 Speaker 2: different version of the theory of natural selection around the 21 00:01:20,150 --> 00:01:25,430 Speaker 2: same time Darwin did, just some sort of differences of emphasis, basically. 22 00:01:26,280 --> 00:01:30,289 Speaker 2: Though Darwin's writings ultimately proved more influential in convincing his 23 00:01:30,370 --> 00:01:34,150 Speaker 2: peers on the reality of common descent and on articulating 24 00:01:34,190 --> 00:01:37,770 Speaker 2: the mechanisms by which species evolve. Wallace was also something 25 00:01:37,950 --> 00:01:40,170 Speaker 2: of a celebrity at his time. It's not like one 26 00:01:40,190 --> 00:01:44,530 Speaker 2: of those tragic cases of somebody else who also came 27 00:01:44,569 --> 00:01:47,750 Speaker 2: across a great idea but was just totally forgotten. Wallace 28 00:01:47,800 --> 00:01:50,740 Speaker 2: was kind of a celebrity, especially because of the quality 29 00:01:50,860 --> 00:01:53,960 Speaker 2: of his writings. And that would be in books like 30 00:01:54,060 --> 00:01:58,740 Speaker 2: The Malay Archipelago, published in 1869, in which he vividly 31 00:01:58,800 --> 00:02:02,059 Speaker 2: described his earlier travels in that region of the world, 32 00:02:02,120 --> 00:02:07,060 Speaker 2: including lots of very well-observed biological and cultural detail. And 33 00:02:07,080 --> 00:02:09,880 Speaker 2: we read a bunch of selections from that book in 34 00:02:09,919 --> 00:02:14,780 Speaker 2: the last episode. And it's somewhat magical to read. Yeah, absolutely. 35 00:02:14,940 --> 00:02:17,690 Speaker 1: Again, you can see why this book was such a success. 36 00:02:17,750 --> 00:02:20,669 Speaker 1: And it was read by other naturalists, but also just biologists. 37 00:02:21,389 --> 00:02:23,570 Speaker 1: just members of the general public who are interested in 38 00:02:23,590 --> 00:02:26,970 Speaker 1: the topic, interested in faraway lands and in the natural world. 39 00:02:27,310 --> 00:02:30,010 Speaker 2: Yeah, so we read some selections from the chapters where 40 00:02:30,050 --> 00:02:33,119 Speaker 2: he goes exploring, initially against his will, by the way, 41 00:02:34,060 --> 00:02:37,480 Speaker 2: on the islands of Bali and Lombok. And this included 42 00:02:37,520 --> 00:02:41,320 Speaker 2: everything from these evocative descriptions of the land itself, talking 43 00:02:41,340 --> 00:02:43,780 Speaker 2: about the terrorist agriculture and the way the fields are 44 00:02:43,840 --> 00:02:48,630 Speaker 2: irrigated and all that, to discussions about the geographic distribution 45 00:02:48,650 --> 00:02:52,100 Speaker 2: of ghosts to complaints about how hard it is to 46 00:02:52,139 --> 00:02:56,380 Speaker 2: do science when everything smells putrid and is covered in ants. Right. 47 00:02:56,419 --> 00:02:59,040 Speaker 1: Now, to be clear, it was putrid smelling because of 48 00:02:59,100 --> 00:03:03,020 Speaker 1: all the bird skin. This is not a general comment 49 00:03:03,240 --> 00:03:06,059 Speaker 1: on on the region or the peoples there. This was 50 00:03:06,380 --> 00:03:07,860 Speaker 1: this was his mess. No, no. 51 00:03:07,880 --> 00:03:10,580 Speaker 2: It's not like Lombok smells bad. It was my room 52 00:03:10,660 --> 00:03:11,220 Speaker 2: smells bad. 53 00:03:11,240 --> 00:03:11,799 Speaker 1: Yeah. Yeah. 54 00:03:14,440 --> 00:03:18,340 Speaker 2: Also, we talked about the concept of biogeography, the study 55 00:03:18,380 --> 00:03:22,160 Speaker 2: of what lives where and why. Wallace is considered a 56 00:03:22,380 --> 00:03:25,840 Speaker 2: very important founding figure in biogeography, with one of his 57 00:03:25,919 --> 00:03:30,130 Speaker 2: most enduring observations being what is now called, in his honor, 58 00:03:30,150 --> 00:03:34,070 Speaker 2: the Wallace Line, an invisible boundary passing in the ocean 59 00:03:34,130 --> 00:03:38,470 Speaker 2: between the islands of originally Borneo and Sulawesi, and even 60 00:03:38,530 --> 00:03:43,340 Speaker 2: more astonishingly, in the tiny, narrow strait between Bali and Lombok. 61 00:03:43,800 --> 00:03:47,780 Speaker 2: which marks the westernmost boundary of a lot of characteristic 62 00:03:48,260 --> 00:03:52,890 Speaker 2: Australasian fauna, marsupials, cockatoos, and things like that. So we 63 00:03:52,950 --> 00:03:55,650 Speaker 2: are back today to talk more about Wallace and the 64 00:03:55,690 --> 00:03:58,510 Speaker 2: Wallace line. Now, one thing I think we've got to 65 00:03:58,530 --> 00:04:01,430 Speaker 2: do before we move on any further is just a 66 00:04:01,450 --> 00:04:04,510 Speaker 2: bit of cleanup, because as I mentioned in the last episode, 67 00:04:05,190 --> 00:04:09,790 Speaker 2: our model of the Wallace line has undergone some some 68 00:04:09,850 --> 00:04:14,560 Speaker 2: major revisions since Wallace first proposed it in the mid-19th century. 69 00:04:15,160 --> 00:04:17,599 Speaker 2: I'm not going to do a whole detailed play-by-play of 70 00:04:17,680 --> 00:04:20,460 Speaker 2: the shifting history of the line, but for a brief 71 00:04:20,540 --> 00:04:24,060 Speaker 2: summary of developments, I was just looking at the abstract 72 00:04:24,080 --> 00:04:29,000 Speaker 2: of a paper called Wallace's Line, Wallacea, and Associated Divides 73 00:04:29,140 --> 00:04:33,990 Speaker 2: and Areas, History of a Tortuous Tangle of Ideas and Labels. 74 00:04:34,370 --> 00:04:37,349 Speaker 2: This is by Ali and Heaney. published in the journal 75 00:04:37,390 --> 00:04:41,780 Speaker 2: Biological Reviews in 2021. So the authors go through the concept, 76 00:04:41,820 --> 00:04:44,380 Speaker 2: which we discussed in the last episode, the idea of 77 00:04:44,420 --> 00:04:47,340 Speaker 2: a faunal boundary being basically a place where you find 78 00:04:48,120 --> 00:04:50,970 Speaker 2: animals mainly of one sort on one side of the 79 00:04:51,010 --> 00:04:53,810 Speaker 2: line and animals mainly of a different sort on the 80 00:04:53,870 --> 00:04:56,550 Speaker 2: other side of the line. And this raises questions, how 81 00:04:56,610 --> 00:04:59,930 Speaker 2: did it end up like that? The authors write that 82 00:04:59,970 --> 00:05:03,990 Speaker 2: the earliest dividing lines in this region were considered quite sharp, 83 00:05:04,110 --> 00:05:08,830 Speaker 2: especially the line Wallace drew in 1863. And this was 84 00:05:08,890 --> 00:05:12,090 Speaker 2: based on looking at the distribution of land mammals and 85 00:05:12,190 --> 00:05:15,100 Speaker 2: some birds. This is the line we've been talking about 86 00:05:15,150 --> 00:05:18,839 Speaker 2: so far, passing between Bali and Lombok, with Asian animals 87 00:05:18,920 --> 00:05:24,660 Speaker 2: found west from the western coast of Bali and Australasian 88 00:05:24,760 --> 00:05:30,230 Speaker 2: animals running east from Lombok. This particular theoretical boundary proved 89 00:05:30,390 --> 00:05:33,210 Speaker 2: very influential and it got, you know, reproduced in a 90 00:05:33,230 --> 00:05:35,950 Speaker 2: lot of texts. It was baked into maps and plates 91 00:05:36,029 --> 00:05:38,170 Speaker 2: and stuff all over. So like it had a big 92 00:05:38,390 --> 00:05:43,150 Speaker 2: cultural footprint and within the discipline of biogeography, it came 93 00:05:43,230 --> 00:05:47,480 Speaker 2: to be seen as something of a fixed marker in nature, 94 00:05:47,560 --> 00:05:51,000 Speaker 2: maybe like the tree line on a mountain. But over time, 95 00:05:51,400 --> 00:05:54,760 Speaker 2: it also became obvious to experts in the field that Yeah. 96 00:05:54,779 --> 00:05:54,859 Speaker 1: Yeah. 97 00:06:20,150 --> 00:06:24,000 Speaker 2: By later in the 19th century, many biogeographers had started 98 00:06:24,060 --> 00:06:28,300 Speaker 2: to think about zones instead of lines. For example, there 99 00:06:28,380 --> 00:06:32,560 Speaker 2: is now a biogeographic region known as Wallasea. I've also 100 00:06:32,600 --> 00:06:37,400 Speaker 2: heard it pronounced Wallasia. So Wallasia or Wallasea, named after, again, 101 00:06:37,520 --> 00:06:40,740 Speaker 2: Alfred Russell Wallace. This region was sort of proposed in 102 00:06:40,760 --> 00:06:45,589 Speaker 2: the 1920s, which is a faunal transition zone where you 103 00:06:45,630 --> 00:06:49,270 Speaker 2: essentially have Australasian fauna. to the east of the zone, 104 00:06:49,490 --> 00:06:52,090 Speaker 2: Asian fauna to the west of the zone, and more 105 00:06:52,110 --> 00:06:56,050 Speaker 2: of a mix within. Though the western boundary of Wallacea 106 00:06:56,310 --> 00:07:00,170 Speaker 2: is still basically Wallace's line, passing between Bali and Lombok, 107 00:07:00,490 --> 00:07:03,690 Speaker 2: and in between Borneo and Sulawesi. So we're actually here 108 00:07:03,870 --> 00:07:07,370 Speaker 2: creeping a bit back toward that gradual transition idea of 109 00:07:07,450 --> 00:07:10,480 Speaker 2: animal ranges that we talked about in part one, though 110 00:07:10,570 --> 00:07:13,800 Speaker 2: some of the divisions you see, especially between Bali and Lombok, 111 00:07:14,200 --> 00:07:17,250 Speaker 2: are still actually quite striking. So, Rob, I included for 112 00:07:17,290 --> 00:07:19,730 Speaker 2: you to look at in our outline here an illustration 113 00:07:19,810 --> 00:07:22,200 Speaker 2: from one of the papers I was looking at. The 114 00:07:22,240 --> 00:07:25,240 Speaker 2: region highlighted in red and all the islands within that 115 00:07:25,320 --> 00:07:27,600 Speaker 2: is what is generally considered Wallasea today. 116 00:07:27,620 --> 00:07:29,960 Speaker 1: Yeah. And on this map here, it looks like a 117 00:07:29,980 --> 00:07:31,850 Speaker 1: big old heart, like a big old Valentine. They even 118 00:07:31,880 --> 00:07:32,430 Speaker 1: colored it red. 119 00:07:32,810 --> 00:07:34,790 Speaker 2: Happy Valentine's Day. You get some marsupials. 120 00:07:36,030 --> 00:07:38,490 Speaker 1: Yeah. And I was in the eastern part of this 121 00:07:38,530 --> 00:07:39,050 Speaker 1: very region. 122 00:07:39,470 --> 00:07:44,360 Speaker 2: Okay. So Ali and Heaney write that in the last 123 00:07:44,420 --> 00:07:47,980 Speaker 2: decade before their paper, even more new regions and boundary 124 00:07:48,020 --> 00:07:51,540 Speaker 2: modifications have been proposed, and the authors paint a truly 125 00:07:51,660 --> 00:07:55,620 Speaker 2: headache-inducing picture of the historical understanding of all this. As 126 00:07:55,660 --> 00:07:58,300 Speaker 2: they say in their title, it is a tortuous tangle 127 00:07:58,780 --> 00:08:01,810 Speaker 2: of ideas and labels. For example, I'm just going to 128 00:08:01,850 --> 00:08:05,690 Speaker 2: read one section of their abstract to give you an idea. Quote, 129 00:08:06,070 --> 00:08:10,510 Speaker 2: Wallace's 1863 line is not the one he finally settled 130 00:08:10,570 --> 00:08:15,250 Speaker 2: upon in 1910. Its path around Sulawesi was transferred from 131 00:08:15,270 --> 00:08:19,510 Speaker 2: the west to the east of the island. Ideally, Huxley's Divide, 132 00:08:19,570 --> 00:08:22,480 Speaker 2: and that's referring to Thomas Henry Huxley, who proposed a 133 00:08:22,710 --> 00:08:28,680 Speaker 2: modification to where the line goes, Huxley's Divide, 1868, should 134 00:08:28,720 --> 00:08:32,500 Speaker 2: carry his name rather than Wallace's. The latter never accepted 135 00:08:32,540 --> 00:08:36,920 Speaker 2: the proposition. Leidecker's line of 1896 ought to be labeled 136 00:08:36,980 --> 00:08:43,050 Speaker 2: the Heilprin-Leidecker line in recognition of Angelo Heilprin's 1887 contribution. 137 00:08:43,450 --> 00:08:47,950 Speaker 2: Concerning transition zones, ideally Wallasea should correspond to its original 138 00:08:47,950 --> 00:08:55,070 Speaker 2: 1924 description, which incorporated the Philippine islands bar the Palawan group. Notably, though, 139 00:08:55,210 --> 00:08:58,050 Speaker 2: a smaller form introduced by Darlington in 1957, used frequently 140 00:08:58,080 --> 00:09:02,640 Speaker 2: from 1998 onwards, in which all of the Philippine islands 141 00:09:02,679 --> 00:09:06,300 Speaker 2: are excluded, is entrenched within the recent literature, but this 142 00:09:06,380 --> 00:09:10,380 Speaker 2: is often without evident justification. It should also be recognized 143 00:09:10,500 --> 00:09:15,370 Speaker 2: that the reduced, meaning southern, Wallacea area was effectively defined 144 00:09:15,420 --> 00:09:19,970 Speaker 2: by Heilprin in 1887, but was then labeled the Austro-Malaysian 145 00:09:20,030 --> 00:09:24,350 Speaker 2: Transition Zone. So it's a mess. This is one reason 146 00:09:24,390 --> 00:09:27,750 Speaker 2: why I really enjoyed researching for these episodes, but when 147 00:09:27,770 --> 00:09:29,530 Speaker 2: I was reading all this stuff for the last episode, 148 00:09:29,570 --> 00:09:31,559 Speaker 2: I was just like, Oh, I can't. 149 00:09:32,460 --> 00:09:35,099 Speaker 1: Yeah. I mean, it's again, it's it's not like if 150 00:09:35,140 --> 00:09:37,240 Speaker 1: you take a kangaroo and have it walk over the 151 00:09:37,260 --> 00:09:41,600 Speaker 1: Wallace line, it will explode. So there's no it becomes 152 00:09:42,260 --> 00:09:45,310 Speaker 1: very difficult to actually test out some of these things. 153 00:09:45,410 --> 00:09:48,069 Speaker 1: It's based on a number of observations and vectors. 154 00:09:48,690 --> 00:09:52,370 Speaker 2: Well, these modifications absolutely are based on empirical observations. And 155 00:09:52,490 --> 00:09:56,030 Speaker 2: it's not just people kind of jousting around about absolutely 156 00:09:56,090 --> 00:10:01,180 Speaker 2: nothing There are reasons based on the different kinds of 157 00:10:01,320 --> 00:10:03,959 Speaker 2: fauna that have been observed and the underlying theory about 158 00:10:04,200 --> 00:10:10,109 Speaker 2: the geologic causes and so forth. But unfortunately, the theoretical 159 00:10:10,400 --> 00:10:14,150 Speaker 2: definition of the Wallace line and Wallacea are kind of 160 00:10:14,190 --> 00:10:17,440 Speaker 2: a mess. There have been a few details that have persisted, 161 00:10:17,660 --> 00:10:21,579 Speaker 2: but there has not been clear or consistent agreement across 162 00:10:21,679 --> 00:10:25,059 Speaker 2: time on where to place the boundaries, whether it's a 163 00:10:25,100 --> 00:10:28,280 Speaker 2: line or a zone, what to call those lines and zones, 164 00:10:28,340 --> 00:10:31,400 Speaker 2: and what exactly they mean. So you might be wondering 165 00:10:31,440 --> 00:10:34,359 Speaker 2: based on that, like, well, if we can't agree on 166 00:10:34,380 --> 00:10:37,240 Speaker 2: what we're talking about, is the idea of a faunal 167 00:10:37,280 --> 00:10:40,970 Speaker 2: boundary here just useless or is it nonsense? I think 168 00:10:41,000 --> 00:10:43,660 Speaker 2: the answer is no. I mean, for one thing, Some 169 00:10:43,700 --> 00:10:46,780 Speaker 2: of this confusion is historical, like there have been general 170 00:10:46,880 --> 00:10:49,630 Speaker 2: trends in how the idea is getting refined over time. 171 00:10:49,690 --> 00:10:51,830 Speaker 2: So there's nothing wrong with that. I mean, obviously ideas 172 00:10:51,850 --> 00:10:55,330 Speaker 2: get updated, but some of the confusion is also because 173 00:10:55,350 --> 00:10:58,570 Speaker 2: we're trying to figure out what exactly is being proposed here. 174 00:10:58,630 --> 00:11:00,950 Speaker 2: And so like you have gotten away from the idea 175 00:11:01,590 --> 00:11:04,450 Speaker 2: of a simple boundary line on a map that, you know, 176 00:11:04,470 --> 00:11:06,110 Speaker 2: where you have one thing on one side and one 177 00:11:06,170 --> 00:11:08,569 Speaker 2: on another and more into say the idea of a 178 00:11:08,630 --> 00:11:12,089 Speaker 2: transition zone. And it is absolutely still safe to say 179 00:11:12,150 --> 00:11:15,990 Speaker 2: that there is something very interesting with reference to biogeography 180 00:11:16,230 --> 00:11:19,900 Speaker 2: that's happening in the islands between Borneo and Bali to 181 00:11:19,920 --> 00:11:22,960 Speaker 2: the west and Papua New Guinea to the east, let's say. 182 00:11:23,540 --> 00:11:26,480 Speaker 2: And this boundary line or transition zone can tell us 183 00:11:26,559 --> 00:11:29,440 Speaker 2: a lot about the history of life on the surrounding 184 00:11:29,500 --> 00:11:31,900 Speaker 2: continents and the history of the Earth itself. 185 00:11:32,730 --> 00:11:35,150 Speaker 1: Yeah, and this is what they were trying to figure out, obviously, 186 00:11:35,290 --> 00:11:39,530 Speaker 1: in the late 19th century. But as we'll be discussing here, 187 00:11:39,770 --> 00:11:44,120 Speaker 1: they didn't have all the information they needed in order 188 00:11:44,160 --> 00:11:48,080 Speaker 1: to really understand and to make what we would think 189 00:11:48,100 --> 00:11:51,100 Speaker 1: of as a modern theory as to why it was 190 00:11:51,179 --> 00:11:51,600 Speaker 1: like this. 191 00:11:52,040 --> 00:11:54,160 Speaker 2: That's right. And so that brings us to the question 192 00:11:54,200 --> 00:11:58,219 Speaker 2: of what causes the boundary. We raised this in the 193 00:11:58,260 --> 00:12:00,510 Speaker 2: last episode, but we didn't really have time to answer it. 194 00:12:00,900 --> 00:12:04,449 Speaker 2: What causes the faunal boundary between the islands of, say, 195 00:12:04,490 --> 00:12:08,569 Speaker 2: Bali and Lombok? Why do you get mostly one set 196 00:12:08,610 --> 00:12:12,290 Speaker 2: of animals on Lombok and a fairly different set on Bali, 197 00:12:12,510 --> 00:12:15,630 Speaker 2: even though the straight between these two islands is just 198 00:12:15,690 --> 00:12:18,969 Speaker 2: a few dozen kilometers wide. It's like it's barely any 199 00:12:19,070 --> 00:12:22,230 Speaker 2: ocean at all. And also the environment on the two 200 00:12:22,690 --> 00:12:25,189 Speaker 2: islands is very similar. So it seems like you would 201 00:12:25,230 --> 00:12:27,630 Speaker 2: expect that the animals you find on one to be 202 00:12:27,730 --> 00:12:29,630 Speaker 2: the same as the ones you'd find on the other. 203 00:12:30,510 --> 00:12:31,000 Speaker 1: Right, right. 204 00:12:31,460 --> 00:12:35,230 Speaker 2: So to summarize sort of the original mainstream explanation, and 205 00:12:35,260 --> 00:12:37,610 Speaker 2: there will be some additions to this as we move 206 00:12:37,690 --> 00:12:42,070 Speaker 2: on in this episode, Wallace understood the cause of the 207 00:12:42,110 --> 00:12:45,869 Speaker 2: apparent faunal boundary between Bali and Lombok to be a 208 00:12:45,950 --> 00:12:52,320 Speaker 2: result of geological history. This is a core insight of biogeography. 209 00:12:52,580 --> 00:12:57,339 Speaker 2: Studying where animals live can tell us not only about 210 00:12:57,520 --> 00:13:01,890 Speaker 2: the animals, but also about the land. And there are 211 00:13:01,910 --> 00:13:05,429 Speaker 2: actually really awesome examples of this. If you get into 212 00:13:05,470 --> 00:13:11,750 Speaker 2: the way paleontology has helped interact with the geohistory of Earth, 213 00:13:11,830 --> 00:13:16,859 Speaker 2: like fossil organisms from hundreds of millions of years ago 214 00:13:17,240 --> 00:13:21,440 Speaker 2: that appeared to live only in Africa and South America. 215 00:13:21,460 --> 00:13:22,280 Speaker 1: Huh? 216 00:13:23,240 --> 00:13:26,859 Speaker 2: Well, one example of this, there's this early Permian reptile 217 00:13:27,360 --> 00:13:30,760 Speaker 2: called Mesosaurus that sort of shaped like a little crocodile. 218 00:13:31,270 --> 00:13:35,579 Speaker 2: It lived exclusively in freshwater lakes and rivers almost 300 219 00:13:35,580 --> 00:13:38,979 Speaker 2: million years ago, and its remains have only been found 220 00:13:39,179 --> 00:13:44,820 Speaker 2: in southern South America and southern Africa. Wait a minute. 221 00:13:44,920 --> 00:13:48,140 Speaker 2: If it only lived in freshwater, like lakes and rivers, 222 00:13:48,780 --> 00:13:52,270 Speaker 2: how did it get from Africa to South America and, 223 00:13:52,490 --> 00:13:55,570 Speaker 2: as far as we can tell, nowhere in between? And 224 00:13:55,590 --> 00:13:57,890 Speaker 2: then you've got other examples like this, like there's a 225 00:13:57,950 --> 00:14:03,990 Speaker 2: Triassic land-based therapsid called Sinonathus, also found in the fossil 226 00:14:04,050 --> 00:14:07,410 Speaker 2: record of South America and Africa, among a few other 227 00:14:07,590 --> 00:14:13,429 Speaker 2: equally baffling locations like Antarctica. These examples showed, along with 228 00:14:13,470 --> 00:14:16,130 Speaker 2: lots of other evidence that we have now, that these 229 00:14:16,200 --> 00:14:19,920 Speaker 2: two land masses used to be one, that the range 230 00:14:19,980 --> 00:14:23,180 Speaker 2: was one continuous range hundreds of millions of years ago. 231 00:14:23,760 --> 00:14:27,400 Speaker 2: and these animals died, their remains were deposited, they were 232 00:14:27,420 --> 00:14:31,140 Speaker 2: quickly buried, they became fossilized, and then the land split apart, 233 00:14:31,260 --> 00:14:34,250 Speaker 2: and the Atlantic Ocean in between was formed. So that's 234 00:14:34,350 --> 00:14:37,370 Speaker 2: one example of how biogeography can tell us not just 235 00:14:37,430 --> 00:14:50,610 Speaker 2: about the animals, but also about the land. Coming back 236 00:14:50,630 --> 00:14:54,850 Speaker 2: to Wallace, at the time Wallace lived plate tectonics was 237 00:14:55,170 --> 00:14:58,880 Speaker 2: not yet an accepted theory. In fact, it wasn't even 238 00:14:58,910 --> 00:15:01,820 Speaker 2: really proposed in a form that would be recognizable to 239 00:15:01,960 --> 00:15:05,140 Speaker 2: us until I think like the 1910s around then. And 240 00:15:05,160 --> 00:15:09,400 Speaker 2: it wouldn't be widely accepted by geologists until the 1960s. 241 00:15:09,960 --> 00:15:13,840 Speaker 2: So Wallace and his contemporaries did not know that the 242 00:15:13,940 --> 00:15:18,860 Speaker 2: continents and land masses of the earth moved around, splitting 243 00:15:18,900 --> 00:15:22,340 Speaker 2: and rejoining on the timescale and of tens or hundreds 244 00:15:22,380 --> 00:15:26,510 Speaker 2: of millions of years. But Wallace did know that the 245 00:15:26,550 --> 00:15:30,890 Speaker 2: surface of the Earth could change drastically due to other factors, 246 00:15:31,410 --> 00:15:36,390 Speaker 2: and one of those was climate. Climate patterns determine Earth's 247 00:15:36,490 --> 00:15:40,600 Speaker 2: average temperature and weather, and in instances long ago when 248 00:15:40,700 --> 00:15:43,680 Speaker 2: Earth's surface was colder and more of Earth's water was 249 00:15:43,760 --> 00:15:47,260 Speaker 2: locked up in polar ice caps, sea levels were lower, 250 00:15:47,820 --> 00:15:51,340 Speaker 2: much lower. As a result, many areas that are now 251 00:15:51,600 --> 00:15:55,160 Speaker 2: ocean were once dry land, and many parts of the 252 00:15:55,200 --> 00:15:59,330 Speaker 2: world that are now islands surrounded by shallow seas were 253 00:15:59,430 --> 00:16:04,550 Speaker 2: once continuous land masses, allowing land animals to cross freely 254 00:16:04,610 --> 00:16:07,580 Speaker 2: between them, which is how you end up with large 255 00:16:07,650 --> 00:16:11,300 Speaker 2: land mammals like tigers and elephants living on what appear 256 00:16:11,320 --> 00:16:15,170 Speaker 2: to be remote islands. In most cases, they didn't swim there, 257 00:16:15,290 --> 00:16:19,490 Speaker 2: certainly not in stable breeding populations. They crossed on land 258 00:16:19,610 --> 00:16:22,710 Speaker 2: at a time when there was a land bridge. And 259 00:16:23,270 --> 00:16:27,520 Speaker 2: for the most part, Wallace correctly identified that many islands 260 00:16:27,880 --> 00:16:31,140 Speaker 2: east of the line, of the Wallace line, were once 261 00:16:31,320 --> 00:16:36,160 Speaker 2: joined as a single land mass with Australia. This land 262 00:16:36,180 --> 00:16:40,180 Speaker 2: mass now known as the Paleocontinent Sahul, with islands west 263 00:16:40,240 --> 00:16:42,360 Speaker 2: of the line being once being part of a more 264 00:16:42,400 --> 00:16:48,200 Speaker 2: continuous landmass with Asia now known as Sunda. However, just 265 00:16:48,240 --> 00:16:51,660 Speaker 2: because islands are close to each other does not mean 266 00:16:51,680 --> 00:16:55,640 Speaker 2: a land bridge always forms between them when sea levels drop. 267 00:16:56,600 --> 00:17:00,380 Speaker 2: What Wallace did not know for sure, but what later 268 00:17:00,470 --> 00:17:04,690 Speaker 2: proved perfectly consistent with his observation of the faunal boundary, 269 00:17:05,490 --> 00:17:09,950 Speaker 2: is that between Bali and Lombok, there is a deep 270 00:17:10,230 --> 00:17:14,490 Speaker 2: ocean trench. The Strait of Lombok is not wide. Again, 271 00:17:14,570 --> 00:17:16,830 Speaker 2: it's just a few kilometers wide at the narrowest point, 272 00:17:17,150 --> 00:17:20,230 Speaker 2: but it is very deep, meaning that even when sea 273 00:17:20,270 --> 00:17:23,689 Speaker 2: levels were at their lowest, a land bridge between the 274 00:17:23,730 --> 00:17:27,360 Speaker 2: two islands never formed, and thus there was much less 275 00:17:27,440 --> 00:17:32,240 Speaker 2: opportunity for land-based animals to colonize one island from the other. 276 00:17:33,640 --> 00:17:36,420 Speaker 2: The reason for the existence of this deep ocean trench, 277 00:17:36,460 --> 00:17:39,720 Speaker 2: by the way, brings us back once again to plate tectonics. 278 00:17:39,840 --> 00:17:43,780 Speaker 2: This trench is the meeting point between two plates where 279 00:17:43,920 --> 00:17:47,840 Speaker 2: one is undergoing subduction, meaning it's being driven down underneath 280 00:17:47,920 --> 00:17:51,080 Speaker 2: the other plate at the meeting point. Subduction zones tend 281 00:17:51,100 --> 00:17:54,820 Speaker 2: to create deep ocean trenches along with other geologic activity 282 00:17:54,900 --> 00:17:59,730 Speaker 2: like earthquakes and volcanic eruptions. So plate tectonics also, it 283 00:18:00,330 --> 00:18:03,609 Speaker 2: explains that, the deep ocean trench that keeps the islands apart, 284 00:18:04,500 --> 00:18:08,180 Speaker 2: never forming a land bridge. But plate tectonics also helps 285 00:18:08,220 --> 00:18:13,280 Speaker 2: explain why there were such different collections of animals on 286 00:18:13,359 --> 00:18:17,040 Speaker 2: Sunda and Sahul to begin with. They were once separated 287 00:18:17,100 --> 00:18:21,120 Speaker 2: by much more ocean than they are now. Sahul, and again, 288 00:18:21,140 --> 00:18:24,220 Speaker 2: this is modern-day Australia and New Guinea and some other 289 00:18:24,260 --> 00:18:28,790 Speaker 2: associated islands, this was once part of the same landmass 290 00:18:28,950 --> 00:18:33,200 Speaker 2: as what is now Antarctica. And over tens of Millions 291 00:18:33,220 --> 00:18:37,640 Speaker 2: of years in isolation from the Afro-Eurasian and American landmasses, 292 00:18:38,080 --> 00:18:42,649 Speaker 2: this ancient continent experienced its own distinct branch of evolution, 293 00:18:43,130 --> 00:18:47,110 Speaker 2: giving us, for example, marsupials instead of the placental mammals 294 00:18:47,170 --> 00:18:48,830 Speaker 2: that you would find on the rest of the globe. 295 00:18:49,450 --> 00:18:51,930 Speaker 2: It was only a little more than 30 million years 296 00:18:51,990 --> 00:18:55,419 Speaker 2: ago that Sahul actually broke away from the landmass that 297 00:18:55,440 --> 00:18:58,909 Speaker 2: would become Antarctica. And so who will, after that slowly 298 00:18:58,950 --> 00:19:02,649 Speaker 2: drifted north and then collided with the continental plates of 299 00:19:02,730 --> 00:19:06,149 Speaker 2: Southeast Asia, giving us the arrangement of islands that we 300 00:19:06,190 --> 00:19:09,160 Speaker 2: see today in Indonesia and the Malay archipelago. And some 301 00:19:09,180 --> 00:19:12,379 Speaker 2: of the islands we see, uh, in that archipelago were, uh, 302 00:19:12,540 --> 00:19:16,100 Speaker 2: were created by the collision. They were raised up. Um, 303 00:19:16,420 --> 00:19:19,550 Speaker 2: but again, at the place where the plates collide, we 304 00:19:19,590 --> 00:19:22,310 Speaker 2: get a subduction zone and a deep ocean trench, which 305 00:19:22,390 --> 00:19:25,720 Speaker 2: means even though the islands are now close. Land bridges 306 00:19:25,780 --> 00:19:29,300 Speaker 2: never form between Bali and Lombok, so even though they 307 00:19:29,420 --> 00:19:32,340 Speaker 2: have been close now for millions of years, there is 308 00:19:32,460 --> 00:19:37,880 Speaker 2: relatively little interchange of large land animals back and forth. However, 309 00:19:38,080 --> 00:19:42,210 Speaker 2: there is some interchange, and as we've discussed already, all 310 00:19:42,290 --> 00:19:45,990 Speaker 2: faunal boundaries are to some extent permeable, and studying those 311 00:19:46,070 --> 00:19:49,070 Speaker 2: crossover examples can tell us even more about how this 312 00:19:49,150 --> 00:19:51,340 Speaker 2: boundary works. I'm going to come back to that in 313 00:19:51,380 --> 00:19:53,040 Speaker 2: a bit. But Rob, I think you also had some 314 00:19:53,060 --> 00:19:55,760 Speaker 2: good stuff about how this interacts with plate tectonics. 315 00:19:56,500 --> 00:19:58,340 Speaker 1: Yeah, and just getting a little bit into a little 316 00:19:58,359 --> 00:20:00,979 Speaker 1: more into just sort of the history of Wallace and 317 00:20:01,040 --> 00:20:05,640 Speaker 1: Darwin in trying to figure out why the Wallace line 318 00:20:05,680 --> 00:20:08,240 Speaker 1: seemed to be a thing. How this boundary worked and 319 00:20:08,260 --> 00:20:10,900 Speaker 1: what were the factors behind it. Again, as you mentioned, 320 00:20:11,100 --> 00:20:14,300 Speaker 1: we didn't have continental drift in a sort of crystallized 321 00:20:14,340 --> 00:20:18,419 Speaker 1: form until 1912, and we didn't have plate tectonics until 322 00:20:18,700 --> 00:20:22,030 Speaker 1: the 1960s, again, in its more crystallized accepted form. At 323 00:20:22,050 --> 00:20:25,290 Speaker 1: the time, a leading approach to understanding all this was 324 00:20:25,350 --> 00:20:30,910 Speaker 1: a theory of continental extensionism, which Radical by Nature author 325 00:20:30,950 --> 00:20:36,070 Speaker 1: James T. Costa describes as land bridges on steroids. So, 326 00:20:36,109 --> 00:20:39,970 Speaker 1: you know, we've been talking here about the concept of 327 00:20:40,010 --> 00:20:42,930 Speaker 1: land bridges and how they work. And again, they're certainly real. 328 00:20:43,930 --> 00:20:47,649 Speaker 1: The Isthmus of Panama is a current land bridge. Lost 329 00:20:47,710 --> 00:20:51,050 Speaker 1: land bridges once connected India and Sri Lanka. And a 330 00:20:51,090 --> 00:20:54,840 Speaker 1: landmass known as the Bassian Plain once connected Tasmania to 331 00:20:54,880 --> 00:20:57,760 Speaker 1: mainland Australia. And of course, we've also talked about the 332 00:20:57,920 --> 00:21:00,960 Speaker 1: now submerged North Sea landmass of Doggerland. 333 00:21:01,500 --> 00:21:03,280 Speaker 2: Yeah, we did a couple of episodes on that. Go 334 00:21:03,300 --> 00:21:05,479 Speaker 2: back and look them up. They're from sometime last year. 335 00:21:06,109 --> 00:21:09,889 Speaker 1: So land bridges as an explanation for certain regional slash 336 00:21:09,970 --> 00:21:14,330 Speaker 1: local examples of geological distribution, that's all good. The problem 337 00:21:14,410 --> 00:21:17,859 Speaker 1: with continental extensionism as it was used at the time 338 00:21:18,180 --> 00:21:20,920 Speaker 1: was that it leaned heavily on this as the prime 339 00:21:20,980 --> 00:21:23,899 Speaker 1: or even the only way that many forms of fauna 340 00:21:23,940 --> 00:21:28,570 Speaker 1: had spread, employing actual and likely examples of land bridges, 341 00:21:28,590 --> 00:21:32,129 Speaker 1: you know, sunken land masses and shallow seas and but 342 00:21:32,170 --> 00:21:35,970 Speaker 1: then adding in other necessary lost land masses and land 343 00:21:36,010 --> 00:21:40,100 Speaker 1: bridges as required to fill in the gaps, often with 344 00:21:40,170 --> 00:21:43,919 Speaker 1: little or no actual evidence, and even dipping into lost 345 00:21:44,000 --> 00:21:47,520 Speaker 1: continent myth-making and pseudoscience in order to get the job done. 346 00:21:47,859 --> 00:21:49,200 Speaker 2: Gotta love a lost continent. 347 00:21:49,880 --> 00:21:52,639 Speaker 1: I mean, we all do. It's a wonderful concept in 348 00:21:52,760 --> 00:21:57,310 Speaker 1: myth and in fiction and science fiction. But yeah, this 349 00:21:57,330 --> 00:21:59,730 Speaker 1: was especially the case when trying to connect the dots 350 00:21:59,790 --> 00:22:03,929 Speaker 1: across abyssal seas. So you'd have respected naturalists of the 351 00:22:03,970 --> 00:22:09,010 Speaker 1: day suddenly leaning into the idea of Lemuria, but even Atlantis. 352 00:22:09,609 --> 00:22:11,590 Speaker 2: We may have also talked about them in a series 353 00:22:11,609 --> 00:22:15,389 Speaker 2: of episodes we did, I think, starting with the El 354 00:22:15,430 --> 00:22:18,889 Speaker 2: Tannin antenna, where we were talking about how people take 355 00:22:19,570 --> 00:22:22,980 Speaker 2: anomalous underwater imagery that kind of looks interesting and then 356 00:22:23,140 --> 00:22:25,980 Speaker 2: kind of run wild with it, deciding that, oh, this 357 00:22:26,060 --> 00:22:29,859 Speaker 2: thing underwater has got to be an alien antenna. And actually, 358 00:22:29,900 --> 00:22:32,980 Speaker 2: it's probably a sponge. And this other thing has got 359 00:22:33,020 --> 00:22:36,220 Speaker 2: to be evidence of Atlantis when actually it's probably a rock. 360 00:22:36,740 --> 00:22:41,380 Speaker 1: That's right. And we definitely talked about Lemuria. This one's 361 00:22:41,420 --> 00:22:44,619 Speaker 1: a little different compared to Atlantis. It was proposed in 362 00:22:44,619 --> 00:22:48,659 Speaker 1: 1864 by zoologist Philip Sclater to explain the presence of 363 00:22:48,760 --> 00:22:53,330 Speaker 1: lemur fossils, thus Lemuria, on Madagascar and in India, but 364 00:22:53,400 --> 00:22:55,730 Speaker 1: not in Africa or the Middle East. So you can 365 00:22:56,150 --> 00:22:59,490 Speaker 1: see how Lemuria is very much about filling in that gap. 366 00:22:59,940 --> 00:23:02,300 Speaker 1: saying these creatures had to get from one side of 367 00:23:02,359 --> 00:23:04,659 Speaker 1: the world as we know it to another. How did 368 00:23:04,700 --> 00:23:06,760 Speaker 1: they do it? There had to be a land bridge, 369 00:23:07,060 --> 00:23:08,810 Speaker 1: but not just any land bridge. There had to be 370 00:23:08,869 --> 00:23:11,230 Speaker 1: a lost continent right there in the middle. 371 00:23:11,590 --> 00:23:13,850 Speaker 2: That's funny because it would be trying to explain actually 372 00:23:13,950 --> 00:23:17,650 Speaker 2: what is evidence for continental drift or plate tectonics. 373 00:23:18,109 --> 00:23:21,670 Speaker 1: Right, right. So initially it's just, it was an idea to, 374 00:23:22,630 --> 00:23:25,379 Speaker 1: Lemuria was just a way to hypothetically fill in the 375 00:23:25,420 --> 00:23:31,340 Speaker 1: blanks here using continental extensionism. to explain everything. And other 376 00:23:31,600 --> 00:23:35,600 Speaker 1: individuals like biologist Ernst Haeckel considered the idea that human 377 00:23:35,680 --> 00:23:38,719 Speaker 1: origins might tie to this lost continent as well. But 378 00:23:38,760 --> 00:23:42,280 Speaker 1: then in the late 19th century, occultists began to appropriate 379 00:23:42,320 --> 00:23:45,890 Speaker 1: the concept. And Lemuria, of course, dies as a scientific 380 00:23:45,930 --> 00:23:50,390 Speaker 1: hypothesis in the 1960s, but refuses to die in occultism, 381 00:23:50,550 --> 00:23:54,040 Speaker 1: conspiracy theory, and of course, fiction. You can look to 382 00:23:54,080 --> 00:23:57,240 Speaker 1: various examples, such as the fiction of Robert E. Howard, 383 00:23:57,260 --> 00:24:01,379 Speaker 1: the fiction of Lynn Carter. You'll find Lemuria showing up 384 00:24:01,480 --> 00:24:04,990 Speaker 1: as a location for various fantastic magical adventures. 385 00:24:05,350 --> 00:24:08,250 Speaker 2: It's a great place to have a leather diaper barbarian 386 00:24:08,310 --> 00:24:09,770 Speaker 2: face some psychic monsters. 387 00:24:10,210 --> 00:24:16,909 Speaker 1: Yes. So continental extensionism, this was a concept that Wallace 388 00:24:16,930 --> 00:24:20,290 Speaker 1: himself was rather taken with early on. Again, it seemed 389 00:24:20,350 --> 00:24:24,710 Speaker 1: a possible way to explain geological distribution of fauna and 390 00:24:24,770 --> 00:24:27,649 Speaker 1: explain some of what he was seeing. Though obviously, as 391 00:24:27,690 --> 00:24:31,390 Speaker 1: we've also discussed, he clearly wasn't opposed to viewpoints outside 392 00:24:31,410 --> 00:24:34,510 Speaker 1: of the scientific mainstream. Again, he was very interested in 393 00:24:34,550 --> 00:24:38,169 Speaker 1: spiritualism and defended spiritualism and so forth. So it's not 394 00:24:38,210 --> 00:24:42,919 Speaker 1: a stretch to imagine that he wouldn't have strong objections 395 00:24:42,980 --> 00:24:46,050 Speaker 1: to some of these concepts, which again, at the time, 396 00:24:46,109 --> 00:24:48,369 Speaker 1: were not like firmly wrapped up in a lot of 397 00:24:48,430 --> 00:24:54,310 Speaker 1: occultist dreaming and was more firmly within the realm of 398 00:24:54,630 --> 00:24:56,790 Speaker 1: possible scientific explanations for the world. 399 00:24:57,090 --> 00:24:59,910 Speaker 2: That's right. And again, to clarify, we talked about this 400 00:24:59,950 --> 00:25:02,700 Speaker 2: last time, but spiritualism is different than what people mean 401 00:25:02,720 --> 00:25:05,980 Speaker 2: when they say, like, I'm spiritual today. Spiritualism then meant 402 00:25:06,020 --> 00:25:08,859 Speaker 2: the belief that you could make contact with and communicate 403 00:25:08,920 --> 00:25:12,140 Speaker 2: with the dead or with spirits other than living humans. 404 00:25:12,820 --> 00:25:16,119 Speaker 2: And that kind of contact was exciting to a lot 405 00:25:16,140 --> 00:25:18,780 Speaker 2: of people who were in the sciences. They were like, hey, look, 406 00:25:18,820 --> 00:25:22,320 Speaker 2: here's something we can study empirically. Let's study it. Let's 407 00:25:22,359 --> 00:25:22,899 Speaker 2: take notes. 408 00:25:23,700 --> 00:25:25,359 Speaker 1: And this is another place where we kind of get 409 00:25:25,400 --> 00:25:29,000 Speaker 1: into the butting heads of Darwin and Wallace. So again, 410 00:25:29,080 --> 00:25:33,430 Speaker 1: these two were not enemies. They wrote to each other. 411 00:25:33,530 --> 00:25:36,970 Speaker 1: They seemed friendly with each other. And Wallace looked up 412 00:25:37,010 --> 00:25:39,770 Speaker 1: to Darwin. But Darwin really hated all of this. He 413 00:25:39,850 --> 00:25:42,570 Speaker 1: hated that naturalists would even flirt with the idea of 414 00:25:42,670 --> 00:25:46,010 Speaker 1: Atlantis and And Darwin believed that over the course of 415 00:25:46,090 --> 00:25:51,650 Speaker 1: life's history on Earth, wind, wing, flotation, these were sufficient 416 00:25:51,710 --> 00:25:54,590 Speaker 1: to explain everything that we saw. In fact, Darwin favored 417 00:25:54,630 --> 00:25:58,149 Speaker 1: the permanence of ocean basins and continents in his calculations. 418 00:25:58,609 --> 00:26:01,010 Speaker 1: So not to say he thought everything was set in stone. 419 00:26:01,030 --> 00:26:05,110 Speaker 1: You know, he recognized that there would be regional uplift 420 00:26:05,170 --> 00:26:08,300 Speaker 1: and subsidence. For example, this was a key part of 421 00:26:08,340 --> 00:26:11,660 Speaker 1: his understanding of how reefs and atolls formed. We've talked 422 00:26:11,700 --> 00:26:15,290 Speaker 1: about that on the show before. But, you know, he 423 00:26:15,350 --> 00:26:19,710 Speaker 1: was he was not keen on the idea that there 424 00:26:19,770 --> 00:26:24,270 Speaker 1: were lost continents that would have connected one landmass to 425 00:26:24,330 --> 00:26:27,070 Speaker 1: another and didn't think they were necessary. More to the point. 426 00:26:29,190 --> 00:26:32,710 Speaker 1: And this is all interesting because everyone here had some 427 00:26:32,770 --> 00:26:36,830 Speaker 1: really good ideas going on. But those ideas had to 428 00:26:36,910 --> 00:26:39,429 Speaker 1: ultimately be overclocked to make up for what we had 429 00:26:39,470 --> 00:26:42,800 Speaker 1: yet to settle on regarding continental drift and plate tectonics. 430 00:26:44,060 --> 00:26:48,420 Speaker 1: So again, land bridges are a local slash regional reality, 431 00:26:48,820 --> 00:26:52,399 Speaker 1: but you can't apply them globally. It's not a solution 432 00:26:52,440 --> 00:26:55,960 Speaker 1: to every problem in the distribution of fauna. Right. 433 00:26:56,140 --> 00:26:58,459 Speaker 2: Land bridges explain a lot, but they don't explain how 434 00:26:58,520 --> 00:27:01,600 Speaker 2: life forms got to Easter Island or to Hawaii, for 435 00:27:01,619 --> 00:27:02,060 Speaker 2: that matter. 436 00:27:02,520 --> 00:27:06,580 Speaker 1: Right, right. And wing wind and flotation can get the 437 00:27:06,600 --> 00:27:10,500 Speaker 1: job done over the fullness of time, sometimes in remarkable ways, 438 00:27:10,920 --> 00:27:13,800 Speaker 1: but there are limitations to that as well. But there 439 00:27:13,859 --> 00:27:16,900 Speaker 1: are also some pretty amazing examples. I'm reminded of my 440 00:27:16,980 --> 00:27:19,580 Speaker 1: recent interview with Tom Lathan about his book, Lost Wonders, 441 00:27:19,920 --> 00:27:22,149 Speaker 1: regarding a number of species that wind up in rare, 442 00:27:22,230 --> 00:27:27,250 Speaker 1: far-flung places, including both the Galapagos tortoise, which that's, as 443 00:27:27,290 --> 00:27:29,270 Speaker 1: we've discussed in the show before, that's an example of 444 00:27:29,310 --> 00:27:33,650 Speaker 1: flotation in action. But then you have the now extinct St. 445 00:27:33,710 --> 00:27:37,410 Speaker 1: Helena olive of St. Helena Island in the South Atlantic. 446 00:27:38,840 --> 00:27:42,720 Speaker 1: The olive, as listeners might remember, possibly became established there 447 00:27:42,760 --> 00:27:45,840 Speaker 1: by dropping off of an albatross. So it's one of 448 00:27:45,880 --> 00:27:50,109 Speaker 1: these things that was extremely unlikely to occur, but unlikely 449 00:27:50,230 --> 00:27:54,450 Speaker 1: rare events do occur over the course of geological time. 450 00:27:55,430 --> 00:27:58,650 Speaker 1: So Wallace did eventually come around to a different understanding 451 00:27:59,119 --> 00:28:02,920 Speaker 1: and wrote the 1880 book, Island Life, in which he 452 00:28:03,080 --> 00:28:06,640 Speaker 1: sets aside really any thought of lost continents in favor 453 00:28:06,720 --> 00:28:09,600 Speaker 1: of kind of a combo of both land bridges and 454 00:28:09,720 --> 00:28:14,550 Speaker 1: long-distance dispersal via wind, wing, and flotation. And so in this, 455 00:28:14,830 --> 00:28:17,410 Speaker 1: it brought his line of thinking closer to Darwin's own, 456 00:28:17,950 --> 00:28:20,430 Speaker 1: but ultimately leaning on a combination of factors. 457 00:28:21,190 --> 00:28:23,590 Speaker 2: And again, he was aware of the idea of past 458 00:28:23,710 --> 00:28:26,720 Speaker 2: sea level changes due to changes in how much of 459 00:28:27,119 --> 00:28:28,680 Speaker 2: Earth's water is locked up in ice. 460 00:28:29,100 --> 00:28:32,919 Speaker 1: Absolutely. And again, those deep ocean trenches, though, would have 461 00:28:32,940 --> 00:28:35,610 Speaker 1: just been too deep to have been impacted by these 462 00:28:35,630 --> 00:28:38,120 Speaker 1: sea level drops, you know, I mean, sea level can 463 00:28:38,160 --> 00:28:40,060 Speaker 1: only drop so much and you're still going to have 464 00:28:40,080 --> 00:28:49,550 Speaker 1: to contend with trenches at that point. 465 00:28:51,630 --> 00:28:54,750 Speaker 2: So I was looking for some more recent papers on 466 00:28:54,810 --> 00:28:57,210 Speaker 2: the Wallace line, and I came across one that I 467 00:28:57,370 --> 00:29:00,880 Speaker 2: thought was pretty interesting. This was a 2023 study published 468 00:29:00,910 --> 00:29:05,320 Speaker 2: in the journal Science by Skeels et al. called Paleoenvironments 469 00:29:05,540 --> 00:29:11,460 Speaker 2: Shaped by Exchange of Terrestrial Vertebrates Across Wallace's Line. The 470 00:29:11,540 --> 00:29:14,940 Speaker 2: authors in this paper start off by establishing a concept 471 00:29:15,000 --> 00:29:20,140 Speaker 2: called biotic interchange. This is what happens when the flora 472 00:29:20,240 --> 00:29:26,020 Speaker 2: and fauna of two previously separate regions are suddenly allowed 473 00:29:26,040 --> 00:29:29,200 Speaker 2: to move into each other. They're allowed to freely colonize 474 00:29:29,320 --> 00:29:33,190 Speaker 2: one another's regions. Examples of this usually occur when a 475 00:29:33,330 --> 00:29:37,510 Speaker 2: barrier to travel between two places is suddenly removed, and 476 00:29:37,710 --> 00:29:42,300 Speaker 2: suddenly here would be a relative modification. suddenly on geologic time. 477 00:29:42,940 --> 00:29:46,180 Speaker 2: One example of this is the American Interchange, where land 478 00:29:46,370 --> 00:29:49,990 Speaker 2: and freshwater animals from North and South America were suddenly 479 00:29:50,230 --> 00:29:54,550 Speaker 2: able to migrate across into each other's territory and After, Rob, 480 00:29:54,590 --> 00:29:58,630 Speaker 2: you mentioned this earlier, the idea of the Panama Isthmus. Oh, man, 481 00:29:58,670 --> 00:30:00,690 Speaker 2: that word is so hard to say. Isthmus for me. 482 00:30:00,920 --> 00:30:06,600 Speaker 2: It's difficult. After the Panama Isthmus was raised by volcanic activity. 483 00:30:07,380 --> 00:30:10,060 Speaker 2: So that came up from the seafloor. And previously there 484 00:30:10,080 --> 00:30:13,020 Speaker 2: had been a saltwater barrier between North and South America 485 00:30:13,080 --> 00:30:16,240 Speaker 2: for some time. But you have this volcanic activity. Now 486 00:30:16,260 --> 00:30:19,900 Speaker 2: there's a land bridge in Central America that happens between 487 00:30:19,940 --> 00:30:22,650 Speaker 2: two and three million years ago. And now there's all 488 00:30:22,670 --> 00:30:26,620 Speaker 2: this exchange of life forms across the barrier, or across 489 00:30:26,630 --> 00:30:30,920 Speaker 2: the former barrier. Another one of these great biotic mingling 490 00:30:30,980 --> 00:30:36,780 Speaker 2: events is the Indo-Australian Interchange, which arose when the Australian 491 00:30:36,880 --> 00:30:41,320 Speaker 2: and Eurasian tectonic plates smashed together, forming some islands in 492 00:30:41,360 --> 00:30:44,180 Speaker 2: between within the region we were talking about earlier, known 493 00:30:44,300 --> 00:30:47,920 Speaker 2: as Wallasea. Now, we've already talked about how there are 494 00:30:48,120 --> 00:30:52,480 Speaker 2: some barriers to exchange along this connection process. The extent 495 00:30:52,520 --> 00:30:56,180 Speaker 2: of that barrier to cross colonization was the original observation 496 00:30:56,220 --> 00:30:58,900 Speaker 2: of the Wallace line. It's like what Wallace observed is, hey, 497 00:30:58,940 --> 00:31:01,440 Speaker 2: there's not a lot of animal species going across here. 498 00:31:02,370 --> 00:31:06,210 Speaker 2: Unlike the American interchange, there there is not and was 499 00:31:06,290 --> 00:31:10,430 Speaker 2: never a full land bridge between Sunda and Sahul. But 500 00:31:11,090 --> 00:31:14,590 Speaker 2: as Wallace also observed, all boundaries are permeable. And we 501 00:31:14,650 --> 00:31:18,070 Speaker 2: now know a good bit of exchange does happen across 502 00:31:18,150 --> 00:31:22,880 Speaker 2: this this line. And there are some more faunally mixed 503 00:31:23,100 --> 00:31:27,870 Speaker 2: transition zones in between in the islands of Wallacea. But 504 00:31:27,880 --> 00:31:31,910 Speaker 2: the authors of this paper point out something interesting. Biotic 505 00:31:31,950 --> 00:31:36,989 Speaker 2: interchanges are rarely symmetrical. They're rarely totally even. Usually you 506 00:31:37,030 --> 00:31:40,469 Speaker 2: have more life flowing in one direction across the new 507 00:31:40,530 --> 00:31:44,350 Speaker 2: corridor than flowing in the other direction. Why would that be? 508 00:31:44,590 --> 00:31:50,360 Speaker 2: Why the asymmetry? Some answers lie in characteristics of the organisms. 509 00:31:50,760 --> 00:31:54,300 Speaker 2: Maybe some organisms are just more adaptable. They're better at 510 00:31:54,320 --> 00:31:57,760 Speaker 2: dispersing into new environments. Maybe they're better at evolving more 511 00:31:57,820 --> 00:32:01,470 Speaker 2: quickly and changing what they're adapted to. But some answers, 512 00:32:01,570 --> 00:32:04,310 Speaker 2: on the other hand, might lie in characteristics of the 513 00:32:04,450 --> 00:32:08,070 Speaker 2: land and environment on either side of the new corridor 514 00:32:08,590 --> 00:32:12,690 Speaker 2: or within the corridor itself. What if something about the 515 00:32:12,850 --> 00:32:18,150 Speaker 2: geography favors dispersal one way but not the other? And 516 00:32:18,170 --> 00:32:20,739 Speaker 2: to be clear here, the authors do not argue that 517 00:32:20,820 --> 00:32:23,380 Speaker 2: Wallace was wrong about the deep ocean trench in the 518 00:32:23,420 --> 00:32:25,740 Speaker 2: Lombok Strait being a barrier to dispersal. 519 00:32:26,140 --> 00:32:26,640 Speaker 1: It is. 520 00:32:26,740 --> 00:32:29,600 Speaker 2: It does stop a lot of exchange. And they note 521 00:32:29,640 --> 00:32:32,680 Speaker 2: that the only mammals which seem to have successfully crossed 522 00:32:32,720 --> 00:32:37,410 Speaker 2: that boundary naturally are bats and rodents. Big mammals seemingly 523 00:32:37,490 --> 00:32:41,190 Speaker 2: do not cross. But of the animals that have crossed, 524 00:32:41,550 --> 00:32:45,750 Speaker 2: one thing that is clear is which way the asymmetry goes. 525 00:32:46,430 --> 00:32:49,930 Speaker 2: Over the last 20 million years, way more animals from 526 00:32:50,130 --> 00:32:54,290 Speaker 2: Asia have successfully crossed the barrier and made their way 527 00:32:54,490 --> 00:32:58,650 Speaker 2: into New Guinea and onto the Australian continent. Relatively little 528 00:32:58,710 --> 00:33:02,320 Speaker 2: dispersal has gone the other direction, from Australia and New 529 00:33:02,340 --> 00:33:07,140 Speaker 2: Guinea to the west into Asia. Why would that be? Well, 530 00:33:07,180 --> 00:33:10,979 Speaker 2: the authors argue, based on analysis of a huge dataset 531 00:33:11,120 --> 00:33:14,590 Speaker 2: and a sophisticated computer model, that the answer has to 532 00:33:14,650 --> 00:33:19,490 Speaker 2: do with the climate of the islands within and on 533 00:33:19,690 --> 00:33:24,410 Speaker 2: either side of Wallacea, especially how wet or dry those 534 00:33:24,550 --> 00:33:27,800 Speaker 2: islands are and the precipitation tolerance of the animals that 535 00:33:27,840 --> 00:33:32,230 Speaker 2: evolved on either side. So to quote the authors, quote, Here, 536 00:33:32,310 --> 00:33:35,969 Speaker 2: analysis of more than 20,000 vertebrate species with a model 537 00:33:36,030 --> 00:33:41,350 Speaker 2: of geoclimate and biological diversification shows that broad precipitation tolerance 538 00:33:41,510 --> 00:33:45,810 Speaker 2: and dispersal ability were key for exchange across the deep-time 539 00:33:45,910 --> 00:33:51,590 Speaker 2: precipitation gradient spanning the region. Sundanian, meaning Southeast Asian lineages, 540 00:33:52,050 --> 00:33:55,930 Speaker 2: evolved in a climate similar to the humid, quote, stepping 541 00:33:55,990 --> 00:34:01,890 Speaker 2: stones of Wallasea. facilitating colonization of the Sahulian, meaning Australian, 542 00:34:02,110 --> 00:34:09,090 Speaker 2: continental shelf. By contrast, Sahulian lineages predominantly evolved in drier conditions, 543 00:34:09,570 --> 00:34:15,130 Speaker 2: hampering establishment in Sunda and shaping faunal distinctiveness. So, in 544 00:34:15,150 --> 00:34:19,029 Speaker 2: other words, the islands in the transition zone here are 545 00:34:19,090 --> 00:34:23,470 Speaker 2: typically full of tropical rainforests, like you would find further 546 00:34:23,710 --> 00:34:28,160 Speaker 2: up on the Malay Peninsula and the Asian mainland. New Guinea, 547 00:34:28,420 --> 00:34:32,370 Speaker 2: on the same tectonic plate with Australia, is also dominated 548 00:34:32,489 --> 00:34:37,770 Speaker 2: with tropical rainforest. So animals adapted to Asian tropical rainforests 549 00:34:38,230 --> 00:34:42,930 Speaker 2: would find generally familiar and tolerably wet climates throughout most 550 00:34:42,989 --> 00:34:46,759 Speaker 2: of the islands that formed these stepping stones leading to 551 00:34:46,860 --> 00:34:51,339 Speaker 2: Australia and New Guinea. And once they reached Australia, there 552 00:34:51,380 --> 00:34:54,280 Speaker 2: would be different conditions. The continent would be much drier. 553 00:34:54,739 --> 00:34:58,420 Speaker 2: But they could have more evolutionary time to adapt by 554 00:34:58,500 --> 00:35:02,239 Speaker 2: colonizing the islands along the way or by landing in 555 00:35:02,260 --> 00:35:06,450 Speaker 2: the friendly climate of New Guinea. Meanwhile, animals adapted to 556 00:35:06,489 --> 00:35:09,850 Speaker 2: the dry climate of Australia would have a quite difficult 557 00:35:09,930 --> 00:35:15,069 Speaker 2: time finding hospitable conditions along the humid stepping stones. And 558 00:35:15,330 --> 00:35:17,690 Speaker 2: once you get to the Asian mainland, it's still just 559 00:35:17,730 --> 00:35:22,740 Speaker 2: humid and dominated by tropical rainforests. So because the transitional 560 00:35:22,880 --> 00:35:26,700 Speaker 2: islands in between were more easily tolerated by the Asian animals, 561 00:35:27,110 --> 00:35:30,330 Speaker 2: more Asian animals flowed into the land masses of the 562 00:35:30,390 --> 00:35:33,609 Speaker 2: Australian plate than the other way around. And I thought 563 00:35:33,630 --> 00:35:37,290 Speaker 2: that was really interesting because it, I don't know if 564 00:35:37,550 --> 00:35:39,780 Speaker 2: it often occurs to us to think when we think 565 00:35:39,840 --> 00:35:44,560 Speaker 2: about like animals dispersing from one region into another, we 566 00:35:44,600 --> 00:35:47,319 Speaker 2: think about the, the sort of end stage reach, like 567 00:35:47,360 --> 00:35:50,180 Speaker 2: they start here and then they end up here. But 568 00:35:50,380 --> 00:35:53,930 Speaker 2: the place that they're having to move through as they 569 00:35:53,989 --> 00:35:57,529 Speaker 2: migrate also plays a big role in whether that migration 570 00:35:57,590 --> 00:35:58,930 Speaker 2: can take place at all. 571 00:35:59,910 --> 00:36:00,850 Speaker 1: Yeah, that's a great point. 572 00:36:01,410 --> 00:36:02,850 Speaker 2: I was trying to think of a good analogy, and 573 00:36:03,150 --> 00:36:06,759 Speaker 2: this doesn't exactly work, but to grossly oversimplify. What if 574 00:36:06,820 --> 00:36:11,440 Speaker 2: there were a highway suddenly opened across the Atlantic Ocean 575 00:36:11,660 --> 00:36:15,410 Speaker 2: between Great Britain and the United States, and you could 576 00:36:15,469 --> 00:36:18,550 Speaker 2: cross it by car? Do you think you'd have more 577 00:36:18,650 --> 00:36:22,160 Speaker 2: people crossing one way or another? I mean, in reality, 578 00:36:22,180 --> 00:36:24,540 Speaker 2: there would be a lot of things influencing this. But 579 00:36:24,960 --> 00:36:27,520 Speaker 2: you could imagine that which side of the highway you 580 00:36:27,780 --> 00:36:30,960 Speaker 2: have to drive on on the highway going in between 581 00:36:31,420 --> 00:36:33,799 Speaker 2: might determine a lot about who decides to make the 582 00:36:33,840 --> 00:36:36,320 Speaker 2: journey more often. Like if you got to be if 583 00:36:36,340 --> 00:36:37,739 Speaker 2: you got to be on the left side of the road, 584 00:36:37,800 --> 00:36:39,900 Speaker 2: I can imagine a lot of Americans saying, I'm not 585 00:36:39,920 --> 00:36:41,500 Speaker 2: driving that far on the left side. I don't know 586 00:36:41,520 --> 00:36:43,680 Speaker 2: how to do that. So if we were driving on 587 00:36:43,700 --> 00:36:45,420 Speaker 2: the left side, maybe it would be a motorway and 588 00:36:45,480 --> 00:36:46,680 Speaker 2: not a highway. I'm not sure. 589 00:36:46,719 --> 00:36:48,839 Speaker 1: Yeah, yeah. But I see what you're going for here. 590 00:36:48,860 --> 00:36:52,360 Speaker 1: Like the side of the car that you drive upon 591 00:36:52,440 --> 00:36:56,090 Speaker 1: is kind of like the environmental conditions of the passage. Yeah. Yeah. 592 00:36:56,530 --> 00:37:00,190 Speaker 1: And how conducive drivers on either side are going to 593 00:37:00,270 --> 00:37:01,710 Speaker 1: be to that passage. Yeah. 594 00:37:01,770 --> 00:37:04,290 Speaker 2: It's not just how well adapted you already are to 595 00:37:04,330 --> 00:37:07,130 Speaker 2: the end point. It's like how well adapted you are 596 00:37:07,150 --> 00:37:08,850 Speaker 2: to each little step along the way. 597 00:37:08,870 --> 00:37:09,450 Speaker 1: Yeah. Yeah. 598 00:37:10,050 --> 00:37:13,410 Speaker 2: And in the case of Wallacea, it proved easier for 599 00:37:13,510 --> 00:37:19,230 Speaker 2: the humid adapted Asian mainland fauna to make the journey into, 600 00:37:19,350 --> 00:37:20,550 Speaker 2: especially into New Guinea. 601 00:37:22,430 --> 00:37:26,030 Speaker 1: Now, as we begin to reach the end of this episode, 602 00:37:26,590 --> 00:37:28,440 Speaker 1: I want to bring it back a little bit to 603 00:37:28,480 --> 00:37:32,920 Speaker 1: my travel experience in Indonesia, where I actually visited these 604 00:37:32,980 --> 00:37:35,000 Speaker 1: stepping stones or some of these stepping stones we've been 605 00:37:35,020 --> 00:37:38,480 Speaker 1: talking about. So again, I was east of the Wallace 606 00:37:38,520 --> 00:37:42,560 Speaker 1: line in Raja Ampat. which situated us also in an 607 00:37:42,780 --> 00:37:47,299 Speaker 1: area that is often called the Coral Triangle. Joe, I've 608 00:37:47,340 --> 00:37:49,890 Speaker 1: included a map of the Coral Triangle for you here. 609 00:37:50,610 --> 00:37:54,550 Speaker 1: This one isn't heart-shaped, and it's also not really triangle-shaped. 610 00:37:54,950 --> 00:37:58,069 Speaker 1: It's located between the Pacific and Indian Oceans and encompasses 611 00:37:58,150 --> 00:38:03,590 Speaker 1: portions of two biogeographic regions, so the Indonesian Philippines region 612 00:38:04,150 --> 00:38:08,470 Speaker 1: and the far southwestern Pacific region. If it looks like anything, 613 00:38:08,530 --> 00:38:10,430 Speaker 1: it looks more like a rough sketch of a fish. 614 00:38:11,210 --> 00:38:13,600 Speaker 2: Yeah, I can see that. It's a psilocybin triangle. 615 00:38:15,540 --> 00:38:18,440 Speaker 1: Yeah, yeah. And so why do we call it the 616 00:38:18,460 --> 00:38:22,700 Speaker 1: coral triangle? Well, because it is super rich in coral. 617 00:38:23,140 --> 00:38:27,520 Speaker 1: According to the Coral Reef Alliance, this region contains over 76% 618 00:38:27,520 --> 00:38:32,330 Speaker 1: of the world's coral species and 37% of reef fish species. 619 00:38:33,130 --> 00:38:37,469 Speaker 1: So we're talking about somewhere around 500 of the 840 620 00:38:38,320 --> 00:38:41,660 Speaker 1: coral species that we know of. So just a rich 621 00:38:41,739 --> 00:38:46,250 Speaker 1: hotbed of marine biodiversity. There's a reason that snorkelers and 622 00:38:46,310 --> 00:38:48,770 Speaker 1: divers from around the world seek it out. There's just 623 00:38:49,010 --> 00:38:53,270 Speaker 1: breathtaking abundance there. I've never experienced snorkeling like this before. 624 00:38:54,510 --> 00:38:56,370 Speaker 1: Unless I go back there, I'm not sure I will again. 625 00:38:57,070 --> 00:38:59,890 Speaker 2: Well, as I've said, I have no experience snorkeling myself, 626 00:38:59,930 --> 00:39:02,589 Speaker 2: but I'm still envious of what you got to see there. 627 00:39:03,790 --> 00:39:07,440 Speaker 2: But this does raise the question, Does the Wallace line 628 00:39:07,600 --> 00:39:11,529 Speaker 2: hold at all for underwater fauna? We know that it 629 00:39:11,590 --> 00:39:16,950 Speaker 2: holds to some extent for land mammals, but you might 630 00:39:17,090 --> 00:39:19,730 Speaker 2: think intuitively, well, surely there would be no way that 631 00:39:19,750 --> 00:39:22,750 Speaker 2: the Wallace line would have any impact on, say, fish 632 00:39:22,830 --> 00:39:24,730 Speaker 2: or other things that can swim through. They can just 633 00:39:24,750 --> 00:39:26,229 Speaker 2: swim right across the strait, right? 634 00:39:26,489 --> 00:39:29,009 Speaker 1: Right. You would think, well, the fish just have a free-for-all, 635 00:39:29,100 --> 00:39:31,320 Speaker 1: and so they don't have to obey the rules of 636 00:39:31,360 --> 00:39:35,460 Speaker 1: the Wallace line, and neither do the birds. But this 637 00:39:35,500 --> 00:39:38,790 Speaker 1: is not the case. Despite the fact that we're under 638 00:39:38,810 --> 00:39:41,950 Speaker 1: the water here, we're still subject to some of the 639 00:39:41,969 --> 00:39:45,670 Speaker 1: boundary effects of deep ocean channels. So these deep trenches 640 00:39:45,690 --> 00:39:49,700 Speaker 1: are seem to act as persistent barriers that prevent the 641 00:39:49,760 --> 00:39:54,520 Speaker 1: widespread migration of many coral larvae and many other marine 642 00:39:54,560 --> 00:40:00,360 Speaker 1: invertebrates as well. Additionally, there's the Indonesian throughflow, which moves 643 00:40:00,540 --> 00:40:03,730 Speaker 1: massive amounts of water from the Pacific to the Indian Ocean. 644 00:40:04,170 --> 00:40:06,649 Speaker 1: And so it plays a crucial role here as well. 645 00:40:06,690 --> 00:40:10,470 Speaker 1: It'll transport some larvae, but also acts as a barrier 646 00:40:10,550 --> 00:40:14,689 Speaker 1: to others. influencing the genetic flow between populations of coral 647 00:40:14,730 --> 00:40:17,190 Speaker 1: on either side of the line. So some coral species 648 00:40:17,230 --> 00:40:20,870 Speaker 1: have wide Indo-Pacific ranges and can be found on both sides, 649 00:40:21,310 --> 00:40:25,170 Speaker 1: but others follow distribution patterns that are more in line 650 00:40:25,250 --> 00:40:27,989 Speaker 1: with some of the terrestrial animals that are impacted by 651 00:40:28,030 --> 00:40:31,610 Speaker 1: the Wallace line. And we also see this play into 652 00:40:31,650 --> 00:40:36,110 Speaker 1: distinct species. For instance, there are two distinct subpopulations of 653 00:40:36,150 --> 00:40:39,450 Speaker 1: the Indo-Pacific leopard shark, and they are separated by the 654 00:40:39,489 --> 00:40:44,870 Speaker 1: Indonesian throughflow current, which again coincides roughly with the Wallace 655 00:40:44,910 --> 00:40:47,930 Speaker 1: line here. For instance, the Missoula Foundation, which runs the 656 00:40:48,010 --> 00:40:52,279 Speaker 1: Missoula Resort in Raja Ampat, they are part of a 657 00:40:52,320 --> 00:40:56,920 Speaker 1: Star Project ReShark program to help reestablish the eastern subpopulation 658 00:40:57,000 --> 00:41:01,029 Speaker 1: of the species in Raja Ampat. Meanwhile, there's another program, 659 00:41:01,090 --> 00:41:06,190 Speaker 1: Star Project Thailand, focused on the western variety. So one 660 00:41:06,310 --> 00:41:10,839 Speaker 1: variety of Indo-Pacific leopard shark on one side and then 661 00:41:10,900 --> 00:41:12,459 Speaker 1: another variety on the other side. 662 00:41:12,800 --> 00:41:15,300 Speaker 2: Wow. I mean, even though we've established that the line 663 00:41:15,360 --> 00:41:20,299 Speaker 2: is not impermeable and sometimes animals do cross, uh, it, 664 00:41:20,420 --> 00:41:23,840 Speaker 2: I don't know. It's fascinating how, just like how much 665 00:41:24,160 --> 00:41:26,689 Speaker 2: of a barrier there could be. That's just totally invisible 666 00:41:26,730 --> 00:41:30,549 Speaker 2: to us. And, and even, even affects creatures. You would 667 00:41:30,610 --> 00:41:33,350 Speaker 2: think that it, that it couldn't like many underwater creatures. 668 00:41:33,390 --> 00:41:35,450 Speaker 1: Yeah. That we can read it in the coral. We 669 00:41:35,489 --> 00:41:38,920 Speaker 1: can read it in the, uh, the leopard sharks and, Yeah, 670 00:41:39,080 --> 00:41:44,650 Speaker 1: it's fascinating. The powerful interplay of division and mixing between 671 00:41:44,770 --> 00:41:49,950 Speaker 1: rich ecosystems here. Another interesting thing about the leopard shark 672 00:41:49,989 --> 00:41:53,810 Speaker 1: program there is that they were having to get, you know, 673 00:41:53,830 --> 00:41:55,690 Speaker 1: you wanted to make sure that you were using the 674 00:41:55,790 --> 00:42:01,010 Speaker 1: right variety of Indo-Pacific leopard shark to repopulate the region 675 00:42:01,030 --> 00:42:03,460 Speaker 1: there in Raja Ampat. So they had to reach out 676 00:42:03,500 --> 00:42:08,980 Speaker 1: to various aquariums to get surplus eggs from Indo-Pacific leopard 677 00:42:09,000 --> 00:42:12,280 Speaker 1: sharks of the right variety. And one of the aquariums 678 00:42:12,340 --> 00:42:17,880 Speaker 1: is actually the Georgia Aquarium here in Atlanta. So it 679 00:42:17,900 --> 00:42:19,520 Speaker 1: was entirely, I don't know for certain, but it was 680 00:42:19,560 --> 00:42:23,960 Speaker 1: entirely possible that some of the baby leopard sharks that 681 00:42:24,000 --> 00:42:25,420 Speaker 1: I saw in the tanks that were then going to 682 00:42:25,440 --> 00:42:30,660 Speaker 1: be gradually reintroduced into the wild, perhaps were descendants of 683 00:42:30,890 --> 00:42:33,870 Speaker 1: eggs that were produced all the way back home in Atlanta. 684 00:42:34,430 --> 00:42:35,169 Speaker 2: Circle of life. 685 00:42:35,570 --> 00:42:43,210 Speaker 1: Yeah. circle of life with leopard shark eggs taking international 686 00:42:43,270 --> 00:42:47,310 Speaker 1: flights for days across the Earth, which in a way 687 00:42:47,370 --> 00:42:49,770 Speaker 1: is interesting because it brings it back into the vast 688 00:42:49,850 --> 00:42:52,660 Speaker 1: way that humans end up moving around. And of course, 689 00:42:52,700 --> 00:42:54,760 Speaker 1: we've talked before on the show about how the movements 690 00:42:54,820 --> 00:42:57,819 Speaker 1: of humans has, of course, been another huge factor in 691 00:42:57,840 --> 00:43:02,560 Speaker 1: the way other organisms are intentionally and unintentionally spread around 692 00:43:02,580 --> 00:43:02,960 Speaker 1: the world. 693 00:43:03,340 --> 00:43:03,899 Speaker 2: Yeah, of course. 694 00:43:04,930 --> 00:43:08,410 Speaker 1: But occasionally we get strategic about it. We attempt to 695 00:43:08,469 --> 00:43:11,250 Speaker 1: fix things that we had broken before because, you know, 696 00:43:11,750 --> 00:43:15,050 Speaker 1: there's a reason that sharks are missing, as we've discussed before, 697 00:43:15,650 --> 00:43:20,360 Speaker 1: or shark populations are greatly decreased in various areas. And 698 00:43:20,420 --> 00:43:23,080 Speaker 1: it's because we have hunted them. We fish for them. 699 00:43:23,160 --> 00:43:25,899 Speaker 1: We have feared them and so forth. And in doing so, 700 00:43:25,920 --> 00:43:28,960 Speaker 1: you know, we end up damaging the ecosystem that they 701 00:43:29,000 --> 00:43:32,390 Speaker 1: were a part of because they're Those apex predators are 702 00:43:32,840 --> 00:43:36,610 Speaker 1: essential to the overall structure of things. And also, as 703 00:43:36,630 --> 00:43:39,210 Speaker 1: we've discussed in the show, their place is fragile at 704 00:43:39,250 --> 00:43:40,989 Speaker 1: the top. Yeah. All right. 705 00:43:41,010 --> 00:43:43,890 Speaker 2: Well, I have enjoyed this journey with Alfred Russell Wallace. 706 00:43:44,510 --> 00:43:47,430 Speaker 1: Yeah. Like I say, a fascinating individual. If you want 707 00:43:47,469 --> 00:43:50,610 Speaker 1: to read more about him, that book Radical by Nature 708 00:43:51,050 --> 00:43:53,570 Speaker 1: by James T. Costa is quite good. And there are 709 00:43:53,590 --> 00:43:55,210 Speaker 1: a number of other books as well that have come 710 00:43:55,290 --> 00:43:58,459 Speaker 1: out in over the recent decades that about his work. 711 00:43:58,500 --> 00:44:02,060 Speaker 1: There's kind of been a resurgence of interest in Alfred 712 00:44:02,120 --> 00:44:02,820 Speaker 1: Russell Wallace. 713 00:44:03,540 --> 00:44:06,120 Speaker 2: I enjoyed so much just reading Wallace's own writing in 714 00:44:06,140 --> 00:44:08,189 Speaker 2: the Malay Archipelago that I may want to come back 715 00:44:08,230 --> 00:44:11,590 Speaker 2: and plug that, plumb that maybe for some future topics. 716 00:44:11,930 --> 00:44:15,009 Speaker 1: Yeah, yeah. Plus, yeah, he wrote many, many books on 717 00:44:15,050 --> 00:44:17,880 Speaker 1: a number of topics. So, yeah, he may pop up 718 00:44:17,920 --> 00:44:18,900 Speaker 1: again in a future. 719 00:44:18,660 --> 00:44:19,859 Speaker 2: Episode of Stud to Play Your Mind. 720 00:44:20,800 --> 00:44:22,300 Speaker 1: All right. We're going to go ahead and close it 721 00:44:22,360 --> 00:44:24,400 Speaker 1: up there. But we'd love to hear from everyone out 722 00:44:24,420 --> 00:44:26,620 Speaker 1: there if you have thoughts about the Wallace line and 723 00:44:26,680 --> 00:44:30,060 Speaker 1: about some of the organisms that we've discussed here. Just 724 00:44:30,080 --> 00:44:31,760 Speaker 1: a reminder, the Stuff to Blow Your Mind is primarily 725 00:44:31,780 --> 00:44:34,049 Speaker 1: a science and culture podcast with core episodes on Tuesdays 726 00:44:34,090 --> 00:44:36,850 Speaker 1: and Thursdays, short form episode on Wednesdays. And on Fridays, 727 00:44:36,890 --> 00:44:38,950 Speaker 1: we set aside most serious concerns to just talk about 728 00:44:38,969 --> 00:44:41,270 Speaker 1: a weird film on Weird House Cinema. 729 00:44:41,710 --> 00:44:45,390 Speaker 2: Huge thanks, as always, to our excellent audio producer, J.J. Posway. 730 00:44:45,860 --> 00:44:47,279 Speaker 2: If you would like to get in touch with us 731 00:44:47,320 --> 00:44:49,760 Speaker 2: with feedback on this episode or any other, to suggest 732 00:44:49,820 --> 00:44:51,760 Speaker 2: a topic for the future, or just to say hello, 733 00:44:52,120 --> 00:44:55,590 Speaker 2: you can email us at contact at stufftoblowyourmind.com. 734 00:44:55,890 --> 00:45:05,310 Speaker 1: Stuff to Blow Your Mind is a production of iHeartRadio. 735 00:45:05,690 --> 00:45:09,009 Speaker 2: For more podcasts from iHeartRadio, visit the iHeartRadio app. Apple 736 00:45:09,030 --> 00:45:11,390 Speaker 2: Podcasts are wherever you listen to your favorite shows. 737 00:45:18,950 --> 00:45:19,180 Speaker 1: Thank you.