Speaker 1: Welcome to Stuff to Blow Your Mind from how Stuff
Speaker 1: Works dot Com. Hey, welcome to Stuff to Blow your Mind.
Speaker 1: My name is Robert Lamb and I'm Joe McCormick. You know,
Speaker 1: I realized I don't know why exactly this happened, but
Speaker 1: towards in the last couple of months, I feel like
Speaker 1: we have been really focusing on the animal kingdom that
Speaker 1: wasn't by design. I guess we just can't stop with
Speaker 1: the things with legs and blood. Well, I think maybe
Speaker 1: what's happening is that we have, without realizing it, being
Speaker 1: constructing a major and Nativity scene. Okay, and of course
Speaker 1: you have to have your various animals present, and and
Speaker 1: so we've been arranging the animal and I guess others
Speaker 1: bearing gifts of of nursery web spider style wrapped up
Speaker 1: packages of dead insect husks and sticks and stuff. I
Speaker 1: don't know who the shepherds would be. Well, whatever the
Speaker 1: shepherds are, we know that at the heart of the
Speaker 1: of the Nativity you have to have that that baby Jesus. Granted,
Speaker 1: we did an episode last year on the Baby Jesus
Speaker 1: homunculus and that is rerunning this year. But at the
Speaker 1: heart of this story of the Christmas story and Christian
Speaker 1: traditions is the story of a virgin birth. Now, the
Speaker 1: story of a miraculous birth, of course, is very common
Speaker 1: in in mythology and legend around the world. A god
Speaker 1: being the father of a famous or heroic person is
Speaker 1: a very common motif to appear wise settle for an
Speaker 1: earth dad when you can have a cosmic dad. Yeah,
Speaker 1: it's a it's it's a time tested story. Right. You
Speaker 1: have your demigod heroes that are that that have have
Speaker 1: we at least one parent that is of divine lineage. Now,
Speaker 1: before we go any further, I do want to just
Speaker 1: summarize the Christmas story as it's presented in Christmas Christian traditions,
Speaker 1: just really quickly here, so it's probably familiar to a
Speaker 1: lot of you. You have a first century BC woman
Speaker 1: by the name of Mary, and she finds out via
Speaker 1: angelic visitation that she's destined to become a first century
Speaker 1: CE mom, and not in the way she'd plan. No,
Speaker 1: instead of using offspring via relations with her husband Joseph,
Speaker 1: she has been impregnated by the High God. She is
Speaker 1: a virgin, but will give birth to a divine son.
Speaker 1: And like you, said, this is not an anomaly in
Speaker 1: global myths, legends, and religions, we have other stories of
Speaker 1: some sort of miraculous birth taking place, right, And what
Speaker 1: we wanted to focus on today was the fact that
Speaker 1: though this may in fact be some form of miracle
Speaker 1: if it were to actually happen to a human being,
Speaker 1: in other corners of the natural world, stories like this
Speaker 1: are actually not all that miraculous. They in fact happen
Speaker 1: all the time. Right. So today we're gonna be talking
Speaker 1: about parthenogenesis. That is the the scientific term for what's
Speaker 1: occurring here. It's taken from the Greek words parthenos meaning virgin,
Speaker 1: and genesis meaning origin. So this means in the animal world,
Speaker 1: or in the world of sexually reproducing species, a female
Speaker 1: that reproduces without fertilization by male sex cells, right, And
Speaker 1: it occurs pretty commonly among lower plants and invertebrate animals,
Speaker 1: particularly rotifers, a fids, ants, wasps, and bees. I do
Speaker 1: want to hit just two of my favorite examples from
Speaker 1: the invertebrate invertebrate world. First of all, in the termite
Speaker 1: world is pointed out in a two thousand nine research
Speaker 1: paper from North Carolina State University. Certain female termite primary
Speaker 1: queens of the species Radical Attorney's Separatus reproduce both sexually
Speaker 1: and a sexually during their lifetimes, sexually with the male kings,
Speaker 1: and a sexually to essentially clone themselves to create secondary queens.
Speaker 1: And these are the successor queens that will then mate
Speaker 1: with the king, So it's important for them to have
Speaker 1: no genes in common with them. So that's just I think,
Speaker 1: a fun example. All right, Well here you can you
Speaker 1: can clearly see in this picture why it is advantageous
Speaker 1: to use a sexual reproduction alongside sexual reproduction. Of course,
Speaker 1: the greatest benefit of sexual reproduction is that you get
Speaker 1: some variety in there. You don't have the a stagnant
Speaker 1: gene pool right sexual recombination. If you were just making
Speaker 1: copies of your own genes over and over again, it
Speaker 1: becomes much easier for say, parasites to find exploits with
Speaker 1: your body. But if you're constantly randomly recombining your genes
Speaker 1: with other members of your species, then you add some
Speaker 1: diversity to the mix and give yourself more room to
Speaker 1: more genetic wiggle room. It's kind of like say Hollywood
Speaker 1: made the same movie for ten years straight, Like the same,
Speaker 1: say superhero movie, just the same one time after time,
Speaker 1: and it was a really tremendous design. Everyone loved it.
Speaker 1: But then suddenly everyone's decides, you know, not that into
Speaker 1: superhero movies anymore. Bam, an entire decade wasted. Right, that's
Speaker 1: a very loose um explanation, but but that's why you
Speaker 1: get the genre mix up. Throw some zombies in there. No,
Speaker 1: and now you got a whole new thing. Now it's
Speaker 1: fresh again. Yeah, and now people will get into it. Uh.
Speaker 1: Here's another example that I love. This is probably my
Speaker 1: absolute favorite. It's a particular type of Amazonian ant micro
Speaker 1: Capris Smithy, like Alan Smithy speaking films. Uh. This is
Speaker 1: a fungi growing species. It's not unlike the leaf cutter
Speaker 1: aunt and they've actually given up on sexual reproduction altogether
Speaker 1: and have become an all female species. It's a colony
Speaker 1: of clones, so there are a lot more efficient in
Speaker 1: some ways, but they're highly vulnerable due to their lack
Speaker 1: of gene diversity. But they're an example of a species
Speaker 1: that took a reproductive tactic that existed in balance with
Speaker 1: sexual reproduction and eventually made it their own. Means. They're
Speaker 1: only means of reproduction. Now, while this might be more
Speaker 1: common and of course a sexual reproduction is the norm
Speaker 1: amongst a like single celled organism, but while it may
Speaker 1: be more common among invertebrates and these sort of what
Speaker 1: are considered lower order animals, though I don't know if
Speaker 1: it really makes sense to consider them lower or higher.
Speaker 1: What does lower or higher means? But anyway, it is
Speaker 1: going to be more surprising to find something like this
Speaker 1: in vertebrates, which normally would expect to be sexually reproducing animals.
Speaker 1: You've got a backbone, you should be having sex, right, yeah,
Speaker 1: I mean that's why it's such a rarity. Roughly seventy
Speaker 1: backbone species have been known to engage in parthenogenesis or
Speaker 1: exhibit parthenogenesis. That's a roughly point one percent of all vertebrates. Now,
Speaker 1: just a few basic category categories of parthenogenesis before we
Speaker 1: move on to specific examples. Uh, there's accidental. This is
Speaker 1: spontaneous parthenogenesis. Uh, it's not part of the plan, not
Speaker 1: part of the plan, but it does occur. And one
Speaker 1: example we'll see that later is in sharks. There's also facultative.
Speaker 1: This is when a female can produce offspring either sexually
Speaker 1: or via a sexual reproduction. Um, this is a common example,
Speaker 1: but one that we'll look at here in a minute
Speaker 1: is komodo dragons. And then there's obligate Uh, this is
Speaker 1: exclusive a sexual reproduction. That doesn't mean that a given
Speaker 1: species can't use sexual reproduction, but it's certainly not their
Speaker 1: primary means of reproduction. So, you know, think of the
Speaker 1: various invertebrates as an example of this, including the ants
Speaker 1: that I mentioned earlier. Single sex species, yes, especially especially
Speaker 1: single sex species. Well, let's take a look at those
Speaker 1: komodo dragons. Yeah, so the komodo dragon, which is Verona's
Speaker 1: komodo insists, is of course the largest lizard species in
Speaker 1: the world. And Robert, I don't know about you, but
Speaker 1: this was one of my favorite animals when I was
Speaker 1: a kid. I could not get enough of them. I
Speaker 1: love pictures of them. I think I would actually if
Speaker 1: I could get like a national geographic with a picture
Speaker 1: of one, I would cut it out. I seem to
Speaker 1: have some memories of that. Oh yeah, because it's the
Speaker 1: really it's the closest thing you can get to to
Speaker 1: a storybook dinosaur, like not counting not getting into like,
Speaker 1: you know, the the evolution of avian species and all that,
Speaker 1: But just in terms of like, I want a giant
Speaker 1: lizard creature like I see in my children's books. This
Speaker 1: is the closest you're gonna get. So yeah, I remember
Speaker 1: being super into it. I remember being like weirdly excited
Speaker 1: when I think was it Kim not Kim Baysinger, Sharon
Speaker 1: Stone's husband was bitten by one. I just remember being
Speaker 1: in thee and yeah, not to make light of that,
Speaker 1: I mean, I'm thinking that now it's probably horrific, but
Speaker 1: I remember the time it was like, oh my goodness,
Speaker 1: the Komodo dragons are coming after our celebrities, Like there
Speaker 1: was something weirdly exciting about that. And yet at the
Speaker 1: same what if they get Richard Gear. No, not Richard Gear.
Speaker 1: He's a national treasure. But in terms of seeing them
Speaker 1: in zoos, though, this is one of those animals it
Speaker 1: is both impressive and boring to see in most zoos
Speaker 1: because it's a it's a cold boded creature. It's it's
Speaker 1: just going to be sitting there most of the time.
Speaker 1: An impressive organism, but very little movement unless you're lucky.
Speaker 1: At the same time, there's there's some tremendous footage of
Speaker 1: them in the wild. If you've watched any of the
Speaker 1: the BBC Earth documentaries, you've seen some of this footage
Speaker 1: of of the active Komodo dragon. And there's nothing, there's
Speaker 1: nothing more terrifying than watching them, say, move in on
Speaker 1: a on a a vulnar horble cow that is trapped
Speaker 1: in the mud. Have you ever watched them doing acrobatic barfing? Oh,
Speaker 1: they're quite They are quite adept at barfing, aren't they
Speaker 1: unbelievable barfing? Like there, I've seen footage of them barfing
Speaker 1: where it looks like they barf up more than their
Speaker 1: own body mass. They are also Remember one of the
Speaker 1: notable things about them is that they will sling intestines
Speaker 1: around to remove the fecal matter from them so they
Speaker 1: can eat the intestines. Okay, I don't think i've read that,
Speaker 1: but I think maybe i've heard you mentioned that before. Yeah, yeah,
Speaker 1: they're they're voracious eaters. So the young commodo dragons have
Speaker 1: to hide from the adults so they don't get eating.
Speaker 1: I believe they climb trees, and of course the grown
Speaker 1: ups cannot really go after them. Yes, they can be
Speaker 1: quite aggressive, even to one another. So this species. They
Speaker 1: live on a number of islands in Indonesia, and as
Speaker 1: adults they get huge. They can grow up to about
Speaker 1: three meters or tin feet in length. Actually, I think
Speaker 1: the UH the largest one ever I read was even
Speaker 1: bigger than that. It was like tin point three feet
Speaker 1: in length, and they can weigh over a hundred and
Speaker 1: thirty kg or about three hundred pounds. Again, I think
Speaker 1: I read that the biggest one ever measured was something
Speaker 1: like three hundred and sixty pounds. They are venomous. They
Speaker 1: deliver a bite that prevents the praise blood from clotting. However,
Speaker 1: they do not primarily hunt live prey, because the majority
Speaker 1: of their diet from scavenging dead or dying animals, though
Speaker 1: of course they do also hunt, and when they hunt
Speaker 1: live prey. Those prey species can be all kinds of things,
Speaker 1: mainly dear, I think dear is the biggest one, but
Speaker 1: also bovines, pigs, rodents, monkeys, goats, and they have on occasion,
Speaker 1: as we said, attacked and killed humans. But this does
Speaker 1: not make them our enemy. These are magnificent scaly beasts,
Speaker 1: and they themselves are threatened in conservation status terms, you know,
Speaker 1: like you got the UH the i u c N classifications,
Speaker 1: they are not yet considered endangered, but they are considered
Speaker 1: vulnerable according to the w WF. They're only about six
Speaker 1: thousand and left on Earth and only about three fifty
Speaker 1: breeding females, and for that reason there are these conservation
Speaker 1: and captivity breeding efforts going on around the world. But
Speaker 1: so I want to tell a komodo dragon story. In
Speaker 1: two thousand five, a female komodo dragon named Sung Guy
Speaker 1: was living at the London Zoo and that year she
Speaker 1: produced a clutch of twenty two eggs, four of which
Speaker 1: were viable. But there was a problem. It had been
Speaker 1: two and a half years since Sung Guy had been
Speaker 1: anywhere near a male komodo dragon, so in order in
Speaker 1: order to explain her laying these eggs, it would seem
Speaker 1: she either had to somehow store sperm from a male
Speaker 1: for over two years, which is technically possible sometimes in
Speaker 1: reptiles there are like sperm storage methods that sometimes happen,
Speaker 1: or she had performed parthenogenesis and her eggs hatch seven
Speaker 1: and a half months after she laid them, and her
Speaker 1: offspring seemed healthy. Uh. In two thousand six, a female
Speaker 1: komodo dragon named Flora was living at the Chester Zoo
Speaker 1: in the UK, and she was at the time one
Speaker 1: of only two sexually mature female komotos in the whole
Speaker 1: continent of Europe. As I said, you know, many zoos
Speaker 1: around the world do these komodo dragon breeding programs to
Speaker 1: try to help get the numbers back up, and at
Speaker 1: the time Flora had not been breeding. In fact, she
Speaker 1: had never even once been kept in an enclosure with
Speaker 1: a male. Nevertheless, in two thousand six she produced a
Speaker 1: clutch of twenty five eggs and eleven seemed viable at first.
Speaker 1: So what could explain this? I mean, you have to wonder,
Speaker 1: was there like a male komodo dragon running loose in England,
Speaker 1: secretly getting into the pins when nobody's watching. And if
Speaker 1: we do entertain that possibility, we have to name that
Speaker 1: English komodo dragon. What was his name? Oh, I don't know,
Speaker 1: a rogue English komodo dragon. Uh, that'd be Rupert, right,
Speaker 1: Rupert May or maybe kind of it's kind of a
Speaker 1: Robin Hood type figure. It could be a Komoto Hood.
Speaker 1: Robin Koma's not Clive, He's Clive, Okay, So Clive? Did
Speaker 1: Clive get in there or did something else happen. Turns
Speaker 1: out it was not clive. So there was a paper
Speaker 1: published in Nature in two thousand and six by Watts, Bully, Sanderson, Boardman, CPI,
Speaker 1: and Gibson called parthenogenesis and Komodo Dragons, and the authors
Speaker 1: here performed genetic fingerprinting tests on the eggs of these dragons,
Speaker 1: and they found that in both cases the offspring were
Speaker 1: what are known as parthenogens, which are made entirely out
Speaker 1: of their own mother's DNA, rather than through sexual recombination
Speaker 1: with a mail. And in the case of Flora, this
Speaker 1: was true virgin birth. But in both cases they had
Speaker 1: created baby komodo dragons without the help of a mail.
Speaker 1: So the author's note that the offspring were homozy guess
Speaker 1: at all loci on on their genome, but that they
Speaker 1: were not identical clones of their mothers. So how would
Speaker 1: that work? Well, you've got to think about what happens
Speaker 1: in sexual recombination of an animal like this. So the
Speaker 1: mother contributes half of her genome and the father contributes
Speaker 1: half of his genome, and they combine to produce a
Speaker 1: mix of the two. And in this case the mother
Speaker 1: still only contributed half of her genome. So in order
Speaker 1: to produce an entire genome in the offspring without any
Speaker 1: mail input, the mother's half set of chromosome simply doubled itself.
Speaker 1: So the offspring are not clones of the mother, their
Speaker 1: homozygous at all loci. So everywhere you look on their genome,
Speaker 1: there's a double copy of the same allele, all made
Speaker 1: from half of the mother's genes. But so, how does
Speaker 1: this happen? You know, I was wondering, what are the
Speaker 1: actual mechanics here? Uh, there's a there's a pretty good
Speaker 1: summary in a Scientific American article from the time by
Speaker 1: Philip y am Uh and yam rights quote. Evidently, in
Speaker 1: the case of these komotos, the doubling of the egg
Speaker 1: genes occurred when, in essence, another egg, rather than sperm,
Speaker 1: did the job of fertilization. Oh genesis, the biological process
Speaker 1: of making an egg cell typically also yields a polar body,
Speaker 1: a mini ovum of sorts containing a duplicate copy of
Speaker 1: egg d NA. Normally, this polar body shrivels up and disappears.
Speaker 1: In the case of the komodos, though, polar bodies evidently
Speaker 1: acted as sperm and turned over into embryos. So it's
Speaker 1: like the eggs cell had a little copy of itself
Speaker 1: there with it that would normally shrivel up and go away,
Speaker 1: but instead it pretended it was sperm and then fertilized
Speaker 1: its own copy another thing. After producing some offspring parthenogenically,
Speaker 1: the one Komodo dragon, Sun Guy went on to produce
Speaker 1: a normal clutch of eggs with a male named Raja.
Speaker 1: So the researchers also concluded that parthenogenesis is not a
Speaker 1: fixed reproductive trait that lasts forever. In the Komodo dragons,
Speaker 1: you can go back and forth. So, in fact, the
Speaker 1: findings suggests that this is probably probably a form of
Speaker 1: reproductive plasticity. It's the ability to switch between sexual reproduction
Speaker 1: and asexual reproduction when mates are not available. Amazing. Yeah,
Speaker 1: I mean you can see why this would be a
Speaker 1: tremendous survival advantage. I mean, in particular, when you have
Speaker 1: a case where a female is not exposed to males
Speaker 1: at all for an extended period of time and yet
Speaker 1: is capable of producing viable eggs. Like if there's no
Speaker 1: mail around this, this show still has to start one
Speaker 1: way or another. Yeah, Now there are some reasons you
Speaker 1: might think that there are genetic drawbacks to that. In fact,
Speaker 1: the author is right that there is a downside to
Speaker 1: this discovery. Quote, parthenogenesis presents a previously unrecognized problem for
Speaker 1: the genetic management of threatened populations. Why would this be well,
Speaker 1: in captive breeding programs designed to help commodo dragons build
Speaker 1: their numbers back up, females are often kept isolated from males,
Speaker 1: and males are only brought in occasionally for the obvious
Speaker 1: reason there are good sense to do it like this,
Speaker 1: like sometimes these animals are aggressive toward one another, and
Speaker 1: you don't want them unnecessarily fighting or injuring one another,
Speaker 1: that kind of thing. But this means that if you
Speaker 1: keep females in all female environments with no mates, they
Speaker 1: may spontaneously give birth to parthenogens. Now what's wrong with that?
Speaker 1: Why Why wouldn't that just help increase their numbers even more? Well,
Speaker 1: it doesn't quite work like that. The problem is parthenogenesis
Speaker 1: reduces the fitness of the komodo dragon gene pool. The
Speaker 1: author's right quote oppressing concern with parthenogenesis is instantaneous homozygosity
Speaker 1: of the entire genome, as this inbreeding carries an associated
Speaker 1: risk of reduced fitness and an increased probability of extinction. Uh.
Speaker 1: And then there's another problem with the parthenogenesis, and it's
Speaker 1: that it biases the sex ratio of the offspring. Uh.
Speaker 1: The author's right quote. In Verona species, females have dissimilar
Speaker 1: chromosomes Z and double you sort of like human chromosomes
Speaker 1: sex chromosomes X and Y, uh, continuing with their quote.
Speaker 1: Whereas the combination Z Z produces males, so the parthenogenic
Speaker 1: mechanism can produce only homozygous ZZ or w W individuals
Speaker 1: and therefore no females. So the parthenogenesis in the Komodo dragons,
Speaker 1: because of the way their sex cells work, they can
Speaker 1: only make male offspring. Uh. It's sort of the opposite
Speaker 1: of the way like human sex chromosomes work, that males
Speaker 1: have an x Y chromosome and females in humans have
Speaker 1: an x X chromosome. In the dragons, it's the other
Speaker 1: way around. The males have the same two sex chromosomes
Speaker 1: and the females have the two different sex chromosomes. If
Speaker 1: you can only make a duplicate copy, you can only
Speaker 1: make new male dragons. Yeah, and this is important to
Speaker 1: keep in mind as we move forward, because we're going
Speaker 1: to see, um, you know, the exact chromosome. All situation
Speaker 1: is going to play into what kind of offspring are
Speaker 1: produced by a given species density for parthenogenesis. Yes, so
Speaker 1: back to that question about whether this is uh, this
Speaker 1: is useful in the wild. It does seem like it's
Speaker 1: probably an adaptation right for the reason you mentioned earlier.
Speaker 1: Assume a wild female Kommoto dragon finds herself isolated on
Speaker 1: an island environment. Maybe she gets washed up somewhere after
Speaker 1: a storm. She could help her genes survive by parthenogenetically
Speaker 1: producing a clutch of males with which to mate and
Speaker 1: establish a new colony genetically. This is not ideal, but
Speaker 1: it's better than nothing, But it's not good for the
Speaker 1: dragon populations that are you know, trying to be sustained
Speaker 1: right now, for the females to be laying clutches exclusively
Speaker 1: of essentially inbred males. This may be better than nothing
Speaker 1: in the wild when there are no males present, like
Speaker 1: we said, but it actually interferes with the breeding programs
Speaker 1: that conservationists are using to help like replenish the species.
Speaker 1: So this leads to the idea that hey, maybe we
Speaker 1: should be careful about keeping female dragons in isolation in
Speaker 1: captivity because when there's no mail around, this can happen
Speaker 1: and it's not actually what's best for the species if
Speaker 1: we can help it. Yeah, that's fascinating because it's easy
Speaker 1: to just on the surface of things think, yeah, I
Speaker 1: go way to go. Commoto dragons just reproduce whether there's
Speaker 1: a mail around or not. But well, it is better
Speaker 1: than nothing probably. I mean, if there literally is no
Speaker 1: mail to reproduce with, this makes sense to do. But
Speaker 1: the problem is in these cases it's not actually that
Speaker 1: there's no male, it's just there's no mail right now.
Speaker 1: And by the way, it does appear that other female
Speaker 1: Commodo dragons in captivity have shown this same same phenomenon
Speaker 1: since the initial batch of observations. For example, it was
Speaker 1: reported in two thousand and eight that healthy male dragons
Speaker 1: hatched at the Sedgewick County Zoo in Wichita, Kansas from
Speaker 1: a female who had not made it with a male.
Speaker 1: But Commodo dragons are certainly not the only reptiles that
Speaker 1: exhibit parthenogenesis. Some lizards are even obligate parthenogens that you
Speaker 1: mentioned earlier, the ones that have no choice, like the
Speaker 1: hybrid new male Mexico whiptail lizard. Uh, this is an
Speaker 1: all female species and there's no sexual reproduction whatsoever. Or well, actually,
Speaker 1: what is true is that there is no sexual fertilization
Speaker 1: there uh, because in fact, these lizards have been observed
Speaker 1: to perform a series of same sex female courtship and
Speaker 1: mating rituals, the biological function of which is an interesting
Speaker 1: subject that we could return to in the future. Uh.
Speaker 1: And I guess it's just a reminder that even in
Speaker 1: the animal world, the fact that you don't have to
Speaker 1: have sexual fertilization doesn't mean that there's not sexual behavior.
Speaker 1: All right. On that note, we're gonna take a quick
Speaker 1: break and we come back. We'll get into another reptilian
Speaker 1: species that exhibits virgin birth. Thank alright, we're back. So
Speaker 1: we've been talking about komodo dragons. We mentioned lizards reptiles
Speaker 1: that exhibit parthenogenesis. Snakes are another great source of examples
Speaker 1: of parthenogenesis. There is at least one species of snake
Speaker 1: called Indo tie flops brahminus, also known as the Brahminy
Speaker 1: blind snake, which appears to be an obligate parthenogen. It's
Speaker 1: a burrowing blind snake, so you'll find it, you know,
Speaker 1: down underneath the soil and rotten wood and leaf litter
Speaker 1: and stuff like that. It's found naturally in parts of
Speaker 1: Africa and Asia, though it has been introduced in other places,
Speaker 1: and as far as we know, all members of this
Speaker 1: species are female and they reproduce completely without sex. However,
Speaker 1: plenty of other snake species have been shown to exhibit
Speaker 1: facultative parthenogenesis, like the Komodo dragons. It appears to be
Speaker 1: some kind of adaptation. Now, apparently, for a while this
Speaker 1: had only been observed in captive snakes that we're living in,
Speaker 1: you know, in tanks or in zoos or something like that,
Speaker 1: so it was believed to be some sort of captive syndrome.
Speaker 1: But more recently it appears that facultative parthenogenesis has been
Speaker 1: observed in wild snakes, sometimes even when males are present.
Speaker 1: Just to cite one example by Booth, Smith, Eskridge, Hass, Mendelssohn,
Speaker 1: and Shoit, facultative parthenogenesis discovered in wild vertebrates in Biology
Speaker 1: Letters in two thousand and twelve. These researchers used quote
Speaker 1: micro satellite DNA genotyping and litter characteristics to determine that
Speaker 1: there was evidence of facultative parthenergenesis in snakes in the
Speaker 1: wild in populations of wild North American pit viper snakes
Speaker 1: like the copper head and the cotton mouth. So the
Speaker 1: world may may yet be full of a sexually reproducing
Speaker 1: copper head queens. Well, that's amazing. Now we've so far
Speaker 1: we've talked about two different reptile species. It's I think
Speaker 1: it's time to move on to the birds, and not
Speaker 1: just any bird, but a bird that we've discussed a
Speaker 1: fair amount on stuff to blow your mind, especially given
Speaker 1: that we've never devoted and have we devoted an entire
Speaker 1: episode to them before? Did we do an episode on
Speaker 1: the turkey? No, I think we've mostly talked about turkeys
Speaker 1: in the context of Benjamin Franklin and electrocuting them. Yes. Yeah,
Speaker 1: I think that's the main reason they keep coming up,
Speaker 1: So that's come up more than once. Yeah, Well, we're
Speaker 1: bringing up turkeys again because parthenogenesis has been observed in
Speaker 1: several bird species, though it usually results in non viable
Speaker 1: embryos that never become adults, and the turkey is one
Speaker 1: of the one of them. Reports of turkeys exhibiting virgin births.
Speaker 1: These begin to roll in, especially in the eighteen hundreds,
Speaker 1: and it received a fair amount of attention in the
Speaker 1: decades to follow. Breeders were particularly interested because potential pitfalls aside,
Speaker 1: and we've discussed what those those are regarding, you know,
Speaker 1: stagnant gene pools and all the idea. They really like
Speaker 1: the idea of one prize turkey creating another prize turkey
Speaker 1: without mightying the genetics horror. Yeah, but you know, we
Speaker 1: we're talking about the poultry industry here, so the shadowy
Speaker 1: mechanical priests of poultry science. So according to studies in
Speaker 1: the seventies and nineties, in particular, thirty two tot of
Speaker 1: infertile eggs may initiate development, but most embryos die at
Speaker 1: an early stage. Parthener genesis has also been observed in
Speaker 1: domestic hens, Chinese painted quails, and the zebra finch. For
Speaker 1: the turkey, however, it's only going to result in a
Speaker 1: viable offspring in extreme situations, and when it does result
Speaker 1: in an actual hatchling, the turkey is always male due
Speaker 1: to sex chromo chromosome dominance. Now I was looking around
Speaker 1: for some more information about this, and I realized, well,
Speaker 1: the best place to look is probably the world of
Speaker 1: of of Agricultural sciences and animal sciences. And indeed I
Speaker 1: found a wonderful overview of this from Thomas F. Savage, PhD,
Speaker 1: Professor and head advisor at the Department of Animal Sciences,
Speaker 1: Oregon State University in Corvallis, and he points out that
Speaker 1: the parthenogenesis and turkeys, it all comes down to environmental
Speaker 1: and genetic factors. So, first of all, the environmental factors
Speaker 1: that the outlines here age, he says, there's a higher
Speaker 1: rate in younger hens, and then and then there's also
Speaker 1: a viral influence here, there's an increased occurrent and turkey
Speaker 1: hens exposed to certain diseases such as Newcastle disease, foul pox, etcetera. Also,
Speaker 1: it can be affected by what you're feeding them. There
Speaker 1: are certain additives used to enhance reproductive efficiency that can
Speaker 1: stimulate parthenogenic development, specifically the yeast culture UH sacro mices
Speaker 1: sera visa. And then also inactivated or I radiated sperm.
Speaker 1: In experiments, they found that if they if they had
Speaker 1: this irradiated sperm, it was unable to contribute genetically, but
Speaker 1: it could lead to a higher rate of parthenogenesis. Oh,
Speaker 1: because it could like um stimulate the egg to start dividing,
Speaker 1: but it wouldn't actually provide genetic material. Yeah, that's my
Speaker 1: understanding of it. Also, temperature, even elevated pre incubation edge
Speaker 1: egg storage temperatures can play play a role and in
Speaker 1: all these you know, and we're talking about increasing the
Speaker 1: likelihood of it occurring, not necessarily like a trigger switch exactly.
Speaker 1: And then their genetic aspects as well. Uh, some genetic
Speaker 1: strains just have a predisposition for it, and you can
Speaker 1: actually increase the chances via genetic selection. And this was
Speaker 1: proved out in a nineteen five study by this guy Olsen,
Speaker 1: who when you look at he's the turkey parthener genesis.
Speaker 1: Yeah he is. It's like it's you look at who
Speaker 1: has done research about it, and it'll be you know,
Speaker 1: various names and then like like twenty something different search
Speaker 1: results for this awesome guy. All right, so that's turkeys
Speaker 1: and uh and imagined some of you out there listening
Speaker 1: to this podcast have some experience with turkeys or at
Speaker 1: least hens um. Maybe you can write in and tell
Speaker 1: us give us your take. On Parthener genesis in the
Speaker 1: Turkey world. Now, not to downplay the dangers of turkeys,
Speaker 1: but I think we should go to a little bit
Speaker 1: of a wilder territory. Can you give me a thrill ride, Robert. Yeah,
Speaker 1: let's talk about parthener genesis in sharks. And also we'll
Speaker 1: get into raise a little bit. Uh. This is actually
Speaker 1: I believe this is a topic that that Mara hart Um,
Speaker 1: who wrote Sex in the Sea, touched on a little
Speaker 1: bit when she appeared on the program in the past. Uh.
Speaker 1: And I'm certainly going to cite her book Sex in
Speaker 1: the c because it is a tremendous book about uh,
Speaker 1: the wild world of reproduction in in Earth's oceans. But yes,
Speaker 1: as it happens, sharks have been observed to engage in
Speaker 1: facultative parthenogenesis. It's it's not obligatory, and it creates offspring
Speaker 1: genetically distinct from the mother or sibling species, so these
Speaker 1: are not outright clones. Uh. This was first observed in
Speaker 1: sharks back in two thousand seven when Uh, studied by
Speaker 1: a Chapman at All, conducted tests on bonnet head sharks
Speaker 1: born in captivity. Um. The female in this Listnari had
Speaker 1: been isolated for from males for more than three years,
Speaker 1: and there was so and it turned out that they
Speaker 1: were able to produce without any male DNA. Also, in
Speaker 1: two thousand seven, Chapman and his team found evidence of
Speaker 1: parthenogenesis in female black tip sharks. These in captivity for
Speaker 1: nine years without access to males, and a female black
Speaker 1: tip what happened is it died in captivity with a
Speaker 1: near term embryo inside it. Zebra sharks and white spotted
Speaker 1: sharks shark cases have also been confirmed UH and UH.
Speaker 1: Chapman and his team have also found genetic evidence for
Speaker 1: hammerhead virgin birth as well. So the ability seems like
Speaker 1: it might be pretty common actually, from big sharks to
Speaker 1: a little sharks, from egg layers to lie birthers. But
Speaker 1: does it happen in the wild or is it just
Speaker 1: something that occurs in captivity? This is in this we're
Speaker 1: encountering a similar situation that we have with the study
Speaker 1: of commodo dragons, like is this is this something that
Speaker 1: is actually occurring in the wild, and if so, how
Speaker 1: can we study it? It's actually pretty hard to study
Speaker 1: in the wild, though, because to do so you really
Speaker 1: need to look at the DNA of of the mother.
Speaker 1: You need to look at the DNA of the offspring.
Speaker 1: And the thing about shark uh, the world of shark
Speaker 1: parents is that they're pretty much donezo after the birth.
Speaker 1: You know, the the parents are not going to hang
Speaker 1: around and look after the baby. Sharks not big into nurturing, right, Yeah. Now,
Speaker 1: Chapman and other re searchers, they have found examples of
Speaker 1: parthenogenesis in the critically endangered small tooth sawfish, which is
Speaker 1: threatened by over fishing and the loss of mangrove habitats.
Speaker 1: Now it's technically a ray, it's not a shark, but
Speaker 1: it winds up in shark fin soup a lot. According
Speaker 1: to mar j Hart in her book Sex and the Sea,
Speaker 1: this uh, this creature's population has declined, she says, more
Speaker 1: than since the nineteen sixties. Now, meanwhile, we have Dr
Speaker 1: Jim gel Sliter who has conducted test using an ultrasound
Speaker 1: one which which he described he himself describes as looking
Speaker 1: like a Ghostbusters proton pack. It's a pretty expensive piece
Speaker 1: of equipment. But the but that's how they can bring
Speaker 1: it out of the field, because it's quite a production
Speaker 1: they have to go through here, they have to they
Speaker 1: have to catch the ray, they have to keep invited
Speaker 1: by the side of the boat, and then they have
Speaker 1: to uh, you know, use the wand on it to
Speaker 1: see what's going on inside it. Um. What do they
Speaker 1: find with that wand? Well, the thing is that they
Speaker 1: have confirmed parthenogenesis. Uh. Now uh, it's a There are
Speaker 1: a couple of things that should know here. One is
Speaker 1: that investigations regarding sharks and rays they can be complicated
Speaker 1: for the same reason that like the commodo dragon situation
Speaker 1: is complicated uh, in that you have to ask yourself,
Speaker 1: well are they storing sperm from a previous encounter um
Speaker 1: and And that can sometimes be the case with sharks
Speaker 1: and rays um. But in the case of the sawfish,
Speaker 1: this is an example where this amazing adaptation could prove
Speaker 1: vital and helping them bounce back from the brink of
Speaker 1: extinction while new protections are in place, because there at
Speaker 1: a point now where again they're threatened by by overfishing
Speaker 1: and habitat loss, but certain legal protections that have been
Speaker 1: put in place, and so parthenogenesis could be the tool
Speaker 1: that helps them reach a sustainable level while those protections
Speaker 1: are in place. However, over the generations it's you know,
Speaker 1: likely gonna uh you know, a negatively impact the species
Speaker 1: hopes for survival as well. So again it's that's that's
Speaker 1: similar scenario with the komodo dragon. It's better than nothing,
Speaker 1: but it is also potentially genetically devastating. So the reasons
Speaker 1: would be what that it limits genetic diversity essentially it's
Speaker 1: similar to inbreeding, and that it produces sex bias in
Speaker 1: the offspring. In this case, they would be almost always
Speaker 1: female offspring. Yes, I believe so, the I mean think
Speaker 1: of it, It would just be it would be terrible
Speaker 1: when your your species bounces back from the brink of
Speaker 1: of of extermination and you're able to do so via
Speaker 1: this miraculous virgin birth, but then some sort of disease
Speaker 1: just wipes all of you out because you lack the
Speaker 1: genetic diversity to survive it. And this is actually outside
Speaker 1: of the world of partheno genesis. This is something that
Speaker 1: is encountered to in efforts to restore certain species to
Speaker 1: the wild, Like if a population becomes uh too shallow,
Speaker 1: then you know you're you're not going to have the
Speaker 1: genetic diversity to really um have a have has a
Speaker 1: robust a genetic presence for the species. Yeah, but when
Speaker 1: you're when you're that low as a species, you're you're
Speaker 1: in a tough situation anyway. So best of luck to
Speaker 1: the parthenogens. All right, we want that note. We're gonna
Speaker 1: take one more break when we come back. We're gonna
Speaker 1: ask the question, what about parthenogenesis in mammals than alright,
Speaker 1: we're back. So we've been discussing parthenogenesis in sharks and
Speaker 1: reptiles and birds. Uh. One thing that is certainly true
Speaker 1: is that you're going to find way fewer examples of
Speaker 1: this in mammals. In fact, if what I've read is correct,
Speaker 1: there are no known wild examples of parthenogenesis in mammals.
Speaker 1: There have been examples that have been induced under synthetic
Speaker 1: lab conditions, but we've never found an example out in
Speaker 1: the world that's correct. That's that's what I was finding
Speaker 1: as well. Um, the really the only uh, the million
Speaker 1: examples that we run across our ones in human created
Speaker 1: uh myths and legends and religious stories. So I was
Speaker 1: reading an article titled parthenogenesis, Birth of a new lineage
Speaker 1: or Reproductive accident by Casper J. Vander Koo from the
Speaker 1: University of Groningen and Tanja Schwander, and this was published
Speaker 1: in Current Biology in two thousand fifteen. And the authors
Speaker 1: they make an interesting choice, an entertaining choice in directly
Speaker 1: approaching the birth of Jesus Christ. Oh yeah, that's a
Speaker 1: dangerous move. And Algy I was I was hesitant to
Speaker 1: incorporate too much Nativity story into this episode, but then
Speaker 1: the scientists did it, so I can only follow them.
Speaker 1: In fact, I want to read a quote from this paper. Quote.
Speaker 1: This reference to parthenogenesis, and by this reference is referring
Speaker 1: to the Nativity story is unusual in two ways. First,
Speaker 1: it is the only account of quote unquote natural parthenogenesis
Speaker 1: in a mammal. Mammals are believed to be completely unable
Speaker 1: to report to reproduce via parthenogenesis because of a number
Speaker 1: of developmental and genetic constraints. Second, while the blessed Virgin
Speaker 1: Mary might have been able to conceive a daughter via parthenogenesis,
Speaker 1: the conception of a son is highly unlikely, as male
Speaker 1: sex and humans is determined by genes on the Y chromosome. Mary,
Speaker 1: as a woman, could not have transmitted any hy chromosomes
Speaker 1: to her offspring. In contrast to humans, parthenogenetic production of
Speaker 1: sons is expected in species with other types of sex determination. Yeah,
Speaker 1: so that's dealing with the opposite of the komodo dragons
Speaker 1: issue we talked about earlier. Right now, I have to
Speaker 1: say it. I can't help but think of certain late
Speaker 1: medieval traditions in which Christ is illustrated or described in
Speaker 1: terms of feminine qualities. Um. And then this is based
Speaker 1: in the idea that it's, you know, to an expression
Speaker 1: of the feminine characteristics of Christ nature, and of course
Speaker 1: has nothing to do with genetics or even any sort
Speaker 1: of egalitarian ideal. But yet I can't help but think
Speaker 1: about that. And when we're thinking about well, uh, yes,
Speaker 1: Mary could have genetically speaking, had this virgin offspring, but
Speaker 1: it would have had to have been a female. Now
Speaker 1: I assume that they are just having a little bit
Speaker 1: of fun with the subject. They're not like trying to say,
Speaker 1: how can we explain the story of Jesus birth. Let's
Speaker 1: try to go to the science of parthenogenesis. I feel
Speaker 1: it's kind of like, uh, in the same way that
Speaker 1: we talked about papers about hemorrhoids. They feel that they
Speaker 1: just have to mention the the the the ark of
Speaker 1: the Covenant, just because you can get a little bit
Speaker 1: of Bible flavoring in there. It's kind of hard to
Speaker 1: resist incorporating this, the story of the birth of the
Speaker 1: Christ Child into your paper on genetics and parthenogenesis. Yes,
Speaker 1: I can certainly imagine that temptation. But so so they're
Speaker 1: not actually saying, this story is a historical record and
Speaker 1: we're going to explain how it happened biologic correct um.
Speaker 1: So you know, they point out a lot of what
Speaker 1: we've been talking about already. That male producing parthener genesis
Speaker 1: is rare, female producing parthenogenesis is widespread and mostly obligate,
Speaker 1: though only a few examples invertebrates, and there are no
Speaker 1: examples among mammals. And then is this whole issue with
Speaker 1: the female or the or the male offspring? They say
Speaker 1: that accidental parthenogenesis is the method that can produce male
Speaker 1: offspring due to the way that the chromosomes come together.
Speaker 1: But that quote, the developmental and genetic constraints in humans
Speaker 1: and other mammals would most likely prevent the emergence of
Speaker 1: adaptive parthenogenesis in natural populations. Well, I do think it's
Speaker 1: interesting they say, most likely. I wonder exactly how unlikely,
Speaker 1: it is, so could parthenogenesis in in mammals like humans?
Speaker 1: Is that essentially impossible or just so unlikely we wouldn't
Speaker 1: expect to see it? Well and true? And then also
Speaker 1: the question is like what kind of time frame we're
Speaker 1: talking about. Are we talking about tomorrow, our next year
Speaker 1: or hundred years from now? Are we looking at at
Speaker 1: at a longer history for our species? Wouldn't expect to
Speaker 1: see it over a population of X number? Right, But
Speaker 1: then again, it's we're going beyond mere humans here, right,
Speaker 1: we're talking about mammals in general. And so if we
Speaker 1: have no examples from the mammalian world, uh that that
Speaker 1: that have presented themselves or have survived to present themselves
Speaker 1: uh to scientists today, then it does it does make
Speaker 1: you wonder how many mammals other than humans could there be?
Speaker 1: What you've got, dogs, you got rats, Uh, that's about
Speaker 1: it in there, well, all the all the bat species.
Speaker 1: So yeah, yeah, yeah, yeah, you have considerable member species
Speaker 1: to consider here, but yeah, there if none of them
Speaker 1: are presenting an example of partheno genesis, then um, I
Speaker 1: don't know, it seems like a pretty safe bed alright.
Speaker 1: So there you have it, parthenogenesis, virgin birth, a little
Speaker 1: bit of holiday full air thrown in there. Uh, And
Speaker 1: I think just the big take home is that, as always,
Speaker 1: when we're looking at something that is miraculous to humans,
Speaker 1: take it out to the animal world, and generally you're
Speaker 1: gonna find that it's actually no big deal. There's there's
Speaker 1: much weirder stuff going on, and plenty of if examples
Speaker 1: of virgin birth going on. Uh, certainly in the invertebrate world,
Speaker 1: but then also in the verse of your world as well.
Speaker 1: It tends to remain the case that no myth, no
Speaker 1: magical story, no monster movie, no sci fi special can
Speaker 1: come up with anything as weird as nature. All right,
Speaker 1: So hey, as always, if you want to check out
Speaker 1: more episodes of Stuff to Blow your Mind, head out
Speaker 1: and over to stuff to Blow your Mind dot com.
Speaker 1: That is our website. That it's where you will find
Speaker 1: all of the episodes. You'll find links out to our
Speaker 1: social media accounts. You'll find a tab for our store.
Speaker 1: We can go check out some cool designs, get him
Speaker 1: on stickers, shirts, et cetera. It's a cool way to
Speaker 1: support the show. And if you want to support the
Speaker 1: show in a way that doesn't cost you any money.
Speaker 1: Simply rate and review us wherever you have the power
Speaker 1: to do so, and hey, check out Invention. Invention is
Speaker 1: the new podcast that we've launched. If you like stuff
Speaker 1: to blow your mind, you're gonna love Invention as well.
Speaker 1: It publishes every Monday, and in each episode, Joe and
Speaker 1: I look at a different invention, a different revolution in
Speaker 1: in uh in technology, where it came from, how it
Speaker 1: came about, and how it's changed the world forever. You
Speaker 1: can find that wherever you get your podcasts. If you
Speaker 1: search for Invention Invention podcasts, you put in our names.
Speaker 1: You might even might want to throw in something like
Speaker 1: our names or throwing an iHeart Media, etcetera. iHeart Radio
Speaker 1: and see if that helps the search results. But you
Speaker 1: can also find everything about it at invention pod dot com.
Speaker 1: Big thanks as always to our excellent audio producers Alex
Speaker 1: Williams and Torii Harrison. If you would like to get
Speaker 1: in touch with us directly with feedback on this episode
Speaker 1: or any other, to let us know a topic you'd
Speaker 1: like us to cover in the future, or just to
Speaker 1: say hi, you can email us at blow the Mind
Speaker 1: at how stuff works dot com for more on this
Speaker 1: and thousands of other topics. Is it how stuff works?
Speaker 1: Dot com Don't Busy pointed to part F