Speaker 1: Welcome to Stuff to Blow Your Mind production of iHeartRadio. Hello,
Speaker 1: and welcome to Stuff to Blow Your Mind the listener mail.
Speaker 1: My name is Joe McCormick. My regular co host Robert
Speaker 1: Lamb is out today, so I'm trekking on my own
Speaker 1: once again, with none but Carney the mailbot at my side.
Speaker 1: But Rob is going to be back with me soon.
Speaker 1: We're going to have a vault episode for you tomorrow.
Speaker 1: That's going to be Tuesday, and then there should be
Speaker 1: an all new short form on Wednesday and a new
Speaker 1: core episode with Rob and me back together on Thursday
Speaker 1: of this week. All right, I guess we should jump
Speaker 1: right into the messages. This first message is from Vic.
Speaker 1: She says, Hi, Robert and Joe. I love your podcast.
Speaker 1: I was hooked after I listened to the multi part
Speaker 1: episode on mirrors, but my favorite of all time is
Speaker 1: the history of the odometer, absolutely blew my mind. For
Speaker 1: my question or possible show suggestion, do you know any
Speaker 1: theories on why humans evolved away from having thick fur
Speaker 1: or hair like that of our closest living relatives in
Speaker 1: the Great Ape family. I heard somewhere recently that humans
Speaker 1: actually have the same amount of hair on average as
Speaker 1: a chimpanzee. But human body hair is so fine and
Speaker 1: or short for the most part that it doesn't appear
Speaker 1: to be fur. I don't know if this is true.
Speaker 1: I had a good laugh wondering if our early ancestors
Speaker 1: started wearing coverings while they still had thick coats, and
Speaker 1: my brain started playing Planet of the Apes. Maybe there
Speaker 1: are advantages to our naked mole rat status in the
Speaker 1: great ape family, maybe something about fleas lice and other
Speaker 1: fur loving pests. Sorry for the long email, would love
Speaker 1: to know what you think. Thank you for all the
Speaker 1: great shows, Vic. Thank you for the message. Vic. Now,
Speaker 1: initially I did not know the answer to your question
Speaker 1: about hair follical density and hair thickness in humans versus chimpanzees.
Speaker 1: But interesting thing in trying to answer your other question,
Speaker 1: I came across an answer to that one too, So
Speaker 1: more on that in a bit. But the main question here,
Speaker 1: how did humans come to be relatively hairless compared to
Speaker 1: our nearest relatives in the animal kingdom. This is a
Speaker 1: really interesting question and one we've looked at on the
Speaker 1: show before, so I just did a little reviewing to
Speaker 1: refresh myself on it. So we don't know for sure.
Speaker 1: With a lot of these evolutionary questions, we can come
Speaker 1: up with good guesses at the answer, but sometimes it's
Speaker 1: hard to know for certain what the actual reasoning or
Speaker 1: pressure driving and adaptation in the distant past was. But
Speaker 1: I think there are some pretty good guesses about what
Speaker 1: drove the human adaptation for comparative nakedness. One thing to
Speaker 1: note starting off is that although we are relatively hairless
Speaker 1: overall compared to most st other mammals, there's a fair
Speaker 1: amount of variation in the amount of body hair present
Speaker 1: on humans, like in between different human individuals, and I
Speaker 1: think it's interesting that there are pretty consistent patterns of
Speaker 1: hairiness versus hairlessness on different regions of the body that
Speaker 1: are common to almost all people. So, for example, we
Speaker 1: don't grow hair on the palms of our hands or
Speaker 1: the soles of our feet for the most part. Though
Speaker 1: if you look, these skin surface patterns are somewhat shared
Speaker 1: by our closest relatives, even the very hairy ones. So chimpanzees, gorillas,
Speaker 1: and other great apes also don't have fur on their palms,
Speaker 1: and this is probably all for the same reason. In
Speaker 1: all of us. It's so that we can have improved
Speaker 1: grip and dexterity. Imagine trying to grip a tree branch,
Speaker 1: to climb a tree, or swing from a tree branch,
Speaker 1: or to manipulate objects in your hands. If those hands
Speaker 1: were covered in fur, things would really kind of slide
Speaker 1: around in there, it seems. However, when it comes to
Speaker 1: the general loss of over the covering the whole body,
Speaker 1: one of the major explanations is that it has to
Speaker 1: do with thermoregulation, the ability to manage the body's internal temperature.
Speaker 1: Fur helps insulate the body against the cold. It's very
Speaker 1: useful for that, and many mammals use it to that end,
Speaker 1: but as an insulation method it's inflexible. A mammal with
Speaker 1: thick fur can't quickly take its fur off when it
Speaker 1: gets hot, so it has to be careful to avoid, say,
Speaker 1: overexerting itself out in the sun. And the thermoregulation hypothesis
Speaker 1: says well, human ancestors, by losing most of their body
Speaker 1: hair massively increased their ability to cool the body, especially
Speaker 1: during exercise in hot climates, maybe under the direct sun.
Speaker 1: And I think one thing that makes the thermoregulation hypothesis
Speaker 1: strong is that the loss of body hair is the
Speaker 1: only observed genetic change that would serve this purpose. In fact,
Speaker 1: you can see other signs that there was intense pressure
Speaker 1: on human ancestors to develop genetic adaptations for cooling the body.
Speaker 1: And a big example here is sweat glands. So if
Speaker 1: I asked you to think what distinguishes us from our
Speaker 1: closest relatives like chimpanzees, what are some body differences you
Speaker 1: can think of? You might think of things like bipedal locomotion.
Speaker 1: We tend to walk upright on two legs, the relative
Speaker 1: lack of body fur as in your question here. Of course,
Speaker 1: other behavioral and intellectual things like the capacity for language
Speaker 1: and so forth. But another major difference is that humans
Speaker 1: have way more sweat glands, also known as ekrone glands.
Speaker 1: We have something like ten times the density of ekron
Speaker 1: glands found in animals like chimpanzees and macaques. So we
Speaker 1: are not only the ape that can walk, the ape
Speaker 1: that can talk, We are by far the sweatiest of
Speaker 1: all apes. And so I was looking for some research
Speaker 1: on the genetic basis of this difference in the sweat glands,
Speaker 1: and I found the following study. It was won by
Speaker 1: Daniel aldea at all called repeated mutation of a developmental
Speaker 1: enhancer contributed to human thermoregulatory evolution. This was published in
Speaker 1: Proceedings the National Academy of Sciences in twenty twenty one,
Speaker 1: and it was by a team of researchers I think
Speaker 1: primarily from the University of Pennsylvania School of Medicine, and
Speaker 1: they write in their summary quote, the effectiveness of human
Speaker 1: thermoregulatory sweating is underlain by the evolution of a dramatically
Speaker 1: increased density of water secreting ekrone sweat glands in human
Speaker 1: skin relative to that of other primates. Here we show
Speaker 1: that the accumulation of human specific mutations in a developmental
Speaker 1: enhancer collectively promoted the production of ekrone glands in humans
Speaker 1: by upregulating the expression of the engrailed one also known
Speaker 1: as the e in one transcription factor in the skin.
Speaker 1: So here is apparently the genetic basis of the difference.
Speaker 1: I was reading some comments by the authors in a
Speaker 1: press release associated with this study, and one thing they
Speaker 1: highlighted is that while a lot of other human genetic
Speaker 1: traits that show differences from our nearest relatives are thought
Speaker 1: to come from a complex interaction of different heritable factors.
Speaker 1: The human beings ability to outsweat its relatives seems largely
Speaker 1: traceable to mutations in one single regulatory region called the
Speaker 1: he CE eighteen. Now also related to the study here, Vic,
Speaker 1: We're going to come back to something you asked in
Speaker 1: your email, the part where you wrote, quote, I heard
Speaker 1: something recently that humans actually have the same amount of
Speaker 1: hair on average as a chimpanzee. But human body hair
Speaker 1: is so fine and or short for the most part
Speaker 1: that it doesn't appear to be fur. Well, I was
Speaker 1: reading about the paper I just mentioned in an exerpt
Speaker 1: from a book called The Joy of Sweat, The Strange
Speaker 1: Science of Perspiration by Sarah Everts. This exerpt was published
Speaker 1: by Science Friday, and Everts here cites one of the
Speaker 1: authors of the twenty twenty one study, who is the
Speaker 1: upin Geneticistiana Kambarov, and she confirms that quote we look naked,
Speaker 1: but we are not actually naked. We have the same
Speaker 1: density of hair follicles as apes have fur follicles end
Speaker 1: of quote. But most of those hairs are miniatureized. They're
Speaker 1: shrunken down to the point that they are nearly invisible.
Speaker 1: So yes, it appears vic what you heard was true.
Speaker 1: It's not that we have fewer hair follicles. It's just
Speaker 1: that most of that hair doesn't really it doesn't really
Speaker 1: become you know, it doesn't achieve hair's full potential, so
Speaker 1: we don't have fur coats. Instead, we got little bumps
Speaker 1: and sweat glands and things. So it looks like human
Speaker 1: ancestors underwent multiple changes would have helped keep our bodies
Speaker 1: cooler than would be possible if those bodies were more
Speaker 1: like the bodies of chimpanzees. And those changes are the
Speaker 1: reduction and body fur and the higher density of sweat
Speaker 1: glands for evaporative cooling. Now, another thing that's worth noting
Speaker 1: is that these adaptations stack. The loss of body hair
Speaker 1: appears to make sweating more useful as a cooling technique,
Speaker 1: because if you think about it, it's like harder to
Speaker 1: achieve much evaporative cooling if you are covered in a
Speaker 1: mat of fur. And it also seems that these two
Speaker 1: changes could even have a common cause. Coming back to
Speaker 1: that exerpt from the book by Sarah Everts, she's writing
Speaker 1: about research by Camperov and colleagues. Quote. Camberov and her
Speaker 1: colleagues are finding evidence that the biological signals nudging these
Speaker 1: precursor cells toward an ekrone sweat gland density also inhibit
Speaker 1: the formation of hair. So given all this evidence, it
Speaker 1: seems very plausible to me that there was a pressure
Speaker 1: on our ancestors causing them to survive and reproduce better
Speaker 1: if they could cool their bodies more efficiently. Now, what
Speaker 1: would that pressure be. It could be that they changed habitats,
Speaker 1: maybe say from living in fully shaded forests with like
Speaker 1: a thick canopy cover to living in more direct sunlight,
Speaker 1: either in an open savannah or in a woodland that
Speaker 1: was less dense with thinner canopy and more direct sun.
Speaker 1: Or it could be a change in survival niches, behavioral
Speaker 1: survival niches, So imagine a change to relying on more strenuous,
Speaker 1: prolonged exercise to survive, maybe through endurance running during hunting
Speaker 1: or something else. Or there could be reasons that we're
Speaker 1: not even thinking of that would have caused this need
Speaker 1: to cool the body. So the thermoregulation explanation seems pretty
Speaker 1: strong to me, maybe the probably the strongest explanation I've
Speaker 1: come across, But there are plenty of other possible reasons
Speaker 1: for ancestral fur laws, and they could have been complementary
Speaker 1: to one another. I'm not going to cover all of
Speaker 1: the hypotheses out there, but one other idea we've talked
Speaker 1: about on the show before is the role of ectoparasites.
Speaker 1: And here I'm going to consult a paper called a
Speaker 1: naked ape would have fewer parasites. This was published in
Speaker 1: two thousand and three by Mark Pagel and Walter Bodner
Speaker 1: in Proceedings of the Royal Society of London Series B
Speaker 1: Biological Sciences. From their abstract, they write, quote, Unusually among
Speaker 1: the mammals, humans lack an outer layer of protective fur
Speaker 1: or hair. We propose the hypothesis that humans evolved hairlessness
Speaker 1: to reduce parasite loads, especially ectoparasites that may carry disease.
Speaker 1: We suggest that hairlessness is maintained by these naturally selected
Speaker 1: benefits and bisexual selection operating on both sexes. Hairlessness is
Speaker 1: made possible in humans owing to their unique abilities to
Speaker 1: regulate their environment via fire, shelter, and clothing. So, to
Speaker 1: summarize elements of this hypothesis, you know we can get ticks,
Speaker 1: we can get lice, and these parasites infest body hair,
Speaker 1: they become harder to remove if that hair is thick,
Speaker 1: and they're not just annoying like they spread disease. So
Speaker 1: they do actually have an impact on survival and fitness
Speaker 1: in a natural setting. Once humans could control fire and
Speaker 1: could surround themselves with external insulation, now that might be
Speaker 1: what you would think of his clothing, like maybe animal
Speaker 1: skins or grass or other auxiliary materials from the environment,
Speaker 1: or it could be thinking of shelters. All of these
Speaker 1: changes make it less important to have biological equipment for
Speaker 1: keeping warm, meaning the fur that other mammals have for
Speaker 1: warmth is just less necessary for survival if you've got fire, clothes, shelter.
Speaker 1: It's also possible that if hairlessness enhances survival benefits by
Speaker 1: reducing parasite loads, it could also help enhance reproductive fitness
Speaker 1: through sexual selection by providing an honest signal to potential
Speaker 1: mates of the lack of external parasites. Sort of, you know,
Speaker 1: look and see how attractive I am, And in this case,
Speaker 1: attractive means relatively free of lice and ticks. And there's
Speaker 1: another interesting point of comparison the authors make. They say,
Speaker 1: you know, what are some other mammals that are relatively hairless, well,
Speaker 1: one would be naked mole rats. These are animals that
Speaker 1: live in large colonies underground where you would expect a
Speaker 1: lot of parasite transmission, but their hairlessness offers resistance against ectoparasites.
Speaker 1: And they can of course cope with the lack of
Speaker 1: fur for warmth because they huddle together and they share
Speaker 1: body heat and they stay away from cold air in
Speaker 1: their subterranean layers. So what a naked mole rat has
Speaker 1: in a warmth from underground rat piles? We have in
Speaker 1: technology through fire and clothing, and I guess in evaluating
Speaker 1: this hypothesis, I would have questions about, Like my big
Speaker 1: questions would be like, how do the timelines compare. What
Speaker 1: is the evidence of when our ancestors started undergoing mutations
Speaker 1: to lose their fur, and how would that match up
Speaker 1: against to our best guests at the timeline when we
Speaker 1: started controlling fire or wearing clothes or had other forms
Speaker 1: of external insulation. But anyway, very interesting question. Thank you, vic.
Speaker 1: All Right, this next message is about our episodes on
Speaker 1: heart burial, heart removal and heart burial. It's from Kenneth
Speaker 1: in Glasgow. Kenneth says Hi, Rob and Joe, thanks for
Speaker 1: the fascinating episodes discussing all the ins and outs of
Speaker 1: heart removal. You finally helped me make sense of the
Speaker 1: post mortem journey of the Heart of the Bruce. Robert
Speaker 1: the Bruce was the Scottish king responsible for the defeat
Speaker 1: of the English army at Bannockburn, effectively ending plantagenet claims
Speaker 1: to the Scottish throne. When it came time for him
Speaker 1: to consider his own death, he requested that his heart
Speaker 1: be taken on a tour of the Holy Land. His
Speaker 1: entrails were buried where he died in Cardross, and his
Speaker 1: body went to dunferm Lean Alley. A night by the
Speaker 1: name of Sir James Douglas took the heart in the
Speaker 1: form of a metal urn on a necklace with him.
Speaker 1: I assume this means on one of the Crusades, but
Speaker 1: I'm not sure. But then Kenneth continues, but on the
Speaker 1: way he was called to help fight the Moors in Spain.
Speaker 1: At some point during the Battle of Taba, Douglas is
Speaker 1: said to have hurled the heart into the midst of
Speaker 1: the enemy with the cry, lead on, braveheart, I'll follow
Speaker 1: the entheses. No prizes for guessing where the movie got
Speaker 1: its title. Douglas, killed in battle, was then transported back
Speaker 1: to Scotland with the heart and buried near Melrose Abbey.
Speaker 1: The heart itself was exhumed and reburied within the abbey
Speaker 1: in nineteen ninety six. I had no idea heart burial
Speaker 1: had been such a widespread tradition, so the story of
Speaker 1: Robert the Bruce's heart had always seemed very strange. Thank
Speaker 1: you for giving it context. Kenneth from Glasgow. Thank you, Kenneth.
Speaker 1: Very interesting all right. This next message is in response
Speaker 1: to our episodes on tea. This is from Eric. Eric says, hey,
Speaker 1: Rob and Joe. I enjoyed your episodes about tea and
Speaker 1: its accessories. One thing that could have been mentioned is
Speaker 1: the Utah teapot, which is an object commonly rendered when
Speaker 1: testing computer graphics. I remember seeing teapots everywhere in my
Speaker 1: early computer science courses, and it's pretty common to see
Speaker 1: a teapot hid or not so hidden in various video
Speaker 1: games or rendering engines like CAD software that's computer aided
Speaker 1: design or something CAD software. You can look up what
Speaker 1: it stands for. It's sort of an in joke for
Speaker 1: computer nerds. I always thought that a teapot was an
Speaker 1: odd choice since everyone knows that software is ultimately fueled
Speaker 1: by coffee. But it makes sense since the teapot is
Speaker 1: a really unique and non uniform object, so it's more
Speaker 1: complicated than a simple sphere or polyhedron. But it's also
Speaker 1: smooth and shiny, which is a lot easier to render
Speaker 1: than something with rough or fuzzy textures. Thanks for the
Speaker 1: great episodes, Eric, Okay. One last message this comes from Kurt.
Speaker 1: Kurt says, hey guys, longtime listener over the years. I
Speaker 1: don't know why this just occurred to me today. I
Speaker 1: was listening to the three part series on tea recently.
Speaker 1: In the third part, Joe started to talk about the
Speaker 1: drip tea spout problem and Russell's teapot analogy. This started
Speaker 1: to take the conversation outside the realm of the subject,
Speaker 1: with just a thread of the original topic. This isn't
Speaker 1: a criticism at all. I like the tangents that bring
Speaker 1: up the things that I probably wouldn't otherwise think about
Speaker 1: in that moment. My question is what is your process
Speaker 1: for creating episodes based on a topic. Do you have
Speaker 1: discussions beforehand about areas you'd like to investigate, or do
Speaker 1: you both investigate certain areas individually and just see where
Speaker 1: it takes you without the other person knowing what topics
Speaker 1: you'll bring up. If so, is it more of a
Speaker 1: surprise where the conversations take you based on this, as
Speaker 1: neither of you would have a full indication as to
Speaker 1: where a conversation might go. I don't know if you've
Speaker 1: outlined this before. You guys have a ton of episodes
Speaker 1: and mail ins, so it might have been addressed previously. Anyway,
Speaker 1: Thanks for what you guys are doing. Love being in
Speaker 1: on the conversations no matter where they go. Kurt, Well, Kurt,
Speaker 1: thank you for the message. Yeah, I guess our method
Speaker 1: is somewhat free form, but I'll try to explain as
Speaker 1: best I can. We don't approach every episode exactly the
Speaker 1: same way, but most of the time it looks something
Speaker 1: like this. You know, one of us gets an idea
Speaker 1: and shares it with the other and we will talk
Speaker 1: it over and figure out if it will actually make
Speaker 1: for a good episode. So after we do that, after
Speaker 1: we figure out that something is probably a solid episode
Speaker 1: or has a series in it, we you know, work
Speaker 1: from a shared notes document which contains some pre written
Speaker 1: thoughts and information that we want to refer back to.
Speaker 1: But it's not like a strict script. So what you
Speaker 1: hear in an episode is a mix of some pre
Speaker 1: written thoughts, some paraphrasing and summarizing of notes, some extemporaneous
Speaker 1: thoughts and conversation. And ultimately this means that we know
Speaker 1: some things, but not everything that's going to happen going
Speaker 1: in and so are there are still often plenty of
Speaker 1: surprises we have for ourselves and for each other during
Speaker 1: a recording session, and sometimes we do agree beforehand on
Speaker 1: which subtopics we'll focus on, but sometimes not often. I've
Speaker 1: said this on the show before, but the you know,
Speaker 1: the contents of the episode are kind of an emergent
Speaker 1: result of the research process. It's not like we can
Speaker 1: know before researching what all of the interesting things to
Speaker 1: talk about will be. It's kind of through the process
Speaker 1: of reading about something that we discover even what questions
Speaker 1: there are to look into. So so, yeah, a lot
Speaker 1: of times we just kind of end up going on
Speaker 1: our own tangents and then we have something interesting to
Speaker 1: come share with each other when we return. But other times, yeah,
Speaker 1: we know about certain things we're going to look into,
Speaker 1: and we we kind of divvy it up accordingly. So
Speaker 1: to answer your question as directly as I can, it's
Speaker 1: just it's a mixed bags. Our conversations on Mike are
Speaker 1: partly predictable to each other and partly surprising to each other.
Speaker 1: All right, I think that's going to do it for
Speaker 1: the mail bag today. One more reminder. We're going to
Speaker 1: be running a vault episode tomorrow, and then we'll be
Speaker 1: back with new episodes for you on Wednesday, and going
Speaker 1: forward after that, we should have a new Core episode
Speaker 1: for you on Thursday of this week. If you're new here,
Speaker 1: this is the Stuff to Blow your Mind podcast. Our
Speaker 1: Core episodes publish every Tuesday and Thursday. Those are most
Speaker 1: often about science, but we also hop across disciplines and
Speaker 1: get into all sorts of things. On Mondays, we read
Speaker 1: back listener mail in episodes like this one, though usually
Speaker 1: both Robert and I are co hosting them. On Wednesdays,
Speaker 1: we do a short form episode called The Artifact or
Speaker 1: the Monster Fact. On Fridays. When the week is done,
Speaker 1: it's time for Weird House Cinema. That's a series we
Speaker 1: do where Rob and I just to feature and discuss
Speaker 1: a weird movie. Weird is really the only criterion. Sometimes
Speaker 1: we look at great movies, sometimes we look at bad movies.
Speaker 1: Some are well known classics, are obscure that nobody's ever
Speaker 1: heard about. Basically all of its fair game as long
Speaker 1: as it's weird. And then, finally, on Saturday's we feature
Speaker 1: an episode from The Fault So Big thanks to our
Speaker 1: audio producer JJ Pauseway. If you would like to get
Speaker 1: in touch with us with feedback on this episode or
Speaker 1: any other, to share your thoughts, or to share something
Speaker 1: that you think we'd be interested in, to suggest a
Speaker 1: topic for the future, or just to say hello, you
Speaker 1: can email us at contact at stuff to blow your
Speaker 1: Mind dot com. Stuff to Blow Your Mind is a
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