Listener Mail: Fields of Ancient Void

That's going to be Tuesday, and then there should be an all new short form on Wednesday and a new core episode with Rob and me back together on Thursday of this week. All right, I guess we should jump right into the messages. This first message is from Vic. She says, Hi, Robert and Joe. I love your podcast. I was hooked after I listened to the multi part episode on mirrors, but my favorite of all time is

the history of the odometer, absolutely blew my mind. For my question or possible show suggestion, do you know any theories on why humans evolved away from having thick fur or hair like that of our closest living relatives in the Great Ape family. I heard somewhere recently that humans actually have the same amount of hair on average as a chimpanzee. But human body hair is so fine and or short for the most part that it doesn't appear to be fur. I don't know if this is true.

I had a good laugh wondering if our early ancestors started wearing coverings while they still had thick coats, and my brain started playing Planet of the Apes. Maybe there are advantages to our naked mole rat status in the great ape family, maybe something about fleas lice and other fur loving pests. Sorry for the long email, would love to know what you think. Thank you for all the

great shows, Vic. Thank you for the message. Vic. Now, initially I did not know the answer to your question about hair follical density and hair thickness in humans versus chimpanzees. But interesting thing in trying to answer your other question, I came across an answer to that one too, So more on that in a bit. But the main question here, how did humans come to be relatively hairless compared to

our nearest relatives in the animal kingdom. This is a really interesting question and one we've looked at on the show before, so I just did a little reviewing to refresh myself on it. So we don't know for sure. With a lot of these evolutionary questions, we can come up with good guesses at the answer, but sometimes it's hard to know for certain what the actual reasoning or pressure driving and adaptation in the distant past was. But I think there are some pretty good guesses about what

drove the human adaptation for comparative nakedness. One thing to note starting off is that although we are relatively hairless overall compared to most st other mammals, there's a fair amount of variation in the amount of body hair present on humans, like in between different human individuals, and I think it's interesting that there are pretty consistent patterns of hairiness versus hairlessness on different regions of the body that

are common to almost all people. So, for example, we don't grow hair on the palms of our hands or the soles of our feet for the most part. Though if you look, these skin surface patterns are somewhat shared by our closest relatives, even the very hairy ones. So chimpanzees, gorillas, and other great apes also don't have fur on their palms, and this is probably all for the same reason. In all of us. It's so that we can have improved

grip and dexterity. Imagine trying to grip a tree branch, to climb a tree, or swing from a tree branch, or to manipulate objects in your hands. If those hands were covered in fur, things would really kind of slide around in there, it seems. However, when it comes to the general loss of over the covering the whole body, one of the major explanations is that it has to do with thermoregulation, the ability to manage the body's internal temperature.

Fur helps insulate the body against the cold. It's very useful for that, and many mammals use it to that end, but as an insulation method it's inflexible. A mammal with thick fur can't quickly take its fur off when it gets hot, so it has to be careful to avoid, say,

overexerting itself out in the sun. And the thermoregulation hypothesis says well, human ancestors, by losing most of their body hair massively increased their ability to cool the body, especially during exercise in hot climates, maybe under the direct sun. And I think one thing that makes the thermoregulation hypothesis strong is that the loss of body hair is the

only observed genetic change that would serve this purpose. In fact, you can see other signs that there was intense pressure on human ancestors to develop genetic adaptations for cooling the body. And a big example here is sweat glands. So if I asked you to think what distinguishes us from our closest relatives like chimpanzees, what are some body differences you can think of? You might think of things like bipedal locomotion. We tend to walk upright on two legs, the relative

lack of body fur as in your question here. Of course, other behavioral and intellectual things like the capacity for language and so forth. But another major difference is that humans have way more sweat glands, also known as ekrone glands. We have something like ten times the density of ekron glands found in animals like chimpanzees and macaques. So we are not only the ape that can walk, the ape that can talk, We are by far the sweatiest of

all apes. And so I was looking for some research on the genetic basis of this difference in the sweat glands, and I found the following study. It was won by Daniel aldea at all called repeated mutation of a developmental

enhancer contributed to human thermoregulatory evolution. This was published in Proceedings the National Academy of Sciences in twenty twenty one, and it was by a team of researchers I think primarily from the University of Pennsylvania School of Medicine, and they write in their summary quote, the effectiveness of human thermoregulatory sweating is underlain by the evolution of a dramatically increased density of water secreting ekrone sweat glands in human

skin relative to that of other primates. Here we show that the accumulation of human specific mutations in a developmental enhancer collectively promoted the production of ekrone glands in humans by upregulating the expression of the engrailed one also known as the e in one transcription factor in the skin. So here is apparently the genetic basis of the difference.

I was reading some comments by the authors in a press release associated with this study, and one thing they highlighted is that while a lot of other human genetic traits that show differences from our nearest relatives are thought to come from a complex interaction of different heritable factors. The human beings ability to outsweat its relatives seems largely traceable to mutations in one single regulatory region called the

he CE eighteen. Now also related to the study here, Vic, We're going to come back to something you asked in your email, the part where you wrote, quote, I heard something recently that humans actually have the same amount of hair on average as a chimpanzee. But human body hair is so fine and or short for the most part that it doesn't appear to be fur. Well, I was reading about the paper I just mentioned in an exerpt from a book called The Joy of Sweat, The Strange

Science of Perspiration by Sarah Everts. This exerpt was published by Science Friday, and Everts here cites one of the authors of the twenty twenty one study, who is the upin Geneticistiana Kambarov, and she confirms that quote we look naked, but we are not actually naked. We have the same density of hair follicles as apes have fur follicles end of quote. But most of those hairs are miniatureized. They're shrunken down to the point that they are nearly invisible.

So yes, it appears vic what you heard was true. It's not that we have fewer hair follicles. It's just that most of that hair doesn't really it doesn't really become you know, it doesn't achieve hair's full potential, so we don't have fur coats. Instead, we got little bumps and sweat glands and things. So it looks like human ancestors underwent multiple changes would have helped keep our bodies cooler than would be possible if those bodies were more

like the bodies of chimpanzees. And those changes are the reduction and body fur and the higher density of sweat glands for evaporative cooling. Now, another thing that's worth noting is that these adaptations stack. The loss of body hair appears to make sweating more useful as a cooling technique, because if you think about it, it's like harder to achieve much evaporative cooling if you are covered in a mat of fur. And it also seems that these two

changes could even have a common cause. Coming back to that exerpt from the book by Sarah Everts, she's writing about research by Camperov and colleagues. Quote. Camberov and her colleagues are finding evidence that the biological signals nudging these precursor cells toward an ekrone sweat gland density also inhibit the formation of hair. So given all this evidence, it seems very plausible to me that there was a pressure on our ancestors causing them to survive and reproduce better

if they could cool their bodies more efficiently. Now, what would that pressure be. It could be that they changed habitats, maybe say from living in fully shaded forests with like a thick canopy cover to living in more direct sunlight, either in an open savannah or in a woodland that was less dense with thinner canopy and more direct sun.

Or it could be a change in survival niches, behavioral survival niches, So imagine a change to relying on more strenuous, prolonged exercise to survive, maybe through endurance running during hunting or something else. Or there could be reasons that we're not even thinking of that would have caused this need

to cool the body. So the thermoregulation explanation seems pretty strong to me, maybe the probably the strongest explanation I've come across, But there are plenty of other possible reasons for ancestral fur laws, and they could have been complementary to one another. I'm not going to cover all of the hypotheses out there, but one other idea we've talked about on the show before is the role of ectoparasites. And here I'm going to consult a paper called a

naked ape would have fewer parasites. This was published in two thousand and three by Mark Pagel and Walter Bodner in Proceedings of the Royal Society of London Series B Biological Sciences. From their abstract, they write, quote, Unusually among the mammals, humans lack an outer layer of protective fur or hair. We propose the hypothesis that humans evolved hairlessness to reduce parasite loads, especially ectoparasites that may carry disease.

We suggest that hairlessness is maintained by these naturally selected benefits and bisexual selection operating on both sexes. Hairlessness is made possible in humans owing to their unique abilities to regulate their environment via fire, shelter, and clothing. So, to summarize elements of this hypothesis, you know we can get ticks, we can get lice, and these parasites infest body hair, they become harder to remove if that hair is thick,

and they're not just annoying like they spread disease. So they do actually have an impact on survival and fitness in a natural setting. Once humans could control fire and could surround themselves with external insulation, now that might be what you would think of his clothing, like maybe animal skins or grass or other auxiliary materials from the environment,

or it could be thinking of shelters. All of these changes make it less important to have biological equipment for keeping warm, meaning the fur that other mammals have for warmth is just less necessary for survival if you've got fire, clothes, shelter. It's also possible that if hairlessness enhances survival benefits by reducing parasite loads, it could also help enhance reproductive fitness through sexual selection by providing an honest signal to potential

mates of the lack of external parasites. Sort of, you know, look and see how attractive I am, And in this case, attractive means relatively free of lice and ticks. And there's another interesting point of comparison the authors make. They say, you know, what are some other mammals that are relatively hairless, well,

one would be naked mole rats. These are animals that live in large colonies underground where you would expect a lot of parasite transmission, but their hairlessness offers resistance against ectoparasites. And they can of course cope with the lack of fur for warmth because they huddle together and they share body heat and they stay away from cold air in their subterranean layers. So what a naked mole rat has

in a warmth from underground rat piles? We have in technology through fire and clothing, and I guess in evaluating this hypothesis, I would have questions about, Like my big questions would be like, how do the timelines compare. What is the evidence of when our ancestors started undergoing mutations to lose their fur, and how would that match up against to our best guests at the timeline when we started controlling fire or wearing clothes or had other forms

of external insulation. But anyway, very interesting question. Thank you, vic. All Right, this next message is about our episodes on heart burial, heart removal and heart burial. It's from Kenneth in Glasgow. Kenneth says Hi, Rob and Joe, thanks for the fascinating episodes discussing all the ins and outs of heart removal. You finally helped me make sense of the

post mortem journey of the Heart of the Bruce. Robert the Bruce was the Scottish king responsible for the defeat of the English army at Bannockburn, effectively ending plantagenet claims to the Scottish throne. When it came time for him to consider his own death, he requested that his heart be taken on a tour of the Holy Land. His entrails were buried where he died in Cardross, and his

body went to dunferm Lean Alley. A night by the name of Sir James Douglas took the heart in the form of a metal urn on a necklace with him. I assume this means on one of the Crusades, but I'm not sure. But then Kenneth continues, but on the way he was called to help fight the Moors in Spain. At some point during the Battle of Taba, Douglas is said to have hurled the heart into the midst of the enemy with the cry, lead on, braveheart, I'll follow

the entheses. No prizes for guessing where the movie got its title. Douglas, killed in battle, was then transported back to Scotland with the heart and buried near Melrose Abbey. The heart itself was exhumed and reburied within the abbey in nineteen ninety six. I had no idea heart burial had been such a widespread tradition, so the story of Robert the Bruce's heart had always seemed very strange. Thank you for giving it context. Kenneth from Glasgow. Thank you, Kenneth.

Very interesting all right. This next message is in response to our episodes on tea. This is from Eric. Eric says, hey, Rob and Joe. I enjoyed your episodes about tea and its accessories. One thing that could have been mentioned is the Utah teapot, which is an object commonly rendered when

testing computer graphics. I remember seeing teapots everywhere in my early computer science courses, and it's pretty common to see a teapot hid or not so hidden in various video games or rendering engines like CAD software that's computer aided design or something CAD software. You can look up what it stands for. It's sort of an in joke for computer nerds. I always thought that a teapot was an odd choice since everyone knows that software is ultimately fueled

by coffee. But it makes sense since the teapot is a really unique and non uniform object, so it's more complicated than a simple sphere or polyhedron. But it's also smooth and shiny, which is a lot easier to render than something with rough or fuzzy textures. Thanks for the great episodes, Eric, Okay. One last message this comes from Kurt. Kurt says, hey guys, longtime listener over the years. I

don't know why this just occurred to me today. I was listening to the three part series on tea recently. In the third part, Joe started to talk about the drip tea spout problem and Russell's teapot analogy. This started to take the conversation outside the realm of the subject, with just a thread of the original topic. This isn't a criticism at all. I like the tangents that bring up the things that I probably wouldn't otherwise think about in that moment. My question is what is your process

for creating episodes based on a topic. Do you have discussions beforehand about areas you'd like to investigate, or do you both investigate certain areas individually and just see where it takes you without the other person knowing what topics you'll bring up. If so, is it more of a surprise where the conversations take you based on this, as neither of you would have a full indication as to where a conversation might go. I don't know if you've

outlined this before. You guys have a ton of episodes and mail ins, so it might have been addressed previously. Anyway, Thanks for what you guys are doing. Love being in on the conversations no matter where they go. Kurt, Well, Kurt, thank you for the message. Yeah, I guess our method is somewhat free form, but I'll try to explain as best I can. We don't approach every episode exactly the same way, but most of the time it looks something

like this. You know, one of us gets an idea and shares it with the other and we will talk it over and figure out if it will actually make for a good episode. So after we do that, after we figure out that something is probably a solid episode or has a series in it, we you know, work from a shared notes document which contains some pre written thoughts and information that we want to refer back to.

But it's not like a strict script. So what you hear in an episode is a mix of some pre written thoughts, some paraphrasing and summarizing of notes, some extemporaneous thoughts and conversation. And ultimately this means that we know some things, but not everything that's going to happen going in and so are there are still often plenty of surprises we have for ourselves and for each other during a recording session, and sometimes we do agree beforehand on

which subtopics we'll focus on, but sometimes not often. I've said this on the show before, but the you know, the contents of the episode are kind of an emergent result of the research process. It's not like we can know before researching what all of the interesting things to talk about will be. It's kind of through the process of reading about something that we discover even what questions

there are to look into. So so, yeah, a lot of times we just kind of end up going on our own tangents and then we have something interesting to come share with each other when we return. But other times, yeah, we know about certain things we're going to look into, and we we kind of divvy it up accordingly. So to answer your question as directly as I can, it's just it's a mixed bags. Our conversations on Mike are partly predictable to each other and partly surprising to each other.

All right, I think that's going to do it for the mail bag today. One more reminder. We're going to be running a vault episode tomorrow, and then we'll be back with new episodes for you on Wednesday, and going forward after that, we should have a new Core episode for you on Thursday of this week. If you're new here, this is the Stuff to Blow your Mind podcast. Our Core episodes publish every Tuesday and Thursday. Those are most often about science, but we also hop across disciplines and

get into all sorts of things. On Mondays, we read back listener mail in episodes like this one, though usually both Robert and I are co hosting them. On Wednesdays, we do a short form episode called The Artifact or the Monster Fact. On Fridays. When the week is done, it's time for Weird House Cinema. That's a series we do where Rob and I just to feature and discuss a weird movie. Weird is really the only criterion. Sometimes we look at great movies, sometimes we look at bad movies.

Some are well known classics, are obscure that nobody's ever heard about. Basically all of its fair game as long as it's weird. And then, finally, on Saturday's we feature an episode from The Fault So Big thanks to our

audio producer JJ Pauseway. If you would like to get in touch with us with feedback on this episode or any other, to share your thoughts, or to share something that you think we'd be interested in, to suggest a topic for the future, or just to say hello, you can email us at contact at stuff to blow your Mind dot com. Stuff to Blow Your Mind is a

production of iHeartRadio. For more podcasts from my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.