The Decibel - The evolutionary advantage of curly hair

Episode Date: August 9, 2023

Curly hair often gets a bad reputation for being too high maintenance but research has shown that it plays an important role in our evolutions – and even our brains.Dr. Tina Lasisi, a biological anthropologist who focuses on studying the evolution and genetics of human hair and skin, will talk to us about the importance of curly hair.Questions? Comments? Ideas? Email us at [e-mail]

Curly hair sometimes gets a bad rap. It's called frizzy, poofy, out of control. Let's keep this simple. Our hair is difficult hair. The best part of frizz? Getting rid of it. No one has to live with frizz. But those coily strands may have played an important role in our evolution

and in growing our brains. That's according to research from Dr. Tina Licisi. She's a biological anthropologist and focuses on studying the evolution and genetics of human hair and skin. She's also an assistant professor of anthropology at the University of Michigan. Dr. Lasisi is on the show today to help us untangle what we're learning about the evolutionary importance of curly hair. I'm Maina Karaman-Wilms, and this is The Decibel from The Globe and Mail. Tina, thank you so much for speaking with me. You're welcome. I'm happy to be here.

So I'm curious, what first got you interested in studying hair? So my interest in hair goes back pretty long in the sense that I'm a Black woman who has thought about my hair a lot from a cosmetic sense. But my scientific interest in it only came about after I started studying anthropology, because I'd never thought of hair as something that could possibly have a function. But when you look at mammalian biology, you see that hair is very important for mammals. It has all of these functions. And so it makes you think, could it have one of those functions for humans? Now that I've been looking at hair as something that could protect you from solar radiation, it made me think back to this time

when I was an undergrad with a friend of mine who had very straight hair. We were outside in the sun. It was some kind of picnic situation and their hand brushed up against my hair and they kind of just pulled it back and were like, oh, your hair is hot. And I didn't know what they were talking about, but I touched it and I felt that the top of my hair was really, really hot, but I didn't feel any of it on my scalp. So without any kind of hat or anything like that, if I just had my

big curly hair, it seemed to be doing something. And the funny thing is, I didn't really give it a second thought until I started doing these experiments. Interesting. That's so funny. Okay, so well, let's fast forward to today. You're now a biological anthropologist. Why is the hair in our head something worth studying? So I always like to point out to people that mammals can be hairy, mammals can be naked, but we're the only weirdos that have hair on our heads and have naked bodies. So that is something that is so out there in terms of mammals that it makes you want to ask, what was it about the evolutionary history of our lineage that made it make sense to have this combination of traits. So this is what you kind of started investigating. And you recently published a study in the Proceedings of the National Academy of Sciences. So that's a big journal. And the study

is called, quote, human scalp hair as a thermoregulatory adaptation, end quote. So Tina, can you just explain what that means? What were you actually looking at? Yeah, sure. So this was some experiments that we ran to test whether human scalp hair could have some kind of function in protecting us from solar radiation. And so the point of this paper was to kind of put this idea out there of, hey, hair is this thing that you think about cosmetically. From the evolutionary perspective, you might see some people talking about it in terms of sexual selection, but consider it might have some kind of physical or physiological

function. And so what we did is we did some experiments in a climate controlled chamber with something called a thermal mannequin, which is a thing that looks like a robot that stepped out of Terminator and has plugs that go right into its eye sockets, which is my favorite design choice of all time. And then we put a bunch of wigs on it and did experiments in different conditions to see how much heat was being transferred through to the scalp. Okay, yes. And this mannequin, I believe, is named Newton. It's a great, great choice there too. Can you just tell me, like you said, he's a thermal mannequin. What is that and what kind of things are they usually used for? So thermal mannequins are basically like a human-shaped hot plate, you can think of it. It's this thing that can measure differences in temperature. So

companies like Adidas or Nike might use them if they're trying to claim that a certain kind of fabric that they're using is moisture wicking, but allows you to, you know, have air flowing through. It's also used to test things like the suits that firefighters are going to wear and see how much heat is going through those materials in one direction or another. The thing that I did differently is with my collaborators, I thought, well, hey, what if we put a bunch of wigs on it? Will that tell us something about how different hair textures can affect heat transfer? Yeah. And when I look at Newton at this picture of him, he's kind of like this red mannequin. He's sitting in a wheelchair in front of these big fans. So Tina, can you just describe what is happening in this picture? A lot is

happening. So Newton is actually a dark gray metal and we put a red suit, like one of those full body suits that you see people walking in sometimes that covers their heads and everything. One of those and it's made of cotton and that is serving as his skin, which is something that we use to test, for example, how much you could evaporate by making his skin wet. So, well, first you put Newton in a little chair in this wind tunnel because we want to test different wind speeds. And we have a bunch of floodlights behind him that are simulating solar radiation, which we measure to represent a certain amount of solar radiation, the same as a sunny day near a region near the equator. So what we would do is we would put on the wigs and just sit there and start taking measurements.

Okay. So what types of wigs? What did you go through? So we got three human hair wigs, one that was completely straight, one that was curled moderately, and one that was curled very tightly. And so we looked at those three wigs as well as the nude condition when Newton had nothing on his head. And that gave us an idea of what is the difference between having no hair in addition to telling us something about different hair textures. And so what did you find? The main thing that I found is if you are someone who does not have hair on their head,

whether it is by choice or by necessity, please wear a hat because solar radiation is so powerful that it made our mannequin, it made our mannequin overheat once to the point that we had to change the settings because we couldn't get any data anymore. It was overheating so much when it had nothing to protect its head. So that really made me appreciate the fact that coverage does something. And that was mainly the difference between no hair and hair. But I was also very surprised to see the difference between different hair textures. So what we saw is that straight hair offers protection. And we know this from mammals. Any hair offers protection against solar radiation. But usually you have this trade-off. You have this trade-off in the same way

that, let's say, firefighters have their suits that protect them. They stop any of that blazing heat from going in, but they also stop any heat from going out just because it's pure insulation. And so that's what straight hair does. And when you get to curly hair, it seems as though it's able to minimize how much radiation is coming through, but also because of the air spaces between the curls, probably allow you to lose heat, especially if there's like a lot of wind flowing through it. Okay. So this is a really fascinating thing. So what is, what exactly is the advantage then of the, you know, having the curls on your head as opposed to the straight hair? So the advantage that you see comes to play, especially in a dry, sunny climate. So

let's say that you're trying to survive and stay cool in a place where the ambient temperature is really, really, really high, but it's not very sunny. In that case, nothing is going to help you. You should be as naked as possible because you just want to lose heat. But if the thing that is causing you to overheat is solar radiation, then having something that can block the radiation is much more helpful. And that's where the curly hair comes in. It turns into this kind of like one way mirror where you can't have the solar radiation travel through, but you can have this heat that you're evaporating from your body, especially from your scalp, go out. If you have really curly hair, you can have way more volume and therefore much more distance between

your scalp and the top of your hair. And what we know from studies in mammals and mammalian fur is that depth is the thing that protects them from radiation. So interesting. Yeah. And I want to ask you about sweat, too, because I know like that's how we cool the rest of our body, right? We don't have hair, fur on the rest of our body. And so we have this process to evaporate heat off of us. So how does that like why couldn't we just do that on our heads as well? Why do we have to have hair on our scalp in order to protect us? That is a great question. Sweating is this fantastic mechanism that we evolved to be really, really good at. And part of why we lost our body hair is probably also to maximize how efficient that sweating is, because if sweat evaporates

from your skin, that's how it cools you down. If it evaporates from your clothes or your hair, that's not as useful. But the reason that that may not have been enough for the brain is because the brain is very, very heat sensitive. So you actually don't want to be getting to that point of you have to sweat because that means you're already heating up a lot. So what you may have seen at some point in human evolution is that hair is evolving as this passive mechanism. So while sweat is something active that is not free because you lose water, you lose electrolytes, hair can kind of be there as this thing that's not costing you anything physiologically, but it's still protecting you so much that it makes enough of a difference

that you don't even have to sweat. And that's what we found with our experiments is that if you had tightly curled hair, you didn't even get hot enough that you needed to break into a sweat to cool yourself down versus if you had no hair or even straight hair, you would need to start sweating to bring your body temperature down again. We'll be back in a moment. Okay, so we've established that curlier hair is good at keeping our heads cooler in intense heat. But Tina, your research actually goes further to say that this could have played a role in our ancestors even growing bigger brains. So can you explain that?

Humans are really interesting in how we are different from our closest living relatives, like chimpanzees and bonobos. We are apes that walk upright, that do not have body hair for the most part. And we have, you know, these large brains and we also use tools. And so one of the great, uh, mysteries of the last hundred or so years has been trying to put together in what order these human specific traits evolved. And so we've learned that a lot of apes actually use tools. So we're not that special for it. That probably came pretty early. Um, we have found a lot of apes actually use tools. So we're not that special for it. That probably came pretty early. We have found a lot of fossils that tell us something about when we started walking upright. And it seemed that larger brain size was the last one of those traits to come along in our lineage. And what we noticed from the fossil record is that we get to Homo erectus,

and it basically looks like a modern human, except for brain size isn't quite where modern humans are. And so it's made people wonder, was there some kind of limit? And we know that brains are energetically expensive. So some people have suggested that part of our diet may have contributed to a limit. You can't grow a massive brain if you can't get enough consistent nourishment. And then another thing to think about is you don't want to have this massive brain in a place where it's going to be a liability. So brain is very heat sensitive. It also generates a lot of heat. And so it may have been that it couldn't get any larger until there was something that evolved that

was able to reliably keep our heads cool. So essentially, the hair, growing hair on our head could have allowed us to grow bigger brains then? Yes. So being able to have this tightly coiled hair that minimizes how much heat you're getting from solar irradiation may have released this constraint that existed on how large human brains could get. And so just to be clear, though, this does not mean that curly haired people have bigger brains. That's not the connection here. No, this is something that would have happened long, long ago when we all had the same shared ancestors so far back in human history that we don't think it would have made a huge difference now. And the reason that we say this and emphasize is that when you look around the world at different hair textures, you don't see the same pattern as you do with skin color. And that to us made us think, well, it could have been something that was important early in human evolution.

If curly hair appears to be better at keeping our brains cool, why do we have different hair types today? And like some people are even bald today. So why do we have different hair types today? And like some people are even bald today. So why, why, why do we have that variation? So at some point, whenever I talk about my research, I inevitably have to explain to people who ask about why do bald people exist if hair is important, that evolution does not care about you post-reproductively. So anything that happens after you've had the chance to have offspring is no longer the realm of evolution. They have done what they needed to Well, the first reason is there is no best. There is optimal or even remotely useful under particular climatic circumstances. And so it can become subject to something called genetic drift. So if you have a trait that has a genetic basis and it is no longer being forced to stay a particular way, as people go to different parts of the world, you can have some variations of genes that just disappear or some variations

of genes that become the most common in a population. And that is how you can have people and different populations become different from each other without there being a reason from natural selection. So we said that curly hair actually will help keep you cool, but does that mean like straighter hair can help keep the heat in? So is that better in, you know, like a colder climate then? Yes, that could be the case. So straight hair was better at just straight insulation. It could be the case that for some populations who are in very cold places, that was important. It could be the case that for some populations who are in very cold places, that was important. It could be that this was important before modern humans and it was important to Neanderthals. That's something that we won't be able to know until we know more about

the genetic basis for different hair textures and can ask questions of ancient DNA. So what kind of version of these genes did Neanderthals have? What about Denisovans? Yeah. And did you, I wonder about color too, right? Because I think about like my dark hair really gets very hot, but like blonde hair doesn't seem to get as hot. Like is that a factor here too? So counter to many people's intuition, light hair is not particularly good or useful in a very sunny environment because that radiation goes right through the hair or it bounces off in all kinds of directions. That means it gets through to your scalp as opposed to if you have dark hair, it gets absorbed by that dark hair and the melanin in that hair. So it doesn't have to necessarily reach your scalp. Wow. So interesting. Okay. So Tina,

your research, not just this study, but even your research more broadly, you're looking at often the hierarchy that we might associate different traits in humans. And when it comes to hair, we sometimes hear the term good hair. That originates from the black community and generally favors less tightly coiled curls in favor of more hair that has more Eurocentric traits, right? Like straighter, silkier hair. I wonder, did these social ideas about hair types, did that at all influence how you think about your research?

It does in the sense that it gives me an opportunity to present a story and information that departs from those subjective biases and ideas of one thing being better than the other. What you're referring to in terms of good hair and what is considered to actually be beautiful has a lot to do with histories of oppression, marginalization, and power. You are never going to see in human history a group of people who is oppressing another and says, oh, you know who's really pretty, perfect, and great? The people that we're oppressing. What I get to study is, okay, we have all of these biased opinions about this is a good trait and this is a bad trait, but can we actually learn something about its evolutionary history? So when we think about skin color, a lot of the discussions around it have become very

positive in terms of having dark skin because people know that that is skin that has a lot of melanin. And now a broader group of people can talk about the function of melanin and how it protects you from the sun and how that means that your ancestors evolved this thing that you still have to survive and to thrive in a particular environment. And I want to see if we can shift the discussion in hair to a similar way to allow people to appreciate that tightly curled hair that people might have all these negative connotations with actually is this uniquely human trait that no other mammal has and that our ancestors evolved because it was useful for our survival in certain

circumstances. Yeah, so true. Thank you so much, Tina, for speaking with me. This was really fascinating. Absolutely. It was a pleasure. That's it for today. I'm Mainika Raman-Wells. Our summer producer is Nagin Nia. Our producers are Madeline White, Cheryl Sutherland, and I'll talk to you tomorrow.