Rachel Feltman: Have you ever really thought about the hair that grows out of your head? I mean, I’m sure you’ve thought about your hair—in terms of which way to get it cut and how to get that one really wonky piece to behave itself—but have you ever considered why it is the way it is?
For Scientific American’s Science Quickly, I’m Rachel Feltman. My guest today is biological anthropologist Tina Lasisi, an assistant professor at the University of Michigan. She leads a lab that studies the “evolution and genetic basis of human phenotypic variation, with a focus on pigmentation and hair.” In other words she’s figuring out why human skin and hair comes in so many gorgeous varieties.
Thanks so much for joining us to chat today.
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Tina Lasisi: Great to be here.
Feltman: So I’ve been a fan of your research for a few years now ’cause, among other things, you’re really asking and answering questions about hair that I don’t think anyone else is tackling. How did you get interested in your field of study, and would you tell our listeners a little bit about it?
Lasisi: Absolutely. So I got interested in this when I was an undergrad. I did my undergrad at the University of Cambridge, where I was studying archaeology and anthropology, which there consists of studying archaeology, biological anthropology and social anthropology.
And I was always someone who really liked culture and traveling, so I thought I was gonna be a cultural anthropologist, but I got this lecture in the evolution of human skin color that really had me intrigued, and it was a lecture where they showed, you know, those really famous map pairings where you see the distribution of skin color around the world and the distribution of UV radiation, and it was just like this [makes explosion noise], you know, brain-exploding moment of like, “Wow, like I never thought about that,” and learning more about evolution and how there’s all these processes that can shape the way that humans are—the way that a lot of different species are, right—that really got me intrigued, and I felt like, “Okay, now I understand why my skin is the color that it is,” but my immediate next question was: “Well, why is my hair curly?”
Feltman: Hmm.
Lasisi: And there wasn’t a great answer at the time, and I was lucky enough to be in a really supportive environment, and I had a mentor who said, “You know, why don’t you just go into the science side of anthropology and study this?” And so, what year are we in—2025? Okay, 14 years later, here I am [laughs] still working on that.
Feltman: Yeah, well, and, you know, it sounds like the nature of your work is pretty interdisciplinary. You know, how would you summarize everything you’re looking at to someone who’s not familiar with your work?
Lasisi: That’s such a great question. I’m actually teaching an introduction to anthropology class right now, and I’m trying to explain to the students, like, “Anything can be anthropology, and everything can be anthropology.” You can use so many different methods. So right now, I would say I am definitely an evolutionary biologist. I work on human biology. I also work on—thermoregulation is work that I’ve worked on. I’ve worked with thermal engineers. I also have worked on genetics; that’s a big part of what I do. I’m also in a Department of Ecology and Evolutionary Biology. So all of those little bits and pieces, they give a different insight into the question that you can ask, and so everything that I do involves sitting [laughs] behind a computer, mostly, but also collecting samples from people and measuring things with various instruments and a lot of computer imaging, basically [basically].
Feltman: Very cool. And so, broadly speaking, why is it that people have so much variation in their hair and skin?
Lasisi: Mm-hmm. So the reason is simultaneously because of natural selection and because of the absence of natural selection. So the story that we’ve been able to piece together for skin color is that very long ago—somewhere between, you know, two to one million years ago—as the genus Homo was emerging, we were completely bipedal and at some point would have started losing our body hair, so really reducing those hair follicles so that we have like, this, tiny peach fuzz all over our body. And by doing that we have lost a really important barrier, right? So a lot of people can associate hair with keeping you warm, but it can also protect you from UV radiation. And so those ancestors probably would have been under selective pressure to evolve darker skin because by having more melanin in your skin, that’s another way that you can protect yourself from that UV radiation.
The story afterwards is one of adaptation to different environments. So it turns out that having all of that wonderful melanin to protect you is great when there’s a lot of solar radiation, but if you’re in an environment with not a lot of radiation, you end up running into issues with being able to produce enough vitamin D …
Feltman: Hmm.
Lasisi: Which is something you can only do in your body with the power of solar radiation that helps you convert it into an active form. Now, there are, of course, exceptions to that because there are places in the world where people have diets that are rich in naturally occurring vitamin D, like in the Arctic.
And since all those times we’ve moved to so many different places, and you have all of this variation that’s evolved because of that. And in the last, let’s call it 200 years what’s really nice is that we have developed all of these cultural ways of adapting to different places. So instead of being someone who maybe doesn’t have a lot of melanin and going to a place that is very, very sunny and being like, “Well, geez, I’m gonna have to wait a couple of generations for evolution to fix it for my ancestors,” we now have sunscreen and all of these other things that we can do. We have vitamin D supplementation.
Now the story with hair, it’s much more complicated to tell because we really don’t know. The thing about hair and skin is that in both cases, they don’t fossilize, and so we’re having to infer a lot from the past. And we do that by putting together hypotheses and saying, “Well, if this is the reason that natural selection would have selected for this kind of hair or that kind of skin, what’s the distribution that we expect to see?” And with hair we don’t have a lot of thoroughly tested hypotheses, but some of the work that I did in my Ph.D. that got published a few years ago was asking the question: “Well, does tightly curled hair reduce how much heat we might gain from solar radiation?” And I found in my experiments that, yes, it really does have this role. And so now the question is: “Can we also use genetics to ask, ‘Well, how did this happen? What’s the history of this? And what’s the story for every group of people around the world?’”
Feltman: Yeah, that’s so cool. I loved that study. It’s not apparent ’cause it’s pulled back and bleached within an inch of its life, but I have very curly hair [laughs]. And I was like, “I’ve always wondered why when I get a blowout, I feel [laughs], I feel like my head is gonna sweat right off.” Meanwhile, when people are like,”‘I don’t know how you live through the summer with that long hair,” and I’m like, “I don’t know what you’re talking about [laughs]. It’s fine.” So I love when the science answers questions I didn’t even know I had.
So a lot of the ways that we’ve historically categorized different variations in hair and skin are, of course, really lacking and sometimes quite racist. What factors are actually at play that lead to differences in the makeup of our skin and hair, and how has your work changed the way you think about how we might describe or categorize those variations?
Lasisi: Mm-hmm, that’s really an interesting question. So there’s a number of factors that we can tease apart there, right? We can ask the question of: “What are the mechanisms and the biological processes that contribute to this variation?” When it comes to skin color, we’ve known for a long time that it’s melanin, but measuring how much melanin is in someone’s skin is actually [laughs] really invasive. It’s really invasive—like you’d have to have a skin punch, you’d have to do various chemical analyses to measure exactly how much melanin and what kind of melanin is in there. So that’s really difficult, and people need a shorthand, especially if you’re doing population-wide studies. So people have tried to come up with really good descriptions, but descriptions can only go so far, and measuring something is so much better.
So with the rise of reflectance spectrophotometers, we finally had a tool that could really easily and noninvasively measure the color of skin. So this can be done at various levels of detail.
You can have one that is specifically trying to estimate the visible range of melanin, and it can give you something called melanin index, which is something that’s been developed to say, “Okay, well, how much melanin is in someone’s skin?” And so that really helped us collect a lot of accurate data, and in 2017, 2018 there were a lot of papers that came out saying, “Oh, wow, look at all of this variation in skin color that we didn’t realize existed in Africa.”
And so that’s where you have this really interesting insight of, “Oh, sometimes the words that we use and the variation that we think we’re seeing doesn’t align with what it is that we’re measuring,” which is why it’s so important to have tools that measure things. With hair we suffer from a similar problem, where, okay, well, we have all these descriptions of straight, wavy, curly, but is that really what the range of the variation is?
However, there isn’t a single thing that you can measure to define hair shape. There’s a lot of things that you can measure—if you are narrowing down to the level of a single hair fiber, in a single hair fiber you can get a cross section. You can slice that in half, look at that cross section and say, “Well, how thick is that hair fiber? What shape is it?” And that’s something that we’ve been doing for over 100 years, and we’ve noticed that there’s a variation there. But when it comes to thecurl it’s really difficult because hair curves in three dimensions.
So that is the thing that I actually worked on the longest—it took me 10 years to develop a method that I’m, you know, remotely happy with. And it involves getting a little strand of hair, chopping it up into little pieces so that it only curves in two dimensions and then measuring the curvature by trying to, basically, fit a circle to it. So you can imagine: you have different types of curls, different sizes of curls, and the smaller the circle is that fits to that curl, the more curly that hair is, you could say. And so that is one method that you can have of really precisely, accurately measuring hair curvature.
To answer the question of, “Why does hair curl?”: well, we don’t really know yet, and that’s really interesting because when it comes to sheep’s wool, so that doesn’t curl, but it crimps; it has this wave. We know that it has to do with two different types of cells that are deposited in different ways. But when it comes to human hair curl we don’t know what the mechanism is that makes hair curl, and it might be that there are many mechanisms that contribute to the shape. Some people have said that it’s the shape of the hair follicle, but we still have a lot of work to do to be sure about that.
Feltman: Yeah, well, and, you know, for folks who don’t think about hair texture or curl at all, why is it important to answer these questions?
Lasisi: Mm-hmm, so it’s important on a number of levels. First, from the perspective of someone who is really interested in human evolution, human origins, my desire to answer this comes from, you know, being, I don’t want to say a natural historian, but that’s really what you are when you’re studying evolution and asking, like, “Wow, what is the story of our people as a whole?” I would love to know: What is it that makes our hair the way that it is, and why are we the only mammals that have naked bodies and hair on their heads? That’s weird. Not trying to judge here, but it’s a little odd compared to all the other mammals. But there’s a lot of other reasons that it might be useful to understand.
So something that I’m incredibly fascinated with is the potential to understand the variation within your ownbody through the hair follicle, right? You have hair follicles all over your body. Your eyebrows are hair, you know, your eyelashes are hair, and they are very different than the hair on your head. You might have body hair in various places. And yet you have the same DNA across your body; it’s just how that DNA is used. And because you have this incredible structure, this hair follicle, which is the same thing all over your body, we have this unique opportunity to ask, “Okay, well, how can we use the same DNA and a similar structure around the body and create different things?”
And that’s the kind of knowledge that you can apply to a lot of different ends. You could be asking questions about, “Well, why do things go wrong when they go wrong? And what are various processes that affect how our DNA’s able to express itself?” Something that’s incredibly interesting is a lot of people have reported to me, for themselves or someone they know, when they went through chemotherapy their hair texture changed.
Feltman: Mm.
Lasisi: Your DNA didn’t change, right? But something about how your DNA is being used in those hair follicles has changed, and if we’re able to make those associations, see what those links are, we can break down what the biological processes are that are going on, and that might lead to—who knows what; you never know what you’re gonna find in the type of science that I’m doing [laughs], and that’s what I love about it.
Feltman: [Laughs] Yeah, awesome. What are some other big questions that you’re still hoping to answer?
Lasisi: So there are a number of adventures that I still want to go on when it comes to hair science, and one of them is, you know, understanding how various physiological processes can affect our hair. So thinking of even our own trajectories [laughs] through to adulthood, there was a time when we were probably marginally less hairy, and then puberty happened, and all of a sudden there was hair in places where it wasn’t before, and maybe our hair was a little bit different [laughs] in places where we already had hair. And that’s really interesting because we know that there’s something going on endocrinologically that is, is changing our body and we have this external marker that is telling us, “Okay, well, here are some changes,” and so it’s really interesting to ask that question.
And then on the other end of that, once we’re talking about aging, we have people who maybe start losing hair in certain places. It gets thinner or maybe it gets coarser, is something I’ve heard people say. And so we can ask questions, again, about what’s going on in your body and can we learn something from this external marker that is very noninvasive to say, “Okay, this is giving me a window into your body about what could be going on”?
And then the second part of hair science that I’m really interested in right now is what we can learn from the hair fibers that are coming out of your body in terms of biomarkers.
Feltman: Mm.
Lasisi: So there’s a lot you can measure from hair. For example, right now in my lab one of my students is working on extracting cortisol from hair, and the way that your hair works it ends up being, like, this ice core of your body’s physiology; it’s constantly capturing bits of what’s going on in your bloodstream. And so there’s this incredible potential to get this slice-of-time view, if we can get our methods to be precise enough, of: “This is what was going on in your body a month ago, two months ago, three months ago.” And it would be an incredible, noninvasive way to be able to keep track of cortisol, other hormones, and there’s also a lot of toxicology that you can do with hair.
Feltman: Very cool. Thank you so much for coming on to talk about this. I hope we can have you back soon to talk about more of your research.
Lasisi: Absolutely, this was so much fun.
Feltman: That’s all for today’s episode. Tune in on Monday for our usual science news roundup.
Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Kelso Harper, Madison Goldberg, Naeem Amarsy and Jeff DelViscio. Shayna Posses and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.
For Scientific American, this is Rachel Feltman. Have a great weekend!
