February 20, 2025Where Did Curly Hair Come From? Biological Anthropology May Provide InsightsHumans have a surprising lack of hair for mammals. Biological anthropology may provide insights into why the hair we have sometimes comes out curly.By Rachel Feltman & Jeffery DelViscio Anaissa Ruiz Tejada/Scientific AmericanSUBSCRIBE TO Science QuicklyRachel Feltman: Have you ever really thought about the hair that grows out of your head? I mean, Im sure youve thought about your hairin terms of which way to get it cut and how to get that one really wonky piece to behave itselfbut have you ever considered why it is the way it is?For Scientific Americans Science Quickly, Im 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 shes figuring out why human skin and hair comes in so many gorgeous varieties.Thanks so much for joining us to chat today.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Tina Lasisi: Great to be here.Feltman: So Ive been a fan of your research for a few years now cause, among other things, youre really asking and answering questions about hair that I dont 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 theres all these processes that can shape the way that humans arethe way that a lot of different species are, rightthat 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 wasnt 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 dont you just go into the science side of anthropology and study this? And so, what year are we in2025? 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 youre looking at to someone whos not familiar with your work?Lasisi: Thats such a great question. Im actually teaching an introduction to anthropology class right now, and Im 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 onthermoregulation is work that Ive worked on. Ive worked with thermal engineers. I also have worked on genetics; thats a big part of what I do. Im 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 weve been able to piece together for skin color is that very long agosomewhere between, you know, two to one million years agoas 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, thats 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 theres a lot of solar radiation, but if youre 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 weve moved to so many different places, and you have all of this variation thats evolved because of that. And in the last, lets call it 200 years whats really nice is that we have developed all of these cultural ways of adapting to different places. So instead of being someone who maybe doesnt have a lot of melanin and going to a place that is very, very sunny and being like, Well, geez, Im 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, its much more complicated to tell because we really dont know. The thing about hair and skin is that in both cases, they dont fossilize, and so were 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, whats the distribution that we expect to see? And with hair we dont 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? Whats the history of this? And whats the story for every group of people around the world?Feltman: Yeah, thats so cool. I loved that study. Its not apparent cause its pulled back and bleached within an inch of its life, but I have very curly hair [laughs]. And I was like, Ive 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 dont know how you live through the summer with that long hair, and Im like, I dont know what youre talking about [laughs]. Its fine. So I love when the science answers questions I didnt even know I had.So a lot of the ways that weve 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, thats really an interesting question. So theres 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, weve known for a long time that its melanin, but measuring how much melanin is in someones skin is actually [laughs] really invasive. Its really invasivelike youd have to have a skin punch, youd have to do various chemical analyses to measure exactly how much melanin and what kind of melanin is in there. So thats really difficult, and people need a shorthand, especially if youre 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 thats been developed to say, Okay, well, how much melanin is in someones 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 didnt realize existed in Africa.And so thats where you have this really interesting insight of, Oh, sometimes the words that we use and the variation that we think were seeing doesnt align with what it is that were measuring, which is why its 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 isnt a single thing that you can measure to define hair shape. Theres a lot of things that you can measureif 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 thats something that weve been doing for over 100 years, and weve noticed that theres a variation there. But when it comes to thecurl its really difficult because hair curves in three dimensions.So that is the thing that I actually worked on the longestit took me 10 years to develop a method that Im, 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 dont really know yet, and thats really interesting because when it comes to sheeps wool, so that doesnt 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 dont 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 its 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 dont think about hair texture or curl at all, why is it important to answer these questions?Lasisi: Mm-hmm, so its 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 dont want to say a natural historian, but thats really what you are when youre 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? Thats weird. Not trying to judge here, but its a little odd compared to all the other mammals. But theres a lot of other reasons that it might be useful to understand.So something that Im 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; its 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 thats 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 DNAs able to express itself? Something thats 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 didnt change, right? But something about how your DNA is being used in those hair follicles has changed, and if were 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 towho knows what; you never know what youre gonna find in the type of science that Im doing [laughs], and thats what I love about it.Feltman: [Laughs] Yeah, awesome. What are some other big questions that youre 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 wasnt before, and maybe our hair was a little bit different [laughs] in places where we already had hair. And thats really interesting because we know that theres 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 its really interesting to ask that question.And then on the other end of that, once were talking about aging, we have people who maybe start losing hair in certain places. It gets thinner or maybe it gets coarser, is something Ive heard people say. And so we can ask questions, again, about whats 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 Im 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 theres 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 bodys physiology; its constantly capturing bits of whats going on in your bloodstream. And so theres 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 theres 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: Thats all for todays 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!