April 30, 2024 • 35 mins
Why do humans have most of our hair on our heads, not our bodies? Why do we have so many varieties of hair color, thickness, and curliness? Dr. Tina Lasisi is a biological anthropologist whose work explores these evolutionary mysteries. In this episode, she shares her research into why humans have scalp hair as well as her insights on why curly hair is uniquely human.
Links to learn more:
- Dr. Tina Lasisi's website
- Why Am I Like This? - PBS Terra series
- Dr. Lasisi's AMNH/Leakey Foundation SciCafe lecture
- Why Care About Hair? Leakey Foundation event
- Quantifying variation in human scalp hair - research paper
Origin Stories is a project of The Leakey Foundation, a nonprofit organization dedicated to human origins research and education.
Donate to support the show. Your gift will be quadruple-matched! Click here to give!
This episode was produced by Ray Pang. Our editor is Audrey Quinn. Theme music by Henry Nagle, additional music by Blue Dot Sessions and Lee Roservere.
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Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
(00:05):
This is Origin Stories, the LeakyFoundation podcast. I'm Meredith Johnson.
Today on the show we're talking aboutone of the things that makes humans
different from other animals, our hair.
From why we have it on the top of ourheads instead of all over our bodies to
how we evolved so many variationsin color, texture, and curliness.
Our guest is Dr. Tina Lasisi.
(00:28):
She's an assistant professorat the University of Michigan where she leads a lab
researching the evolution and geneticbasis of human variation with a focus
on pigmentation and hair.
She's also the host of a PBSshow called Why Am I Like this?
And she's the recipient ofthe 2024 Science Communication Award from the Leakey
Foundation and the American Associationof Biological Anthropologists.
(00:52):
I always frame it as we talk abouthumans being the naked ape, but actually,
there are plenty of mammals that arenaked. You have mole rats, elephants,
depending on how you look at them,
and definitely a bunch ofmammals that are in the sea,
but we're actually the only weirdosthat have no fur on our bodies,
but decided to keep thefur on our heads mostly.
(01:13):
And that's what I emphasize isespecially weird about humans and has not
been studied enough for my liking.
When we have something like this that'sso, so different from other animals,
what does that tell you asan evolutionary scientist?
So evolution is creative but also lazy.
So if you find a goodsolution for a problem,
(01:33):
you tend to apply it again and again.
That's how we have things likeconvergent evolution of wings.
But if you see somethingthat has been evolved once,
like scalp hair on a naked body,that really tells you, okay,
something must have happenedhere. Some combination of traits,
(01:55):
characteristics for that species andthe situation it was in must have been
special enough that a newsolution had to arise.
What was our situationand how do you know?
That's a great question. We don't know,
but we do a lot of scientifically informed
theorizing. Some would call itguessing, but it's a lot more intense.
(02:19):
I would say it's a lot morecareful work than guessing.
So basically we put togetherevidence from a lot of different
avenues.
One of the things that we can dois look at the fossil evidence and
understand what species wereclosest to us and what their
evolutionary history was.
(02:39):
And what you start seeing isbasically the sequence of traits
that appears in our lineage.
We have this uprightposture, we have bipedalism,
we have these large brains,
and you see that there's thisbipedalism that emerges about
2 million years when youstart seeing Homo erectus.
(03:02):
Now what you see in Homo erectusis this modern day build.
They have the sameproportions bodily as we do,
but the brain size doesn't seem to be
quite where it is today in modern humans.
And so there's this really interestingoutstanding question in human evolution
(03:22):
of, well, why did it take so long?
Was there something that was preventingbrains from getting to their modern
day size? And that's kindof where the hair comes in.
And hair and skin are very difficult tothink about in terms of human evolution
(03:44):
because they don't leave thisreally nice fossil evidence.
So what we have to do then isinfer what makes sense in part
using genetics.
And what we know from theskin pigmentation side is that
there is evidence that the last commonancestors of all humans had darker
skin.
(04:05):
And what I would love to do is seeif we could do a similar thing for
hair,
but we're not quite there yet becausewe don't know what genes are involved in
hair morphology very well.
But what we can do is put togethertestable evolutionary hypotheses.
So you have a hypothesis aboutwhy we have hair on the top of our
heads and not so much on our bodies.
(04:27):
Can you tell us about that andabout the research you did and how
robots are involved.
How robots are involved? Yes.We will not forget the robots.
So basically what me and my
PhD advisor,
Nina Jablonski were wondering is how hair
(04:48):
might have a parallelstory to skin pigmentation.
So Nina did the leadingwork on the evolution
of skin color in relation tovitamin D and UV radiation.
So we know that where there'sa lot of UV radiation,
you benefit from having more pigmentationbecause it protects the Foley in your
bloodstream. So thequestion is what about hair?
(05:09):
Could that help with anything?
And we were testing outthis hypothesis that tightly
coiled hair in particular couldreduce the amount of heat you gain
specifically from solar radiation.
And so I'm going to back up here a littlebit because I did talk about humans
being very special in terms ofhaving scalp hair on naked bodies.
(05:30):
But what's even more exciting,
it's the presence of tightly curled hair.And that is not something that you see
in any other mammal.
And this is something I always sayon podcast shows wherever I'm at,
as far as I know,
I have not seen any mammal naturallyoccurring that has tightly coiled
(05:50):
hair. Anything as close to thetightest coils that you see in humans.
If someone finds a mammal thatdoes fit that description,
please send me pictures.I'm always open to it.
But that adds to this layer of, well,
if we were the first ones tohave to evolve scalp hair,
why were we also the first ones tohave to evolve this tightly coiled hair
(06:11):
texture?
And what we know from researchon mammalian coats is that hair
offers a lot of protection.
So a lot of the discourse that we havein human evolution on hair hairlessness
is of course you want to be naked, right?If it's hot, you want to be naked.
However, there are hairymammals in very hot places.
(06:31):
And if it's so beneficial,
why would you have mammalsin the desert that have hair?
And that's because haircan offer protection,
especially when it comes to reducingheat gain from solar radiation.
And I specify that because youhave ambient temperature and
solar radiation, itworks in a different way.
(06:53):
If you're ever outside on a very,very sunny day, what do you do?
You seek shade.
And it's significantly cooler when youare in a place where the sun's rays
are not hitting you directly.
So what we wanted to do is seeif we could find any evidence
for that function. Andin order to do that,
(07:13):
we bought a bunch of human hair wigsand put them on a bunch of robots
in climate controlled chambers andturned them on and saw what happened.
That's a really creative solution. Sowhat were you testing and what happened?
Yeah, so there are these robots
(07:35):
that are very much shaped likethe terminator that are used
across many fields to measure the
insulation value of various fabrics.
And so there are people who use them.
So we reasoned, well,
you can put a wig on it andbasically treat it the same as you
(07:58):
would treat a piece of fabric.
And so the way a thermal mannequinworks is it has a surface
that is set to a particular temperature,
and in order to keep that set temperature,
it needs to pump in energy, electricity.
If the external environment is warmer,
(08:19):
then it doesn't need topump in as much electricity.
If the external environment is colder,
then it needs to pump in more electricity.
And so that difference in terms of howmuch energy is required to keep that
stable temperature,
that's what tells us abouthow much insulation a given
fabric or wig gives it.And so we had four experimental hair
(08:40):
conditions, a straight wig,a moderately curled wig,
and then a tightly curled wig.
And then of course we had to havethe baseline calibration of no hair.
So we also ran all theexperiments without hair,
and we looked at how heat transferwas affected without solar
radiation, and then we simulatedsolar radiation with floodlights.
(09:00):
And what we noticed was an
incredible undeniableeffect of not only the
presence and absence of hair,
but the curlier hairwas the more heat gain
was reduced from thatsolar radiation. Wow.
It actually got to the point wherewhen we were running these experiments,
(09:24):
we were randomizing the sequencein which we were doing them.
And so it started out with the tightlycurled wig ran the experiments,
and when I ran them with the straight wig,
the mannequin was overheating.
And so we had to figure out how to changethe settings because that's how much
of a protective effect tightly coiledhair gave that we needed to adjust
(09:45):
the experimental settings so that itworked across all of the conditions.
That's.
Amazing. So if curly hair,
tightly coiled hair protectsfrom solar radiation, so well,
why doesn't every human have curly hair?
How did we end up withso many different kinds?
That's one of the big thingsthat makes evolution so
(10:07):
complicated.
If there is a trait that is good, thenwhy doesn't everyone have that trait?
And the reason is thatthis trait may not always
be under selection. So let'stake skin color for example.
When you look at skincolor around the world,
(10:30):
mostly yes,
it does adhere to this patternof where there is more uv
radiation skin is darker, and wherethere's less uv radiation skin is lighter.
But especially once yougo into the Americas,
you see that that doesn'thold as well anymore.
And our understanding of thisis that there hasn't been as
(10:52):
much time for that traitto be under selection.
And so how much does having this traitor not having this trait affect your
ability to produce surviving offspring?
Now when it comes to hair,
the pattern doesn't seem tohold at all, does it? Right?
(11:13):
There are many places that have a lotof solar radiation where people have
straight maybe wavy hair.If you look across South Asia for
example, and my thinking aroundthis is that this may have been an
important point of selectionearly on in human evolution.
So going back to homo rectus 1.8 to
(11:36):
1.5 million years ago after we'refully bipedal, fully naked in the sun,
but brains are not quitethe size that they were yet,
maybe tightly curled hairrepresented a solution to
release that constraint.
So brains are very heat sensitiveand they also generate heat.
The bigger your brain is, the moredire your situation is going to be.
(11:58):
So it's very plausible that it mayhave been the case that humans evolved
this tightly coiled tear,
which was able to minimize howmuch heat they were gaining,
minimize how much water they were losing,
and now it was viable to have alarge brain. But the thing is,
once you have this large brain,you come up with solutions.
And in much of the same wayas many people who turn red on
(12:21):
the beach do not have tosuffer if they have sunscreen,
there may have been other shadeseeking behavior or other behavioral
adaptations.
Okay. Is there a difference betweenhair and fur? Is it the same thing?
Hair and fur are exactly the same thing.
Humans to make ourselves specialby using different words for us.
And also it's a pet peeve ofmine because people talk about it
(12:46):
with dogs as well. My dog, I have apoodle, is right next to me right now.
So a lot of people will talk about, oh,well this breed of dog doesn't have fur,
they have hair. And a lot oftimes when I ask people, well,
what do you mean by that? They'retalking about how the hair is finer,
but you have thick hair, you can havethick hair fibers, thin hair fibers,
(13:08):
the hair follicle is thisincredible, honestly,
a super mini organ becauseunlike many of our other
tissues or other organs thatdevelop once and then you're set
and hopefully you don't have tolose them for the rest of your life.
Hair follicles go through a growth phase,
(13:31):
a resting phase,
and then they completelyminiaturize and regenerate a
whole new hair follicle. So thatentire cycle is the regeneration of an
entire mini organ,
and there is a supply of stem cells therethat helps with that regeneration of
the hair follicle each time.And going through that process,
(13:52):
you have asynchronybetween our hair fibers.
So our hair fibers grow foranywhere between a couple of weeks.
If you're talking about our eyebrowsor our eyelashes to a couple of months
maybe, depending on what kind of bodyhair you have to two to seven years,
if you're talking about scalp hair,I've even heard like 10 years.
(14:14):
So you have hair that isgrowing for that long,
but it's not all synchronized. If itwas then however many years or weeks,
all of it would fall out. Butyou can have synchronization.
And that's some stuff that wesee across different mammals,
especially when you'rethinking about seasonal coats.
That's the synchronization of differenttypes of hair follicles falling,
(14:34):
shedding at different times andregenerating at other times. Which again,
I think hair is awesome. It's super cool.
Yeah, it's so interesting.
I guess I never I mean Ithink about eyebrows like you
do, but I never considered that.
What if they grew like ourhead hair and just kept going.
And they do. Once you become an emeritusprofessor, I just want to specify.
(14:57):
And our hair changes over ourlifetimes. It changes color.
Some people lose their hair.
And going through puberty andgoing through chemotherapy,
for example, can change its texture.
So that's something that I get questionsabout all the time, and honestly,
it's the next thing I think I'mgoing to focus on because that to me
(15:21):
is very exciting.
And you mentioned that we're the onlyanimals that have this kind of tight,
curly hair pattern. But then alot of people will say, well,
what about poodles whatyou have right next to you?
And then when Ray and I were doing ourresearch, we found all these cute, cute,
cute pictures of tiny baby gorillasin the midst with their curly hair.
(15:46):
They're so cute. They'reso cute. I love them.
So.
Much. Yes, absolutely.But let's dig into that.
So funnily enough, see,
this is how I know I'm in an anthrocrowd because y'all will bring up the
gorillas before the sheep,which is usually what people do. People will be like,
oh, what about sheep?
(16:06):
So sheep have wool,right? Wool is also hair,
wooler hair, it's all the same thing.
And one of the misnomers of tightlycoiled human hair is woolly,
right? Like, oh, you have woolly hair.
And that connection betweenwool and tightly coiled
hair, that has definitelysome racist roots,
(16:29):
but even that aside,
it confuses people and it makes sensewhy nobody looked at this until I did.
And my advisor thought to look atit because they were thinking, well,
wool keeps you hot. So if you havetightly coiled hair that's like wool,
it must be hot.
But those are two very differentstructures. So wool has a bilateral
(16:50):
wave,
and we actually know the processthat is occurring in order to
create that bilateral wave becausewool is an industry and it has
money and you need to understand it.
So we have spent so many yearslooking at what the process is
there,
and we actually understand it really wellwhen people try to look for that same
(17:11):
process in humans, they didnot find those in humans.
If you pay attention to human hair,you'll note that curls are hele.
They're not waves. Humanhair coils, it curls.
Now, poodles, that's easy.
There's a lot of weird dogs, domesticatedanimals, not to make them not count,
(17:33):
but we can make a lothappen. So I would argue,
and this is me even looking at my dog,
even if I see some thingsthat are approaching a coil,
even though I would say a lot ofwhat I see is this bilateral waving,
it's not the samestructure human hair curl,
and this is not me being pedantic, butafter having done the experimentation,
(17:55):
there actually is a reallysignificant functional difference.
If you have a bunch of especiallyvery thin hairs that are
lining up very closely together,
you have a lot of density, a lot ofhair fibers packed closely together.
That's not good if you wantto be losing heat versus human
(18:18):
coils are this chaoticlattice of coils where
you have a lot of airspace, alot of empty space in between.
And that's what allows us to have thisincredible absence of a trade-off,
which there usually is with hair of wecan reduce how much heat is coming down
from the radiation, but we can alsomaximize how much heat we're losing.
(18:39):
That's not the case with wool for sure,
because that stacks up perfectlywith dogs like Winston,
my poodle. That's not the caseeither. You have all of this density,
there's no airspace in thehair. And with gorillas, well,
I'm going to need a gorilla hair sample.But from the pictures that I saw,
(18:59):
it doesn't appear to be astightly coiled as human hair.
And I would add to that,
that I'm starting to thinkthat there is a lower
density of hair when Ilook at human hair curls.
It's not as closely packed together,
but that's still somethingthat we're having to explore.
(19:20):
And a lot of your work has sort ofdefined what our curls are, right?
You've come up with ways totalk about more precisely.
Can you tell us a little bit about that?
Yes. So any trait that you want to study,
you have to operationalize,
and that means you are definingit in a very specific way.
(19:44):
I try to be very carefulwhen I talk about it,
but it's especially evident inthe way that I measured hair.
I spent a lot of time literally over adecade of my life trying to figure out
how best to measure haircurl because there is a
lot that is captured withinthe concept of hair texture.
And when we're talking about hair shape,
(20:04):
we're talking about a lot ofthings combined together. This.
Must be such an exciting area of study.
There's still so manyquestions to answer. Yes.
I'm very still after allthese years. I'm very excited,
otherwise I would not be here.
So we have some more questionsand I was wondering if I could
ask Ray to come on because he has ahaircare hairstyle related question.
(20:30):
Hi, Meredith. Hi Tina.
Hi Ray. Hi Ray.
So when we were getting ready for this,
we both heard you say a bunch ofdifferent times in different places.
So much of research is mesearch. And as you can see,
I have curly,
and I usually don't letit get this long because
(20:53):
I've always been under the impressionthat also because my hair is black,
it gets really hot in the summer.
It just holds all of thisheat on my head because it's
absorbing all the sun raysand then I am sweating.
And so I was kind of blownaway by the finding that
(21:15):
maybe I might be better offwith some curly hair in the
summer versus just slathering my
bald head and a lot ofsunscreen every day.
And so I guess maybe thisis a dear Tina question,
but would I be better off in thesummer with my curly hair versus
(21:39):
no hair?
Well, first of all, thank you so muchfor offering to extend our research.
I'm really excited about this partnership.We're going to do good work together.
Yes, trust me on this.
Even if you leave your hair to what itis now, if you want to grow it out more,
that also works.
Stand in the sun and see how you feel
(22:03):
and look at the difference ifyou can even just touching it
in temperature between your scalpand then the top of your hair.
And here's another fun anecdote.10 years ago or something,
I was outside somewhere with afriend who had very straight light
hair that laid very flat onhis head and he touched the
(22:27):
top of my hair. Consensually
always ask if you want to touch someoneelse's hair. And he was like, ow.
He burned his hand. He was like,oh, it's so hot. Are you not hot?
And I didn't feel anythingbut the top of my hair,
not the head top of my hair was reallyhot. And yes, it does absorb that heat,
but again,
this is one of the peculiaritiesof how radiative heat works.
(22:53):
And we have seen this in mammals.
There are really interestingstudies from the eighties,
I want to say from the seventiesthrough the nineties of various
mammals, they were looking at theircoats and looking at the effect of color.
Everyone has this idea of, well,
you must be better offhaving lighter hair and less
(23:14):
hair if you're somewhere wherethere's a lot of solar radiation,
it should reflect the light. Butit turns out that in practice,
it's not how it works becausethis idea of dark objects,
heat up light objects reflectlight is so misapplied.
And we even see this all the wayfrom people thinking that, well,
people with dark skin,
(23:35):
they must be in so much trouble inthe sun because black objects heat up,
right?Meanwhile,
black people are fine and somepeople are turning into lobsters.
So what happens is that you don'thave these flat surfaces like what we
usually think about when we're measuringthis reflectance and absorbance of
heat. Now, when it comesto hair specifically,
(23:56):
especially if you have these fibers thatare pointing in all these directions,
the straight radiation of the sunbounces off. It gets absorbed,
but your hair is not living tissue.
So if it gets absorbed by the top ofyour hair and it bounces off some of it,
that's great. Meanwhile,
if you have straight hair that is flat
(24:20):
against your scalp,
there is no distance between the topof your hair and the top of your scalp.
And that's something that we see in thatmammalian literature that they say that
once you have over twoinches of fur, hair, coat,
color doesn't matter anymore. Coat colordoesn't make a difference in how much
you heat up or don't because it's thatdistance from the skin that matters the
(24:42):
most. And if you have light hair on topof that, yes, you have this reflection,
but it's not necessarilygoing to bounce off,
it's going to bounce around yourhair and probably hit your scalp.
So having it absorb in themelanin that is kept in your dead
hair shaft that is there to protect youis much better than it coming down to
(25:02):
your living scalp. So I expect afull report by the end of the summer.
Thank you.
Okay.
I feel really emboldenedto keep my hair over the
summer. Thank you so much, Tina.
Thank you, Ray.
Back to you Meredith.
Okay.
So how did you first get interestedin studying hair from an evolutionary
perspective?
(25:23):
So it all started with a lecture on
human skin color variation andhow it relates to UV radiation.
And just seeing those maps of thedistribution of skin color and the
distribution of UV radiation wassuch a eureka moment for me that
I was just so impressed at such an elegant
(25:44):
explanation. I had never thoughtabout evolution in that way.
And going back to the wholeresearch is me search the way
my 20 something year old brainprocessed, it was like, cool,
now I know why my skin isbrown. Why is my hair curly?
And that didn't havea satisfactory answer.
And so I was like a dog witha bone clenched between my
(26:07):
jaws, and I needed to get my answer.And here I am over a decade later,
still trying to get this answer.
And that's really cool that you were ableto join Nina's lab and study with her,
the person that did that elegantresearch about skin color variation and
vitamin D. That's so cool.
Yeah, it was incredible,
and especially because I actuallywasn't intending to be a biological
(26:30):
anthropologist.
I did my undergrad at the Universityof Cambridge where they taught it as a
three field cultural anthropology orsocial anthropology as they call it over
there, archeology andbiological anthropology.
And I was so sure I wanted to do cultural.
And it wasn't until this lecture thatI had entertained the idea of doing
(26:50):
biology. And if it wasn't for myundergraduate mentor at the time,
I wouldn't have gone down this path.
It very much wasn't a strategicplan or the result of a lifelong
at that point, interest insomething, but more, Hey,
this is kind of cool.
And getting the kind of encouragementthat I got of you can do this was
(27:11):
instrumental to me feeling like I could.
And so I really tried to pay this forwardnow because I noticed that when I talk
about my research, it's reallyintelligible to people. They're like,
oh yeah, no, that makes sense to methat you would ask that question.
I also have questions and Iwant to tell people, I'm like,
your questions are good.
You have good questions incase no one has told you this.
(27:33):
Your questions are awesome.
And I might be the first person toentertain the idea that they are
having really good questions, and.
We love that.
And it feels like sucha new area of study.
So you have the opportunity todo a lot of foundational work,
and that's pretty exciting.
(27:53):
I mean, I can see how from theoutside, it might seem this way,
to be honest, being in it, I don't know.
It doesn't feel, that'snot to say that it isn't,
but when something's in front of youand you're doing it, you're like, yeah,
I know. I'm just doing it.
And hopefully over theyears, over the decades,
(28:16):
it'll accumulate to somethingthat is very valuable. And I mean,
really one of my biggestinspirations is my former advisor,
Nina Jablonski, because Iremember when I was younger,
nobody knew what melanin was.That's not a word that people used.
And now there's literally melaninmerch you can get on Instagram.
(28:37):
We're living in a different world,
and I think most of us couldn't imaginea world now where not only did we not
know what melanin was,
but maybe even believed thatdark skin had no benefit in
solar radiation. Yeah.
How do you think theevolutionary perspective of this
topic benefits people are?
(28:58):
So I would say one of the things that'sreally interesting about having done the
work that I've done is that, yes,
within biological anthropology andlet's say anthropology generally,
but especially biologicalanthropology, I am weird.
I stand out because I work on hair.
It's a multi-billion dollarindustry. Dermatology is a thing.
(29:20):
And so I could not possibly claim to bethe first person to have ever thought
about it. But what you see is thisreally interesting conundrum of,
well,
why do people who workon hair look at it so
differently? And that's reallywhere just the benefit of
(29:41):
coming up academically, intellectually,
in an evolutionaryanthropology environment,
it shapes the way you look at the world.
It shapes the way that you ask questions.
And no one would argue that there areincredible benefits to thinking directly
about how can you make certain haircareproducts to make hair do certain kinds
of things? How can you fix variousissues that people have with their
(30:05):
hair and skin from a medical perspective?
There's a need for basicscientific research to be funded,
which absolutely includesevolutionary biology,
evolutionary anthropology work,
because I'm looking at just this tiny
piece of something and saying,how does this thing work?
(30:27):
How does this thing humans work?
What are all of the fundamentalprocesses and structures
that affect us?
And that gives you power and that itallows you to make sense of things,
how they fit together, and in a lotof ways allows you to predict, right?
And that is really what we're seeing withthe research that's been done on skin
(30:48):
color.
Knowing that there would have beensome kind of selection in both
directions allows us to then say, okay,
well what would that thing have been?
We know that it has to be somethingthat probably influences fitness,
the birth of offspring, folate,
folate is really important. And beingable to put all those things together,
(31:09):
you now have this incrediblescaffolding for being able to
personalize and even think about howthese things are affecting different
people.
Like if you have darker skin ina place that does not have a lot
of solar radiation, justbecause you don't have rickets,
just because you're not bow-legged doesn'tmean that you may not have a vitamin
(31:31):
D deficiency that might affect you sosignificantly that 2 million years ago,
it would've meant that your offspringwouldn't have survived at the same rates
as people with lighter skin.
And the same thing can be saidof what we're learning now
about folate and what it has to do withpregnancy and how it travels through the
(31:52):
bloodstream. Just all of this stuffis incredibly useful and interesting,
and a lot of the money
and how it flows wouldmake you think that it's
superfluous research that'svery just like useless.
And it is so important to be able totell the difference between things that
(32:15):
have direct application versusthings that are useful and
they can be different.
Yeah. I and I work for theLeakey Foundation, so we obviously know this. Some
type of basic research is soimportant for understanding who
we are and why we are the waywe are and how it all happened.
(32:38):
So do you have a closing thoughtthat you'd like to share to wrap
up our interview then? So you can go.
It's like holding me hostage until Isay something interesting. Just kidding.
So what I'll say is Ijust opened my lab at the
University of Michigan. The actualphysical lab space is still being built,
(32:59):
but it should be done by the summer.
And I've taken on a couple of studentsand we're working on some really
interesting stuff.
And one of the things I wanted to talkabout especially is some of the work that
I'm starting to do withmy student, Sarah Taylor.
We are really interested insexualism and natal coats in
non-human primatesacross the primate order,
(33:21):
because that's another dimensionof hair morphology that we
kind of touched on in the beginning ofhow it changes over time and different
parts of your body. Well,
one aspect of that is this dimensionof variation that sex gives us, right?
Sex is this dynamic thing that changesover time. You go through puberty,
and depending on what receptorsyou have at different places,
(33:44):
different parts of your body are goingto respond differently to hormones being
there.
And so what we're trying to understandnow is how do sex hormones interact with
hair follicles to createdifferences in hair growth,
but also differences in haircolor. So watch out for that.
Well, thank you so much for joining ustoday and sharing your work and all this
interesting information about hair.
(34:05):
Thank you for having me.
You can learn more about TinaLai and her work on her website,
tinalasisi.com. We have thatlink and more in your show notes.
Origin Stories is a projectof the Leaky Foundation,
a nonprofit dedicated to funding humanorigins research and sharing discoveries.
(34:29):
You can support this show by going toleaky foundation.org/origin stories and
clicking the origin stories donate button.
Your donation will be quadruple matchedthanks to Jeannie Newman and the Ann
Gordon Getty Foundation. So you canturn $10 into $40 to support the show.
Support for Origin Stories comes fromlisteners like you with additional support
(34:52):
from the Anne Go Getty Foundation,Camilla and George Smith, Jeannie Newman,
and the Joan and ArnoldTravis Education Fund.
This episode was produced by RayPang. Our editor is Audrey Quinn.
Theme music by Henry Nagel andAdditional music by Blue dot Sessions.
Thanks for listening.
This is Origin Stories, the LeakyFoundation podcast. I'm Meredith Johnson.
Today on the show we're talking aboutone of the things that makes humans
different from other animals, our hair.
From why we have it on the top of ourheads instead of all over our bodies to
how we evolved so many variationsin color, texture, and curliness.
Our guest is Dr. Tina Lasisi.
(00:28):
She's an assistant professorat the University of Michigan where she leads a lab
researching the evolution and geneticbasis of human variation with a focus
on pigmentation and hair.
She's also the host of a PBSshow called Why Am I Like this?
And she's the recipient ofthe 2024 Science Communication Award from the Leakey
Foundation and the American Associationof Biological Anthropologists.
(00:52):
I always frame it as we talk abouthumans being the naked ape, but actually,
there are plenty of mammals that arenaked. You have mole rats, elephants,
depending on how you look at them,
and definitely a bunch ofmammals that are in the sea,
but we're actually the only weirdosthat have no fur on our bodies,
but decided to keep thefur on our heads mostly.
(01:13):
And that's what I emphasize isespecially weird about humans and has not
been studied enough for my liking.
When we have something like this that'sso, so different from other animals,
what does that tell you asan evolutionary scientist?
So evolution is creative but also lazy.
So if you find a goodsolution for a problem,
(01:33):
you tend to apply it again and again.
That's how we have things likeconvergent evolution of wings.
But if you see somethingthat has been evolved once,
like scalp hair on a naked body,that really tells you, okay,
something must have happenedhere. Some combination of traits,
(01:55):
characteristics for that species andthe situation it was in must have been
special enough that a newsolution had to arise.
What was our situationand how do you know?
That's a great question. We don't know,
but we do a lot of scientifically informed
theorizing. Some would call itguessing, but it's a lot more intense.
(02:19):
I would say it's a lot morecareful work than guessing.
So basically we put togetherevidence from a lot of different
avenues.
One of the things that we can dois look at the fossil evidence and
understand what species wereclosest to us and what their
evolutionary history was.
(02:39):
And what you start seeing isbasically the sequence of traits
that appears in our lineage.
We have this uprightposture, we have bipedalism,
we have these large brains,
and you see that there's thisbipedalism that emerges about
2 million years when youstart seeing Homo erectus.
(03:02):
Now what you see in Homo erectusis this modern day build.
They have the sameproportions bodily as we do,
but the brain size doesn't seem to be
quite where it is today in modern humans.
And so there's this really interestingoutstanding question in human evolution
(03:22):
of, well, why did it take so long?
Was there something that was preventingbrains from getting to their modern
day size? And that's kindof where the hair comes in.
And hair and skin are very difficult tothink about in terms of human evolution
(03:44):
because they don't leave thisreally nice fossil evidence.
So what we have to do then isinfer what makes sense in part
using genetics.
And what we know from theskin pigmentation side is that
there is evidence that the last commonancestors of all humans had darker
skin.
(04:05):
And what I would love to do is seeif we could do a similar thing for
hair,
but we're not quite there yet becausewe don't know what genes are involved in
hair morphology very well.
But what we can do is put togethertestable evolutionary hypotheses.
So you have a hypothesis aboutwhy we have hair on the top of our
heads and not so much on our bodies.
(04:27):
Can you tell us about that andabout the research you did and how
robots are involved.
How robots are involved? Yes.We will not forget the robots.
So basically what me and my
PhD advisor,
Nina Jablonski were wondering is how hair
(04:48):
might have a parallelstory to skin pigmentation.
So Nina did the leadingwork on the evolution
of skin color in relation tovitamin D and UV radiation.
So we know that where there'sa lot of UV radiation,
you benefit from having more pigmentationbecause it protects the Foley in your
bloodstream. So thequestion is what about hair?
(05:09):
Could that help with anything?
And we were testing outthis hypothesis that tightly
coiled hair in particular couldreduce the amount of heat you gain
specifically from solar radiation.
And so I'm going to back up here a littlebit because I did talk about humans
being very special in terms ofhaving scalp hair on naked bodies.
(05:30):
But what's even more exciting,
it's the presence of tightly curled hair.And that is not something that you see
in any other mammal.
And this is something I always sayon podcast shows wherever I'm at,
as far as I know,
I have not seen any mammal naturallyoccurring that has tightly coiled
(05:50):
hair. Anything as close to thetightest coils that you see in humans.
If someone finds a mammal thatdoes fit that description,
please send me pictures.I'm always open to it.
But that adds to this layer of, well,
if we were the first ones tohave to evolve scalp hair,
why were we also the first ones tohave to evolve this tightly coiled hair
(06:11):
texture?
And what we know from researchon mammalian coats is that hair
offers a lot of protection.
So a lot of the discourse that we havein human evolution on hair hairlessness
is of course you want to be naked, right?If it's hot, you want to be naked.
However, there are hairymammals in very hot places.
(06:31):
And if it's so beneficial,
why would you have mammalsin the desert that have hair?
And that's because haircan offer protection,
especially when it comes to reducingheat gain from solar radiation.
And I specify that because youhave ambient temperature and
solar radiation, itworks in a different way.
(06:53):
If you're ever outside on a very,very sunny day, what do you do?
You seek shade.
And it's significantly cooler when youare in a place where the sun's rays
are not hitting you directly.
So what we wanted to do is seeif we could find any evidence
for that function. Andin order to do that,
(07:13):
we bought a bunch of human hair wigsand put them on a bunch of robots
in climate controlled chambers andturned them on and saw what happened.
That's a really creative solution. Sowhat were you testing and what happened?
Yeah, so there are these robots
(07:35):
that are very much shaped likethe terminator that are used
across many fields to measure the
insulation value of various fabrics.
And so there are people who use them.
So we reasoned, well,
you can put a wig on it andbasically treat it the same as you
(07:58):
would treat a piece of fabric.
And so the way a thermal mannequinworks is it has a surface
that is set to a particular temperature,
and in order to keep that set temperature,
it needs to pump in energy, electricity.
If the external environment is warmer,
(08:19):
then it doesn't need topump in as much electricity.
If the external environment is colder,
then it needs to pump in more electricity.
And so that difference in terms of howmuch energy is required to keep that
stable temperature,
that's what tells us abouthow much insulation a given
fabric or wig gives it.And so we had four experimental hair
(08:40):
conditions, a straight wig,a moderately curled wig,
and then a tightly curled wig.
And then of course we had to havethe baseline calibration of no hair.
So we also ran all theexperiments without hair,
and we looked at how heat transferwas affected without solar
radiation, and then we simulatedsolar radiation with floodlights.
(09:00):
And what we noticed was an
incredible undeniableeffect of not only the
presence and absence of hair,
but the curlier hairwas the more heat gain
was reduced from thatsolar radiation. Wow.
It actually got to the point wherewhen we were running these experiments,
(09:24):
we were randomizing the sequencein which we were doing them.
And so it started out with the tightlycurled wig ran the experiments,
and when I ran them with the straight wig,
the mannequin was overheating.
And so we had to figure out how to changethe settings because that's how much
of a protective effect tightly coiledhair gave that we needed to adjust
(09:45):
the experimental settings so that itworked across all of the conditions.
That's.
Amazing. So if curly hair,
tightly coiled hair protectsfrom solar radiation, so well,
why doesn't every human have curly hair?
How did we end up withso many different kinds?
That's one of the big thingsthat makes evolution so
(10:07):
complicated.
If there is a trait that is good, thenwhy doesn't everyone have that trait?
And the reason is thatthis trait may not always
be under selection. So let'stake skin color for example.
When you look at skincolor around the world,
(10:30):
mostly yes,
it does adhere to this patternof where there is more uv
radiation skin is darker, and wherethere's less uv radiation skin is lighter.
But especially once yougo into the Americas,
you see that that doesn'thold as well anymore.
And our understanding of thisis that there hasn't been as
(10:52):
much time for that traitto be under selection.
And so how much does having this traitor not having this trait affect your
ability to produce surviving offspring?
Now when it comes to hair,
the pattern doesn't seem tohold at all, does it? Right?
(11:13):
There are many places that have a lotof solar radiation where people have
straight maybe wavy hair.If you look across South Asia for
example, and my thinking aroundthis is that this may have been an
important point of selectionearly on in human evolution.
So going back to homo rectus 1.8 to
(11:36):
1.5 million years ago after we'refully bipedal, fully naked in the sun,
but brains are not quitethe size that they were yet,
maybe tightly curled hairrepresented a solution to
release that constraint.
So brains are very heat sensitiveand they also generate heat.
The bigger your brain is, the moredire your situation is going to be.
(11:58):
So it's very plausible that it mayhave been the case that humans evolved
this tightly coiled tear,
which was able to minimize howmuch heat they were gaining,
minimize how much water they were losing,
and now it was viable to have alarge brain. But the thing is,
once you have this large brain,you come up with solutions.
And in much of the same wayas many people who turn red on
(12:21):
the beach do not have tosuffer if they have sunscreen,
there may have been other shadeseeking behavior or other behavioral
adaptations.
Okay. Is there a difference betweenhair and fur? Is it the same thing?
Hair and fur are exactly the same thing.
Humans to make ourselves specialby using different words for us.
And also it's a pet peeve ofmine because people talk about it
(12:46):
with dogs as well. My dog, I have apoodle, is right next to me right now.
So a lot of people will talk about, oh,well this breed of dog doesn't have fur,
they have hair. And a lot oftimes when I ask people, well,
what do you mean by that? They'retalking about how the hair is finer,
but you have thick hair, you can havethick hair fibers, thin hair fibers,
(13:08):
the hair follicle is thisincredible, honestly,
a super mini organ becauseunlike many of our other
tissues or other organs thatdevelop once and then you're set
and hopefully you don't have tolose them for the rest of your life.
Hair follicles go through a growth phase,
(13:31):
a resting phase,
and then they completelyminiaturize and regenerate a
whole new hair follicle. So thatentire cycle is the regeneration of an
entire mini organ,
and there is a supply of stem cells therethat helps with that regeneration of
the hair follicle each time.And going through that process,
(13:52):
you have asynchronybetween our hair fibers.
So our hair fibers grow foranywhere between a couple of weeks.
If you're talking about our eyebrowsor our eyelashes to a couple of months
maybe, depending on what kind of bodyhair you have to two to seven years,
if you're talking about scalp hair,I've even heard like 10 years.
(14:14):
So you have hair that isgrowing for that long,
but it's not all synchronized. If itwas then however many years or weeks,
all of it would fall out. Butyou can have synchronization.
And that's some stuff that wesee across different mammals,
especially when you'rethinking about seasonal coats.
That's the synchronization of differenttypes of hair follicles falling,
(14:34):
shedding at different times andregenerating at other times. Which again,
I think hair is awesome. It's super cool.
Yeah, it's so interesting.
I guess I never I mean Ithink about eyebrows like you
do, but I never considered that.
What if they grew like ourhead hair and just kept going.
And they do. Once you become an emeritusprofessor, I just want to specify.
(14:57):
And our hair changes over ourlifetimes. It changes color.
Some people lose their hair.
And going through puberty andgoing through chemotherapy,
for example, can change its texture.
So that's something that I get questionsabout all the time, and honestly,
it's the next thing I think I'mgoing to focus on because that to me
(15:21):
is very exciting.
And you mentioned that we're the onlyanimals that have this kind of tight,
curly hair pattern. But then alot of people will say, well,
what about poodles whatyou have right next to you?
And then when Ray and I were doing ourresearch, we found all these cute, cute,
cute pictures of tiny baby gorillasin the midst with their curly hair.
(15:46):
They're so cute. They'reso cute. I love them.
So.
Much. Yes, absolutely.But let's dig into that.
So funnily enough, see,
this is how I know I'm in an anthrocrowd because y'all will bring up the
gorillas before the sheep,which is usually what people do. People will be like,
oh, what about sheep?
(16:06):
So sheep have wool,right? Wool is also hair,
wooler hair, it's all the same thing.
And one of the misnomers of tightlycoiled human hair is woolly,
right? Like, oh, you have woolly hair.
And that connection betweenwool and tightly coiled
hair, that has definitelysome racist roots,
(16:29):
but even that aside,
it confuses people and it makes sensewhy nobody looked at this until I did.
And my advisor thought to look atit because they were thinking, well,
wool keeps you hot. So if you havetightly coiled hair that's like wool,
it must be hot.
But those are two very differentstructures. So wool has a bilateral
(16:50):
wave,
and we actually know the processthat is occurring in order to
create that bilateral wave becausewool is an industry and it has
money and you need to understand it.
So we have spent so many yearslooking at what the process is
there,
and we actually understand it really wellwhen people try to look for that same
(17:11):
process in humans, they didnot find those in humans.
If you pay attention to human hair,you'll note that curls are hele.
They're not waves. Humanhair coils, it curls.
Now, poodles, that's easy.
There's a lot of weird dogs, domesticatedanimals, not to make them not count,
(17:33):
but we can make a lothappen. So I would argue,
and this is me even looking at my dog,
even if I see some thingsthat are approaching a coil,
even though I would say a lot ofwhat I see is this bilateral waving,
it's not the samestructure human hair curl,
and this is not me being pedantic, butafter having done the experimentation,
(17:55):
there actually is a reallysignificant functional difference.
If you have a bunch of especiallyvery thin hairs that are
lining up very closely together,
you have a lot of density, a lot ofhair fibers packed closely together.
That's not good if you wantto be losing heat versus human
(18:18):
coils are this chaoticlattice of coils where
you have a lot of airspace, alot of empty space in between.
And that's what allows us to have thisincredible absence of a trade-off,
which there usually is with hair of wecan reduce how much heat is coming down
from the radiation, but we can alsomaximize how much heat we're losing.
(18:39):
That's not the case with wool for sure,
because that stacks up perfectlywith dogs like Winston,
my poodle. That's not the caseeither. You have all of this density,
there's no airspace in thehair. And with gorillas, well,
I'm going to need a gorilla hair sample.But from the pictures that I saw,
(18:59):
it doesn't appear to be astightly coiled as human hair.
And I would add to that,
that I'm starting to thinkthat there is a lower
density of hair when Ilook at human hair curls.
It's not as closely packed together,
but that's still somethingthat we're having to explore.
(19:20):
And a lot of your work has sort ofdefined what our curls are, right?
You've come up with ways totalk about more precisely.
Can you tell us a little bit about that?
Yes. So any trait that you want to study,
you have to operationalize,
and that means you are definingit in a very specific way.
(19:44):
I try to be very carefulwhen I talk about it,
but it's especially evident inthe way that I measured hair.
I spent a lot of time literally over adecade of my life trying to figure out
how best to measure haircurl because there is a
lot that is captured withinthe concept of hair texture.
And when we're talking about hair shape,
(20:04):
we're talking about a lot ofthings combined together. This.
Must be such an exciting area of study.
There's still so manyquestions to answer. Yes.
I'm very still after allthese years. I'm very excited,
otherwise I would not be here.
So we have some more questionsand I was wondering if I could
ask Ray to come on because he has ahaircare hairstyle related question.
(20:30):
Hi, Meredith. Hi Tina.
Hi Ray. Hi Ray.
So when we were getting ready for this,
we both heard you say a bunch ofdifferent times in different places.
So much of research is mesearch. And as you can see,
I have curly,
and I usually don't letit get this long because
(20:53):
I've always been under the impressionthat also because my hair is black,
it gets really hot in the summer.
It just holds all of thisheat on my head because it's
absorbing all the sun raysand then I am sweating.
And so I was kind of blownaway by the finding that
(21:15):
maybe I might be better offwith some curly hair in the
summer versus just slathering my
bald head and a lot ofsunscreen every day.
And so I guess maybe thisis a dear Tina question,
but would I be better off in thesummer with my curly hair versus
(21:39):
no hair?
Well, first of all, thank you so muchfor offering to extend our research.
I'm really excited about this partnership.We're going to do good work together.
Yes, trust me on this.
Even if you leave your hair to what itis now, if you want to grow it out more,
that also works.
Stand in the sun and see how you feel
(22:03):
and look at the difference ifyou can even just touching it
in temperature between your scalpand then the top of your hair.
And here's another fun anecdote.10 years ago or something,
I was outside somewhere with afriend who had very straight light
hair that laid very flat onhis head and he touched the
(22:27):
top of my hair. Consensually
always ask if you want to touch someoneelse's hair. And he was like, ow.
He burned his hand. He was like,oh, it's so hot. Are you not hot?
And I didn't feel anythingbut the top of my hair,
not the head top of my hair was reallyhot. And yes, it does absorb that heat,
but again,
this is one of the peculiaritiesof how radiative heat works.
(22:53):
And we have seen this in mammals.
There are really interestingstudies from the eighties,
I want to say from the seventiesthrough the nineties of various
mammals, they were looking at theircoats and looking at the effect of color.
Everyone has this idea of, well,
you must be better offhaving lighter hair and less
(23:14):
hair if you're somewhere wherethere's a lot of solar radiation,
it should reflect the light. Butit turns out that in practice,
it's not how it works becausethis idea of dark objects,
heat up light objects reflectlight is so misapplied.
And we even see this all the wayfrom people thinking that, well,
people with dark skin,
(23:35):
they must be in so much trouble inthe sun because black objects heat up,
right?Meanwhile,
black people are fine and somepeople are turning into lobsters.
So what happens is that you don'thave these flat surfaces like what we
usually think about when we're measuringthis reflectance and absorbance of
heat. Now, when it comesto hair specifically,
(23:56):
especially if you have these fibers thatare pointing in all these directions,
the straight radiation of the sunbounces off. It gets absorbed,
but your hair is not living tissue.
So if it gets absorbed by the top ofyour hair and it bounces off some of it,
that's great. Meanwhile,
if you have straight hair that is flat
(24:20):
against your scalp,
there is no distance between the topof your hair and the top of your scalp.
And that's something that we see in thatmammalian literature that they say that
once you have over twoinches of fur, hair, coat,
color doesn't matter anymore. Coat colordoesn't make a difference in how much
you heat up or don't because it's thatdistance from the skin that matters the
(24:42):
most. And if you have light hair on topof that, yes, you have this reflection,
but it's not necessarilygoing to bounce off,
it's going to bounce around yourhair and probably hit your scalp.
So having it absorb in themelanin that is kept in your dead
hair shaft that is there to protect youis much better than it coming down to
(25:02):
your living scalp. So I expect afull report by the end of the summer.
Thank you.
Okay.
I feel really emboldenedto keep my hair over the
summer. Thank you so much, Tina.
Thank you, Ray.
Back to you Meredith.
Okay.
So how did you first get interestedin studying hair from an evolutionary
perspective?
(25:23):
So it all started with a lecture on
human skin color variation andhow it relates to UV radiation.
And just seeing those maps of thedistribution of skin color and the
distribution of UV radiation wassuch a eureka moment for me that
I was just so impressed at such an elegant
(25:44):
explanation. I had never thoughtabout evolution in that way.
And going back to the wholeresearch is me search the way
my 20 something year old brainprocessed, it was like, cool,
now I know why my skin isbrown. Why is my hair curly?
And that didn't havea satisfactory answer.
And so I was like a dog witha bone clenched between my
(26:07):
jaws, and I needed to get my answer.And here I am over a decade later,
still trying to get this answer.
And that's really cool that you were ableto join Nina's lab and study with her,
the person that did that elegantresearch about skin color variation and
vitamin D. That's so cool.
Yeah, it was incredible,
and especially because I actuallywasn't intending to be a biological
(26:30):
anthropologist.
I did my undergrad at the Universityof Cambridge where they taught it as a
three field cultural anthropology orsocial anthropology as they call it over
there, archeology andbiological anthropology.
And I was so sure I wanted to do cultural.
And it wasn't until this lecture thatI had entertained the idea of doing
(26:50):
biology. And if it wasn't for myundergraduate mentor at the time,
I wouldn't have gone down this path.
It very much wasn't a strategicplan or the result of a lifelong
at that point, interest insomething, but more, Hey,
this is kind of cool.
And getting the kind of encouragementthat I got of you can do this was
(27:11):
instrumental to me feeling like I could.
And so I really tried to pay this forwardnow because I noticed that when I talk
about my research, it's reallyintelligible to people. They're like,
oh yeah, no, that makes sense to methat you would ask that question.
I also have questions and Iwant to tell people, I'm like,
your questions are good.
You have good questions incase no one has told you this.
(27:33):
Your questions are awesome.
And I might be the first person toentertain the idea that they are
having really good questions, and.
We love that.
And it feels like sucha new area of study.
So you have the opportunity todo a lot of foundational work,
and that's pretty exciting.
(27:53):
I mean, I can see how from theoutside, it might seem this way,
to be honest, being in it, I don't know.
It doesn't feel, that'snot to say that it isn't,
but when something's in front of youand you're doing it, you're like, yeah,
I know. I'm just doing it.
And hopefully over theyears, over the decades,
(28:16):
it'll accumulate to somethingthat is very valuable. And I mean,
really one of my biggestinspirations is my former advisor,
Nina Jablonski, because Iremember when I was younger,
nobody knew what melanin was.That's not a word that people used.
And now there's literally melaninmerch you can get on Instagram.
(28:37):
We're living in a different world,
and I think most of us couldn't imaginea world now where not only did we not
know what melanin was,
but maybe even believed thatdark skin had no benefit in
solar radiation. Yeah.
How do you think theevolutionary perspective of this
topic benefits people are?
(28:58):
So I would say one of the things that'sreally interesting about having done the
work that I've done is that, yes,
within biological anthropology andlet's say anthropology generally,
but especially biologicalanthropology, I am weird.
I stand out because I work on hair.
It's a multi-billion dollarindustry. Dermatology is a thing.
(29:20):
And so I could not possibly claim to bethe first person to have ever thought
about it. But what you see is thisreally interesting conundrum of,
well,
why do people who workon hair look at it so
differently? And that's reallywhere just the benefit of
(29:41):
coming up academically, intellectually,
in an evolutionaryanthropology environment,
it shapes the way you look at the world.
It shapes the way that you ask questions.
And no one would argue that there areincredible benefits to thinking directly
about how can you make certain haircareproducts to make hair do certain kinds
of things? How can you fix variousissues that people have with their
(30:05):
hair and skin from a medical perspective?
There's a need for basicscientific research to be funded,
which absolutely includesevolutionary biology,
evolutionary anthropology work,
because I'm looking at just this tiny
piece of something and saying,how does this thing work?
(30:27):
How does this thing humans work?
What are all of the fundamentalprocesses and structures
that affect us?
And that gives you power and that itallows you to make sense of things,
how they fit together, and in a lotof ways allows you to predict, right?
And that is really what we're seeing withthe research that's been done on skin
(30:48):
color.
Knowing that there would have beensome kind of selection in both
directions allows us to then say, okay,
well what would that thing have been?
We know that it has to be somethingthat probably influences fitness,
the birth of offspring, folate,
folate is really important. And beingable to put all those things together,
(31:09):
you now have this incrediblescaffolding for being able to
personalize and even think about howthese things are affecting different
people.
Like if you have darker skin ina place that does not have a lot
of solar radiation, justbecause you don't have rickets,
just because you're not bow-legged doesn'tmean that you may not have a vitamin
(31:31):
D deficiency that might affect you sosignificantly that 2 million years ago,
it would've meant that your offspringwouldn't have survived at the same rates
as people with lighter skin.
And the same thing can be saidof what we're learning now
about folate and what it has to do withpregnancy and how it travels through the
(31:52):
bloodstream. Just all of this stuffis incredibly useful and interesting,
and a lot of the money
and how it flows wouldmake you think that it's
superfluous research that'svery just like useless.
And it is so important to be able totell the difference between things that
(32:15):
have direct application versusthings that are useful and
they can be different.
Yeah. I and I work for theLeakey Foundation, so we obviously know this. Some
type of basic research is soimportant for understanding who
we are and why we are the waywe are and how it all happened.
(32:38):
So do you have a closing thoughtthat you'd like to share to wrap
up our interview then? So you can go.
It's like holding me hostage until Isay something interesting. Just kidding.
So what I'll say is Ijust opened my lab at the
University of Michigan. The actualphysical lab space is still being built,
(32:59):
but it should be done by the summer.
And I've taken on a couple of studentsand we're working on some really
interesting stuff.
And one of the things I wanted to talkabout especially is some of the work that
I'm starting to do withmy student, Sarah Taylor.
We are really interested insexualism and natal coats in
non-human primatesacross the primate order,
(33:21):
because that's another dimensionof hair morphology that we
kind of touched on in the beginning ofhow it changes over time and different
parts of your body. Well,
one aspect of that is this dimensionof variation that sex gives us, right?
Sex is this dynamic thing that changesover time. You go through puberty,
and depending on what receptorsyou have at different places,
(33:44):
different parts of your body are goingto respond differently to hormones being
there.
And so what we're trying to understandnow is how do sex hormones interact with
hair follicles to createdifferences in hair growth,
but also differences in haircolor. So watch out for that.
Well, thank you so much for joining ustoday and sharing your work and all this
interesting information about hair.
(34:05):
Thank you for having me.
You can learn more about TinaLai and her work on her website,
tinalasisi.com. We have thatlink and more in your show notes.
Origin Stories is a projectof the Leaky Foundation,
a nonprofit dedicated to funding humanorigins research and sharing discoveries.
(34:29):
You can support this show by going toleaky foundation.org/origin stories and
clicking the origin stories donate button.
Your donation will be quadruple matchedthanks to Jeannie Newman and the Ann
Gordon Getty Foundation. So you canturn $10 into $40 to support the show.
Support for Origin Stories comes fromlisteners like you with additional support
(34:52):
from the Anne Go Getty Foundation,Camilla and George Smith, Jeannie Newman,
and the Joan and ArnoldTravis Education Fund.
This episode was produced by RayPang. Our editor is Audrey Quinn.
Theme music by Henry Nagel andAdditional music by Blue dot Sessions.
Thanks for listening.
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