The History of Naked Sweaty and Colorful Skin in the Human Lineage

The History of Naked Sweaty and Colorful Skin in the Human Lineage


(upbeat music) – Good afternoon, everyone, and welcome. My name is Gibor Basri. I’m a professor of the
graduate school in astronomy and the former Vice Chancellor
of Equity & Inclusion and a member of the Hitchcock
Professorship Committee. We’re very pleased along
with the Graduate Council to present to you this
afternoon Nina Jablonski, who is this spring’s speaker in the Charles M. and Martha
Hitchcock Lecture Series. As a condition of the bequest
I am obliged but happy to give you some of the verbal information that is also in your
program about the endowment and how it came to Berkeley. It’s a story that exemplifies
the many ways in which this campus is linked to
the history of California and to the Bay Area. Dr. Charles Hitchcock, a
physician for the Army, came to San Francisco
during the Gold Rush, where he opened a
thriving private practice. In 1885, not long after
this place started, he established a
professorship here at Berkeley as an expression of his
long-held interest in education. His daughter, Lillie Hitchcock Coit, whose name has probably been seen by you in reference to a certain
tower in San Francisco, had a very colorful personality
and was also very generous. She greatly expanded her
father’s original gift to establish a
professorship at UC Berkeley and also make it possible for us to present this series of lectures. The Hitchcock Fund has become one of the most cherished endowments for the University of California and it recognizes the highest distinction of scholarly thought and achievement. Thank you Lillie and Charles. And now a few words about our speaker. Dr. Nina Jablonski is a
renowned anthropologist whose current research comprises basic, clinical, and educational projects. These include a study of the lifestyle and genetic factors that
affect vitamin D status in healthy young adults in South Africa, the writing of a graphic
novel about skin color for South African middle-school children, and the development of a
science summer-camp curriculum for minority and underserved middle-school students in the US. Her research is funded by grants from the National Science Foundation, the Robert Wood Johnson Foundation, and the Rockefeller Foundation. She is the author of books, Living Color: The Biological
and Social Meaning of Skin Color, and
Skin: A Natural History, both from the University
of California Press. Dr. Jablonski earned her
doctorate in anthropology from the University of Washington in 1981, and her undergrad degree
from Bryn Mawr College in biology in 1975. She is the Evan Pugh University
Professor of Anthropology at the Pennsylvania State University. She is the director of the Center for Human
Evolution and Diversity and the associate director of the Huck Institutes
of the Life Sciences, both at Penn State, and a
permanent visiting fellow at the Stellenbosch
Institute for Advanced Study in Stellenbosch, South Africa. Dr. Jablonski has been
recognized most recently as the recipient of a
2012 Guggenheim Fellowship for the project Naturalistic
Studies of the Dynamics of Vitamin D Status in Human Populations, and the 2005 Alphonse
Fletcher Sr. Fellowship for the project Improving
the Public Understanding of the Biological and Social
Meaning of Skin Color. I think it’s safe to say she’s an expert on her subject for this afternoon. She currently serves as a member of the Scientific Executive Committee for the Leakey Foundation,
and a member of the board for the behavioral,
cognitive, and social sciences of the National Research Council of the National Academy of Sciences. Please join me in welcoming Dr. Jablonski. (audience applauding) – Thank you very much for
that generous introduction, Gibor, and thank you, Ellen, for your logistical arrangements. It’s a great pleasure to be here and such an honor to be part of the Hitchcock Lecture Series. It’s been wonderful to
reconnect with colleagues that I’ve known for years
as well as meet some new young students who hold the promise of the future for all of us. Years ago people asked me, “Why, Nina, are you studying skin?” Most anthropologists,
most paleoanthropologists study bones, or fossils, or the genetics of humans, but they don’t try to understand aspects of human evolution by looking at skin. First of all, skin isn’t
preserved in the fossil record, so there are some real shortcomings, if you’re trying to study
the physical remains of skin. But I realized that by overlooking skin we overlooked probably one of the most important parts of the human body. Our physical interface
with the environment, our protection, our organ
of thermal regulation, and our organ of communication via touch and body decoration. By missing out on skin we
missed out on a big part of the study of human evolution. And so despite the obstacles, I have enjoyed studying the
evolution of human skin, and I’m going to share with
you over the next few days a little bit of that journey. Today talking about general aspects of the evolution of human skin, how we came to have
naked, potentially sweaty, and extremely colorful skin, and then tomorrow about what skin color means to all of us in terms of our health and
our social relationships over centuries and millennia. In 2005 colleagues began to take a little bit more notice of skin. In 2005 the genome of the
chimpanzee was published, and everyone looked at this
paper with great anticipation, because they expected certainly when we compare the genomes
of humans and modern chimps what we would see are enormous differences in genes dictating the
differentiation of the brain or the musculoskeletal system. What was revealed was a
surprise to many, but not to me. Because the major set of loci that turned out to be under most rapid evolution
in the human genome was that governing the differentiation of the human epidermis. In other words it was our skin that was the most differentiating
part of our genome. This is because having
mostly naked body skin is a big departure from
the condition present in our primate relatives and our more distant mammalian relatives. Fur and hair does a lot and without it we have to compensate in various
ingenious biological ways that I’ll elaborate on
in the next few minutes. So this really got people
thinking about the evolution of skin in a much more serious way. And I must say in the last 12 years since the chimp genome was published there has been a greater swell of interest in the evolution of skin. One of my favorite visuals is what I call the hairy timeline of human evolution, where we have here at the back end around 7 1/2 million years ago when we last shared a common ancestor with our closest relatives, chimpanzees. And our skin, if we could
look at it back then, we reconstruct it to be
mostly lightly pigmented and covered with dark hair,
that of a chimpanzee today. But through time and critically just around two million years
ago we see important changes, and I want to focus on those changes, because this is when we
really see the transition to what we would call
ostensibly modern skin: mostly naked, and sweaty, and colorful. And it’s about this time,
around two million years ago, and here represented by this impeccable partial skeleton from Kenya, we find an early member of the genus Homo, a beautiful skeleton representing one of our ancient ancestors. What’s important for you
here is that this individual, a young man, has very
modern body proportions, quite different from that of
the Australopithecine ancestors from previous millions of years, and the lifestyle of this
hominin is what sets him apart, and what sets the genus Homo apart, because it is these long
legs, the broad pelvis, the relatively short arms that indicate that this is a person with a modern build. A strider. Potentially a runner. And very different from any kind of slightly more hesitant biped or more arboreally competent
biped that existed previously. We reconstructed the
skin of this individual to be really mostly naked
and darkly pigmented, but here what I want to talk
about is why do we reconstruct this as mostly naked skin at this time? There are lots of primates
that live in east Africa and other hot environments
that run around a lot that have lots of hair. Why did we lose most of our body hair? We know from studying human physiology as well as the physiology
of lots of mammals that basically having hair is great protection against abrasion, great insulation, physical insulation against cold and temperature fluctuations, but it physically impedes the process of the evaporation of sweat. So even in those mammals
that can produce sweat on their surface, if
they sweat into the fur, and the fur gets wet, their skin cannot actually become cool. In other words, the purpose of sweating, which is evaporative cooling, is lost. What happens if you belong
to a lineage like primates where most excess body heat
is lost through the skin? Here are our buddies
that have a lot of hair that run around a lot, a beautiful antelope on the right, a domestic dog on the left. They liberate excess body
heat in a very different way. The carnivore on the left
here is able to pant. The beautiful antelope on the right here has a wonderful big nose with lots of veins and the inspired air that gets brought in through the wet nasal
mucosa cools the veins that drain back to the
proximity of the brain and help to locally cool the brain. So both of these animals can get quite hot but they have local cooling
mechanisms in their head that help their brains to stay cool, when they’re exerting themselves, especially in a hot environment. You would think that our primate cousins, our hairy primate
cousins would do similar, but even in this long-faced baboon, we don’t have any
structures similar to those that we find in hoofed mammals or in the panting respiration of dogs. Instead even our close relative the baboon and chimpanzees for that matter have to lose heat from their body surface through radiant cooling, through radiant heat loss and evaporation. So they lack these specialized
methods of cooling. When a baboon runs full pelt for a long distance it
overheats and it stops. In the evolution of the genus Homo we find the evolution of a primate that is walking, and
running, and foraging, and escaping from predators,
and possibly hunting. And needing to be able to
sustain energetic locomotion for a long period of time. There was natural selection at this time for the loss of body hair in order to facilitate
evaporative cooling. So we hypothesized years ago that the loss of functional body hair was related to the needs of thermal regulation. So here we have this
beautiful young early member of the genus Homo with mostly
functionally naked skin and where did the sweat glands come from? We know that in most mammals sweat glands of the kind that
we have all over our body are found only on the surfaces of the palms and the soles of the feet. So how did human primates manage to get all these sweat glands all over the place? This has been a question that has pressed people for decades. We didn’t lose all of our hair. Rather we reduced the
size of the body hair, so that when you look
at your own body hair it’s this little sort
of measly little things coming out of hair follicles. The hair follicles are
enormously important but where did the sweat glands come from? And this, as I say, was
an unanswered question for years until literally
just a few months ago when my colleague, Elaine Fuchs, and her post-doc, Catherine Lu, published a beautiful paper in Science about how this differentiation occurs in early human development. Long story short, what
happens is that there is an important bone
morphogenetic protein, BMP, that determines where these hair follicles and sweat glands are
going to be differentiated on the surface of the body, and then at a very critical
time in embryonic development there is a little tilt toward BMP in differentiating toward sweat gland development
as opposed to hair follicles. So what could’ve been a terminal
hair like in other primates becomes a sweat gland instead. A beautiful piece of evolutionary developmental biological regulation. And voila, sweat glands all over. What do we do with that naked skin? Well, we sweat a lot, yes. But it’s really important to recognize that in our repertoire
of behaviors as primates we engage in lavish amounts
of meaningful touch. Although we don’t engage
in it so much these days except with our smartphones, gaining or touching one another has been an important part of our communication repertoire
for millions of years, long before we existed as a human lineage. But with hairless skin the surface area for this communication has
become ever much larger. This surface of communication is an important portal for social bonding in
early human development and continues to be very important throughout our ontogeny
and throughout our lives. So even though we legislate against touch in many workplaces and look down upon it it is an essential part of the human communications repertoire. And we know now that
withholding touch from infants, withholding affectionate touch actually stifles infant growth, not just emotional growth,
but physical growth. And so infant massage and affiliative touch are now championed not only for infants, but for people throughout the life course. But the loss of hair had
many other consequences and although I could go into
this alarmingly long, I won’t. But think about when you lose the ability to express heightened emotions, especially fear, and anxiety, and anger, through piloerection, the
standard mode that a mammal uses to show its level of
sympathetic excitation, raising its hackles, raising
its body hair, what do we do? I mean, we can raise our hairs,
but who’s gonna see them? Well, we have something that compensates. There’s no Botox there. We have enhanced facial expressions that help us to
communicate from a distance what our states of emotion are, what our emotional intentions are. And at times that we don’t know, we don’t know how distant this was, but humans with naked skin
began to decorate themselves. We recognize in the archeological record we have traces of pieces of ocher dated from about 70,000
years ago from South Africa. We have other pieces of pigment
from elsewhere in the world, very ancient, some 50 to 25,000 years old. I would guess that these pieces ocher, at least some of them, were
used to decorate human bodies, and that even before that humans who had a sense of self and image were decorating themselves with clay, mud, and making meaningful
marks on their bodies. I can never prove this, but I would think from the evidence of all the symbolic behavior that we see in the lives of early
members of the genus Homo, early Homo sapiens, even
Homo neanderthalensis, that over 100,000 years
ago people were decorating the surfaces of their naked
bodies in significant ways. Tattooing is universal and people have been marking themselves. Otzi, the so-called Iceman
from about 5,000 years ago had several tattoos on his body and many modern people,
including many of our students at Berkeley and elsewhere, have lavish numbers and
varieties of tattoos. It has been one of the
most fundamental modes of communication and self-expression with the very permanence of it being its signal feature. But I’m interested now in
turning to the question of how we came to have this
beautiful range of colors. And it’s been widely recognized that, at least since the mid-20th century, that it’s not just sunlight, but it’s ultraviolet
radiation within sunlight that has been the most important
factor, physical factor, correlated with skin pigmentation
in the human lineage. In our work we have been able
to take advantage of databases that weren’t available to
workers in the mid-20th century. Thanks to NASA’s several generations of Total Ozone Mapping
Spectrometer satellites we’re able to create images
of ultraviolet radiation at the earth’s surface. This one happens to be annual average UVR, but we can actually get
wavelength-specific maps now. This map was created by
my colleague, and husband, and main collaborator in
our studies, George Chaplin. And what we’re able to see in this is more or less what you’d predict, that the highest levels
of ultraviolet radiation are close to the equator, but that humid areas,
like the tropics here, the tropical forests
of Africa, of Amazonia, of southeast Asia have rather lower levels than the hot pink and red areas of the Sahara and the Horn of Africa. But there are very high
levels in the Andes and also in the Himalayas. Very high altitude, even
though not high latitude. So it was in this environment in equatorial and eastern Africa that we think the human lineage and that Homo and Homo
sapiens are emerging, an environment of intense
ultraviolet radiation. Ultraviolet radiation comes
in a variety of forms. The most biologically significant, because they come to earth, UVA and UVB, at the equator in high doses, especially at the vernal
and autumnal equinoxes. UVC is mostly screened
out by the atmosphere. So if we look at a simulation here at the equator the
UVC is mostly screened out or absorbed by the
atmospheric oxygen and ozone, a small but biologically
significant fraction of UVB penetrates, and a
huge amount of UVA travels with the visible light down
to the earth’s surface. So the equator is bathed in
a moderate amount of UVB, in fact fairly high at the
equinoxes, and a lot of UVA. And these wavelengths have
specific biological activity. I’m going to come back to this theme of we evolved under the sun, many times. So in early genus Homo, mostly naked, potentially very sweaty skin, the dark pigmentation being the essential substitute for hair, fur protection against solar, ultraviolet radiation. Most mammals wherever
they’re living are protected from ultraviolet radiation
by a heavy coat of hair. If you lose hair you have
to compensate somehow, and the major compensation
in the human lineage is the evolution of permanent
dark protective pigmentation. Eumelanin is the molecule that
I’ll be talking about a lot, sometimes just referring to it as melanin. This is an amazing
pigment that has been used over and over again by hundreds of millions of different kinds of organisms that live on the earth’s surface and in shallow parts
of marine environments. Eumelanin is the superior absorber of ultraviolet radiation
and visible light. It’s dark, very dark brown to the eye and it’s this beautiful,
incredible multifunction molecule that’s able to absorb UV wavelengths and as it does so the
large polymer structure uncoils a little bit, absorbing energy. It also has the ability chemically to neutralize so-called free radicals, a reactive oxygen species,
that are produced in cells as UV impinges on organisms’ surfaces. So eumelanin has been used
over and over and over again and this is what we
see that is manipulated through an easy genetic series of changes in the Homo lineage in
order to bring about dark pigmentation to protect the skin of our active ancestors. Without going into great detail
about the mechanisms of this there are many genes that
control pigmentation, probably over 120 that have some role in regulating pigmentation in mammals and some role in humans, but
one of the most important at this point in our evolution is one called the
melanocortin 1 receptor locus, which determines the configuration
of this important protein which exists on the surface of the melanin-producing
cells called melanocytes. Basically in darkly pigmented people, and here I’m going to
refer to our ancestors, early members of the genus Homo, what we see is that this locus is under strong natural selection to lose all variation, so that this switch effectively switches on the
production of eumelanin, the photoprotective natural sunscreen, and reduces the production of pheomelanin, the yellow-red form of melanin that we see in red-colored mammals and
primates of various kinds, and red-haired people, and
freckles on human skin. Pheomelanin is not photoprotective at all. Eumelanin is highly photoprotective and this was the switch that was thrown. And so we can summarize
by saying in early Homo we have functionally naked,
or functionally hairless skin even though the hairs were retained. We have enhanced barrier functions. I’m not gonna talk a lot about this, but we have enhanced
ability to repel water, to repel microorganisms through a variety of different compounds
that are actually very good at fighting viruses, and
bacteria, and parasites. And we have enhanced
water-protective functions. So we have this wonderful
series of barrier functions that also helps to
prevent excess abrasion. We might not think of our skin as being very abrasion-resistant, but it’s actually extremely tough. And it’s darkly pigmented. So early Homo skin is very, very different from that of our close primate relatives. When we look at all people
around the world today all indigenous people and
measure their skin reflectance, this is data that we collated from reports collected by anthropologists,
and geographers, and human biologists over many decades, we found that skin reflectance
is very highly correlated with ultraviolet radiation to the extent that over 86% of total variation in skin pigmentation in modern humans can be accounted for by
variation in autumnal levels of ultraviolet radiation alone. That’s a very large
percentage of variation that can be explained by one variable. And so if we look at a
mock-up of human skin here, we’ve got the skin layer
here, the epidermis, there’s the dermis underneath,
and the hypodermis. Here’s the atmosphere, ozone, and oxygen. UVB at the equator is attenuated by atmospheric oxygen and ozone, and is able to penetrate
into the epidermis. It’s slowed down a lot by the dark pigment in the epidermis, but some manages to get through and that turns out to be
incredibly biologically important. A lot of UVA manages to get through, although the eumelanin in the
bottom of the epidermis here is quite a good sunscreen and
reduces the amount of UVA. What happens when UVA impacts naked skin? It causes all sorts of interesting damage to DNA in skin cells. And for the longest time
anthropologists and biologists mused that this must be the major reason that protective pigmentation evolved, to protect against damage to DNA, which could cause skin cancer. But in the 1960s a very
good biologist pointed out that, hold on, people
get skin cancer mostly after their reproductive
years are completed. This cannot have a selective effect. Skin cancer has no evolutionary potency because it mostly affects
people when they’re old. Very few skin cancers affect people during reproductive years. So we must seek another reason
for the presence of melanin. This is where we came in and it was in the early
1990s that I realized that what the connection
between ultraviolet radiation and reproductive success could be was actually mediated by a
different set of molecules, one of which was the B vitamin folate. The reason that I
identified folate initially was that folate and its close biochemical relatives are sensitive to ultraviolet radiation, especially to ultraviolet B radiation, and that folate is also incredibly important in human development because it helps to fuel DNA replication, DNA repair, and DNA
modification or methylation. In other words folate is a linchpin in determining whether DNA in cells, specifically in skin cells,
is going to be healthy. Folate needs to be protected. One of the reasons that
this came to my attention in the early 1990s is
that it was at that time when people were beginning
to realize the importance of folate as a determinant
of maternal health and early embryonic and fetal health because of the implication of folate deficiencies in birth defects. We get our folate from
green leafy vegetables, and citrus fruits, and whole grains. We can’t store it. We have to continue to ingest it and there are lots of environmental agents that can break down folate, not just ultraviolet
radiation, but alcohol, so we need to constantly
replenish our folate intake. With folate being required for all of these important functions, we need to have diets rich in folate. In the absence of diets rich in folate problems in early embryogenesis can ensue. This is what you look
like at 23 to 26 days of embryonic development. Your simple plate of cells is undergoing the process of neurulation, or neural tube formation. This process requires prodigious
amounts of DNA production, cell division, cell migration, and if it all doesn’t happen, then we can have a neural tube defect that affects the cranial end, or the middle part of the spine, of the lower part of the spine, and many of these are lethal. So having made this connection
between a physical force, a physical influence,
ultraviolet radiation, a molecule, a vitamin, folate, and a process, neurulation,
neural tube formation, and reproductive success, we felt that we were onto
something that was worth pursuing. And this really started me
on this quest of studying the evolution of skin
pigmentation over 25 years ago. So now when we think about the effects of ultraviolet radiation
on the human organism we think about primarily folate metabolism involved with birth defects. And now I want to bring
in another chapter. How folate is necessary in
the regulation of temperature, of cutaneous, of the sweating
reaction in the skin. Remember how important naked, sweaty skin is for a hominin that’s
walking and running around, especially in hot environments. The skin is the main event for
liberating excess body heat. And it turns out that folate
is incredibly important in safeguarding the process by which this dilation of blood vessels in the skin thereby provides fluid to
the eccrine sweat glands that then give sweat to
the surface of the skin. So here we bring in another molecular character, nitric oxide. I’m not going to elaborate long on this, but it’s a fascinating mechanism. Folate affects nitric oxide in the body. Nitric oxide is this really
important biochemical messenger, and in the skin many different signals turn on nitric oxide, the
production of nitric oxide, and excite the release of nitric oxide. It turns out that folate
is incredibly important in the activation of nitric oxide and then the vasodilation that
actually occurs in the skin prior to sweat glands starting to sweat is triggered by ultraviolet A radiation penetrating the skin. So you have folate fueling this process that is kicked off by
ultraviolet A radiation. So we have nitric oxide here in the skin and in the cutaneous blood vessels just a little bit of vasodilation. The UVA actually excites the cutaneous and systemic vasodilation
that is important in the control of blood pressure. So we can really begin, or
end, this part of the lecture about the evolution of dark
protective pigmentation by saying that really
as far as we can tell the critical role played
by dark pigmentation is protection of folate availability for these important reasons. And that we have this invariant melanocortin 1 receptor locus that we find in most modern African populations and African diaspora populations. If we dissect the genome, and many of my colleagues
have worked diligently to do this, to look at the
evolution of pigmentation genes, we can see that there was
a so-called selective sweep whereby this locus lost all of its functional variation under these stringent
conditions of natural selection. And we’ll see that this situation changes for some populations
later in human evolution. So during the course of the
evolution of the human lineage in Africa from early Homo
through early Homo sapiens here about 200,000 years
ago, to the modern day, we have the evolution of darkly pigmented, potentially sweaty skin,
and people can stay healthy, very, very healthy under intense sun because the protective
eumelanin still allows a little bit of ultraviolet radiation that turns out to be important. But we have many colors of human skin, this entire glorious sepia rainbow, How did it come about? The story of this is one
of the most fascinating and important ones of human evolution, and it has to do, at least in part, with the importance of
another molecule in the skin. So here’s our darkly pigmented skin under very strong sunlight at the equator there’s still enough UVB
that penetrates the epidermis to start the process
of producing vitamin D. Vitamin D is the second major vitamin that is in our cast of characters and turns out to be just as important to reproductive success as folate. But UVB is only available strongly within the tropics, year in and year out. What happens when people start dispersing out of the tropics? Let’s look at what happens
to ultraviolet radiation in the northern hemisphere
at the winter solstice. UVC is completely absorbed
again by the atmosphere, as is UVB. UVA comes to the earth’s
surface with visible light, so although it’s attenuated
by the atmosphere, by the thick pack of atmosphere, there’s still a lot that makes
it to the earth’s surface, but UVB nothing for a
good part of the year depending on the latitude. This has enormous consequences
for human dispersals and human survival at high latitudes, whether we’re talking about the northern or the extreme southern hemisphere. Because ultraviolet radiation
although mostly bad for us and mostly bad for most organisms has the one important positive effect of stimulating the production
of vitamin D in the skin. From the cholesterol-like
molecule 7DHC, which is present in the dermis of your
skin, the UVB penetrates, converts that 7DHC to
pre-vitamin D3 in the skin, and over the course of a few
chemical steps, conversions, we have biologically active
vitamin D that’s produced. What happens under
partial UVB, seasonal UVB, or low levels, and low levels of UVA? Well, we have some
vitamin D that’s formed, but it takes a much longer time. These two guys, similar in age, sunny day in northern California. The man on the left can
make vitamin D in his skin, assuming that this is summer
sunlight with plenty of UVB, he can make vitamin D
in his skin at a rate five to six times faster
than the man on the right. Both of them will be able
to produce enough vitamin D at the end of the day, or
at the end of several hours, to suit and to meet their
physiological needs, but the man on the right will
take a longer time to do so. This was never an issue for people who were outdoors all the time. But it is an issue today. And it was an issue for
darkly pigmented people who were beginning to disperse outside of equatorial latitudes
during the Pleistocene. And we now really want
to turn to the dispersal of modern humans, Homo sapiens, beginning around 200,000 years ago. The best molecular and
paleontological estimates place the origin of our species around 200,000 years ago in Africa. Most of the evolution of Homo
sapiens occurs in Africa. All of the tremendous linguistic,
cultural, technological, artistic differentiation of our species, the tremendous evolution of our quintessentially human traits occurs in this early phase
of Homo sapiens evolution until 70 or 80,000 years ago. So this tremendously active
Homo sapiens evolution phase occurring here with dispersals
within Africa occurring. Beginning around 60 to 70,000 years ago, and this number changes
in light of new evidence all the time, but we’ll just stick with about 60 to 70,000 years ago, we have the first egress of populations through the Afro-Arabian peninsula, along the southern coast of south Asia, and into the hinterland of central Asia. Down 50 to 60,000 years
ago into southeast Asia, and then 40 to 50,000
years ago from sort of a staging post here near the Black Sea populations dispersing both
westerly and northwesterly into Europe, and northeasterly into Asia, northeastern Asia. Into regions with very low and highly seasonal levels
of ultraviolet radiation. This dispersal is sped along by the incredible cultural
competence of these people. All of these years of evolution
we had this incredibly sophisticated and varied toolkit. We had language. We were behaviorally
modern in every sense. And so these dispersals occurred faster than those of other mammals. But what happened? We were going into these areas that were really very different from our ancestral solar environment. And it’s important to remember that probably during individual lifetimes people didn’t travel a lot. The idea of sort of going somewhere. Yeah, well, yes, you’d
be looking for food, and you’d be escaping predators, but there wouldn’t be
active moves very often. But most people spent time out of doors and without sewn clothing. The earliest common occurrences of needles for the preparation of sewn clothing, of tailored clothes,
about 20,000 years ago. Humans were hoofing it big time, dispersing with mostly naked skin, and without sewn clothes. They certainly had the
ability to use animal hides, and possibly to use plant materials, but they didn’t have the ability to tailor close-fitting clothing. So our skin was the primary
interface with the environment. Throughout the year being outdoors ultraviolet radiation varied by season and we adapted to different levels of temperature and ultraviolet radiation through biological and
cultural modifications. Vitamin D is incredibly important in this. How did we maintain the
ability to make vitamin D when we were dispersing into latitudes that had virtually no
UVB throughout the year? We need vitamin D to build strong bones. In the absence of vitamin
D to help us absorb calcium from our diet in early development infants and children can develop
this bowing of the bones, nutritional rickets, really, really bad, especially if it persists into later life. A young woman who suffers from rickets throughout her early life will
develop a deformed pelvis, the outlet of which is compressed, so that she cannot give birth normally. Natural selection big time. We now recognize that in addition to that classical function of vitamin D that vitamin D controls
important functions of the immune system and of cellular growth and
proliferation in the body. There are vitamin D receptors
on virtually every organ, whether we’re talking about the brain, the pancreas, the skeletal
muscle, as well as bone. So our health turns out to be regulated in part by this vitamin, which we never questioned
in our early evolution. Vitamin D was being produced in our bodies just because we were alive and outdoors. But when humans are now
living in high latitudes being outdoors isn’t enough. And at the highest
latitudes, what we find is that people can only sustain
year-round habitation if they have maximally depigmented skin and if they have cultural adaptations for ingestion of vitamin D-rich foods. Their biology and their culture change. So this dispersal involved both biological and cultural adaptations in what we call the vitamin D compromise. And the first element of this compromise is skin depigmentation. I don’t talk about so much
light skin as depigmented skin. Depigmented skin is a derived condition from our ancestral darkly pigmented skin. And we predicted this even before there was any genomic evidence that these individuals resulting from two sort of
sub-lineages of modern humans dispersing into high latitudes would have evolved independently. And how beautiful that in the
course of the last 15 years genomicists looking at pigmentation genes have found that these groups of people, northwest Europeans and
northeastern Asians, have independently
evolved depigmented skin. One of the genetic loci is similar, but most of the others aren’t. This is music to the ears of
any evolutionary biologist, that you would have a
selective force so strong that it would call upon
whatever genetic variation was available, and we’ve got
a big palette, as it were, of pigmentation genes, that we would use whatever variation was
available to produce lightly pigmented or depigmented skin. And now we know that there are many loci in many populations that are
associated with depigmentation under strong positive selection. And the elucidation of
the different pathways that have been used in
different populations, we now know that depigmentation occurred at least three times and
I would guess it occurred probably even more than
that in Homo sapiens, in addition to having occurred most likely in Neanderthals as well,
our distant cousins. So what happens? Under strong selective pressure low UVB at high latitudes
we have depigmentation, loss of eumelanin pigmentation,
most eumelanin pigmentation, so that we have excellent
vitamin D production. And this is the primary selective force for the evolution of depigmented skin. An example of the vitamin
D compromise at work, and I’m going to take one of many. This is a very extreme example. People started moving into Scotland, modern people, about 10,000 years ago, and mostly inhabiting coastal settlements. The people have undergone in situ maximal loss of eumelanin pigmentation. Not surprising, even on a sunny day at the summer solstice it is not very sunny in northern Scotland. And there are many days where there is very, very
little ultraviolet B. So how did people survive? Maximally depigmented skin. But it turns out that even
with no natural sunscreen they could not make enough
vitamin D in the skin to satisfy their
physiological requirements. So year-round habitation required technology and culture to
harvest vitamin D-rich foods. People lived near the coast, they ate lots of cod fish, cod liver, cod liver stews. People in the hinterland dried fish, kept fish on the roofs of their cottages and ate other sources of protein like blood sausage that had vitamin D. And they stayed healthy. So the vitamin D compromise
also involved, sort of, the tinkering, the genetic tinkering, of genes that affect vitamin D production in the skin and its metabolism. And the introduction
of vitamin D-rich diets in many populations. But let’s not forget vasodilation. What happened? This depigmentation also allows
enhanced penetration of UVA so that healthy levels of
vasodilation can occur, reducing blood pressure
and allowing sweat glands to get the fluid that they need
from the expanded arterials. So here we have a healthy situation with a nicely vasodilating little artery and people are healthy. In skin pigmentation
thus we can really see one of the most interesting
evolutionary compromises that we’ve been able to describe. There is operating here what evolutionary
biologists and geneticists would call a dual cline. One that emphasizes photoprotection, maximal eumelanin
pigmentation at the equator and in other high-UV environments, and a cline in the opposite direction emphasizing depigmented skin that permits photosynthesis
of vitamin D maximally under very seasonal
and low-UVB conditions. A beautiful system honed
by natural selection. And so the eumelanin
concentration in human skin is very much related to the intensity of ultraviolet radiation, and in middle latitudes we
have people who can tan. And we are now looking at
the genetic architecture of tanning, this is some of
my past graduate students, and we’re finding that in all
sorts of different populations whether they’re in the
circum-Mediterranean, or north Africa, or southeast Asia, that have tanning ability. They have different suites of genes that can be turned on and off, or on at various seasons, when there’s high amounts
of ultraviolet radiation. So this is really, really exciting stuff. The tanning too has evolved independently. Similar skin colors have
evolved independently many times under the same UV conditions, and using different combinations of genes. So these three darkly
pigmented individuals, on from Africa, one from
Australia, one from southern India, have darkly pigmented beautifully, naturally, sunscreen-rich skin, and the genetic architecture
of their dark pigmentation is different in all of these cases. Very importantly skin pigmentation genetically is mostly independent of other physical traits. So whether we’re talking about hair color, eye color, nose shape, ear
shape, or other physical traits, skin pigmentation for the
most part is independent. So these groups of characteristics that have sometimes been put together by people for various reasons are not. They don’t sort of walk in lock
step genetically in a group. They aren’t. They aren’t connected. And they have undergone
independent histories through our own history. So we now have this beautiful
sepia rainbow of modern humans that has evolved in
different parts of the world. Over time as humans, modern humans, have dispersed into
different parts of the world similar pigmentations and
different ones evolving under similar UV conditions with different genetic mechanisms. It is a beautiful story of evolution of the human body under natural selection. I tell people, remember Chuck, right? (audience laughing) We as teachers, whether we’re
teaching in our living room with our children and grandchildren, or whether we’re teaching
in our classrooms, we’re always seeking
examples of natural selection and evolution on the human body. Here is one of the best. And, you know, I urge people to use this, because it is understandable,
everybody has skin, this is something that people can grasp. Skin pigmentation is a natural compromise determined by natural selection. And so we can marvel at this beautiful evolutionary compromise and tomorrow we will
consider what this means, what this beautiful compromise means, especially when people start moving around and interacting in ways
that weren’t predicted by our ancestors 20 or 50,000 years ago. Thank you very much. (audience applauding) – [Man] So in one of the very last slides you showed the different
people with different colors. The person in Alaska had
kind of dark pigment. Can you explain that one. – Yes. I didn’t plant you in the audience but I’m so glad that
you asked that question. People always ask me about the
dark pigmentation of Inuit. Inuit and many of the circumpolar peoples have great tanning ability. When you look at their unexposed skin it’s sort of moderately pigmented, but they have tremendous
ability to make melanin in their skin as a result
of direct solar radiation, but also from UV that
bounces off the surface of the water and snow and ice. So how do they manage? So here they are, super high latitudes, Arctic Circle and above,
how do they manage? They get their vitamin D
entirely through their diet. And when we look at the
culture of Inuit people it is built around the harvesting
of vitamin D-rich food. Whether we’re talking
about spearing whales, or seals, sea lions, or eating oily fish, or in the hinterland chasing caribou or reindeer, depending on which part
of the Arctic you’re in. You are pursuing vitamin D-rich prey. And basically people can
maintain good health, Inuit people, when they are
eating vitamin D-rich foods. As soon as they start
moving to settlements and abandon their traditional diet they have terrific problems
of vitamin D deficiency, which are now a cause of great public health
concern and mitigation. But the fascinating thing
is that natural selection has worked to enhance
tanning through genes, complexes that we still don’t understand. Enhanced tanning to protect
against this UVA load in a sense knowing that the vitamin D is coming from dietary sources. – [Man] I’m from the Department
of Nutritional Sciences and I’m fascinated by what
you said about human foods and human food cultures and
their role in evolution, but this makes me think of another element of human food culture and that is when you look at a lot
of different cultures there’s something about
hot foods and cold foods and I wonder if the origin
of the ideas of hot foods and cold foods may have
actually been something that helped us to walk out of Africa. – You mean hot as far
as cooked or hot spicy? – [Man] Or what people culturally call, oh, that’s a hot food,
or that’s a cold food. And if you ask people from
many different cultures what their grandmothers taught them you find a lot of different answers but so many of them talking
about hot foods and cold foods. – Yes, and there’s a lot
of discussion about this that some foods are eaten,
especially in the winter to help protect you against
the temperature fluctuations. We’ve never, to my knowledge
no one has actually looked at the, you know, relative thermogenesis of these so-called hot
foods and cold foods. In traditional east Asian
cultures, for instance, eating turtle, eating
snake in the wintertime is considered very important and avoiding those foods in
the summer is equally important because they’re said
to generate more heat. I would love to know if there was actually more thermogenesis that was
gained from these so-called hot or cold foods, but to my knowledge, no one has looked at this. – [Man] Thank you for that talk, Doctor. My question involves our
very hairy ancestors. (both laughing) Would it be fair to say that their primary method or system of cooling was something other than
evaporative cooling? – Oh, yes, very good question. So with our hairy ancestors and relatives modern monkeys and apes today actually lose body heat
through their skin, through their hairy skin, and they have some sweat glands. So they are able to sweat a little bit. There are some monkeys, the patas monkey of east and west Africa has a relatively thin coat of hair and quite a few eccrine sweat glands. It is the most fast-running
of the non-human primates and people have looked at the patas monkey as sort of a model for human sweating. That there was natural
selection for thinning of hair and increased density
of eccrine sweat glands. But the key thing with
all of these primates is that they did lose heat through the surfaces of their body. There isn’t a specialized
panting mechanism or nasal-cooling mechanism
as in other mammals. – [Woman] A few years ago my husband and I visited the prehistoric museum in Bordeaux on our way to Lescar and there was a mock-up of a small family of Homo neanderthalensis,
which absolutely fascinated me because they had light
skin, nearly hairless, red hair, and they looked like, you know, a lot of guys I’ve known. (chuckles) I know you were careful in
your use of Homo, and so forth, and I know there were
besides the neanderthalensis there were, you know, Homo
ergaster, Homo erectus, I mean, many other Homo species, but having seen the… First of all, was it inaccurate? And then how do you differentiate
the, was it accurate that they had light skin
and fairly hairless? I mean the rib cages were more robust, but in terms of the skin, I’m fascinated. – Yeah, this is a very good question. We know that the loss of
body hair in our lineage, in the Homo lineage, occurred probably more than a million and a half years ago. So the ancestor of the ancestor of the Neanderthals was a mostly hairless, sweaty member of the genus Homo. So whatever kind of species
designation you want to give, Homo erectus, Homo heidelbergensis, the predecessor to Neanderthals, this was a mostly hairless hominin. We have inferred even
before genetic evidence that a hominin that would have
been living deep in the past in a middle latitude, or in, let’s say, about 40 degrees north latitude in Europe, would have lost most of it’s pigmentation. So we hypothesized this
in one of our papers. But then just about 10 years ago using ancient DNA techniques an excellent Spanish human
geneticist, Carles Lalueza-Fox, was able to look at the pigmentation gene, the MC1R locus specifically, of a very important group
of Neanderthals from Spain. What he was able to determine, and this was a very clever piece of genetics that was undertaken. He was able to reconstruct the activity of this particular gene. So even though it was no Neanderthal there to sort of inhabit the gene,
if you know what I mean, he was able to show that the gene product would have been light skin,
or mostly depigmented skin. So they actually used the ancient DNA to reconstruct the action of
the melanin-producing cells and reconstructed that most individuals would have been lightly pigmented and at least, they estimated, around 10 or 20% would have had red hair. You know, I think that’s a bit
more of a sort of question. But there’s no doubt that the strength of natural selection was great when humans were dispersing
into high latitudes. So it was either be depigmented or have a lot of vitamin D in the diet. And I would guess in the
history of various human species and in various Homo sapiens groups, we have all sorts of mixing and matching, that there’s strong selection occurring and some of that is going to be met through genetic modifications of readily available genetic
variation when it’s there, and other times it’s going
to be met by dietary changes, and other times it’s not
going to be met at all and the populations become extinct. – [Woman] I’m going to
ask you a silly question, if that’s all right. – Go ahead. – [Woman] So if you have
a black-and-white cat and you shave it, its skin is
also black-and-white patchy, so why, I mean, obviously
that’s a carnivore, but why is it that human
skin and pelage coloration is so uniform on an individual? – Yeah, it’s a great question, and it’s not a silly question at all. We see throughout primates, and especially throughout apes, that we lose our pattern. So there are some monkeys that have beautifully patterned coats and that have similarly
patterned skin under the coats. But as soon as we get into the ape lineage we lose, and especially the
large, the African ape lineage, we lose all of that patterning for genetic reasons that
we still don’t understand. So when you shave an orangutan, you shave a gorilla or a chimpanzee, it’s all the same color underneath. This is a real question as to why, why we lose this, the relationship between the hair color and
the underlying skin color. And this is, as I say,
it is an open question that primate biologists
who are studying skin and hair coloration have yet to answer. But a very good one, not silly at all. – [Woman] Hi, I have two quick questions The first one is will you be covering in the following lectures
what some refer to as the epidemic of vitamin D deficiencies? And my second question is how has skin pigmentation
evolved independently from other phenotypes if
melanin is responsible for the color of not only skin but our eyes and our hair color? – The first question is easy, yes, I will be talking at length
about vitamin D deficiency. What’s interesting about
the melanin systems in, you know, in the hair and eyes is that they are not under
as strong natural selection. It’s important to have hair on the head. We know that the hair
on the head, scalp hair, does serve an important
thermoregulatory function on the surface of the head, but the color of the
hair probably hasn’t been under strong natural selection. But, and we know also that
it seems to be controlled by many fewer genes
than skin pigmentation. To make a long and interesting story short what has happened in the
history of human dispersals is that there hasn’t
been so much selection of hair color and texture or eye color but, rather, loss of genetic variation. So that when you have a
limited palette of genes and you lose some of that variation because the dispersing
populations are small then you’re sort of
stuck with all dark eyes. If you look at eastern Asian populations all individuals have darkly
pigmented hair and eyes and I would venture that
that’s not a product of natural selection, it was an accident of small-population effect
in human dispersals. Similarly in northwestern Europe where we know we have strong
population bottlenecks occurring in the late
Pleistocene and early Holocene that we have repeated genetic bottlenecks and loss of variation. So we might get some really
interesting variations being thrown up in hair
color and in eye color but this isn’t, it
hasn’t been selected for. Initially it is there because
of a small-population effect, I would venture, and then later it may become acted upon by
natural or by social selection. We do have evidence for
social and sexual selection of certain of these traits
in certain populations. But I think it’s really
important that we look carefully at the range of genetic
and population factors that are occurring and the
sequence in which they acted, and that we don’t just say, oh, yes, yeah, blondes evolved under sexual selection. No. It was a genetic accident
probably then followed by some social and sexual selection. – [Woman] Thank you. – Mm-hmm. – [Man] Two sort of questions. One, why is hair regionally
retained on the body? And a related question, not for myself, but for those in the
audience who might care, is there a selective
advantage or disadvantage to male pattern baldness? – (laughs) A common question. Usually put to me by people
with less scalp hair. In answer to your first question, this is a really good question. Answers to why did we retain these regional accumulations of hair and in addition to pubic
hair, and axillary hair, and scalp hair, why do
men have facial hair? The jury is still out, to be generous, on most of these things. I think scalp hair we
can make a strong case for the fact that it does
locally protect the scalp from solar radiation and overheating, and that is allows sort of a, a space in which the skin
can sweat and lose heat. So I think that’s important. With pubic and axillary hair, I think the primary function
is dispersal of pheromones, because the apocrine glands
that are concentrated there secrete important molecules that are used in chemical communication. We do our level best
to silence them, right, in modern societies, and
we consider it antisocial when we can smell somebody, but smell is part of our
armamentarium of communication and this has been very important. We know that it still is
important in sexual attractiveness even though we do our very
best to eliminate smells. So I think this is a fascinating
and still ill-studied area. With beard hair there has been a lot of interesting recent work
on beards as sexual signals, as signals of male maturity and male age. Because the beard changes
color generally more rapidly than other parts of body hair. And so not only does the
fullness of the male beard indicate sort of a fully mature male but also the change of
color can be a very accurate chronological indicator of male age, and that may have been
important in the past. So these are interesting
hypotheses, all of them, that have not been tested very well. There is still a huge amount
of work to be done on hair. – [Woman] Your very
interesting hairy timeline at the beginning showed
a rather rapid loss of hair in the middle. Is it real, and if so, what
do you think caused it? – Yes, well, that, the rapid loss of hair was probably fairly rapid. For this we really need to
look to the paleontologists and look at the transition from sort of an Australopithecine to a modern Homo skeleton. That occurred over the course of probably a half million years. So, you know, I can’t
really say how quickly the change in skin would’ve occurred, but certainly going along with a skeleton that is fit for walking and running we know that there
would have been build-up of excess body heat under
hot environmental conditions, and if the only physiological mechanisms available to you are from
the surface of the body through radiant and evaporative heat loss there would’ve been
strong natural selection for complete loss of functional body hair. And so I would guess that
transition was quite rapid, and that little sort of signaling and evolutionary developmental biology toward increased differentiation
of eccrine sweat glands, I think the switch was thrown and probably the genetic architecture of that change was under strong positive selection. – [Woman] I have a very young niece, who just had kidney transplant. She’s of Scottish heritage. They’ve said people who’ve
had kidney transplants, of course they’re taking
immune suppressants and the doctors are really dismayed that oftentimes they’ll get
skin cancer within five years. So I was just wondering, shouldn’t they all be taking vitamin D? – This is a really good question and I talk a lot to nephrologists and
kidney transplant surgeons all around the world about this because it is one of the major challenges to keep people healthy
with respect to vitamin D. In the case of your relative
with lightly pigmented skin it is really important that
she stay out of the sun. So I would say that she needs to talk to her physicians quickly and efficiently about what program of
vitamin D supplementation she should take to stay healthy because the majority of,
or, I should say many, if not the majority of
kidney transplant patients are badly vitamin D deficient. – [Woman] And what about folate, or is that a totally different issue? – Folate is a completely different story and folate is, you know, you can get it really, really easily. There are no easy dietary
sources of vitamin D unless you really seek out mackerel and other specific kinds of oily fish. But folate you can get from
green leafy vegetables, mostly of any kind, citrus
fruits, whole grains. You can get folate from
a variety of sources, so it’s easy to top up on folate. Less easy to top up on vitamin D. – [Woman] So, then, supplements. – Yes a supplement but
talk to the physicians to determine the dosage. – Okay, well, let’s thank
our speaker once again, and thanks very much for coming. – Thank you, thanks very much. (upbeat music)

68 thoughts on “The History of Naked Sweaty and Colorful Skin in the Human Lineage

  1. I may not agree with everything you say, but. You are one of the best lecturers that I have watched. I totally enjoy your fact based no nonsense, clear and concise lectures.

  2. This was an excellent lecture; I wish all researchers shared Dr. Jablonski's ability to present information in such an engaging manner. Her tone of voice, pacing, and word choice made already interesting subject matter all the more enjoyable.

    However, I must disagree re: her advice on folate 1:20:54 . I would encourage everyone reading this to track their diet using the cronometer app for a week, even if you do not have a specific health concern. It requires some effort (and a kitchen scale) but it is a highly informative experience. I'm a 'health nut' so I use cronometer every day. I've found my top sources of folate are broccoli, lentils and other pulses, romaine lettuce, spinach and asparagus. It is interesting to note that although spinach and swiss chard are closely related plants, swiss chard is not a rich source of folate. Also, beets contain more folate per weight than beet greens. On the other hand, eating a variety of leafy greens is very health promoting and good for protection against UV damage; there's an expression in the South, 'greens give you color' – and I've found that swiss chard and beet greens give my pale skin that golden tone more than other vegetables.

  3. I love this woman, a great scientist. This is the scientific answer and alternative to racism that should not exist in modern times and that all humans need to hear. It is refreshing to restate that the black African human is the first and original human being on the planet who gave birth to the other so-called races.

  4. "The History of Naked Sweaty and Colorful Skin" Is it permitted to upload this type of thing to the Ootoob ?

  5. This may come as a shock to you mindless science types but evolution as stated by Darwin was the catalyst for Eugenics and the Adolph Hitlers of the world . He can be described as an applied Darwinist .
    Did you every actual read origin of the species or worse yet Darwin’s decent of man
    Darwin is the father of modern racism.
    Slavery was about the sin of Avarice. Nothing else.

  6. Very nice, very informative lecture delivered exceptionally well.
    This was definitely time well spent for me at least. Thank you for producing the work.

  7. The evolution of skin color is more complicated than this, but the main driving force was because of winter. This video explains why:
    https://www.youtube.com/watch?v=t42EsBwnlSY

  8. Although skin cancer may typically affect people later in life and thus not greatly impact reproduction, sun burn is a major problem for light skinned people living in the tropics, even with modern clothes. The harmful effects of sunburn alone are sufficient to explain the need for dark pigmentation.

  9. I find my long beard has a cooling effect on neck. If I walk fast or run, the air moving through my beard and it feels cool. Can someone study weather beards cool the the arteries of the neck? Maybe men kept it for sexual distinction and for cooling.

  10. Excellent talk and not once was it a black or white issue. It was the best explanation of different skin tones that I have ever heard. Wonderful talks and made perfect sense. It might have been an hour but it went by so quickly.

  11. Lots of good information. Only want to know why subcutaneous fat remains in our early African ancestries if loss of hair was so important?

  12. She' a racist and ignores major discoveries in order to retain this Out of Africa Black Supremacy Theory! They I believe think their Morally Superior as well but really their just racist!

  13. This is not true! Many people don't believe this and there's evidence that shows it! Just read in between the Lines and what she aludes to at the end! We are not the same ! Europeans and Asians did not evolve from Africans! They've clearly have an Agenda to blend us all out! Well at the least the Europeans for sure!

  14. I remember back in the (since proven ineffective) days of megadoses of Vit C, etc. that people discovered the danger of taking too much Vitamin D (kidney stones,
    confusion or disorientation, muscle weakness, bone pain, weight loss or poor appetite, extreme thirst, frequent urination, and nausea, vomiting, or constipation)
    and this lecture makes me wonder whether that effect is more pronounced in people with darker pigmented skin. It would seem so.

  15. Interesting. Crohn's disease is most common in higher latitude populations and lowest closest to the equator. But populations from the tropics which move to higher latitudes develope higher incidents of Crohn's. Crohn's is an autoimmune disorder. Perhaps there is a connnection with vitamin D production or lack of same and skin pigmentation. Maybe there is a correlation between Vitamin D loss and autoimmune diseases.

  16. The African genome project found multiple unknown hominid DNA 9-13% in sub Saharan blacks not found in either Asian or Caucasian population. Google "archaic human admixture" so how did we all come from some African ape man 200 k ago? As for the speaker she's a Marxist

  17. This is a half-truth!!! There is research that disproves the out of Africa theory!!! They have found ancient bones in the Americas which are older than those found in Africa yet they continue to push this (Out Of Africa) lie!!!

  18. When you base a THEORY off of another THEORY, and then you present it as TRUTH, you're lying (or at the very least making things up)!!!

  19. ✨(ノ◕ヮ◕)ノ⚡pffft! oh come on! white people lived underground, that's all. so the genetic pairings that went to white pigmentation also drove aggression bc of lack of resources, and more fecundity bc so many died young in the underground cities. Does NO ONE listen to Alex Jones anymore in school?

  20. Interesting, but anyone invited to speak at UCB is immediately suspect. Unavoidably brings up questions of political admixture in the subject matter.

  21. Interesting talk, but anthropocentrically biased IMO. For a biological update of human & ape evolution, google e.g. "coastal dispersal 2049 Verhaegen" or "not Homo but Pan naledi? 2016 update".

  22. Dr. Nina Jablonski, thank you very much fo0r this lecture. I enjoyed not only the content, but your gestures, the kindness of your manners and voice. You are a nice person.

  23. She never answered the fundamental question: Why are humans the only animal to lose our hair? If her hypothesis is true, then all animals evolving in the same environment would lose their hair.

  24. Dr. Jablonski has won another fan in my case. Her deliberate pace of delivery and careful enunciation work well with my download speed.

  25. Skin cancer and reproductivity: it CAN be an evolutionary selective factor if human groups have reached a point where older humans are helping look after the young through the very extended childhood stage. It all goes together. Community, team hunting, family/tribal childrearing, cooking food, technology of tools – all easier with bigger brains. Where the PACKAGE is successful, evolutionary pressure rewards it. We spend too much time specialising as students, and then needing to find some crucial single key factor in our own sphere of research (which justifies our PhD thesis).

  26. 38:22 No mention that dark skin protects against painful sunburn!!!
    41:53 According to this UCTV CARTA video, early European farmers had dark skin and blue eyes, and light skin is only 4000 years old. https://www.youtube.com/watch?v=AZ2H9NUn150&t=2295

  27. They’ll really do anything to disprove the aquatic ape theory. Since chimpanzee’s can’t swim, when did we evolve the ability?

  28. Carl Benz School Germany

    https://cdn-02.belfasttelegraph.co.uk/incoming/article34816114.ece/94f68/AUTOCROP/w620h342/swastika%2002.jpg

    Ruhrwag

    You dont understand it cos you"ve never been burned by a darker person who didn't know he was God"S chosen people the Aeryan.

  29. For modern humans leaving Africa and interbreeding with Neandertals seems to have been essential for the successful colonization of Asia and Europe. We probably retain 35-50% Neandertal DNA in the Asian and European gene pool.

  30. This was wonderful I learnt so much, but I also have a few questions. Firstly Spanish neanderthals may of had white skin but did North African and Levantine Neanderthals have darker skin? I remember seeing recently they have discovered that Khoisan
    races have a variable and random Melanin gene expression that doesn't evolve in different U.V. zones. So whatever shade of colour the parents are the children can be any shade from pale ochre to dark brown to almost black and each child could be different. Kind of like a collective solution to the U.V./folate/vit.D. problem.

  31. Brilliant and enjoyable presentation. I never watched so important and complicated human aspect as color skin in a manner so masterly explained. I never understood very well how UVR plays a key role in vitamin D and complex B yielding and the effect over the color skin until now. I recommend to everybody to watch and understand Dr. Jablonski.

  32. Not convinced..load of bollax,
    Part info is tru & rest false ,
    !! , its a study
    / want ur opions /ur beliefs

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