Scientist: Hugh Hefner Owes Everything to the Evolution of Color Vision

If we humans weren't so bare, we would probably not wear robes. And then there would be no reason to disrobe. If there were no bare skin, there would be no Hefner as we know it.

And, according to Mark Changizi from the Department of Cognitive Science at Rensselaer Polytechnic Institute, the reason we're bare is because we can see in color.


More talk of nudity and other dirty things after the cut...

Changizi's theory, which he details in a post over at ScientificBlogging, is based on both research and speculation. But I kind of love these evolutionary "Just So Stories" like this, not necessarily as hard science, but for their ability to inspire imagination and curiosity about who we are and where we came from. The fact is, without basically re-doing human evolutionary history in a lab, we probably won't ever know for sure why certain features evolved. Or why we have some features that other animals don't. But I do find the speculation fun.

As I have argued in my research, our color vision is a distinctive kind of color vision, one that is specialized for detecting the color changes that happen in skin due to the physiological changes in blood (e.g., oxygenation). Most varieties of color vision - like that in birds, reptiles and bees - do not have this extraordinary capability. Our color vision is for seeing blushes, blanches, red rage, sexual engorgement and the many other skin color changes that occur as one's emotion, mood, or physiology alters. Color is for seeing embarrassment, fear, anger, sexual excitement, and so on.

Our primate ancestors once had furry faces, and one was born with our style of color vision, able to detect the peculiar changes in our underlying blood physiology. Although the faces this ancestor looked at were furry, some skin would have been visible, such as around the eyes, nostrils, lips and any lighter patches of fur. This ancestor would have been born an "empath," able to see the moods of others. Color vision of this kind would thus spread over time.

And once it spread, animals could then have evolved to "purposely" signal colors indicating their mood, and then bare skin would have evolved to have more canvas for signaling. Many of our skin color changes are indeed "purposeful," i.e., not simply inevitable consequences of our underlying physiological state. For example, Peter D. Drummond has shown that peoples' faces blush more on the side which people can see.

Image by Flickr user shufflepath, via CC


  1. This must have happened before we came down from the trees and had to develop dark skin. It might explain why we keep evolving light skin.

  2. “Our color vision is for seeing blushes, blanches…”

    So I’m guessing that Mark Changizi is not of African descent.

    1. Um, although I don’t entirely buy the premise of the argument, I certainly don’t have any trouble seeing blushes and blanches on humans of African descent.

      I’m “white” but I have a mixed race family, so I know what I’m talking about. “Black” people get sunburnt, too, it just takes more radiation to do it, the effect is the same.

      Or were you just trolling? Oh, my bad.

  3. Hmmm. This is an old and much debated subject. There is a common theory that bipedalism (and the resulting change in solar energy load on individuals) led to a full pelt being unnecessary.

    Then there are the “invested monogamy” folks, who see this wrapped up with sex.

    There may not be a reason, of course. It could be that for whatever reason, a coat of hair placed the owner at no advantage or disadvantage, and could be selected against.

  4. @ ncm > We evolved light skin in europe because at the time, it was covered by ice and dark clouds, thus making it a difficult place to live for dark skinned people, whose skin absorb less D vitamin (black europeans still have to take nutritive complements during childhood to avoid rachitism).

    Still, I don’t buy this theory about “social skin coloring”, it seems convoluted. We are monkeys, and monkeys eat fruits, that’s why we see colors, frugivores need to spot ripe fruits in foliage.

  5. I don’t buy it. That might be a reasonable theory as to why we don’t have furry faces, but I’m pretty good at figuring out what kind of mood most people are in without seeing the rest of their body in the buff. For that matter my dog can usually tell what kind of mood I’m in, and she’s colorblind.

    A novel theory to explain an evolutionary adaptation that already has a number of much more compelling explanations.

  6. Actually, human perception of red is very poor compared to other colors in the visible spectrum.

    We can see red, but we’re not good at detecting subtle changes in red as well as we do other visible colors, to the contrary of Changizi’s statements.

    Technologies such as the NTSC color TV standard and “16 bit (R5G6B5) color” from last decade have leveraged the understanding that changes in red are not as detectable.

  7. Regarding the losing of the hair, one major theory I’ve heard is that our bodies may have evolved to be fur-less due mainly to the demand for a more advanced cooling system, which may give us the ability to survive in pretty much any climate on earth. Losing the fur meant that we could more readily regulate our body temperature by sweating all over, something I don’t think most mammals can do.

    The need to see in color is unrelated to losing our fur. We evolved to see color so we don’t become dinner for the predator lurking in the canopy. The human eye has twice as many photo receptors dedicated to decoding greens than any other color.

    1. I recently heard about the (old) theory that we descended from aquatic apes, and that explains our lack of hair.

      I don’t really get the connection, but apparently it also explains the lack of hair in elephants and rhinos and hippos as well.

  8. Sorry Changizi, but I don’t buy it. There are just so many reasons why this doesn’t make sense. People are not that sensitive to red, in fact, a significant portion of the population is colorblind to reds. And then the fact that I could grow a big bushy beard. And then the many other possible reasons for being bare-skinned (need to sweat and dump heat better than other animals for endurance hunting, straight sexual selection for infantile features, etc).

    1. My impression is that Changizi has fallen into the trap that many intelligent people find themselves in when they spend years studying a subject: seeing everything through the lens of a very narrow specialty. In this case the lens in question is the human eye. While I’m sure he knows more about cognitive science and vision than I ever will, that doesn’t mean his “one theory to explain everything” is supported by available evidence.

      1. yeah. tbh, it’s sucky how it’s normal to say ‘scientist says blah’ without any qualifiers anyways.

        like, the guy is a cognitive scientist, not an evolutionary biologist, so it’s a bit like saying ‘sports player’ when you’d expect baseball vs football. or whatever. nm.

  9. Agreed, “Old World monkeys, apes, and humans all enjoy trichromatic color vision” – “Primate photopigments and primate color vision”, G. H. Jacobs, PNAS January 23, 1996 vol. 93 no. 2 577-581 – even those with very little exposed skin.

  10. At some point in our past lots and lots of primitive humans died. I’ve always wondered if it was from predation or starvation. I always figured we have our amazing color vision (second in the animal kingdom only to parrots) because it helps gathering food, but more importantly identifying camouflaged prey or predators. Watch how you see a spot were someone has tried to paint over something in a color that’s similar but slightly different from the original color. That spot will stand out and draw attention to itself. Imagine a hiding predator that was close to the color of the background but slightly different, it also stand out. Maybe seeing obviously painted over spots is an instinct we forgot we have.

    1. Human vision is not second only to parrots in the animal kingdom. Stomatopods (invertebrate crustaceans) have 16 visual pigments (we have three), and can see into the ultraviolet and infrared spectra. AND they can see polarized light. Invertebrates win again, my friend.

  11. Other primates have trichromatic vision, but most don’t quite fall into the same category as us because they’re vision isn’t usually as good or important. I would imagine being able to pick up subtle colour changes is more important when you can’t smell the same thing.

    Colour vision is much older than eating fruits – many fish and birds are trichromatic, for instance. Changizi isn’t talking about the existence of colours in general, though, he’s claiming ours are calibrated differently then other animals. So the simple fact that other primates have colour vision doesn’t actually say much about his theory.

    Our vision being bad at the sort of signals he’s talking about is a more serious objection.

  12. MadRat wrote:
    I always figured we have our amazing color vision (second in the animal kingdom only to parrots)

    Where’d you hear that? I thought most birds had better color vision then us…this page says most birds are tetrachromats, meaning they have four color receptors to our three (our retinas only have receptors for red, green, blue, which is why monitors which only emit combinations of those colors seem to show nearly the full range of shades that we perceive in life), so they should see more colors than we do (this page adds that virtually all reptiles are tetrachromats too, and that ‘some birds, such as the pigeon, and possibly the Black-Capped Chickadee, are even pentachromatic, with 5 different types of cone cells’). primates do have uniquely good color vision among mammals, the theory I’ve heard there is that mammals lost the good color vision of their ancestors they were nocturnal throughout much or all of the dinosaur age (see here for a discussion of the genetic evidence that the ancestral mammals had 3-color vision which was later lost in most branches).

    because it helps gathering food, but more importantly identifying camouflaged prey or predators.

    If identifying camouflaged prey or predators was the key, then why is the color vision of all other mammals so bad? The “gathering food” theory at least offers an explanation for why primates would be different–they eat a lot of fruit, which are easy to pick out against a green background if you can see in color.

  13. This hypothesis is easy to disprove; we share our tricolor vision with the other apes, and even some old world monkeys IIRC. None of those are naked.

    All of us need to be able to spot ripe fruits, and none are nocturnal, unlike our common ancestors from back in the time of dinos (color blindness improves night vision slightly).

  14. Any differences between us and other apes probably boil down to our intelligence and tool-making. I’ve always imagined that the fur loss happened because of an ice age – things got so cold that our fur wasn’t enough. Most creatures would adapt over several generations by selecting for more fur, but we’re clever tool users and invented clothing instead. Soon clothing was part of our culture, so by the time the ice age ended, everyone was used to wearing clothes and nakedness was taboo. Therefore, those with less fur stayed cooler and survived in the heat better. Soon we were nearly furless.

    1. Common misconception about the tool-making. Chimpanzees do it, I know for sure. Others might as well.

      Most of my anthropology undergrad seemed to be a long recitation of “things we thought only humans did and which separated us from the animals…and then we sort of found this thing that did it too, and whoops.”

  15. Maggie, you’re quite correct – chimpanzees and many other animals use tools, but not to the extent we do. When chimps invent clothing, maybe they’ll lose their hair, too.

  16. Also, our senses of smell and hearing are rather poor compared to most of the animals we evolved trying to kill and eat – never mind the ones that were trying to kill and eat us.

    I have to think that avoiding the man-eating beasts played a larger role than did noticing if Bob the Generic Protohuman was horny.

  17. Mark Changizi has a long history of being basically wrong about how vision works. He likes to think it makes him maverick-y and oppressed by the establishment, but it really doesn’t.

    1. On the other hand, It makes taking his class much much more fun. Even if you don’t agree with him he dies give good food for thought.

      @nixar Judging from the paper he wrote up about this – not the TBP stuff – he actually started this study by looking at New World monkeys, and only moved on the humans later.

      also, fwiw, his argument about our colour vision is more to do with the fact that looking at the spectrum, and plotting where our eyes are most sensitive, we see that two of the cones are places very near the wavelengths that change the most when someones blood O2 sat changes.

  18. Wow. Only Caucasians can see colour? Who woulda thunked?

    Without doubt the most amusing hypothesis to explain nakedness I’ve yet come across, but also the least likely to be true. I might have accepted a hypothesis that colour vision was a response to nakedness, something like “as we became hairless due to other evolutionary pressures, our eyes adapted to be able to distinguish subcutaneous blood flow; this is supported by the way different races have different average colour sensitivities, in a way that relates to skin colour, see fig 1” or somesuch. But this? Colour vision as the driving force for nakedness? This isn’t even Sunday Sport worthy, let alone BoingBoing worthy.

    And clearly, given the attempt to link porn to it in the original article, the Sunday Sport is about the level he’s aiming at. And given the last paragraph in the linked post, it looks like it’s all tongue in cheek anyway.

    But if it’s serious? Facts or GTFO.

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