Human Variety
March 29, 2005 4:58 AM   Subscribe

The Nature of Normal Human Variety A talk with Dr. Armand Leroi (his website). "Almost uniquely among modern scientific problems [the problem of normal human variety] is a problem that we can apprehend as we walk down the street. We live in an age now where the deepest scientific problems are buried away from our immediate perception. They concern the origin of the universe. They concern the relationships of subatomic particles. They concern the nature and structure of the human genome. Nobody can see these things without large bits of expensive equipment. But when I consider the problem of human variety I feel as Aristotle must have felt when he first walked down to the shore at Lesvos for the first time. The world is new again." (via Arts & Letters Daily)
posted by Kattullus (17 comments total)
This is an interesting article, but long, so I have not finished it. Two things struck me.

1) I've been reading a book about dogs, which makes the point that dogs are all one species, that the phenotypic expression across breeds, which seems impossibly broad, is all contained within the genome for one species.

2) Leroi seems to be interested in phenotypic expression as an indication of the fitness of the genome. This doesn't really make sense to me. I have no doubt that there are mutations that have an effect on the body which also have an effect on health (the sonic hedgehog mutation he talks about), but it seems very strange to suggest, as he does, that fewer mutations in general leads to more beauty. This paragraph about mutations,

Not everybody has 300. Some people have more, some people have fewer. If this is true—and statistically it must be true — then someone in the world has the fewest mutations of all. Someone in the world is the least mutant human of all. Indeed, we can actually calculate, making some assumptions about the shape of the distribution, how many mutations that person has — and it turns out to be 191 versus the average of 300. This, to my mind, is surprisingly many. I would suggest that if we could find that person, he or she would be a good candidate for being the most beautiful person in the world. At least she would be, assuming she did not grow up in some impoverished underdeveloped nation. Which, statistically, she will have done since most people do.,

seems very much as if it confuses (almost equates) the genotype and the phenotype without presenting any reasoning for why it's acceptable to do so. Perhaps there will be more in the article which I have not read yet.
posted by OmieWise at 5:32 AM on March 29, 2005

Armand Leroi has written a book, Mutants, which is well worth reading if you are interested in human genetics.
posted by aeschenkarnos at 5:59 AM on March 29, 2005

It's difficult to make the case that beauty correlates directly with genetic "purity." It likely does to some degree, but it is undeniable that beauty is also partially socially constructed. Consider our modern love for impossibly thin, near-hairless humans.
posted by mek at 6:10 AM on March 29, 2005

mek writes " It's difficult to make the case that beauty correlates directly with genetic 'purity.'"

Well, and there's the rub, right? Leroi says a bunch of interesting things, but there does seem to be a 'purity is good' argument behind a lot of what he says despite the fact that he admits that there is no wild-type human against which to compare the pure ones. And if there were such a wild-type, it seems likely it would not look like Nicole Kidman.
posted by OmieWise at 6:38 AM on March 29, 2005

I don't get the focus on human variation. What does it have to be so special? Most domestic species (plant and animal ones) have genomes that are incredibly plastic. Humans have used this for millenia and this is not exactly an ignored topic in contemporary science. The global mechanisms are known. Studying the mechanism of skin colour in humans won't discover anything more innovative that another bunch of genes in interaction, just enough for some folks to start selling DNA-based race identification kits (is your neighbour a Hutu? Or a Tutsi in disguise?).

And compared to the variations that occur in, say, dogs, cattle and corn species, normal human variations are barely noticeable. If we had chihuahua-sized people, patterned people, highland-cattle-haired people, fat-tailed people etc. this could be great fun but right now, human variations are less than impressive.
posted by elgilito at 7:12 AM on March 29, 2005

Leroi always gave me the impression that he was at night school learning how to be a Bond villain. A tall, imposing, fabulously educated man with a distinctive face, indistinct accent (garnered from Holland, New Zealand, South Africa and Canada) and an inclination towards narcissism. Most importantly he's strikingly bald.

If he's still pressing on with this genetics malarkey, perhaps the classes are not progressing as he would have liked.
Good luck Armand!
posted by NinjaPirate at 7:12 AM on March 29, 2005

Quick question: what are the "right" 191 mutations? If there were only 300 (I see that's his average, but let's say it for the sake of argument), then there are rather a lot (300!/191!*109!) of different combinations. I'd try to give a useful number for the above, but google calculator only plays nice with factorials up to 170.

I recognize that genetics probably isn't as simple as a game of Lotto191/300 (joke reference for the Canadians in the cheap seats), but still, making a random statement like that is either dumb or dangerous, take your pick.

Oh, and 170! is 7.25741562 × 10306 in case you were interested.
posted by lowlife at 7:16 AM on March 29, 2005

"This is because we have such an extraordinary amount of natural variation in our species. If you go around the world you see tall people, short people, red-haired people, brown-haired people, people with curly hair, people with no hair, and so on. Given all this variation, what exactly, and who exactly, is a mutant?"

This guy is speaking out of his ass. As he says, "Of course, I myself don't actually work on humans." He is making a variety of assumptions about human beings that are A) certainly not rigorous, and B) essential to his argument about human beings. His argument suffers from an unknowing anthropocentricism.

My quote above is intended to point out his chief—and very questionable—assumption: that there is a lot of "variety" in the human phenotype. It hinges on the definition of "variety". I don't see a rigorous, quantified definition; all I see is a commonsensical, intuitive definition. This is particularly dangerous when the subject is human beings. I'll get to that in a moment.

George Williams, probably the most important person to shape contemporary evolution theory, talks about several such fallacies at the beginning of his seminal 1966 book, "Adaptation and Natural Selection" In the passage which follows, he talks about the idea of the "higher animals" being "more complex" [p.42]:
It is often stated or implied that animals of the Recent epoch are morphologically more complex than those of the Paleozoic era, but I am not aware of any objective and unbiased documentation of this point. Is man really more complex structurally than his piscine progenitor of Devonian time? We can certainly describe a more complex series of evolutionary changes in, for example, the human skull than in the Devonian fish skull, but this is at least partly attributable to our ignorance of pre-Devonian chordates. The Devonian-to-Recent lineage of man is mainly a history of changing arrangements and losses of parts, in the skull and elsewhere. Real additions are not a conspicuous part of the story. Mechanically the human skull is exceedingly simple in its working compared to most fish skulls. Even in the Devonian period there were fishes, e.g., Rhizodopsis, with skulls made up of large numbers of precisely articulating bony parts that formed a complex mechanical system. I believe that it would be difficult to document objectively the general conclusion that Recent animals are structurally more complex than known Paleozoic members of the same taxa.

Man must, of course, have had morphologically simple metazoan ancestors somewhere in his history, if not in the Devonian period, then before. The question of the relative complexity of man and fish arises in connection with the popular pair of assumptions that (1) evolutionary progress from lower to higher organisms consists of increasing structural complexity; (2) the change from fish to mammal exemplified such progress. In other respects, such as intergumentary histology, the average fish is much more complex than any mammal. What the verdict after a complete and objective comparison would be is uncertain.
Williams goes on to talk about life-cycle development and points out that the morphological complexity of an organism is more than the structural complexity visible at any one time. The larger significance of this discussion is that it points to the popular anthropocentric fallacy and the teleological fallacy that evolution is a progression from protozoa to homo sapiens. On what objective basis can you rigorously argue that Man is the "most evolved" species? That's rubbish.

Leroi is making a similar unwarranted assumption as the "complexity" assumption—he's assuming that his intuitive sense of human phenotypic variety leads him to the correct conclusion that it is comparatively large. But how to quantify "variety"? Furthermore, our intuitive sense of human variety is very suspect in this case because there's every reason to believe (and, in fact, we know) that humans are extremely sensitive to discerning morphological differences between other humans. That is to say, if there were some cross-species absolute standard for "variation", human beings would perceive our variation to be relatively greater than it really is. I'd assert that we actually look very much alike and an ET would have a lot of trouble telling us apart.

Where Leroi goes wrong in his speculations here is that he departs from his field of expertise without recognizing his incompetency elsewhere. He would need to have a rigorous definition of human "variety" and "beauty"—which would involve work far afield from his expertise—in order to authoritatively construct the arguments that he's constructing.

In fact, there's good reason to guess that he's got it backwards: there's not an "extraordinary variation" (clearly meaning "great") in the human phenotype, there's less. This is because there's a persuasive argument that says that variation correlates positively to the number of chromosomes. Consider the (apparent) large variation in dog breeds: there is everything from the very small and hairless chihuahua to the shaggy sheep dog to the great dane. Contrast this to the variation in cat breeds. Cats don't seem to vary as much. Dogs have 78 chromosomes, cats have 38. And humans? As you know, we have 24.
posted by Ethereal Bligh at 7:43 AM on March 29, 2005

Ethereal Bligh : " In fact, there's good reason to guess that he's got it backwards: there's not an 'extraordinary variation' (clearly meaning 'great') in the human phenotype, there's less. ...Consider the (apparent) large variation in dog breeds: there is everything from the very small and hairless chihuahua to the shaggy sheep dog to the great dane."

This is pretty much exactly my (completely uneducated and unsubstantiated) layman's view. Compare humans to dogs, and it seems insane to say that there's an astounding, or even impressive or notable, amount of variety of phenotypes. People basically look alike, and it's only the fact that we are attuned to our own minor differences that we can tell the difference between people. Ask any redneck: all Asians look alike. Ask any countryside Japanese: all white folks look alike. The fact of the matter is that humans have a range of heights, weights, hair color, and 2 or 3 notable skin tones, and after that are all pretty identical.

(er, perhaps "fact of the matter" was the wrong expression)
posted by Bugbread at 8:02 AM on March 29, 2005

I seriously thought it was all some obscure science joke by the time I read this:

Take, for instance, these children with a single eye in the middle of their foreheads. The syndrome is called, appropriately, Cyclopia. Cyclopia is caused by a deficiency in a gene called Sonic hedgehog.

Then after understanding that the Sega mascot came first, this still struck me as hilarious/frightening/terrible:

For example, just as having too little Sonic hedgehog causes the face to collapse in upon itself, having too much causes it to expand.
posted by themadjuggler at 8:14 AM on March 29, 2005

I think the point of the article is, it is politically incorrect to talk about, much less study, racial genetics, and that we need to "grow up" and start looking at it.

I agree. But it is still dangerous, humans have not evolved or "grown up" much over the past few generations, it would be foolhardy to embark on such a venture without, dare I say, ethics.
posted by stbalbach at 9:39 AM on March 29, 2005

"racial genetics"

There is no such thing. Race may be a meaningful term in some sociological contexts, but it is not a biologically meaningful term and it particularly is not a meaningful genetic term. So it should remain "incorrect" to talk about because it is...incorrect.
posted by Ethereal Bligh at 10:45 AM on March 29, 2005

Ethereal Bligh,

From what I gather, whether or not it is a useful term is unknown because of fears of giving racists something to feed on. So if there was any usefulness, it would be countered by misuse.
posted by john at 11:37 AM on March 29, 2005


From what I gather, it is known to be a meaningless term. There's a bunch more discussion in this thread, which, considering it involves EB and myself, is pretty much the same thing you'd get as if we discussed it now.
posted by Bugbread at 11:47 AM on March 29, 2005

Ah thanks,

Good stuff all. It's not an easy topic especially when considering that on the genetics side any human feature can be expressed by multiple genes. I think that such research is more trouble than it's worth without regard to the viability of the race label.
posted by john at 12:05 PM on March 29, 2005

Omniwise And if there were such a wild-type, it seems likely it would not look like Nicole Kidman.

I say Elizabeth Hurley - remember that BBC show about Phi/the golden mean?
posted by PurplePorpoise at 12:27 PM on March 29, 2005

re: no such thing as "racial genetics"

fwiw :D

but i take OmieWise's and Ethereal Bligh's points that 'race' (breed?) is ill-defined phenotypically and genetically (altho, according to the stanford study, not entirely meaningless!) and that number of chromosomes makes for a better point of reference (for the species née one race :)

[more here & here]

posted by kliuless at 8:37 PM on March 29, 2005

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