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How To Build a Human
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This is a very interesting talk by biologist Armand Leroi about human genetics, embryology, and finally race.

Among other things he reminds us, when talking about mutants, that we're all mutants:

One of the really surprising results in recent years, which comes from the comparison of the genomes of different species, is that every newborn child carries three novel deleterious mutations, that is, mutations that its parents didn't have. Not only that, but each child inherits at least some of the mutations that its parents have as well. It's estimated then — and of course this is just an estimate — that every newly conceived person has something like 300 mutations that affect its health for the worse in some fashion.


When I speak of mutations that do somebody harm what I really mean is not so much that they just affect physiological health; what I really mean is they affect the Darwinian fitness, the probability that they will reproduce. It's an evolutionary definition. It's the kind of definition that can encompass an enormous range of impairments, and the kinds of impairments that you see that are caused by mutations are at times of a degree and of a form that you really just cannot conceive of.

One of the things I find interesting about this description is that he refers to all mutations as harmful, which is strange since he's also invoking Darwin. One of the core principles of evolutionary genetics is that while most mutations will have a negative influence on fitness, some small percentage will improve fitness. It's weird that Leroi doesn't even give that idea a passing nod. Oh well.

Anyway, he talks about remains of children, and in some cases adults, who were born with mutations that had very severe effects.

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. Sonic hedgehog is named after a fruit fly gene which when mutated causes bristles to sprout all over the fruit fly larva, hence "hedgehog". When the gene was found in mammals, some wit called it Sonic hedgehog after the video game character. If you get rid of this gene, bad things happen. You lose your arms beneath the elbow and legs beneath the knee. The face collapses in on itself, such that you get a single eye in the middle of the forehead and the rest of the face collapses into a long, trunk-like proboscis. The forebrain, which is normally divided such that we have a left and a right brain—the left and right cerebral hemispheres—is fused into a single unitary structure. Indeed the technical name for this syndrome is called Holoprosencephaly.

Now all this is very horrible, and actually that's just an initial list of things that can go wrong in infants that have no Sonic hedgehog. But what's really interesting about it is that by looking at infants of this sort you can reverse-engineer and ask what Sonic hedgehog does in the embryo. Instantly it tells you that one of the things that Sonic hedgehog does is to keep our eyes apart because if you don't have the gene the face collapses. It also separates the left and and right sides of our brains. And it's needed for the formation of our arms and legs. In fact, it is one of the most ubiquitous and powerful molecules in the making of our bodies.

Grotesque, as he points out, but very valuable to know that this single gene plays such a huge role in embryonic development.

This case was interesting too.

The star at the Mütter Museum at the College of Physicians of Philadelphia is Harry Eastlack, a man who had a disease called Fibrodysplasia Ossificans Progressiva. It's a disorder in which supernumerary bones form. The Mütter Museum has his skeleton, which he donated at the time of his death when he was in his forties. The skeleton is essentially not one man's skeleton—it is, as it were, one skeleton encased in another. What happens in this disorder is that wherever you get a bruise or a wound, instead of normal cells moving in to regenerate the skin and the flesh and heal the wound, bone forms. So every bruise turns to bone. The kids are born relatively normal, but as they go through life bone accretes all over them such that they can no longer move. They become rigid, locked into place. You can cut it away, of course, but as soon as you make an incision, and that incision heals, more bone forms. So it's a vicious circle. We don't know which gene is mutated in this syndrome. But it's almost certainly got something to do with bone morphogenetic protein, a protein that is, as the name suggests, normally involved in making bone in infants. It's just that in most of us this gene switches off. In these people this protein keeps on being produced throughout life, especially when there's a wound. It's another marvelous instance of how a given mutation can tell us something important about how bones are formed. FOP is a very rare disorder, and the reason why the gene hasn't been cloned is because to identify genes, to clone genes, you need to have big pedigrees. At least it helps. But these people just never have children.

Anyway, he goes on to say that by studying mutations we can better understand how we're put together, but that we're actually quite ignorant when it comes to knowledge about racial differences. He says that a lot of this research is not being done because of the racially-charged political nature of it, but says that it does need to be done.

Of course, there will be people who object. There will be people who will say that this is a revival of racial science. Perhaps so. I would argue, however, that even if this is a revival of racial science, we should engage in it for it does not follow that it is a revival of racist science. Indeed, I would argue, that it is just the opposite. How shall I put it? If you want to prove, what most of us believe, that skin colour does not give the measure of a man, that it tells nothing about his abilities or temperament—then surely the best way is to learn about the genetics of skin colour and the genetics of cognitive ability and demonstrate that they have nothing to do with each other? The point is that there will always be people who wish to construct socially unjust theories about racial differences. And though it is true that science can be bent to evil ends, it is more often the case that injustice creeps in through the cracks of our ignorance than anything else. It is to finally close off those cracks that we should be studying the genetic basis of human variety.

I would agree.

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