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Human recipes
« on: 2004-08-09 21:01:26 » |
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Human recipes
by Matt Ridley
Prospect Magazine, July 2004
http://www.prospect-magazine.co.uk/ArticleView.asp?P_Article=12697
Humans have no more genes than mice, but don't feel small
<snip>
This leads to the most humiliating of all the discoveries consequent on genome reading. Human beings do not just have the same number of genes as a mouse; to all intents they have the same genes. But because they have slightly different switches on many of the genes, they can use them to make very different bodies. Coincidentally, this is similar to the way writers work. They use the same set of words in a different order to make different books. Even the numbers are similar. Shakespeare, for example, used 31,534 different words, though 14,376 appeared only once in his works. Omitting proper names, and allowing for different inflections ("know" and "knows"), most of the 4,686 words in Hamlet appear also in Othello and vice versa. The ten commonest words in Hamlet are the, and, to, if, I, you, my, a, in and it. The ten commonest words in Othello are I, and, the, to, you, of, my, a, that and in. The ten commonest words in King Lear are the, and, I, to, you, of, my, a, that and in.
A genome is constructed, like a Shakespeare play, from a few thousand interchangeable parts. The ten most commonly expressed genes in our bodies are also likely to be the ten most commonly expressed genes in a chimpanzee body, and many of them will also feature in the average fish.
It follows that it may soon be possible to identify the basic set of genes used by all mammals, just as it is possible to define Shakespeare's vocabulary. There then begins the formidable task of working out how slight differences in the place, time and volume of expression of those genes make one species unlike another. One example: the existence of a 400-letter phrase of repetitious text in the promoter of the vasopressin receptor gene of a prairie vole turns the rodent monogamous. That phrase alters the location of expression of the gene in the rodent's brain, making it active in the ventral pallidum, which contains a dopamine system that is responsible for addictive behaviour. A prairie vole therefore becomes "socially addicted" to its mate following sex, which is a grand way of saying it falls in love. A montane vole, lacking the 400-letter phrase, does not.
Human beings also have a repetitious phrase in this same region of the genome, though it is shorter than in prairie voles. As of this writing, the equivalent region of the chimpanzee genome has not yet been looked at. I predict it will be shorter than the human one, because humans commonly form long-term pair bonds, while chimpanzees commonly do not.
Multiply this example 10,000 or 20,000 times and you have explained how human nature differs from chimpanzee nature or vole nature. Make no mistake: this is theoretically possible. But in practice, it is an infinite task, because no sooner have you identified the "human" version than you will have to start defining how each individual slightly differs from it, and how each of those differences will cause you to recalculate the effect of the 25,000 other genes in the new context, and then the effect of those changes, and so on ad infinitum. As usual, far from closing mysteries, science opens new ones.
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