The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution

There is a physicist’s version which is less obviously vainglorious and which I should mention in passing. This is the ‘anthropic’ notion that the very laws of physics themselves, or the fundamental constants of the universe, are a carefully tuned put-up job, calculated to bring humanity eventually into existence. It is not necessarily founded on vanity. It doesn’t have to mean that the universe was deliberately made in order that we should exist. It need mean only that we are here, and we could not be in a universe that lacked the capability of producing us. As physicists have pointed out, it is no accident that we see stars in our sky, for stars are a necessary part of any universe capable of generating us. Again, this does not imply that stars exist in order to make us. It is just that without stars there would be no atoms heavier than lithium in the periodic table, and a chemistry of only three elements is too impoverished to support life. Seeing is the kind of activity that can go on only in the kind of universe where what you see are stars. (View Highlight)

D. K. Belyaev and his colleagues took captive silver foxes, Vulpes vulpes, and set out systematically to breed for tameness. They succeeded, dramatically. By mating together the tamest individuals of each generation, Belyaev had, within 20 years, produced foxes that behaved like border collies, actively seeking human company and wagging their tails when approached. That is not very surprising, although the speed with which it happened may be. Less expected were the by-products of selection for tameness. These genetically tamed foxes not only behaved like collies, they looked like collies. They grew black-and-white coats, with white face patches and muzzles. (View Highlight)

But molecular taxonomy trumps human insight, and molecular evidence clearly shows that all modern breeds of dog are descended from the grey wolf, Canis lupus. The next closest relatives to dogs (and wolves) are coyotes, and Simien ‘jackals’ (which it now seems should be called Simien wolves). True jackals (golden, side-striped and black-backed jackals) are more distantly related, although they are still placed in the genus Canis. (View Highlight)

In some cases, the story of our own domestication is clearly written in our genes. The classic example, meticulously documented by William Durham in his book Coevolution, is lactose tolerance. Milk is baby food, not ‘intended’ for adults and, originally, not good for them. Lactose, the sugar in milk, requires a particular enzyme, lactase, to digest it. (This terminological convention is worth remembering, by the way. An enzyme’s name will often be constructed by adding ‘-ase’ to the first part of the name of the substance on which it works.) Young mammals switch off the gene that produces lactase after they pass the age of normal weaning. It isn’t that they lack the gene, of course. Genes needed only in childhood are not removed from the genome, not even in butterflies, which must carry large numbers of genes needed only for making caterpillars. But lactase production is switched off in human infants at the age of about four, under the influence of other, controlling genes. Fresh milk makes adults feel ill, with symptoms ranging from flatulence and intestinal cramps to diarrhoea and vomiting. (View Highlight)

Before proceeding, I must clear up a possible confusion over the meaning of the word gene. It can mean lots of things to different people, but the particular confusion that threatens here is the following. Some biologists, especially molecular geneticists, strictly reserve the word gene for a location on a chromosome (‘locus’), and they use the word ‘allele’ for each of the alternative versions of the gene that might sit at that locus. To take an oversimplified example, the gene for eye colour comes in different versions or alleles, including a blue allele and a brown allele. Other biologists, especially the kind to which I belong, who are sometimes called sociobiologists, behavioural ecologists or ethologists, tend to use the word gene to mean the same as allele. When we want a word for the slot in the chromosome which could be filled by any of a set of alleles, we tend to say ‘locus’. People like me are apt to say ‘Imagine a gene for blue eyes, and a rival gene for brown eyes’. Not all molecular geneticists like that, but it is a well-established habit with my kind of biologist and I shall occasionally follow them. (View Highlight)