Steve Jones - The Language of the Genes

Einstein once said that 'God does not play dice.' He was wrong: for genes, God does. What number comes up has nothing to do with the DNA involved. That raises an almost theological issue. Is it their own fault that genes, and those who carry them, are damned — or do they perish at random because of simple bad luck? ".

Such evolution by accident is known as genetic drift. The process has been important in our own past. Homo sapiens was until not long ago a rare species that lived in small bands. Until a few tens of thousands of years before the present there were no more people worldwide than live in London today. The few tribal peoples to have survived hint at what society was like.

Until the 1970s, when their lives were destroyed by gold-miners and loggers, about ten thousand Yanomamo Indians lived in a hundred scattered villages in the rainforests of southern Venezuela and northern Brazil. They called themselves 'the fierce people', with good reason.

About a third of all male deaths were due to violence, often in battles between the villages and, the Yanomamo believed, many more to malevolent magic.

Their society was not robust enough to allow groups of more than eighty to a hundred people, including around a dozen young adult males, to stay together. Any larger band tended to split. The splinter group moved away to found a village somewhere else. As a result, the Y.inomamo existed for their whole history (which stretches back in some form to the earliest Americans twelve thousand and more years ago) as a series of small communities in constant conflict.

Most hunter-gatherers may have lived like this. The ancient Siberians who hunted mammoths made houses from their bones. The size of their bony villages suggests that each group, like today's Yanomamo, consisted of a few score people. One odd fact about modern society may also be a hint about the size of ancient groups. Most team efforts involve about the same number of individuals. There are nine members of the US Supreme Court, eleven on a football team, twelve on a jury — and Jesus had twelve disciples. Each Yanomamo band has, curiously enough, about a dozen healthy adult males. Is the difficulty of reaching consensus in a larger group a relic of earlier times? Most people can identify about twelve others whose death would cause them anguish. Aristotle himself pointed out that it is impossible to love more than a few. Could this be a clue (albeit a feeble one) about the size of ancient communities?

Just as for surnames, random genetic change takes place more easily in small populations, when few people bear a particular gene. Then, all or most of the carriers may, by chance, fail to transmit it. In a larger group, a variant may be rare but will be borne by enough people to ensure that at least one will pass it on.

Strange things befall genes in small populations. Again, surnames show what can happen. Their evolution is easy to study, as it needs no more than a telephone book, and names: ire preserved for centuries in marriage records. The world has about a million surnames. Those in China are the oldest and date back to the Han dynasty two thousand years ago. In contrast, Japanese surnames go back only a century or so, when they were ascribed by order of the authorities. Various complications face those who study them. For example, in many places the same name (like my own, Jones, which means 'son of John') appeared independently many times. In some societies, such as those of Spain and Russia, the system breaks down as children take the name of their father and the 'surname' changes each generation. The same was once true in Wales. A boy would take the name of his father and more distant ancestors, each prefixed by the term *ap\ or 'son of; and — the more the names, the more respected the family. Remnants of the system exist in modern Welsh surnames such as Pugh (son of Hugh), Price (son of Rhys) and Parry (son of Harry). In most places this practice has almost gone.

The telephone book in a long-settled part of the world (such as the mountainous country around Berne) shows that villages just a few miles apart each have a distinct set of names, with, in some villages, almost everyone a bearer of the same one. Within each isolated hamlet there has been an accidental loss of names as, by chance and over the years, some men have had no sons. Because the effect is random, different surnames have taken over in each place. The process may be helped by each village having been founded by a group which had, again by chance, its own characteristic set of last names. It is not the case that within a village one family label is somehow better than the others. Instead, its prevalence reflects the errors of history.

The genes of isolated populations are much the same.

Adjacent Yanomamo (and even Alpine) villages have rather different frequencies of blood groups and other variants. In Alpine villages, blood group frequencies diverge to just the extent predicted from what marriage records say about their size since they were founded. They have evolved by accident.

In large modern cities such as Berne the picture is quite different. The phone book contains thousands of names, none of which is particularly common. Again, the rules of chance and time are at work. Cities contain so many people that it is unlikely that any name, or any gene, will go extinct just because its few carriers fail to pass it on. Such places attract immigrants, so that new names (with their associated genes) come in all the time and the population becomes more diverse. A simple but effective way to measure how distinct a community might be is to count the number of surnames in relation to the number of people. If more or less everyone has a different label then the community is open to migration from many places and is, in effect, so big that accident is unimportant. A glance at the New York telephone directory compared to that of, say, Oslo shows at once that the two have had different histories. The USA has a higher proportion of all global names than anywhere else. That reflects its chronicle of immigration from all over the world.

Shared names mean shared ancestors which in turn means shared DNA. A population in which many people carry the same gene (or the same surname) because they have inherited it from a common ancestor is said to be inbred. To some extent we are all inbred as we are all to some degree related. Everyone has two parents, four grandparents and so on. If all were unrelated, the number of ancestors would double each generation to give an absurd number of ancestors within a few centuries. In fact, related people married, and the lines of descent have merged and blended. As a result we all have many ancestors in common.

Pcrh.ips tlu- most inbred individual ever recorded was,m aristocrat, I Jropjtra-Bcrenikc HI, aunt of the Cleopatra enamoured of Anthony. She may have had identical copies of lull her genes because they descended from a single ancestor. As the ancient Egyptians saw the pharaohs as their gods' posterity they were anxious to keep the deities' blood-line as pure as possible with mating among relatives (sometimes, even, between brother and sister). The story is confused by difficulties in reading the hieroglyphs showing degrees of pharaonic relatedness.

Levels of inbreeding vary greatly from place to place. The incidence of marriages between people with the same name is quite a good indicator. This was noticed by George Darwin, son of the more famous Charles (who married his own cousin). He estimated from surnames that the proportion of cousin marriages (the closest legal form of inbreeding) among British aristocrats, by definition a small and exclusive group, was about four and a half per cent — more than twice that in the general population of his time. The pattern of family names shows that the British population as a whole is, on the average, more outbred than much of the rest of Europe. Even in remote and rural East Anglia, just one in fifty of those present at the end of the eighteenth century had been there in the seventeenth, evidence how much movement there had been in comparison to Switzerland or Italy.