Genes, Geography and Culture

The science bug bit me early in life. As a young schoolboy I was fascinated to read the exploits of explorers and collectors. Charles Darwin’s amazing adventures were stirring stuff to a teenager.

The other day I was thinking about all those books that I read after I spotted an interesting article in the Daily Telegraph by Professor Steve Jones, who is a geneticist at University College London, and someone who always makes you think.

Bob Geldof – he of the Boomtown Rats and Live Aid fame – has set up an ambitious project to map cultural differences around the globe before the peoples of the world sacrifice their cultural individuality on the altar of Western consumerism, blue jeans and cell phones.

Anyone who travels as much as I do cannot help but be dismayed at the cultural homogenization that’s happened over the last 25 years. A bit jet lagged, I once woke up in a hotel in the wee small hours and called the front desk to ask which country I was in. I had been in seven in the last two days and there were no clues as to my location when the chauffeur dropped me off just before midnight. It turned out to be Switzerland and the man at the desk told me that it was a common question.

Although I lament the loss of cultural identity, it is not all bad. But it raises some very interesting questions.

While Bob is recording vanishing cultures, geneticists are trying to establish which behavior is determined by DNA and which by our environment.

Steve Jones was meditating on the question of whether local changes in customs inborn or learnt. My schoolboy hero Darwin was also interested in that question and set out to discover whether expressions of fear or joy varied from place to place. The idea was that they might if they were passed on culturally rather than genetically. He corresponded widely on the subject and Steve reminded me of something that I had not read in 30 years:

“Mr. B F Hartshorne… states in the most positive manner that the Weddas of Ceylon never laugh. Every conceivable incitive to laughter was used in vain. When asked whether they ever laughed, they replied: ‘No, what is there to laugh at?”

Darwin finally concluded that expressions of happiness or anger were universal. They had, he thought, evolved, because he fancied that he could detect hints of human laughter in the grin of a tickled chimpanzee.

Some behaviors have a genetic basis. The absence of cheese and milk from Chinese cuisine is normally attributed to the few cows in the country, or the influence of traditional Taoist notions of what items may appear in the same space. But it may have just as much to do with the high rates of lactose intolerance amongst Chinese populations. The Scots have a high frequency of a gene that makes it easier for them to digest cows’ milk, so milk – sometimes cleverly disguised – seems to appear on almost every Scottish menu.

There is an interesting sidebar here. A recent study that analyzed DNA in Neolithic human remains seems to have uncovered the first direct evidence that modern humans have evolved changes in response to natural selection.

According to a new analysis of fossilized bone samples, as recently as 7000 years ago, Europeans were unable to digest milk. Today more than 90% of the Northern European population can. It is most likely that Europeans incurred a rapid change in their genetic make-up because it held an evolutionary advantage for them to be able to digest milk.

Lactose is a sugar in milk, and around the world the majority of humans lose the ability to digest it before reaching adulthood. This is because their gene for the enzyme lactase, that is responsible for breaking down lactose, is switched off by late adolescence. However, over 90% of northern Europeans have a version of the lactase gene that remains active throughout life, enabling them to continue drinking milk as adults. This genetic change appears to have happened around 7,000 years ago and spread rapidly. In the climatic conditions of the time, milk drinking could have conferred a huge survival advantage: unlike water, milk in usually uncontaminated by parasites, and is available year round, unlike seasonal crops. Milk also contains vitamin D and calcium, and in the dim sunlight of Northern Europe, where people may not be able to make enough vitamin D in their bodies, making calcium absorption difficult. Milk would have solved both problems.

So what we might be seeing here is an environmental factor changing gene expression, which in turn has a social and cultural outcome.

Steve Jones’ article talks about some other cultural differences that may have genetic roots. One very recent study purports to show that the number of sexual partners of American male (but not female) college students is related to variation in a gene called dopamine transporter gene (DAT1). The gene codes for a dopamine transporter protein that limits the level and duration of dopamine receptor activation. It is a strong candidate gene for reward-seeking behavior. Dopamine is known to be involved in the reward or “salience” systems of the brain and is known to influence sexual behavior in mice.

The DAT1 gene comes in two distinct forms. Young men with a single or double copy of one of the variants have, it is claimed, twice as many sexual partners on average as do those with a double hit of the different and less common form of the gene. The latter group, about one young man in 10, are far less romantically daring than average. They are also less likely to be involved in drug abuse or to get in trouble with the law. Research like this is complex. To quote Gregory House, “People lie.” And when it comes to doing research on sexual behavior they lie a lot. And it is a fool’s game to try and reduce human behavior to a single gene. I am sure that if you think about it for a moment, you can come up with at least a dozen reasons why people are likely to have more sexual partners.

Levels of promiscuity vary greatly from place to place. There has been a myth circulating that the AIDS pandemic in Africa is caused by promiscuity. In fact there is less promiscuity in Africa than in the West. It is no surprise that young people less sexually active in Bangladesh than in Britain. For years now, anthropologists have speculated about what lies behind these variations, from the wild and socially sanctioned polygamy of a few males in certain ancient – and some not so ancient societies to the modern Western practice of serial (and approximate) monogamy. Recently researchers have begun to ask whether the differences might be due to genetics rather than the ownership of land or cattle, or social or religious mores.

The American DAT1 study shows that although DNA might have a strong effect on the behavior of individual men, it is unlikely to be responsible for cultural differences in sexual behavior. The students in the study were classified as of European, Black, and Asian or Hispanic origin. There are problems about racial classification: few are clear-cut. We are most of us far more mixed than some people would like to believe. The overall frequencies of the two variants were roughly the same within each ethnic group; and within each seemed to have the same effect. The Asian Americans, though, had fewer than half as many partners compared with the others. Social differences, that were most likely imported by their families from the sexually restrained populations of their native lands, overwhelmed any effects of the DNA.

For anyone interested in the complex interactions of genes, the environment, the psyche and culture, this study is yet another nail in the coffin of genetic determinism: that you are the victim of your genes.

Most mice and chimpanzees behave in much the same way from place to place. Yes, there are some subtle differences here and there, but as a general rule, and English mouse and a Chinese mouse will behave in much the same way. But humans show enormous cultural variation. But here is the paradox: at the genetic level we are the most boring of creatures. Yes, there is some genetic variation form place to place, and certain genes are more active, depending on environmental and cultural factors. Just think milk drinking and skin color. Human social diversity is matched by genetic homogeneity: the overall DNA difference between an American and a Chinese is less than that between two groups of chimpanzees living 100 miles apart in Africa.

Though our cultures have evolved over the centuries, it an evolution of mind rather than genes.