Australasian Science: Australia's authority on science since 1938

Polygyny History Found in Non-Coding DNA

By Stephen Luntz

If you want to know about certain aspects of human history you need to avoid looking at the genes, argues Dr Murray Cox, a computational biologist at Massey University’s Institute of Biosciences. Instead it is important to look at non-coding DNA that is located well away from the genes, as data from genes can pollute the sample.

Cox was part of a team seeking evidence for polygyny – the practice of men having multiple wives. He compared patterns in X chromosomes, which spend the majority of their history in women, with those of the non-sex chromosomes, which spend equal time in men and women. The Y chromosome is too small to offer as many data points as Cox was seeking.

From these data Cox found evidence that small numbers of men frequently passed on their genes, indicating that polygyny was occurring. “We sequenced 40 regions of the human genome that were a long way from genes,” Cox says. “We found evidence of polygyny in all six global populations that we studied.”

However, other researchers found no such evidence. The problem, Cox claims, is that the others used the entire genome, including sections that were under pressure from natural selection. “For example, the gene for haemoglobin carries oxygen in the blood, and it’s a big target for malaria,” says Cox. “If there is a mutation there that helps resist malaria, that new variant is going to increase in the population.”

Furthermore, when a particular gene proves successful, any non-coding DNA nearby can hitch a ride to achieve similar success.

So if you want to see what is happening independent of evolutionary pressures you need to look at sections of DNA that are well away from genes, particularly if they are subject to strong selection pressures. This has been known to evolutionary biologists for some time, but “in the last few years you have had the second-generation sequencing technology that makes it so easy to sequence lots of the genome,” says Cox.

Moreover, in recent years a lot of people with a biomedical background have started studying changes in molecular biology. “They tend to think it’s best to throw as much data at a problem as possible,” Cox says.

However, combining data from sections under evolutionary pressure and portions that are not can combine contradictory patterns, making it harder, not easier, to work out what is going on.

Cox admits that what the genetic record reveals is not necessarily official social relationships. “We do find some evidence from societies where older men have multiple wives there is a lot of out-of-marriage sex occurring. However, over time we still see a few men having more than their share of women.”