Want to know more about your genetic roots? Then you are not alone. Around half a million Americans purchase genetic testing kits each year from one of about 40 companies that promise to find distant relatives, or reveal family ties to such famous ancestors as Genghis Khan or Thomas Jefferson.
Most tests trace your maternal and paternal lines, by examining genetic markers on the mitochondrial DNA, which is passed from mother to child, or on the Y chromosome, passed from father to son. Like the roots of a tree, however, your genetic roots keep branching the deeper you look: tracing just two of these lines tells you nothing about all the others.
So a handful of companies will also analyse the 22 pairs of non-sex chromosomes and report what percentage of an individual鈥檚 genome is of European, African, Native American or Asian origin. These analyses are more controversial, says Spencer Wells, who leads , whose ancestry-testing service helps fund its effort to trace ancient migrations.
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It鈥檚 not always clear what it means to tell someone that their DNA is, say, 66 per cent European and 33 per cent African, Wells points out. For someone from Israel or Lebanon, these percentages reflect millennia of mixing. But in a Brazilian, it might tell them something about recent family history.
As we learn more about the genetic make-up of different branches of humanity, through efforts like the , these ancestry tests should become more informative and reliable. For now, though, the results should be treated with caution. The accuracy of many tests cannot be verified, and supposed connections to famous individuals or particular migrations are only interpretations based on the latest science, a recent paper concluded ().
Read more: Unknown genome: What we still don鈥檛 know about our DNA
Evolution鈥檚 secrets
You may be part Neanderthal 鈥� one of the many revelations about us emerging from genome sequencing. 鈥淚t is revolutionising the way that we think about the evolution of humans,鈥� says anthropologist John Hawks of the University of Wisconsin-Madison.
Genomes provide a huge amount of information compared with fossils alone. The DNA in every organism is the latest link in an unbroken chain stretching back more than 3 billion years to the very dawn of life, changing a little with each generation. So by comparing the genomes of different people and animals 鈥� sometimes long-dead ones 鈥� it鈥檚 possible to work out what changed, and even when and where.
Genome studies suggest, for instance, that some modern humans interbred not only with Neanderthals but also with other Homo species after they left Africa. And far from slowing down recently, human evolution began accelerating around 40,000 years ago and has been , Hawks has shown.
The reason? A bigger population produces more potentially beneficial mutations, while the rise of farming and city living are exerting novel selective pressures. For example, gene variants that allow some adults to digest milk first appeared 7000 years ago, around the time that cattle were domesticated.
It is possible to trace not just variants but also when and how genes first evolved. For example, the syncytin gene, which plays a crucial role in pregnancy, was originally acquired from a virus 鈥� one of many examples of gene transfer between different species.
At the moment, we don鈥檛 understand the significance of the vast majority of the differences between genomes. Over the coming decades, however, we will be able to pinpoint the precise mutations that turned our tree-living ancestor into a naked, talking, upright-walking and somewhat smarter ape.
