DNA. image ichromatography.com
The Yoruba of West Africa have been exposed, historically, to the dry conditions of the Sahel on the edge of the Sahara desert. To find out whether they had evolved to cope, Andres Moreno at Stanford University in California and colleagues looked at the variation of a gene known to be involved in water retention in the kidney, called FOXI1, in DNA samples from 20 Europeans, 20 east Asians and 20 Yoruba.
(BMC Evolutionary Biology, DOI: 10.1186/1471-2148-10-267).
The team found that 85 per cent of the Yoruba had an identical sequence of genetic information that was longer than it would have been if it was produced by random recombination and genetic shuffling. Instead, they suggest that it had been naturally selected.The length of the genetic signature suggests that the change occurred in the last 10,000 to 20,000 years, which could have coincided with the initial stages of the desertification of the Sahara. They also analysed a region of the gene in 971 samples from 39 human populations around the world, including the Yoruba, and found that the same genetic sequence was found at higher frequencies in lower latitudes. Since lower latitudes are more likely to be regions of water-stress, this suggests that the selection pressure was climate-related, says Moreno.
Humans are still evolving: the evidence
“Over the long term, if the Earth keeps warming, I would not be surprised to see genetic shifts,” says anthropological geneticist Anne Stone at Arizona State University in Tempe.
While we may look like the finished article, there is plenty of evidence that humans are still evolving. John Hawks at the University of Wisconsin-Madison even argues that population explosions and rapidly changing lifestyles are causing humans to evolve faster now than ever before. Evidence includes:
- The human brain is still evolving. Bruce Lahn at the University of Chicago and colleagues identified two genes involved in regulating brain size that have been subject to recent natural selection.
- The ability to digest milk only evolved in the last 7000 years, says Mark Thomas of University College London.
- Genes for early childbirth will be naturally selected for over time, according to a study by Ian Owen’s team at Imperial College London.
- It took just 3000 years for Tibetans to adapt to life at high altitudes, a record-breaking rate, says Rasmus Nielsen’s team at the University of California, Berkeley.
The k2p blog 