Natural selection is reported to have been responsible for much of the DNA among human beings during the course of the past 50,000 years. The tendency of human beings to live in settlements and cultivate fields can also be traced to this natural selection process.
One way to look for genes that have recently been changed by natural selection is to study mutations called single-nucleotide polymorphisms (SNPs) - single-letter differences in the genetic code, according to the study. The idea is to look for pairs of SNPs that occur together more often than would be expected from the chance genetic reshuffling that inevitably happens down the generations.
Such co-relations were known as linkage disequilibrium, and could occur when natural selection favored a particular variant of a gene causing the SNPs nearby to be selected as well.
For their study, Robert Moyzis along with colleagues from the University of California, searched for instances of linkage disequilibrium in a collection of 1.6 million SNPs scattered across all the human chromosomes. Then, they looked carefully at the instances to distinguish the consequences of natural selection from other phenomena, such as random inversions of chunks of DNA, which can disrupt normal genetic reshuffling.
The findings published in the Proceedings of the National Academy of Sciences revealed that around 1,800 genes, or roughly 7% of the total in the human genome had changed under the influence of natural selection within the past 50,000 years.
A second analysis using a second SNP database also gave similar results. Researchers opine that humans may have 'domesticated' themselves with the emergence of modern civilization, much on the lines of domestication of food grains when they started cultivation.
"One of the major things that has happened in the last 50,000 years is the development of culture. By so radically and rapidly changing our environment through our culture, we've put new kinds of selection [pressures] on ourselves," New Scientist quoted Prof. Moyzis as saying.