History and geography create differences in genes in humans

New research shows that natural selection may form a slower sequence of human genes than one might expect. Other factors - human migration in one continent and between continents, expansion and narrowing of communities, and abnormal genetic changes - all have a strong effect on variables. genetics in human communities around the world.

The study was conducted by a team of scientists from the Howard Hughes Medical Institute, University of Chicago, University of California and Stanford University. The results are published in PLoS Genetics June 5.

In recent years, gene researchers have identified many genes that help communities adapt to new environments over a period of a few thousand years - a relatively short period of time in evolutionary history. However, the team also found that most genes must go through 50,000 to 100,000 years of natural selection to spread a beneficial trait in a community. According to their analysis, gene variants tend to be replicated worldwide in ways that reflect movement and other aspects of ancient community history.

'We do not think that natural selection is strong enough to completely adjust the adaptation of individual communities to the living environment,' said Jonathan Pritchard, one of the study authors. 'In addition to selection, demographic history - how the communities have moved - also has a strong effect on the spread of variations.'

To find out the frequency of a variation caused by natural selection, Pritchard and colleagues compared the spread of variations in gene sequences that affect protein structure and the spread of local variation. Genetic sequences do not affect protein. Because these neutral parts of the gene sequence seem to be less affected by natural selection, scientists deduce that the variants being studied in these areas reflect the demographic history of the community.

Global allele frequencies and haplotype samples in three genes with positive selective signals.(Photo: Coop G, Pickrell JK, Novembre J, Kudaravalli S, Li J, et al . The Role of Geography in Human Adaptation. PLoS Genetics, 2009; 5 (6): e1000500 DOI: 10.1371 / journal.pgen.1000500 )

The team has discovered that many of the previous gene signals have been identified by the actual selection generated by historical and demographic factors. When the group compared communities closely related, they did not see any major genetic differences. Conversely, if the environment of these communities has great pressures that cause genetic changes, these genetic differences are often very obvious.

Natural selection can still occur in many parts of the gene sequence, Pritchard said. But if there is, selection must cause mild effects on many genes, these small effects combined to alter a biological characteristic. 'We have not enough genetic knowledge of most human traits to be able to pick up relevant variations,' Pritchard said. 'When studying the function of achieving new advances, people will find patterns that are related to selective signals,' said Graham, the lead author of the study. 'This is very important, because then we can calculate what pressures are the causes of each natural selection.'

But even in further study, it is still not possible to know all the processes that lead to the characteristics of people today. Pritchard and Coop suggest that caution should be exercised when trying to relate natural selection to complex features, such as intelligence. 'We have just started to find out which signals of selection are related to this property, so it will be a long time before we can consider the relationship between natural selection and group characteristics. and cultural characteristics. '

Refer:
Coop G, Pickrell JK, Novembre J, Kudaravalli S, Li J, et al.The Role of Geography in Human Adaptation.PLoS Genetics, 2009;5 (6): e1000500 DOI: 10.1371 / journal.pgen.1000500