Pygmies are known throughout the world for its low growth: increase in adult male has an average of 150 cm
For a long time the reason why this nation has such a structure of the body, was not clear. Scientists have proposed various theories based on natural selection - some believe the size of pygmies reduce the amount of food required, it helps to better endure the hot climate and the effect on the process of puberty, which occurs at an earlier age.
A new study of West African Pygmies in Cameroon, conducted by geneticists at the University of Pennsylvania, identifies genes that may be responsible for a relatively small growth of pygmies.
The work also provides evidence based on genetic signatures of natural selection, which explains why the evolution of these peoples awarded short, which is responsible for transformation and hormonal regulators of the immune system.
"Among the scientists for a long time there are disputes about why Pygmies have low growth and whether it is an adaptation to the tropical environment, - said Sarah Tishkoff, senior author of the study. - Our results suggest that the genetic basis of complex traits such as growth, can be very different in the global diversity of nationalities ».
While hundreds of studies have focused on the search and identification of genes that play a role in the changes of growth among Europeans (almost 180 of these genes have been precisely defined), it is - the first study of all the genes that are responsible for the height of the African Pygmies.
Sarah Tishkoff, pygmies
"The detailed genetic analysis, Dr. Tishkoff and her colleagues have identified many genes that may play a role in the development of adaptive stunting - said Irene Ekstrend general of the National Institute of Medical Sciences. - This study demonstrates the value of studying the features of a man in his evolutionary and ecological context for the understanding of human adaptation to the environment ».
Africa - the birthplace of humanity, the continent is replete with examples of species changes, including changes in body size from dwarf hunter-gatherer Pygmies to the tall East African pastoralists. Representatives of the West African Pygmies, an average of 17 centimeters lower than their neighbors who speak Bantu.
These two groups of genetically Part 60 000 - 70 000 years ago. But around 4000-5000 years ago, the Pygmies and Bantus close contact, which led to a mixture of blood and, therefore, the exchange of genes.
Using the results of many studies, the team Tishkoff studied differences in the growth and history of genetic exchange between Bantus and Pygmies to find candidate genes responsible for the small size of pygmies.
Geneticists have watched the genomes of 67 Pygmies and 58 Bantus for specific mutations that provide information about the pedigree. They confirmed that the difference in height has a genetic component, so the more impurities Bantu pygmy has, the higher its growth.
Despite the fact that the genomes of the pygmies were heavily mixed with Bantu genomes in the millennial history of genetic exchange, the researchers identified a region of chromosome 3 where stretches of DNA were clearly different between Bantus and Pygmies. The same area is allocated when geneticists sought genome marks of natural selection. Again, this area emerged when the researchers looked for a correlation with height.
"Using a variety of approaches, we continued to emphasize that to the fore a certain region of DNA on chromosome 3," - said Tishkoff.
This uniqueness has attracted the attention of scientists, and they decided to examine closer the genes encoded in this field.
Among those that stood out were DOCK3 and CISH. DOCK3 - a gene associated with a change in the growth of the Europeans. A CISH encodes a protein that regulates growth hormone (HGH) in humans.
The researchers took from the pygmies, who showed signs of natural selection of objects (ie, have a clear mutations that are inherent in evolutionary advantage), samples of SNP (single nucleotide polymorphism). Biological "paths" associated with the identified mutations include those that are related to reproductive hormone activation, activation of thyroid hormone, immune system function, and regulation of growth hormone and insulin.
"The genes in these pathways are important in reproduction and metabolism, which gave birth to the hypothesis that the reason for the small growth of pygmies - the possibility of early to reach reproductive maturity," - said Tishkoff
Early reproductive ability can be a significant advantage pygmies, whose average life expectancy of 15-24 years.
According Tishkoff, the results indicate the probability of the next: short stature is not a feature of natural selection, as is its consequence, as the genes associated with the increase could have other, more important functions.
The evolutionary process is incredibly complex, and it rarely produces obvious genetic signatures. Despite the high accuracy of the study, the researchers anticipate a continuation of the study of this issue.