The University of Pennsylvania under the leadership of geneticist-anthropologist Sarah Tishkoff, revealed DNA regions associated with both the growth of pygmies, and the activity of their immune system.
Tishkov and colleagues scanned the complete genomes of 70 people from three groups of Pygmy hunters in Cameroon. The increase in male Pygmy does not exceed 1 m 52 cm For comparison, the scientists also analyzed the genomic sequences of 60 people from neighboring ethnic groups with the Bantu. Bantu – farmers, tall and slender, are entering into marriage with the pygmies.
In search of single nucleotide substitutions, the so-called SNPs (single-nucleotide polymorphisms, SNPs), variations of genetic sequences characteristic of a population of pygmies, they found these “labels” about the genes involved in the system of chemical signals in the brain. In particular, a cluster of SNPs was found near the thyroliberin receptor gene, a hormone that affects the secretion of thyroid-stimulating hormone by the pituitary gland and indirectly – on the growth of man.
Typical of the Pygmies building codes were found in genes located on chromosome 3.
In previous studies by other scientists (Joseph Jarvis, Coriell Institute for Medical Research, New Jersey) in mice have shown that increased activity of one of these genes, CISH, provides immunity to tuberculosis and malaria. At the same time with this version of the gene stops production of the main receptor of growth hormone, somatotropin.
According to Sarah Tishkov, the fact that the Pygmies are carriers of specific DNA sequences in the gene CISH suggests that the low growth and immunity may be related physiologically. “Perhaps, short stature of pygmies – is the result of better resistance to disease, made in the ongoing fight against germs. Although Pygmies and die young, they manage to overcome a variety of infections,” – says the researcher.
The average life expectancy of pygmies – 17 years. The main cause of their death are infectious diseases, which are favorable conditions for the hot and humid jungle. First it was believed that the low growth of pygmies entrenched in natural selection as a factor that helps make their way through dense vegetation. Another explanation – Pygmies stunted immediately after puberty, and it gives them time for furnishing the offspring, and most importantly – the ability to direct all resources on the reproduction of the organism. None of these assumptions has not been matched genetically.
Study of Pennsylvania researchers, which does not reject the hypothesis put forward earlier, but suggests that the low growth of pygmies has been selected during evolution as a consequence of genetically fixed hormonal regulation of the immune system, published in the journal PLoS Genetics.