Why pygmies are so short?

For years, scientists have been wondering why Pygmies of West Africa have such short stature. Men grow to a maximum of five feet tall and women about a half foot shorter, while in neighboring groups, such as the Bantus, the average height are 5 feet.In order to see whether these differences were genetic or an adaptation to living in a tropical environment, researcher analyzed their genomes.

Pygmies and Bantus in West Africa have mixed for thousands of years but were separated genetically about 60,000 to 70,000 years ago; then 4,000 to 5,000 years ago, they started inbreeding.

Mating between some Pygmy women with Bantu men had as a result half-Bantu babies. This phenomenon integrated Bantu genes into pygmy population. These women and their offspring stayed in the Pygmy population, so there was no mix with the Bantu. Nonetheless, offspring resulting from mating between Pygmy men and Bantuwomen aren’t common, so the Bantus don’t have many Pygmy genes.

Researchers first investigated which regions of the Pygmies’ genomes reflected Pygmy or Bantu ancestry. The conclusion was that the more Bantu ancestry someone had, the taller he or she was, which supported the idea that Pygmy stature has genetic roots.

This study, leaded by Sarah Tishkoff, analyzed the SNPs of 70 Pygmies and 60 Bantus trying to find those that may have been naturally selected as they gave pygmies an advantage in surviving and passing on their genes.

Some of these selected SNPs occurred in a region of chromosome 3 that differed between Bantus and Pygmies, and were linked to height. They also found new changes in hormone pathways and immunity that seemed to have a relation with the short stature of the pygmies. One of the SNPS, called CISH, has been shown to interact with growth hormone receptor by inhibiting the signal; it’s also known that this gene confers immunity against Malaria.

The immunity component could be a result of natural selection, as it helps the pygmies fight off infections, which are prevalent in their habitat. The short height could just be a byproduct of these changes.

Original divulgative article: http://www.nature.com/news/hunt-for-genetic-link-to-pygmy-height-yields-clue-1.10517

The complete study: http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1002641

#Genetics #Pygmies #Short #Africa #Malaria #Bantu #Height #SNP