Short read: How did a Neanderthal Gene for Antibodies Become Predominant in Humans?

All humans share the same African ancestors but as this fascinating article in The Wire explains, 800,000 years of evolution has meant that, some humans have certain genes which are different from the genes other humans have: “Our white blood cells make molecules called antibodies that bind to other molecules called antigens made by bacteria and viruses. Antibody binding aids in destroying the antigen-producing cell, and affords protection against pathogens. An antibody is made up of four protein molecules — two identical molecules of the immunoglobulin heavy chain, and two of the light chain. The IGH gene on our chromosome number 14 codes for the heavy chain protein.

All humans share the same African ancestors. Nevertheless, the predominant IGH gene found in East Asia and Europe, but not elsewhere, originated in the Neanderthals and not in our African ancestors. Who were the Neanderthals? And how did their IGH gene become predominant in East Asians and Europeans?”

Even more fascinatingly, research shows that East Asians and Europeans acquired this Neanderthal gene independently.

To understand how this happened, you should read the whole story in The Wire. Here is the crux of the argument: “Present day humans whose ancestors migrated out of Africa contain haplotypes with close matches to Neanderthal or Denisovan haplotypes in 2-5 % of their genome.  These genome segments have persisted since the time the ancestors interbred with Neanderthals and Denisovans in Eurasia.

Hundreds of non-African genomes were searched to determine whether a Neanderthal- or Denisovan-derived genome segment had attained a high frequency in any present-day population. A Neanderthal-derived 200 kb chromosome 14 segment, that included IGH, was predominant in East Asian and Europeans, but not in others.

The Neanderthal-derived haplotype found in East Asians, however, was slightly different from that found in Europeans. This implied that the ancestors of East Asians and Europeans independently interbred with Neanderthal populations bearing different IGH-linked haplotypes.

The Neanderthal IGH genes might have conferred better resistance to a geographically-restricted pathogen, resulting in their high frequencies today in East Asian and Europeans.  Recall that Neanderthals resided for 700 kya in these geographies before our forebears arrived, and hence likely evolved better pathogen resistance.” [Note: 1 kya = 1000 years]

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