Neanderthal Y Chromosome Is Mysteriously Missing in Modern Human Genome; How Did It Keep Us Apart From Our Ancestors?

Scientists have discovered that modern human DNA contains bits from all over the Neanderthal genome, but one piece is mysteriously missing.

Interaction Between Neanderthals and Homo sapiens

Members of the Homo neanderthalensis species, or Neanderthals, are regarded as the closest relatives of modern humans. They lived in some regions of Asia and Europe until they went extinct about 30,000 years ago.

Aside from archaeological artifacts, data from genetic studies have revealed more about the connection between modern humans and our long-gone relatives. In a recent discovery, it was found that a rush of interbreeding between the two species happened in a short burst of time 47,000 years ago.

More than half a million years ago, Neanderthals and modern humans went their separate ways in Africa. The former wandered off into Europe while the latter stayed put. Then they met again when Homo sapiens migrated into Europe and Asia between 40,000 and 50,000 years ago.

From well-preserved bones and teeth of Neanderthal remains in Europe and Asia, experts discovered that the Neanderthal genome was very similar to ours. Their genome contained about 20,000 genes bundled into 23 chromosomes. However, no modern human genome has been found to possess any part of the Neanderthal Y chromosome.

What Happened to the Neanderthal Y Chromosome?

The lineage of a Y chromosome comes to an end if it does not bear a son. This means that the Neanderthal Y may have never been present when different species mated. It is possible that it was always modern human men who mated with Neanderthal women.

Sons born to these women would always have the Homo sapiens form of the Y chromosome. This idea, however, is hard to accept since there is no trace of Neanderthal mitochondrial DNA in the modern human species.

Another possibility is that the Neanderthal Y chromosome was not as good as its modern counterpart. This is because Neanderthals always existed in small populations, so harmful mutations would have been more likely to happen. Y chromosomes with certain useful genes rapidly replace other Y chromosomes in a population.

Some experts also suggest that the Neanderthal Y chromosome does not work with genes on other chromosomes from modern humans. It is possible that the Y chromosome from one species has evolved to work with genes from other chromosomes of its own kind and may not work with genes from a related species that underwent even small changes. The missing Neanderthal Y may also be explained by "Haldane's rule," which states that if one sex is infertile, unhealthy, or rare, it is always the sex with unlike sex chromosomes.

It was found that genes on the Y evolved much faster than genes on other chromosomes. Several of them play an important role in making sperm, explaining the infertility of male hybrids.

This might also explain the reason behind the loss of the Neanderthal Y. It also raises the possibility that the Y chromosome is the reason why the Neanderthals and modern humans became separate species in the first place.