Inbreeding Neanderthals Left Humans a Harmful Gene That Reduces Reproductive Fitness

Inbreeding among Neanderthals has left a harmful legacy to modern humans that reduce their fitness.

A study from Stanford University published in the journal Genetics reveals that inbreeding among Neanderthals resulted to a gene mutation that made them less reproductively fit. This harmful mutation was then passed to some non-African human populations.

For thousands of years, Neanderthal populations have remained small in numbers and have resorted to inbreeding to populate. Researchers say that this inbreeding has resulted to harmful genetic mutations that made them unable to reproduce effectively. However, around 50,000 to 100,000 years ago, Neanderthals interbred with humans, passing on this gene mutation. Until today, people still carry a small portion of the mutation that reduces their ability to reproduce by 1 percent, especially among non-African individuals.

"Neanderthals are fascinating to geneticists because they provide an opportunity to study what happens when two groups of humans evolve independently for a long time--and then come back together," said Kelley Harris, study leader from Stanford University. "Our results suggest that inheriting Neanderthal DNA came at a cost."

Harris and Rasmus Nielsen from the University of California, Berkeley and University of Copenhagen says that the existence of this gene mutation, even after thousand of years, could be due to natural selection as it allows this kind of weak mutation to survive rather than disappear.

To test their theory, Harris and Nielsen simulated mutation accumulation among Neanderthals and its effect on modern humans through a computer program. The results showed that due to the harmful gene mutation, at least 40 percent of humans is less likely to reproduce, with 2 percent of Non-African populations affected by the genome.

According to Science Daily, the study says that the results could also shed a light on the conservation of endangered species, especially those who face the same circumstances as the Neanderthals. The researchers said that this could show the need of a genetic rescue, which entails improving the health of species by letting them crossbreed with other populations rather than reproducing within their own group.