Modern humans have more of Neanderthals' traits than previously believed

Researchers have analyzed exactly which areas of the human genome retain segments of Neanderthal DNA, passed down throughout the generations.

To determine how the human-Neanderthal genetic mixing may have played out, Lead scientist David Reich, an Howard Hughes Medical Institute (HHMI) investigator at Harvard Medical School, and his colleagues compared that completed Neanderthal genome with the genomes of 1,004 present-day humans from around the globe.

Since humans met Neanderthals as they migrated out of Africa, those populations that remained in Africa had little contact or genetic mixing with Neanderthals.

The researchers found that today, humans in east Asia have, on average, more of their genome originating from Neanderthals than Europeans, and modern-day Africans have little or none.

They found that some genes had variants of Neanderthal origin in more than sixty percent of Europeans or Asians, while other genes were never of Neanderthal heritage.

The scientists discovered that the genetic changes most often inherited from Neanderthals were disproportionately in genes related to keratin, a component of skin and hair.

His group analyzed not only which Neanderthal genes remain in the human population today, but also which parts of today's genomes lack Neanderthal genes altogether.

The most striking area of the human genome that lacked Neanderthal genes was the X chromosome-one of the sex chromosomes. In humans, women have two X chromosomes and men have an X and a Y chromosome.

The team's observation that the X chromosome had very little Neanderthal ancestry suggested something the scientists hadn't predicted -- a biological phenomenon called hybrid sterility. When two organisms are distantly related, Reich explains, genes related to fertility, inherited on the X chromosome, can interact poorly with genes elsewhere in the genome.

The interference between the pairs of genes can render males-who only have one X chromosome-infertile.

The findings have been published in journal Nature.