Modern homo sapiens carry an odd legacy in their genes - many modern people have a genome that contains traces of Neanderthal DNA. And new science suggests that those relic bits of genetic material may have more of an influence than previously thought.
The new study shows that Neanderthal DNA influences many physical traits, including risk factors for disease, height and immune system function.
Before they went extinct, Neanderthals mated with homo sapiens (or vice-versa). Our genetics mixed sometime around 50,000 years ago.
During that time, our bodies were changing. Neanderthal DNA played a diminished role in body parts such as the brain that developed faster. This suggests that when we developed our faculties for language and higher thinking, we stopped mating with Neanderthals. But our strange literal bedfellows continue to have an effect on us.
The study, conducted by the University of Washington in Seattle, analyzed DNA samples from 214 Americans, the majority of them from European stock. They concluded that Neanderthal genes were active in 52 different varieties of human tissue.
They found that some individuals carried both a homo sapiens and a Neanderthal copy of the same gene. In 25% of these people, there were differences in the activity of both copies of the gene, with one being dominant over the other.
One such Neanderthal gene is ADAMTSL3. When it is dominant, it causes people to grow taller and insulates them against developing schizophrenia.
Joshua Akey, leader of the research team, says in an article about the findings in New Scientist: "The results add to increasing evidence that these effects are often the outcome of changes to the genetic switches."
Akey published research last year that suggested Neanderthal genetics play a role in many human illnesses and disorders, including addiction vulnerability and depression.
Interestingly, Neanderthal genes have diminished influence in the areas of the brain that are responsible for perception and fine motor skills, such as the cerebellum and basal ganglia. These brain structures were more sophisticated in homo sapiens than in Neanderthals, contributing to our advanced cognitive faculties.
Another Neanderthal gene that's still found in people is NTRK2, a gene responsible to neuron health. Neanderthal genes also affect a spermatozoa's likelihood of being able to penetrate an egg. When this gene was deactivated, it may have prevented Neanderthals from continuing to mate with homo sapiens.
It is remarkable to realize just how recently we shared the planet with Neanderthals and other species of hominid.