Scientists have just published a groundbreaking new study that blows the lid off of a rather remarkable reality of our modern human existence: we’ve all got a little bit of Neanderthal in us. Despite the fact that this closely related primitive species died out 30,000 years ago, Neanderthals still live within our current DNA thanks to interbreeding from thousands of years ago, when the two species interacted with each other.

Scientists have found that Neanderthal DNA comprises about 2 percent of our genomes for those who are of an Asian or a European heritage, but this latest study goes even further, showing how the DNA influences our genes. Neanderthals and humans split apart on the evolutionary tree about 700,000 years ago, but the two species interbred up until about 50,000 years ago. While genetic differences made reproduction difficult, it still happened, and it influences or genes today.

This opens up a tremendous new avenue of research, and raises a lot of questions. Researchers don’t yet know which genes are affect, and how they impact our traits. Some genes might have a tremendous impact on who we are, while others not so much.

“Even 50,000 years after the last human-Neanderthal mating, we can still see measurable impacts on gene expression,” says geneticist and study co-author Joshua Akey of the University of Washington School of Medicine. “And those variations in gene expression contribute to human phenotypic variation and disease susceptibility.”

“We find that for about 25% of all those sites that we tested, we can detect a difference in expression between the Neanderthal allele and the modern human allele,” says the study’s first author, UW postdoctoral researcher Rajiv McCoy.