Early humans mated with Neandertals, and modern human DNA was changed forever by it. New genetic evidence, announced today, proves that most humans share 1-4% of their DNA with Neandertals. Unless you're from Africa, in which case you're Neandertal-free.

A massive, multiyear study at the Max Planck Institute compared the genomes of three Neandertal women (reconstructed from 38,000-year-old bones) with five humans from across the world - two from Africa, one from Europe, one from China, and one from Papua, New Guinea. The results show that humans and Neandertals did interbreed, possibly as early as 100 thousand years ago when early humans were immigrating out of Africa into Europe and Asia. This immigration pattern also helps to explain why the two human genomes from Africa have no traces of Neandertal in them. The African population never interbred with our hominid cousins. Here's Max Planck scientist Svante Pääbo talking about this:

Early humans and Neandertals encountered each other in the Middle East, Europe, and parts of Asia. They would have had tens of thousands of years to interbreed during this time, and now it seems that their offspring are, in fact, walking among us. The map below shows all the places where early humans and Neandertals lived together.


So how did the Max Planck team, whose research is published today in Science, manage to get Neandertal genomes out of ancient fossils? First, they got bones that were as fresh as possible - the 38,000 to 44,000-year-old bones were taken from one of the last Neandertal populations, who lived in a cave (pictured below) in Croatia. Researchers ground the bones up and sequenced every piece of genetic material in them. Using a process called metagenomics, they painstakingly determined which pieces of DNA in the fossils actually came from the Neandertals, versus the humans who discovered the fossils, versus the bacteria and plants that had been near those bones for thousands of years.


Then the researchers compared the Neandertal genome with a chimp genome, as well as with the five human genomes, looking for similarities. The final results showed that there were unmistakable sequences of Neandertal DNA mixed into some modern human genomes.

The researchers also looked for differences between the human and Neandertal DNA. Looking at these differences allowed them to figure out which transformations have taken place in the human genome relatively recently, over the past say 40 thousand years since we interbred with Neandertals. What they discovered, according to Pääbo, was that there were a number of recent, widespread mutations in the human genome, several of which are related to cognitive development. Below, you can see some of the genes that differ between Homo sapiens and Neandertal - several are connected with cognition (such as the genes associated with autism, schizophrenia and Down syndrome).


So what does this mean? Humans have already met, and interbred with, another species that was both intelligent and nonhuman.

Get tons more information on this discovery via Science and the AAAS