Hybrid humans: How our ancestors' inter-species trysts affect us

New genetic analysis of prehistoric fossils hasshown that most modern humans outside Africa carry the genes of Neanderthals and other extinct human speciesDNA evidencerevealsour ancestorsinterbred with Neanderthals, thenewly discovered Denisovansand possibly other unknown species of humans.

These discoveries change our understanding of human origins and what it means to be human, Toronto-based science journalist and author Alanna Mitchell reports onQuirks & Quarks.

Mitchell explored the science of inter-species human breeding and its implications, speaking to:

• John Hawks, an anthropologist at the University of Wisconsin, whosummarized what is known about Denisovans, whose remains werefound ina particular cave in Russia wherethe remains of modern humans and Neanderthals were alsofound; and other archaic human species that may once have co-existed with our own.
• Chris Stringer, a paleontologist at London's Natural History Museum, who explained why modern humans are considered separate species from the others, despite evidence that we could interbreed.
• Peter Parham, who studies the human immune system at the Stanford School of Medicine in California. He explained how the DNA of other species may haveaffected our immune systemand continues to do so today.
• David Reich, a geneticist at Harvard Medical School in Cambridge, Mass., who pointed out that this is the first time in four million years of human history that we've been the only humans on the planet.