Hybridization: mating with Neanderthals and Denisovans
http://www.livescience.com/9910-humans-neanderthals-mated-making-part- caveman.html
http://www.cbsnews.com/8301-205_162-20128079/human-ancestors-mated-wit h-more-than-neanderthals/
http://johnhawks.net/weblog/reviews/neandertals/neandertal_dna/denisov a-nuclear-genome-reich-2010.html