Humans: a complex history

http://www.livescience.com/12937-10-mysteries-humans-evolution.html

http://www.livescience.com/15196-dna-evidence-neanderthals-sex-humans.html

http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0064539&representation=PDF