http://www.livescience.com/1934-human-ancestors-walked-upright-study-claims.html
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001019http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0001019&representation=PDF