May 17 (UPI) -- Humans and chimpanzees may have interbred millions of years ago after the two species initially separated, according to a study published in Nature. If hybridization -- creating a new form of plant or animal life by combining two species -- did occur between humans and chimpanzees, ``one might need to modify the evolution displays in museums,'' Harvard Medical School Assistant Professor David Reich wrote in an e-mail message. The study, ``Genetic evidence for complex speciation of humans and chimpanzees,'' says the X chromosome is much younger than previously thought and may mean that after human and...