News Anthropology Males of this ancient human cousin weren’t always bigger than females Proteins from a collection of fossils hint at sex and genetic differences in P. robustus A new analysis of proteins preserved in fossil teeth provides the first molecular assessment of size differences between the sexes and genetic diversity in an ancient African hominid, Paranthropus robustus (skull of own shown). Bernhard Zipfel By Bruce Bower 20 hours ago An ancient, distant human cousin from southern Africa called Paranthropus robustus has for the first time revealed molecular clues to its evolutionary status. Protein sequences preserved in four partial P. robustus teeth from different individuals that lived roughly 2 million years ago indicate that larger and smaller fossils of this hominid species cannot always be classed as male or female, as previously thought, researchers report in the May 29 Science. Sequences of a protein derived from a gene located only on the Y, or male, sex chromosome in present-day humans enabled the scientists to identify two teeth as having belonged to males, molecular biologist Palesa Madupe of the University of Copenhagen and colleagues say. One of those teeth was previously thought to have come from a female, based on its small size. Closer analyses of the two teeth lacking that male-specific protein indicated that those fossils, which are around the same size as the smaller male tooth, came from females. Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday.