In a line of human ancestors that lived more than 3 million years ago, adult males were only around 15 percent larger than adult females, a new study finds.
Such a moderate sex difference in Australopithecus afarensis suggests that males in the ancient species formed coalitions with each other and often established monogamous relationships with females just as do modern human males and those of other species with nearly equal-size sexes, say Philip L.
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