The July issue of the American Journal of Adam Gordon presented new research by anthropologist Adam Gordon that re-examined two landmark hominid samples, Australopithecus afarensis and Australopithecus africanus. Using a multivariate resampling method, Gordon incorporated partial crania, limb fragments, and isolated teeth into a single statistical framework, which allowed him to estimate body size from otherwise incomplete fossils.
Gordon then compared those estimates with modern human, chimpanzee, and gorilla data sets. The study found that male A. afarensis individuals were markedly larger and heavier than females. “Sexual size dimorphism in A. afarensis exceeds that of both modern humans and often that of chimpanzees, and is even more pronounced than in gorillas,” said the report, according to Newsam. In some skeletal elements the male-female difference approached gorilla levels. A. africanus also showed a male-female size gap greater than in modern humans but less than in A. afarensis.
“High sexual dimorphism usually indicates strong male competition and a polygynous group structure, where several large males compete to mate with females,” argued the researchers, according to Newsam. By analogy, the early hominids under study may have lived in social arrangements similar to those of gorilla harems.
Because the gap in A. afarensis “is even greater than that seen in gorillas,” as Newsam quoted from the study, reconstructions that treat the female Lucy skeleton as representative of both sexes likely understate male morphology. Gordon’s approach provided a larger effective sample size than earlier efforts, offering fresh insight into early hominid body proportions and the social dynamics that may have shaped them.
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