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Study: Homo genus origins not dictated by body size increase

"This elegant study shows that body size did not make a sharp uptick with the arrival of early Homo," said GW professor Bernard Wood.

By Brooks Hays
Study: Homo genus origins not dictated by body size increase
New research suggests Homo erectus was the first species to show a significant jump in body mass. Photo by Marques/Shutterstock

WASHINGTON, Aug. 3 (UPI) -- Research suggests that the general trajectory of evolution tends to produce larger and larger species. But it's a truism with many exceptions and even more subtleties. One of those exceptions is the Homo genus.

New analysis of the sizes of early hominin specimens suggests, contrary to popular theory, that the origins of the Homo genus -- which spawned Homo sapiens -- did not coincide with, nor was precipitated by, an uptick in body mass.

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According to the new research, published in the Journal of Human Evolution, the earliest Homo specimens did not differ significantly in size from their immediate ancestors.

The work, conducted by scientists at George Washington University, included the largest analysis of early hominids yet performed. The results suggest the earliest specimens from the Homo genus were in fact smaller than previously estimated. Instead of at the outset, researchers place the jump in body size in midst of Homo evolution.

Homo erectus -- the first species that a significant paleontological mark outside of Africa -- is the first to exhibit a true increase in body mass, researchers at the GW Center for the Advanced Study of Human Paleobiology argue in their new study.

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"One of our major results is that we found no evidence that the earliest members of our genus differed in body mass from earlier australopiths (some of the earliest species of hominins)," lead study author Mark Grabowski, a research professor at GW, said in a press release. "In other words, the factors that set our lineage apart from our earlier ancestors were unrelated to an increase in body size, which has been the linchpin of numerous adaptive hypotheses on the origins of our genus."

Previously, researchers have suggested that an improved ability to hunt (and thus include large portions of meat in the diet) led to the larger, more advanced Homo genus. While that hypothesis could explain the increase in body size that came with later Homo erectus, it is not consistent with the rise of the earliest Homo.

"This elegant study shows that body size did not make a sharp uptick with the arrival of early Homo," said Bernard Wood, a professor of human origins at GW who did not participate in the study. "My prediction is that this is just the first of many preconceptions about early Homo that will be debunked in the next few years."

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