The evolution of the human body’s size and shape has gone through four stages, says an international group of anthropologists from the United States, Spain, France, and China.
Sima de los Huesos hominins lived in what is now Spain about 400,000 years ago. Image credit: © Kennis & Kennis / Madrid Scientific Films.
The team, directed by Prof Juan Luis Arsuaga of the Complutense University of Madrid, studied the body size and shape in the fossil collection from the site of the Sima de los Huesos (Pit of Bones) in Spain.
Dated to around 430,000 years ago, this cave site preserves a large collection of fossils attributed to an enigmatic hominin species, named the Sima de los Huesos hominin after the site.
Prof Arsuaga and co-authors found that the Sima de los Huesos individuals were relatively tall, with wide, muscular bodies and less brain mass relative to body mass compared to Neanderthals. They shared many anatomical features with the later Neanderthals not present in anatomically modern Homo sapiens, and analysis of their postcranial skeletons (the bones of the body other than the skull) indicated that they are closely related evolutionarily to Neanderthals.
“This is really interesting since it suggests that the evolutionary process in our genus is largely characterized by stasis (i.e. little to no evolutionary change) in body form for most of our evolutionary history,” said team member Dr Rolf Quam of Binghamton University.
Comparison of the Sima de los Huesos fossils with the rest of the human fossil record suggests that the evolution of the human body has gone through four main stages, depending on the degree of arboreality (living in the trees) and bipedalism (walking on two legs).
The Sima de los Huesos fossils represent the third stage, with tall, wide and robust bodies and an exclusively terrestrial bipedalism, with no evidence of arboreal behaviors.
This same body form was likely shared with earlier members of our genus, such as Homo erectus, as well as some later members, including the Neanderthals.
Thus, this body form seems to have been present in the genus Homo for over a million years.
It was not until the appearance of our own species, Homo sapiens, when a new taller, lighter and narrower body form emerged.
Sima de los Huesos hominins “offer the best look at the general human body shape and size during the last million years before the advent of modern humans,” the scientists said.
They describe their findings in a paper in the Proceedings of the National Academy of Sciences.
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Juan Luis Arsuaga et al. Postcranial morphology of the middle Pleistocene humans from Sima de los Huesos, Spain. PNAS, published online August 31, 2015; doi: 10.1073/pnas.1514828112
