Homo erectus babies helpless like modern infants, skull study suggests

Homo erectus babies helpless in much the same way as modern human newborns may have been part of early human life more than 1 million years ago, according to research led by Yousuke Kaifu of the University of Tokyo. The finding matters because helpless infants require sustained care, raising questions about how early humans shared the burden of raising children.

The study, published in Proceedings of the Royal Society B: Biological Sciences, uses skull shape as evidence for what newborns were like in species known mostly from fragmentary fossils. Kaifu’s team compared living infants, historical human remains, fossil humans and other great apes to look for patterns of cranial deformation.

Were Homo erectus babies helpless?

The researchers argue that some Homo erectus infants likely were physically helpless because their fossil skulls show deformation consistent with deformational plagiocephaly, commonly called flat head syndrome. In modern babies, that condition can occur when a soft skull is pressed by repeated positioning while the infant lacks enough neck strength to move the head easily.

Kaifu’s group reported that human skulls, including fossil specimens, showed a wider range of deformation than skulls from other great apes. Chimpanzees, bonobos, gorillas and orangutans, whose young are born more physically capable than human newborns, clustered within a narrower range of cranial distortion, according to the researchers.

The comparison included CT scans of 123 healthy modern infants from 1 day to 17 months old; measurements from 385 historical human skulls from Japan dating to about 200 to 1,000 years ago; 996 skulls from other great apes; five Homo erectus fossils; and one Homo floresiensis fossil. The team included researchers from Japan and Indonesia.

How skull shape can preserve infancy

Deformational plagiocephaly is not a disease in this context. The researchers treated it as a physical trace of pressure on the cranium around birth or soon after birth, provided the pattern could be separated from disease or damage after burial.

Kaifu began considering the idea after seeing the Homo floresiensis skeleton in Indonesia in 2007, according to the University of Tokyo account of the work. The skull’s distorted form appeared, from the bone structure, to have developed after birth; a hospital clinician later identified the likely cause as deformational plagiocephaly.

That observation led the team to test whether cranial deformation could serve as an indicator of newborn helplessness. The method is useful because infant fossils are rare, while deformation from early life can remain visible in skulls at later ages.

What the finding says about early care

Homo erectus lived from more than 1 million years ago to about 110,000 years ago, and the archaeological record for its behavior is limited, the University of Tokyo said. Kaifu said the evidence for helpless babies would imply diligent care by adults, because a newborn in that condition could not protect or move itself well.

The researchers also link the finding to possible social behavior. Kaifu said a mother alone would have faced difficulty caring for and protecting such an infant in an environment that included large predators, so help from fathers or other group members may have been needed.

Homo floresiensis added an unexpected twist. Although that species had a much smaller brain, comparable in size to a chimpanzee’s, the fossil showed deformation that the team interpreted as part of a human-like newborn stage rather than an ape-like one.

The results do not settle every question about why human infants are born so underdeveloped. They do suggest, according to Kaifu and colleagues, that demanding childcare and support for mothers may reach back at least to the common ancestor of Homo erectus and Homo floresiensis more than 1 million years ago.

This story draws on original reporting from Phys.org.