A neonatal perspective on Homo erectus brain growth.
Level 5 - mechanism / opinion, no new human data
By design analogy; computational simulation and comparative ontogenetic modeling based on fossil reconstruction.
PubMed 25771994 · doi:10.1016/j.jhevol.2015.02.011
What was done
The authors simulated average annual rates (AR) of absolute endocranial volume (ECV) growth and proportional size change (PSC) in *Homo erectus*. Simulations incorporated estimates of *H. erectus* neonatal ECV and a range of estimated ages at death for the Mojokerto calvaria specimen. These trajectories were compared against resampled AR and PSC data from ontogenetic series of modern humans, chimpanzees, and gorillas from birth to six years of age.
What was found
Living species showed extensive PSC overlap through the first postnatal year, with humans maintaining elevated ARs above apes (with modest overlap up to 0.50 years). Simulated *H. erectus* PSC values fell within the range of all living species by 0.50 years, but the median dropped below human and chimpanzee ranges after 2.5 years. *H. erectus* ARs exceeded all extant taxa prior to 0.50 years and remained above ape ranges after two years, though falling below the human range. Assuming an age at death of approximately one year for Mojokerto placed its absolute brain growth rates in the lower half of the modern human range.
Why it matters
The findings support the presence of secondary altriciality in *Homo erectus*, suggesting that maternal energetic adaptations characteristic of modern humans were already established at least 1 million years ago.
Limits
The analysis depends heavily on estimated parameters for a single fossil specimen (Mojokerto), including neonatal endocranial volume and contested age at death. The abstract does not specify the exact sample sizes for the comparative human and ape ontogenetic datasets.
Cited by
- context Chimpanzee brain growth slows rapidly after birth, whereas human brains sustain a fetal-like rate of growth until at least six to ten years of age.