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Image Credit: Cicero Moraes, CC BY-SA 4.0, via Wikimedia Commons
New Fossil Analysis Rethinks How Human Body Size Evolved
A new evolutionary study has revisited one of the long-running questions in human origins research: how and when hominin body size increased. The research compares competing models of body size evolution using a large dataset of fossil body-mass estimates and a statistical framework that accounts for evolutionary relationships and uncertainty in the fossil record.
Body size is important in human evolution because it affects movement, energy use, ecology, life history, and brain-body relationships. Larger body size in hominins has often been linked with changes such as more efficient bipedal walking, wider ranging behaviour, and shifts in diet and ecology.
However, researchers have disagreed on whether hominin body size increased gradually over time, increased mainly within the genus Homo, or changed more sharply only in later members of Homo. Some small-bodied species, such as Homo floresiensis and Homo naledi, have also complicated the picture.
To test these ideas, the new study used body-mass estimates from 386 fossil specimens across 21 taxa. The researchers applied Bayesian phylogenetic generalized linear mixed models, which allowed them to evaluate several explanations at the same time while accounting for phylogenetic relationships, taxonomic uncertainty, variation within species, and differences between body-mass estimation methods.
The results support a moderate overall increase in hominin body size through time. However, the strongest evidence points to a more distinct size increase in later-occurring Homo, especially when Homo habilis is excluded. This suggests that larger body size was not simply a feature of all Homo, but became more pronounced in later members of the genus.
The study found weaker support for a clear size increase across all Homo. This means that early Homo, especially Homo habilis, may not fit neatly into the pattern of larger-bodied later humans. The authors note that this could also affect debates about how the genus Homo should be defined.
The research also identifies Homo floresiensis and Homo naledi as consistent small-bodied outliers. Their presence shows that human body size evolution was not a simple straight-line trend toward larger bodies, but a more complex process with different evolutionary paths.
Overall, the study helps reconcile earlier disagreements by testing several hypotheses in one framework. It suggests that hominin body size did increase over time, but the most important shift occurred in later Homo, rather than across the entire human lineage in a simple, uniform way.
Published on: 23-06-2026
Edited by: Abdulmnam Samakie
Source: PNAS
