Overview
- The paper by Gardner et al., published Monday, June 22, 2026 in PNAS, analyzed 386 fossil mass estimates from 21 hominin species and detected a pronounced average weight rise from about 40 kg to about 60 kg in later members of Homo dated to roughly 2–2.5 million years ago.
- Researchers used comparative statistical models that account for species relationships to test competing ideas and concluded the best fit is a mixed pattern: a background gradual trend plus a lineage-specific size jump within Homo.
- The timing of the jump lines up with inferred changes in locomotion, diet, and range size, with the authors linking larger bodies to more efficient bipedal walking and greater use of meat in the diet.
- The study stresses important caveats: many fossils are fragmentary, mass estimates depend on which bones and scaling formulas are used, and debates over species names and assignments mean the picture is still uncertain.
- The result reframes a long debate by showing heterogeneity in body-size evolution and points to clear next steps—new fossils, refined mass estimates, and further tests of ecological drivers—to confirm how and why early Homo grew larger.