Overview
- The PNAS paper published Monday, June 22, 2026, analyzed 386 fossil specimens from 21 hominin species and found the clearest signal is a rapid size increase about 2 to 2.5 million years ago tied to early Homo such as H. rudolfensis and H. erectus/ergaster.
- Authors used phylogenetic statistical models that compare competing evolutionary scenarios to show a lineage‑specific jump explains the fossil pattern better than a uniform, steady trend across all hominins.
- The timing of the jump matches other changes recorded for later Homo, including more efficient two‑legged walking, greater meat consumption, and wider geographic roaming, which together could favor larger body mass.
- Several lineages buck the pattern: small-bodied species such as Homo floresiensis and Homo naledi and earlier australopiths remained much smaller, demonstrating that size change was mosaic and not universal.
- The study strengthens the field by uniting many previously separate datasets but notes limits from fragmentary fossils, mass‑estimation methods, and species assignments, so the result refines our picture rather than closing debate.