Homo brain size data with MIS bins

Brain size data from DeSilva et al. (2023) were used as a baseline and updated where more recent information was available for date and taxonomy. Juvenile, immature, deformed, and fragmentary crania without enough elements to make a proper estimate of adult brain weight were excluded from the sample. Sources for brain size measurements, taxonomy, and dates are included in the Supplementary Data file. Estimated brain size was derived from 800 cranial capacity measurements using a formula that permits direct comparisons using least-squares regression (R2 = 0.995) of 27 primate species (brain mass = 1.147 x cranial capacity0.976) (Ruff et al., 1997). The final sample included and 11 species with unknown or contested taxonomy, 690 H. sapiens and 99 individuals that have been previously categorized across eight paleospecies: H. erectus (n = 44), H. heidelbergensis (n = 15), H. floresiensis (n = 1), H. habilis (n = 6), H. longi (n = 1), H. naledi (n = 3), H. rudolfensis (n = 3), and H. neanderthalensis (n = 26). Summary data can be found in Table S1. Tests were performed with and without H. floresiensis and H. naledi as there is considerable debate regarding whether each of those species is part of the genus Homo (Tattersall, 2023); including or excluding these specimens did not change the direction or significance of any results. Each specimen was also classified by climatic phase—glacial or interglacial—based on Marine Isotope Stage (MIS) assignment. MIS stages were determined by aligning specimen age with the global oxygen isotope record, a well-established proxy for global ice volume and temperature (Lisiecki & Raymo, 2005). MIS assignments were cross-validated with contextual metadata and paleoclimatic reconstructions where available (Lisiecki & Raymo (2005)).