Updated imaging and phylogenetic comparative methods reassess relative temporal lobe size in anthropoids and modern humans

Abstract

Objectives Two decades ago, Rilling and Seligman, hereafter abbreviated to RAS Study, suggested modern humans had relatively larger temporal lobes for brain size compared to other anthropoids. Despite many subsequent studies drawing conclusions about the evolutionary implications for the emergence of unique cerebral specializations in Homo sapiens, no re‐assessment has occurred using updated methodologies. Methods We reassessed the association between right temporal lobe volume (TLV) and right hemisphere volume (HV) in the anthropoid brain. In a sample compiled de novo by us, T1‐weighted in vivo Magnetic Resonance Imaging (MRI) scans of 11 extant anthropoid species were calculated by‐voxel from the MRI and the raw data from RAS Study directly compared to our sample. Phylogenetic Generalized Least‐Squares (PGLS) regression and trait‐mapping using Blomberg's K (kappa) tested the correlation between HV and TLV accounting for anthropoid phylogeny, while bootstrapped PGLS regressions tested difference in slopes and intercepts between monkey and ape subsamples. Results PGLS regressions indicated statistically significant correlations (r2 < 0.99; p ≤ 0.0001) between TLV and HV with moderate influence from phylogeny (K ≤ 0.42). Bootstrapped PGLS regression did not show statistically significant differences in slopes between monkeys and apes but did for intercepts. In our sample, human TLV was not larger than expected for anthropoids. Discussion Updated imaging, increased sample size and advanced statistical analyses did not find statistically significant results that modern humans possessed a disproportionately large temporal lobe volume compared to the general anthropoid trend. This has important implications for human and non‐human primate brain evolution.

Human temporal lobes have been reorganized: A response to Pearson et al, “updated imaging and phylogenetic comparative methods reassess relative temporal lobe size in anthropoids and modern humans”

“…In their recent article published in AJBA, Pearson et al re-analyze our non-human primate data with updated methods and conclude that the human temporal lobes as a whole do not depart from nonhuman primate allometric trends and are therefore the size one would expect in a primate of our brain size (Pearson et al, 2023). They do not address our conclusion that human temporal lobe white matter is larger than expected.…”