New insights into differences in brain organization between Neanderthals and anatomically modern humans

Abstract

Previous research has identified morphological differences between the brains of Neanderthals and anatomically modern humans (AMHs). However, studies using endocasts or the cranium itself are limited to investigating external surface features and the overall size and shape of the brain. A complementary approach uses comparative primate data to estimate the size of internal brain areas. Previous attempts to do this have generally assumed that identical total brain volumes imply identical internal organization. Here, we argue that, in the case of Neanderthals and AMHs, differences in the size of the body and visual system imply differences in organization between the same-sized brains of these two taxa. We show that Neanderthals had significantly larger visual systems than contemporary AMHs (indexed by orbital volume) and that when this, along with their greater body mass, is taken into account, Neanderthals have significantly smaller adjusted endocranial capacities than contemporary AMHs. We discuss possible implications of differing brain organization in terms of social cognition, and consider these in the context of differing abilities to cope with fluctuating resources and cultural maintenance.

Figure 1.

(a) Absolute and (b) standardized endocranial volumes for different hominin taxa, split into date groups (given in thousands of years ago: ka). The three boxes represent (i) Homo heidelbergensis (Hh) and possible Denisovans (?D), (ii) the Neanderthal lineage, from archaics (AHn) to Neanderthals (Hn) dated 76–200 ka and 27–75 ka, and (iii) the Homo sapiens lineage, from archaics (AHs) to AMHs (Hs) dated 76–200 ka and 27–75 ka. Circles indicate the value for each individual fossil specimen. The horizontal bars show group means ± the s.e.m. (cumulative for b). The light grey shading illustrates that Neanderthals dated 27–75 ka have the same sized brains as Homo sapiens in terms of absolute endocranial volumes, but that once body and visual system sizes are taken into account, the Neanderthal means lie outside the standard errors of the AMH means. The dashed lines in (b) illustrate the AMH means for both date groups, to ease comparison with the Neanderthal means.

Figure 2.

Group sizes estimated from standardized endocranial volumes for Neanderthals and AMHs in the 27–75 ka date group. The dashed line indicates the mean group size expected for living humans based on the size of their neocortex (150 individuals).