Endocast morphology of Homo naledi from the Dinaledi Chamber, South Africa.

Hominin cranial remains from the Dinaledi Chamber, South Africa, represent multiple individuals of the species Homo naledi This species exhibits a small endocranial volume comparable to Australopithecus, combined with several aspects of external cranial anatomy similar to larger-brained species of Homo such as Homo habilis and Homo erectus Here, we describe the endocast anatomy of this recently discovered species. Despite the small size of the H. naledi endocasts, they share several aspects of structure in common with other species of Homo, not found in other hominins or great apes, notably in the organization of the inferior frontal and lateral orbital gyri. The presence of such structural innovations in a small-brained hominin may have relevance to behavioral evolution within the genus Homo.

Handedness measures for the Human Connectome Project: Implications for data analysis.

Open data initiatives such as the UK Biobank and Human Connectome Project provide researchers with access to neuroimaging, genetic, and other data for large samples of left-and right-handed participants, allowing for more robust investigations of handedness than ever before. Handedness inventories are universal tools for assessing participant handedness in these large-scale neuroimaging contexts. These self-report measures are typically used to screen and recruit subjects, but they are also widely used as variables in statistical analyses of fMRI and other data. Recent investigations into the validity of handedness inventories, however, suggest that self-report data from these inventories might not reflect hand preference/performance as faithfully as previously thought. Using data from the Human Connectome Project, we assessed correspondence between three handedness measures - the Edinburgh Handedness Inventory (EHI), the Rolyan 9-hole pegboard, and grip strength - in 1179 healthy subjects. We show poor association between the different handedness measures, with roughly 10% of the sample having at least one behavioural measure which indicates hand-performance bias opposite to the EHI score, and over 65% of left-handers having one or more mismatched handedness scores. We discuss implications for future work, urging researchers to critically consider direction, degree, and consistency of handedness in their data.

Evidence of Grammatical Knowledge in Apes: An Analysis of Kanzi's Performance on Reversible Sentences.

Ape language acquisition studies have demonstrated that apes can learn arbitrary mappings between different auditory or visual patterns and concepts, satisfying the definition of symbol use. The extent to which apes understand aspects of grammar is less well accepted. On the production side, several studies have shown that apes sometimes combine two or more symbols together, in non-random patterns. However, this is quite limited compared to human language production. On the comprehension side, much greater abilities have been reported in apes. One of the most famous examples is Kanzi, a bonobo who reportedly responded correctly to a large number of novel commands. However, based on his performance on a small subset of reversible sentences-where the understanding of English syntax was critical-the extent to which he demonstrated grammatical knowledge has been questioned. Using a randomization study it is shown here that his performance actually vastly exceeds random chance, supporting the contention that he does in fact understand word order grammatical rules in English. This of course represents only one aspect of English grammar, and does not suggest he has completely human grammatical abilities. However, it does show that he understands one of the arbitrary grammatical devices used in many languages: The use of word order to code argument relations. It also removes from serious consideration the view that apes lack any kind of grammatical ability. From an evolutionary perspective, Kanzi's ability is most likely to result from homologous brain circuitry, although this is ultimately an empirical question.

Prefrontal white matter volume is disproportionately larger in humans than in other primates.

Determining how the human brain differs from nonhuman primate brains is central to understanding human behavioral evolution. There is currently dispute over whether the prefrontal cortex, which mediates evolutionarily interesting behaviors, has increased disproportionately. Using magnetic resonance imaging brain scans from 11 primate species, we measured gray, white and total volumes for both prefrontal and the entire cerebrum on each specimen (n = 46). In relative terms, prefrontal white matter shows the largest difference between human and nonhuman, whereas gray matter shows no significant difference. This suggests that connectional elaboration (as gauged by white matter volume) played a key role in human brain evolution.

The coevolution of play and the cortico-cerebellar system in primates.

Primates are some of the most playful animals in the natural world, yet the reason for this remains unclear. One hypothesis posits that primates are so playful because playful activity functions to help develop the sophisticated cognitive and behavioural abilities that they are also renowned for. If this hypothesis were true, then play might be expected to have coevolved with the neural substrates underlying these abilities in primates. Here, we tested this prediction by conducting phylogenetic comparative analyses to determine whether play has coevolved with the cortico-cerebellar system, a neural system known to be involved in complex cognition and the production of complex behaviour. We used phylogenetic generalised least squares analyses to compare the relative volume of the largest constituent parts of the primate cortico-cerebellar system (prefrontal cortex, non-prefrontal heteromodal cortical association areas, and posterior cerebellar hemispheres) to the mean percentage of time budget spent in play by a sample of primate species. Using a second categorical data set on play, we also used phylogenetic analysis of covariance to test for significant differences in the volume of the components of the cortico-cerebellar system among primate species exhibiting one of three different levels of adult-adult social play. Our results suggest that, in general, a positive association exists between the amount of play exhibited and the relative size of the main components of the cortico-cerebellar system in our sample of primate species. Although the explanatory power of this study is limited by the correlational nature of its analyses and by the quantity and quality of the data currently available, this finding nevertheless lends support to the hypothesis that play functions to aid the development of cognitive and behavioural abilities in primates.

Lagrangian frame diffeomorphic image registration: Morphometric comparison of human and chimpanzee cortex.

We develop a novel Lagrangian reference frame diffeomorphic image and landmark registration method. The algorithm uses the fixed Langrangian reference frame to define the map between coordinate systems, but also generates and stores the inverse map from the Eulerian to the Lagrangian frame. Computing both maps allows facile computation of both Eulerian and Langrangian quantities. We apply this algorithm to estimating a putative evolutionary change of coordinates between a population of chimpanzee and human cortices. Inter-species functional homologues fix the map explicitly, where they are known, while image similarities guide the alignment elsewhere. This map allows detailed study of the volumetric change between chimp and human cortex. Instead of basing the inter-species study on a single species atlas, we diffeomorphically connect the mean shape and intensity templates for each group. The human statistics then map diffeomorphically into the space of the chimpanzee cortex providing a comparison between species. The population statistics show a significant doubling of the relative prefrontal lobe size in humans, as compared to chimpanzees.

Seeking Synthesis: The Integrative Problem in Understanding Language and Its Evolution.

We discuss two problems for a general scientific understanding of language, sequences and synergies: how language is an intricately sequenced behavior and how language is manifested as a multidimensionally structured behavior. Though both are central in our understanding, we observe that the former tends to be studied more than the latter. We consider very general conditions that hold in human brain evolution and its computational implications, and identify multimodal and multiscale organization as two key characteristics of emerging cognitive function in our species. This suggests that human brains, and cognitive function specifically, became more adept at integrating diverse information sources and operating at multiple levels for linguistic performance. We argue that framing language evolution, learning, and use in terms of synergies suggests new research questions, and it may be a fruitful direction for new developments in theory and modeling of language as an integrated system.

Evolution of brain and language.

In this chapter evolutionary changes in the human brain that are relevant to language are reviewed. Most of what is known involves assessments of the relative sizes of brain regions. Overall brain size is associated with some key behavioral features relevant to language, including complexity of the social environment and the degree of conceptual complexity. Prefrontal cortical and temporal lobe areas relevant to language appear to have increased disproportionately. Areas relevant to language production and perception have changed less dramatically. The extent to which these changes were a consequence specifically of language versus other behavioral adaptations is a good question, but the process may best be viewed as a complex adaptive system, whereby cultural learning interacts with biology iteratively over time to produce language. Overall, language appears to have adapted to the human brain more so than the reverse.

Validation of plaster endocast morphology through 3D CT image analysis.

A crucial component of research on brain evolution has been the comparison of fossil endocranial surfaces with modern human and primate endocrania. The latter have generally been obtained by creating endocasts out of rubber latex shells filled with plaster. The extent to which the method of production introduces errors in endocast replicas is unknown. We demonstrate a powerful method of comparing complex shapes in 3-dimensions (3D) that is broadly applicable to a wide range of paleoanthropological questions. Pairs of virtual endocasts (VEs) created from high-resolution CT scans of corresponding latex/plaster endocasts and their associated crania were rigidly registered (aligned) in 3D space for two Homo sapiens and two Pan troglodytes specimens. Distances between each cranial VE and its corresponding latex/plaster VE were then mapped on a voxel-by-voxel basis. The results show that between 79.7% and 91.0% of the voxels in the four latex/plaster VEs are within 2 mm of their corresponding cranial VEs surfaces. The average error is relatively small, and variation in the pattern of error across the surfaces appears to be generally random overall. However, inferior areas around the cranial base and the temporal poles were somewhat overestimated in both human and chimpanzee specimens, and the area overlaying Broca's area in humans was somewhat underestimated. This study gives an idea of the size of possible error inherent in latex/plaster endocasts, indicating the level of confidence we can have with studies relying on comparisons between them and, e.g., hominid fossil endocasts.

Brain size scaling and body composition in mammals.

Brain size scales with body size across large groups of animals, but exactly why this should be the case has not been resolved. It is generally assumed that body size is a general proxy for some more important or specific underlying variable, such as metabolic resources available, surface area of the body, or total muscle mass (which is more extensively innervated than is, e.g., adipose tissue). The present study tests whether brain size in mammals scales more closely with muscle mass (and other components of lean body mass) than with total fat. Felsenstein's independent comparisons method was used to control for phylogenetic effects on body composition in organ weight data taken from a previously published comparative sample of 39 species in 8 different orders of mammals, all collected and processed by the same researchers. The analysis shows that the size of the central nervous system (CNS) is more closely associated with components of fat-free weight than it is to fat weight. These results suggest a possible explanation for why metabolic resources and brain size both share the same general relationship with body size across mammals. They also suggest that some measure of lean body mass is a more appropriate scaling parameter for comparing brain size across species than is overall body weight.