Trajectories and Constraints in Brain Evolution in Primates and Cetaceans

A negative allometric relationship between body mass (BM) and brain size (BS) can be observed for many vertebrate groups. In the past decades, researchers have proposed several hypotheses to explain this finding, but none is definitive and some are possibly not mutually exclusive. Certain species diverge markedly (positively or negatively) from the mean of the ratio BM/BS expected for a particular taxonomic group. It is possible to define encephalization quotient (EQ) as the ratio between the actual BS and the expected brain size. Several cetacean species show higher EQs compared to all primates, except modern humans. The process that led to big brains in primates and cetaceans produced different trajectories, as shown by the organizational differences observed in every encephalic district (e.g., the cortex). However, these two groups both convergently developed complex cognitive abilities. The comparative study on the trajectories through which the encephalization process has independently evolved in primates and cetaceans allows a critical appraisal of the causes, the time and the mode of quantitative and qualitative development of the brain in our species and in the hominid evolutionary lineage.     

Late Pleistocene human evolution in Sicily: comparative morphometric analysis of Grotta di San Teodoro craniofacial remains

The paleoanthropological remains from Grotta di San Teodoro near Acquedolci (province of Messina, Italy) represent the oldest and largest skeletal collection yet found documenting human settlement of Sicily. The sample, attributed to the Late Epigravettian (between 14,000 and 10,000 years B.P.), consists of seven variously complete adult individuals (San Teodoro 1–7). We compare the cranial sample to an array of both prehistoric and recent samples using multivariate techniques including D² distance analysis, canonical variate analysis, cluster analysis, and multidimensional scaling. Overall, the San Teodoro cranial sample displays a morphometric pattern close to Western European groups of similar antiquity, in particular those from Central and Southern Italy. The morphometric affinities indicate that these people probably came from peninsular Italy by sea during the Late Epigravettian epoch. An alternative hypothesis is that they descended from immigrants that arrived by land during a low sea level episode corresponding to the maximum Würmian regression, about 18,000 years B.P, with gene flow accounting for the morphological homogeneity with the populations of peninsular Italy. The San Teodoro skeletal sample provides the first reliable evidence for human settlement of Sicily.     

Encephalizations and Cerebral Developments in Genus Homo

As Darwin observed in the second chapter of the The Descent of Man, brain size has the more obvious and direct anatomical correlation with the outstanding cognitive capabilities of our species in comparison with its closest relatives. If we extend the comparison to other mammals, we can observe that cognitive capabilities do not seem to strictly correlate with brain dimension in absolute and in relative terms, and the encephalization quotient (EQ) is not a universal advice of the cognitive capabilities of a particular species, too. Why and how the brain size in our lineage increased dramatically in absolute and in relative way during the last 3 million years? What is the relationship between our outstanding intellective capability and the brain size? The progressive encephalization of our ancestors was the origin or the effect for the development of the intellective capabilities of living humans. Recent advances in the knowledge of intrinsic organization of cerebral cortex and in the patterns of genetic expression are able to better outline the trajectories as the metabolic and structural constraints of the qualitative and quantitative encephalic development. The new scenario led to suggest more accurate explanations of the selective mechanism acting during the evolution of our species.