Human language is a peculiar primate communication tool because of its large neocortical substrate, comparable to the structural substrates of cognitive systems. Although monkey calls and human language rely on different structures, neural substrate for human language emotional coding, prosody, and intonation is already part of nonhuman primate vocalization circuitry. Motherese could be an aspect of language at the crossing or at the origin of communicative and cognitive content.

The article of Finlay et al. is an excellent example of identifying constraints in the development of the brain, and their implications on brain architecture in evolution. Here we further illustrate the importance of constraints by presenting a few examples of how a small number of biophysical mechanisms or even a single life history parameter can have an enormous impact on brain evolution.

The observation that an animal's behavior is largely unaltered even after profound modifications of sizeable brain portions, suggests a large flexibility in the relationships between species-specific brain structures and species-specific behavior. In this perspective, a fascinating example is given by the comparison of jumping spiders and felids, where similar predatory behaviors are achieved with totally different brain substrates. (Published Online May 1 2007).

In offering a detailed view of putative steps towards the emergence of language from a cognitive standpoint, Michael Arbib is also introducing an evolutionary framework that can be used as a useful tool to confront other viewpoints on language evolution, including hypotheses that emphasize possible alternatives to suggestions that language could not have emerged from an earlier primate vocal communication system.

Fossil remains witness the relationship between the appearance of the middle ear and the expansion of the brain in early mammals. Nevertheless, the lack of detachment of ear ossicles in the mammaliaform Morganucodon, despite brain enlargement, points to other factors that triggered brain expansion in early mammals. Moreover, brain expansion in some early mammalian groups seems to have favored brain regions other than the cortex.

Because network scaling costs tend to limit absolute brain size, Striedter suggests that large cetacean brains must have evolved some novel ways to cope with these costs. A new analysis of available data shows that the scaling pattern of interhemispheric connectivity in cetaceans is isometric and differs from that observed in terrestrial mammals.