A molecular phylogeny based on extensive taxon sampling is required to establish systematic relationships within Corvus so that questions pertaining to historical biogeography, brain size and the evolution of innovative foraging habits and tool use might be addressed.
The lack of association between brain size and the evolution of MCPH1 found in cetaceans agrees with the conclusions drawn from a recent study of anthropoid primates which showed that MCPH1 is not associated with the evolution of either absolute or relative brain size [ 25], despite the clear critical importance of MCPH1 in brain development.
Notably, the dramatic increase in brain size and complexity during human evolution was accompanied by accelerated, often positive, selection on several genes involved in regulation of brain size and the nervous system in general [ 7- 15].
In the last decades, the characterisation of neural stem and progenitor cell types in the mammalian cortex has led to a number of hypotheses that subsequently attempted to explain the cellular mechanisms responsible for the increase in brain size and folding during mammalian evolution.
Previous research has shown that the neocortex (or 'neopallium') has played a central role in the evolution of brain size and architecture in primates and other mammals [1].
The evolution of brain size and complexity in the Order Primates has been widely regarded as the hallmark of primate evolutionary history.
The evolution of brain size and complexity in the Order Primates is widely regarded as the hallmark of primate evolutionary history.
On the other hand, under a mosaic evolution model we would expect divergence in patterns of evolution between whole brain size and individual brain structures, and especially among structures, as these are predicted to vary in size independently [ 1].
If future studies examine other hominoid (ape) species in a similar manner, the findings combined with hose of the present study would have implications for the development of hominoid brain size, posture, and evolution.
Indeed, the Machiavellian Intelligence hypothesis argues that an ability to detect (and counter) deceptive behaviors based on cognitive mechanisms has been a major factor underpinning the evolution of large brain size and advanced cognitive abilities among primates [Byrne & Whiten, 1990, 1992].
These findings suggest that allelic variants of some types of intellectual disability genes may have mediated the evolution of human brain size and cognition, and they provide a clear focus for future studies along these lines.
