As far as we know, no dog can compose music, no dolphin can speak in rhymes, and no parrot can solve equations with two unknowns. Only humans can perform such intellectual feats. Anatomically, the human brain is very similar to that of other primates because humans and chimpanzees share an ancestor that walked the earth less than seven million years ago. However, intellect seems to have emerged independently in birds and mammalsand also in cetaceans and primates. The human brain lacks conspicuous characteristics- such as relative (ratio of brain to body mass) or absolute size- that might account for humans' superior intellect.

 

Encephalization quotients (EQs) expresses the extent to which a species' relative brain weight deviates from the average in its animal class, say, mammal, bird or amphibian. Here, the human brain tops the list: it is seven to eight times larger than would be expected for a mammal of its weight.

 

The human brain is densely packed with 11.5 billion cortical neurons-more than any other mammal. However, humans have only about half a billion more cortical neurons than whales and elephants-not enough to account for the significant cognitive differences between humans and these species.

 

A brain's information processing capacity depends on how fast its nerves conduct electrical impulses.The most rapidly conducting nerves aare swathed in sheaths of insulation called myelin. The thicker a nerve's myelin sheath, the faster the neural impulses travel along that nerve.The myelinated nerves in the brains of whales and elephants are demonstrably thinner that they are in primates,suggesting that information travels faster in the human brain that it does in the brains of non-primates.What is more, neuronal messages must travel longer distances in the relatively large brains of elephants and whales than they do in the more compact human brain.The resulting boost in information-processing speed may aat least opartly explain the disparity in aptitude between humans and other big-brained creatures.