Big Brains, Small Brains
Why is there a brain and why are some larger and others smaller? What advantage is there to having them has been often argued. Recently published in the Journal of Evolutionary Biology, new studies reveal that "species which have developed large brains live for longer than those with small brains, as the protective brain theory suggests, and therefore, can reproduce more times".
The Protective Brain Theory states that the brain better protects the body and hence increases the average life span of the body. If the animal is protected by a large brain, this results in greater survival and a longer life. However, the evidence is far from clear on this potential conclusion
According to this hypothesis, the brain would adopt a protective role which would help to reduce mortality and lengthen the reproductive live of the individuals, thereby compensating the for the development costs associated with a large brain. What evidence that exists is based on correlated data and not a definitive cause and effect.
The research team analyzed 493 species of mammals from different regions of the planet. According to the authors, the evidence resulting from the study is "correlative", in other words they do not necessarily indicate cause-effect, but the analysis indicates that the link between a large brain and longevity is not only due to the fact that species with large brains are greater in size and develop more slowly, they also live in specific regions or share the same evolutionary ancestors.
Size of brain does not necessarily mean intelligence but may be related to other social factors as well. Larger mammals also tend to have larger brains.
Elephants and whales both have relatively larger brains as well as bodies. These mammals have larger brains than humans but about the same lifetime.
"As extension of life duration is central to many hypotheses on the advantages of developing large brains, these results offer a solid base which can be used to continue building a general theory on the evolution of the brain", concludes the scientists in their study.
Throughout their evolutionary history some mammals, such as primates, cetaceans and elephants, have developed much larger brains than would be expected for their body size. But a large brain involves a longer development time and proportionately more effort to develop.
In the Descent of Man (1871), the British naturalist Charles Darwin, thought that a large brain, such as that of humans, improved the mental capacity of individuals, because natural selection favors the appearance of large brains. But large brain size is not the only factor in that larger mammals are often larger in brain size too just by being large.
There is still much to learn about the advantages and disadvantages of brain size much less intelligence.
For further information: http://www.eurekalert.org/pub_releases/2010-07/f-sf-tpb071610.php