Humans can speak because their brain development is slow

slow and steady wins the race. The adage holds true even in the case of evolution of the brain. Some of our unique human features, like the ability to use languages, happen to be because of a slow brain development after birth as compared to chimpanzees.

Researchers from Germany, UK and the US studied the expression of genes in humans, chimpanzees and rhesus macaques to understand how much of our development is delayed and how that impacts our physical appearance. The team studied 1,958 genes in the part of the brain that is known to influence our cognitive skills. They found that gene expression is highly influenced by factors like age, gender and species.

In humans, expression of 71 per cent of the genes that were studied was related to age. In both chimpanzees and humans, age-related gene expression changes occur fastest in the first few years of life. This has been found to be true of mice as well, indicating that this trajectory of age-related changes is a common feature among all mammals. But seen from the level of each gene, the changes that occur are quite different for each.

Thirty eight per cent of the genes that were studied were expressed slower in humans compared to chimps of the same age and with the same set of genes. Because of this delay in gene expression, humans reach sexual maturity later than chimpanzees. Again it is the same delay that is associated with our ability to learn languages and suffer from conditions like the attention-deficit disorder and hyperactivity.

The reason for such developmental delay is not known, said the study which was published in the March 18 online edition of the Proceedings of the National Academy of Sciences. One theory says that it gives us more time to adapt to our environment and acquire skills that are beyond the scope of other forms of life.