Hearing before language? Picture by Alice Gray

New Delhi, March 7: Scientists have decoded the full genome sequence of the gorilla, extracting fresh insights into the evolutionary history of humans, chimpanzees and gorillas since they branched out from their common ancestor 10 million years ago.

An international research team announced today that it had analysed the full genome of a 35-year-old gorilla named Kamilah living in the San Diego Wild Animal Park in the US and compared it with human and chimpanzee genomes sequenced earlier.

Their findings, to appear tomorrow in the journal Nature, also show that about 15 per cent of the human genome is closer to the gorilla genome than it is to the chimpanzee genome. Their study shows that gorillas and humans shared parallel genetic changes in about 500 genes, particularly in genes involved in hearing, a discovery that challenges an existing hypothesis linking the evolution of hearing to language.

“Chimpanzees remain our closest living relatives,” said Aylwyn Scally, an Irish biologist at the Wellcome Trust Sanger Institute, and first author of the study. “However, different regions of the genome can have different ancestry,” Scally told The Telegraph.

Scally and his colleagues have proposed a synthesis of genetic and fossil evidence to suggest an evolutionary tree in which gorillas diverged from humans and chimpanzees 10 million years ago, and the chimpanzee-human split occurred six million years ago.

The gorilla genome analysis casts doubt on the hypothesis that rapid evolution of hearing in humans was associated with the development of language. The gorilla genome study shows that the evolution of some genes involved in the process of hearing began much earlier and occurred even in gorillas and did not occur only after humans began developing language.

“Hearing has been evolving rapidly for millions of years in both gorillas and humans, although language is human-specific and much more recent,” said Chris Tyler-Smith, a British geneticist studying human evolution, and a Sanger research team member.

The gorilla genome sequencing exercise has completed the genome sequencing of all the four living great apes — humans, chimpanzees, orang-utans, and gorillas.