Scientists have decoded the DNA of the western lowland gorilla, a feat that could boost conservation efforts for the endangered apes as well as broaden researchers' understanding of human origins.
The complete sequence of 20,962 genes — extracted from the skin cells of Kamilah, a 34-year-old gorilla who lives at the San Diego Zoo Safari Park — was compiled by an international team of more than 60 researchers who worked on the project for about five years.
"The gorilla genome is important because gorillas are our second-closest living relatives," said Richard Durbin, senior author of a paper about the discovery published Wednesday in the journal Nature.
Gorilla are the last of the genus of living great apes (humans, chimpanzees, gorillas and orangutans) to have their DNA decoded, offering new perspectives on their evolution and biology.
For instance, the new genetic data bolster fossil evidence that gorillas split off as a separate species about 10 million years ago and that humans and chimps parted ways about 6 million years ago. Previous genetic evidence had seemed to point to a more recent split, prompting a contentious debate between genetics experts and fossil scholars, said Durbin, who leads the genome informatics group at the Wellcome Trust Sanger Institute in Hinxton, England.
"We're proposing a way to make a consistent story between the genetic evidence and the fossil evidence," Durbin said.
Researchers found that genes relating to sensory perception, hearing and brain development showed "accelerated evolution" in all three, but particularly in humans and gorillas.
"That's significant," said University of Wisconsin anthropologist John Hawks, who was not involved in the research. "There's an argument about early hominids — are they really our ancestors? This helps settle that. It shows it's possible."
The data also show that humans and gorillas differ in only 1.75% of their DNA, much less than previously believed. Humans and chimps, our closest living relatives, differ in only 1.37% of their genomes.
When Durbin and his colleagues matched up the DNA letters of gorillas, chimps and humans, they found that in 15% of cases, gorilla DNA was more like human DNA than was chimp DNA.
This result "tells us that there are individual genes for which, if you want to find the closest sequence to humans, you won't necessarily look at chimpanzees. In a few cases, you'll look at gorillas," said Jeffrey Rogers, a geneticist at Baylor College of Medicine in Houston and coauthor of an editorial on the research, also published in Nature.
One of the similarities is prompting scientists to reconsider how language developed in humans. Previous studies had shown that genes involved in hearing evolved rapidly in humans. But the new study found that auditory genes evolved rapidly in gorillas too — calling into question the interpretation that the genetic changes were linked to the rise of language.
The genome researchers also identified several gene variants that cause diseases in humans, including dementia and a dangerous thickening of the heart muscle, but did not appear to be detrimental to the gorillas' health.
"Why is that the case?" Durbin wondered. "Is there another change in the gene that compensates? Do they not use the gene the way humans do, so when it goes wrong it's not a problem? If we understood what it was that allowed the gorilla to have the bad version that causes disease in humans, that might help us compensate for it in humans. It's a starting point."
As part of the study, the researchers also did a preliminary genetic analysis of two other western lowland gorillas and one eastern lowland gorilla.
In the wild, the western lowland gorilla is the most widespread species of gorilla, according to the World Wildlife Fund (WWF), with a estimated population of 100-200,000 individuals.
The majority are found in Cameroon, Central African Republic, west Congo, Equatorial Guinea, Gabon and Angola.
It's cousin, the eastern lowland gorilla is less prevalent (fewer than 20,000 individuals) and can only be found in the rainforests of the eastern Democratic Republic of Congo, says WWF.