First gorilla genome map offers clues to human evolution

The human genome is stored on 23 chromosome pairs and in the small mitochondrial DNA. Twenty-two of the 23 chromosomes belong to autosomal chromosome pairs, while the remaining pair is sex determinative. But that is human, what about one of our close relatives, the gorilla? Researchers announce today that they have completed the genome sequence for the gorilla - the last genus of the living great apes to have its genome decoded. While confirming that our closest relative is the chimpanzee, the team show that much of the human genome more closely resembles the gorilla than it does the chimpanzee genome. This is the first time scientists have been able to compare the genomes of all four living great apes: humans, chimpanzees, gorillas and orangutans. This study provides a unique perspective on our own origins and is an important resource for research into human evolution and biology, as well as for gorilla biology and conservation. Gorillas are the largest extant species of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies. The DNA of gorillas is highly similar to that of a human, from 95—99% depending on what is counted, and they are the next closest living relatives to humans after the bonobo and chimpanzee. "The gorilla genome is important because it sheds light on the time when our ancestors diverged from our closest evolutionary cousins. It also lets us explore the similarities and differences between our genes and those of gorilla, the largest living primate," says Aylwyn Scally, first author from the Wellcome Trust Sanger Institute. "Using DNA from Kamilah, a female western lowland gorilla, we assembled a gorilla genome sequence and compared it with the genomes of the other great apes. We also sampled DNA sequences from other gorillas in order to explore genetic differences between gorilla species." The team searched more than 11,000 genes in human, chimpanzee and gorilla for genetic changes important in evolution. Humans and chimpanzees are genetically closest to each other over most of the genome, but the team found many places where this is not the case. 15% of the human genome is closer to the gorilla genome than it is to chimpanzee, and 15% of the chimpanzee genome is closer to the gorilla than human. In all three species, genes relating to sensory perception, hearing and brain development showed accelerated evolution - and particularly so in humans and gorillas. "Our most significant findings reveal not only differences between the species reflecting millions of years of evolutionary divergence, but also similarities in parallel changes over time since their common ancestor," says Dr Chris Tyler-Smith, senior author from the Wellcome Trust Sanger Institute. "We found that gorillas share many parallel genetic changes with humans including the evolution of our hearing. Scientists had suggested that the rapid evolution of human hearing genes was linked to the evolution of language. Our results cast doubt on this, as hearing genes have evolved in gorillas at a similar rate to those in humans." The team found that divergence of gorillas from humans and chimpanzees occurred around ten million years ago. The split between eastern and western gorillas was much more recent, in the last million years or so, and was gradual, although they are now genetically distinct. This split is comparable in some ways to the split between chimpanzees and bonobos, or modern humans and Neanderthals. Gorillas survive today in just a few isolated and endangered populations in the equatorial forests of central Africa. Gorillas' natural habitats cover tropical or subtropical forests in Africa. Although their range covers a small percentage of Africa, gorillas cover a wide range of elevations. The mountain gorilla inhabits the Albertine Rift montane cloud forests of the Virunga Volcanoes, ranging in altitude from 7,200—14,100 feet. Lowland gorillas live in dense forests and lowland swamps and marshes as low as sea level, with western lowland gorillas living in Central West African countries and eastern lowland gorillas living in the Democratic Republic of the Congo near its border with Rwanda.