Humans and Gorillas Closer Than Thought, Genome Sequence Says

Humans and Gorillas Closer Than Thought
Photographer: Mark Bridger/Getty Images

Gorillas have been portrayed as militaristic bullies in the Planet of the Apes movies and as “highly social gentle giants” by researcher Dian Fossey.

Now scientists say they’re closer genetically to humans than they once thought.

Sequencing the genome of a female western lowland gorilla named Kamilah determined that most gorilla DNA is similar or identical to those of humans, despite the 10 million-year gap since the two species split off, according to a report today in the journal Nature.

In 30 percent of the genome, the study determined that gorillas are closer to humans and chimpanzees than the latter two are to each other. It’s a finding that may help scientists track changes in how the species have responded over time to shared genetic characteristics, including diseases, the researchers said.

“If we can understand why they’re harmful in humans but not in gorillas, that would have useful medical implications,” said Chris Tyler-Smith, head of the human evolution team at Wellcome Trust Sanger Institute in Hinxton, England.

Gorillas are the last of the great ape genus to have their genome sequenced, the investigators said. The group saw changes in genes involved in sperm production and in the formation of keratin proteins in the skin.

Additionally, gene variants that in humans cause genetic disease don’t seem to affect gorillas similarly, said Tyler-Smith, one of the study’s authors.

Dementia Gene

One of the genes, PGRN, has a mutation that causes frontotemporal dementia in humans. Another, called TCAP, a human variant that causes hypertrophic cardiomyopathy, a condition where the heart muscle thickens, makes it hard for blood to leave the heart.

Both humans and gorillas have accelerated evolution in genes associated with hearing, suggesting that the changes aren’t related to speech, Tyler-Smith said.

Because gorillas live in groups with one male and many females, there isn’t a lot of sperm competition, so many genes involved in sperm formation are either inactive or decreased in numbers in gorillas. And a gene called EVTL, which contributes to keratin formation in the skin, is evolving very rapidly in gorillas, who walk using knuckles that are padded with keratin.

Humans overall are still closer to chimpanzees in 70 percent of the genome, said study author Aylwyn Scally, a postdoctoral fellow at the Wellcome Trust Sanger Institute.

Ape Separation

“When we look at human evolution, there’s an emphasis on chimpanzees because they’re closer, and other great apes get overlooked,” said Tara Stoinski, chief scientist of the Dian Fossey Gorilla Fund International, based in Atlanta.

“This lets us understand the relationships further back in our ancestry,” Stoinski, who wasn’t involved in the research, said in a telephone interview.

Human beings separated from chimpanzees 6 million years ago, and from gorillas about 10 million years ago, according to the report in Nature.

About half a million years ago, gorillas split into two species, the eastern gorilla, featured in Dian Fossey’s book, “Gorillas in the Mist,” and the western gorilla, whose genome sequence was published today.

Fossey was inspired by Jane Goodall’s work with chimpanzees and established a research center called Karisoke, in Rwanda. She knuckle-walked with the gorillas, habituating them to her presence so she could study them. Later, she tried to protect them from poachers after Digit, a gorilla she was especially close to, was killed in 1977. In 1983, she published “Gorillas in the Mist,” a description of her time with the gorillas that underscored conservation. Fossey was murdered in 1985, and buried next to Digit.

Koko the Gorilla

Koko the gorilla, who “speaks” using sign language, is a western lowland gorilla; her relationship with a pet cat was featured in the book “Koko’s Kitten.” Francine Patterson, a scientist who taught a modified form of sign language to the gorilla named Koko, portrayed the relationship between the gorilla and a housecat in the book.

Since the latest species split, eastern and western gorillas appear to have continued exchanging genetic information through sexual liaisons, researcher has suggested.

In the future, the scientists plan to look at the eastern gorillas, which have been studied more extensively in the field than western gorillas, Tyler-Smith said. Both species live in Africa, separated by the Congo River. The western gorillas are critically endangered, threatened by Ebola and being eaten by humans as meat; eastern gorillas are endangered, Stoinski said.

The human genome sequence was declared complete in 2003, the chimpanzee in 2005, and the orangutan in 2011.

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