Our closest evolutionary relatives are chimpanzees, and both of our species are much more related to each other than to gorillas, the next closest relative. But a new genome analysis reveals we share some unexpected traits with our massive gorilla cousins.
Researchers at the Wellcome Trust Sanger Institute have sequenced the gorilla genome, using DNA from a female western lowland gorilla named Kamilah, with additional bits of DNA taken from other gorillas, to understand the genetic different differences between the various gorilla subspecies more clearly. The result is that we now have genome data for all four of the living great ape species: the gorilla, the chimpanzee, the orangutan, and, of course, the human.
Comparing the data confirms that humans and chimps are indeed the most closely related — we share 99% of our DNA, compared to 98% with gorillas and 97% with orangutans — but it's not quite that simple. According to the researchers, 15% of the human genome is more closely related to gorillas than chimps, and chimps also share about 15% of their genome with gorillas instead of humans.
This is because, even though we diverged from gorillas long before we diverged from chimps, some parts of our evolutionary journey have been along parallel paths. Senior author Dr. Chris Tyler-Smith explains, in a press release:
"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. 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."
Now that the language hypothesis has seemingly been debunked, exactly what prompted our aural evolution is a new mystery waiting to be explored. There's also a tantalizing genetic difference between humans and gorillas waiting to be explored — specifically why gorillas have a gene that protects them from dementia, while humans do not.
We also now have a much better sense of when the great apes diverged from us, and they're all a bit earlier than we expected: 14 million years ago for orangutans, ten million for gorillas, and six million for chimpanzees. Intriguingly, the split between eastern and western gorillas only seems to have happened in the last million years or so, and even then was a gradual change, meaning that gorillas have only very recently undergone an evolutionary makeover.