Gorillas have been caught on camera for the first time performing face-to-face intercourse.
Humans and bonobos were the only primates thought to mate in this manner. And while researchers have observed wild gorillas engaged in such an act, it had never been photographed.
"Our current knowledge of wild western gorillas is very limited, and this report provides information on various aspects of their sexual behavior," said Thomas Breuer of the Max Planck Institute for Evolutionary Anthropology. "It is fascinating to see similarities between gorilla and human sexual behavior demonstrated by our observation."
The photographs were taken as part of a study conducted at Nouabale-Ndoki National Park in the Republic of Congo.
The female in the photograph, Leah, also made news in 2005 when she became the first of her kind spotted using tools. Researchers watched her use a stick to test the depth of a pool of water before wading into it.
"Understanding the behavior of our cousins the great apes sheds light on the evolution of behavioral traits in our own species and our ancestors," said Breuer, who led the study. "It is also interesting that this same adult female has been noted for innovative behaviors before."