In the first ever photograph of wild gorillas engaging in the behavior, two lowland gorillas in Congo—nicknamed George and Leah—mate face-to-face as Leah's four-year-old daughter Nancy looks on. Leah is one of four females in George's harem.
Released to the public on February 12, 2008, the 2005 pictures originally accompanied a report in a spring 2007 issue of the Gorilla Gazette, a newsletter for gorilla scientists.
"Leah was lying on the ground and George was looking into Leah's eyes," researchers wrote in the report.
German conservation biologist Thomas Breuer, who took the photos, told National Geographic News, "It leads me to think about how similar gorillas can be to humans, [and yet] we humans are destroying them."
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Photograph by Thomas Breuer/Wildlife Conservation Society