Did ancestral humans, chimps interbreed?

The research, conducted by scientists at Harvard Medical School, the Massachusetts Institute of Technology (MIT), and the Broad Institute of Harvard and MIT, indicates that humans and chimpanzees developed into distinct species less than 6.3 million years ago and probably more recently than 5.4 million years ago. That is about a million years later than the previously accepted range of 6.5 million to 7.4 million years ago.

もちろん今では無理だけど、もしかすると540万年くらい前までは交雑が可能だったのではないかと。