Grandma Manimal. The Loom: A blog about life, past and future

Grandma Manimal. The Loom: A blog about life, past and future

Before this study, the rough consensus among scientists was that our ancestors diverged from the ancestors of our closest relatives--chimpanzees and bonobos--at some point between five to seven million years ago. That evidence came from studies on DNA, as well as from fossils, such as the oldest hominid fossil, Sahelanthropus, which is estimated to have lived 6.5 to 7.5 million years old. Most scientists argued that the hominids made a relatively clean break from other apes, without any significant hybridizing.

But that's not what has emerged from the new study. The Broad Institute scientists lined up millions of bases of DNA in humans and chimps and measured their differences. Humans and chimpanzees both inherited each segment of DNA from a common ancestor. Over time, the copies of that ancestral segment picked up mutations. The differences between them can offer clues to how long they've been evolving along separate paths. It turns out that the ancestors for some of those segments are much older than others. The only way to make sense of these results, according to the scientists, is to conclude that hominids and the ancestors of chimpanzees were interbreeding--to some extent at least--for four million years.