The shape of the large canine teeth in the front of the jaw is important. Male teeth were not larger than females'. It provides clues about social structure, suggesting that the males of the species did not fight each other for the females' attention.
Instead, said Lovejoy, "It is likely that the males went looking for food and brought it back to the females, possibly in return for sex, though that's another story."
He added, "This was probably a species for which male aggressiveness was not something that led to evolutionary success."
Scientists have believed since Charles Darwin's time that apes and human beings have common origins. But they have been hampered by the lack of fossils to trace the evolutionary path.
White and Lovejoy said that is why Ardipithecus is so important.
"This," said Lovejoy, "fills a huge gap."