A new study conducted by American researchers has found that ever since the lineage diverged, chimpanzees, and not humans, have experimented more with sex.
Male chimps are uniquely known to produce thick semen that coagulates into a plug present in the female counterpart's genital tract, which increases the odds of a male fertilising the female's eggs.
But the question that remains is whether male chimps inherited this unique ability from the last shared common ancestor or did they evolve it later, New Scientist reported.
Michael Jensen-Seaman and Scott Hergenrother at Duquesne University in Pennsylvania team, trying to resolve the question, looked at ACPP - an enzyme in semen, which prevents it from coagulating into a plug.
They found that the enzyme is four times as abundant in human semen as in the chimp semen.
For clues about the human-chimp ancestor having similar levels of enzyme to humans or chimps, the team turned towards the gorillas, which separated from the ancestor a few million years earlier.
The test showed that gorillas regulate ACPP similar to humans, which suggests that the human-chimp ancestor did the same.
However, it is difficult to be sure whether the chimps made the change after having split from humans.
It is also possible that the human-chimp ancestor had chimp-like behaviour and that our lineage has since reverted to a gorilla-like condition.