The researchers now asked themselves the question of how it can come to mating despite these different anatomies. They made two hypotheses: either the Erpelpenis is particularly adaptable, or the females change the shape of their vagina. To check this, they first allowed the pilot to board a duck. As soon as the monkey's cloaca swelled as a sign of readiness for copulation, the scientists held differently shaped glass tubes in front of the female's cloaca. The different tubes were modeled on possible forms of the vagina: one was cylindrical, one rotated in one and another in a counterclockwise direction.
Using a high-speed camera, the scientists filmed the "mating". So they could watch as the drakes evert their 20 centimeters long penis in just 0.36 seconds. However, he was able to develop to full length only in the straight tube and in the copy whose turns corresponded to those of the penis. The conclusion of the researchers: If the penis can not adapt to the vagina, it must adapt to the penis. Accordingly, the scientists assume that the female ducks only relax their vaginal muscles and thus allow the penetration of the penis, if they agree with the drake. This theory is also supported by the fact that laying eggs would not be possible with cramped muscles.Patricia Brennan (Yale University in New Haven) et al .: Proceedings of the Royal Society B, doi: 10.1098 / rspb.2009.2139 ddp / science.de? Jessica von Ahn ad