High school biology 101; the penis is the male organ of reproduction in higher vertebrates. To allow for sexual intercourse, it becomes engorged with blood and an erection ensues. The end, right?
One pretty big question puzzled scientist Diane Kelly about the erection; why doesn’t it wiggle? Through her study of skeletons, Kelly hypothesised that the penis was most like the hydrostatic skeletons of worms and other invertebrates.
A hydrostatic skeleton has 2 key elements; a spongy fluid filled inner section surrounded by a firmer collagenous outer wall. The penis fulfils both of these requirements; its central portion is made of spongy tissue which fills with blood, while the outer section is collagen rich. But hydrostatic skeletons are subject to certain movements, such as compression and extension, due to their structure. So Kelly started simulating erections in the outer layers of penile tissue and looked at it under a microscope to see what made the erection behave as it does.
The difference between the outer wall of the penis and most hydrostatic skeletons is in the fibrous structure. Instead of being arranged into cross helices, the outer wall consists of two layers with the fibres of each stacked perpendicularly on the other. This allows for an erect model which resists bending and contraction.
Every year studies reveal new information on our anatomy, with limited funds. Kelly’s take home message is that researchers should take the time to apply ideas broadly between systems; if a link can be found between the penis and worms, who knows what other connections can be discovered?