This article first appeared in Molecular Testicles, February 1994, Volume 93, Number 2, pp. 254-260.
Testicular ascent is being held in great suspicion today. The cremasteric reflex is the physical process which lifts the testes either when it is cold (supposedly to maintain the correct temperature) or when there is danger (supposedly to protect the gonads).
Supposedly (read the article then read the comments). - (Did you notice how the guys who knew about other animal's breeding specifics were easily able to rip apart every detail of the 'temperature regulation hypothesis'?)
Are you thinking what I'm thinking? Yep, you'd have a tough time damaging or freezing my eggs. I keep them inside me, not far from my heart, not far from my stomach.
So why leave the male contribution to reproduction out in the cold? Vulnerable? Why risk the endocrine system? It just does.not.make.sense?
The official explanation? Body temperature is the wrong temperature for producing sperm. Why is this? Why don't all animals and flowers need a different temperature to produce their gametes? It doesn't appear to be a prerequisite of evolution, though it seems to go hand in hand with being a mammal.
Increasing temperature will usually increase the rate at which a chemical reaction or organic process will progress. It will also increase the number of reactions which are permitted to begin.
The only good reason one can think of for having a body part protrude, is to get a better 'look' if it's a sense (eyes on stalks, microphones on stalks) or to get a better reach if it's a mechanical function. It is difficult to establish any useful mechanical function for the testicles so we may begin to wonder what kind of 'sensing' ability the testicles possess?
In comes our team of Italian Scientists who claim to have found a way of recording sound onto junk DNA. Or were they Russian Scientists?...
We hypothesise that the genetic material in newly developed sperm is made 'writeable' by raising the temperature and changing the concentration of chemicals in the testes (Carbonyl Diamide being my favourite name of the prime suspect chemical). In the female, this process would more than likely either be ongoing, not-occurring, or running very slowly and would change more due to internal stimulus from the mother than to external stimulus such as those picked up by the testes.
In a dangerous situation, or a situation where the body is very cold, the testes become writeable then whatever happens to the male, whether it be fending off a sabre tooth tiger or finding a way to warm himself, the events (sounds, feelings, a few thoughts, smells, maybe light) that save his life are written to the junk DNA in the sperm in his testicles. When danger has passed, the testes lower which reduces the temperature and the concentration of chemicals which makes them write-protected. If coitus results in the next two or three days, the survival lessons do not get overwritten by mundane events and can be passed on to progeny who then may gain a millisecond advantage if the same situation comes up again in that lifetime (or if a lady ever needs to speak Japanese, which she's never ever learnt, on television).
Perhaps there is no more dangerous situation than a crocodile or a dragon sneaking up on you. This might explain why monkeys and men can see behind them with their balls yet whales, elephants, and armadillos never saw the need.
750 MB of DNA in each gamete. Only a small part encodes the body architecture. What is the rest for? Long range order has been found in junk DNA and it's purpose is as-yet unknown.
Ask yourself: Why are testicles where they are? If you were designing your own body, where would you put yours?
A recent study (pdf) suggests that women prefer to keep theirs private, while men are more likely to have theirs on display.