Why didn't humans evolve with the testicles safe inside the body?

[KidCharlemagne]

Here we go. Richard Dawkins on the subject:

extracted from: http://www.nyu.edu/classes/neimark/evolution.html

JL: Is survivability the only principle that generated our attributes? What about the benefit for a phenomenon as odd as testicles? It’s as if a heavily armored tank were being ridden by a driver in a balloon on the roof.
RD: Why do we have them dangling outside ourselves, rather than safely cushioned inside?
JL: I’m familiar with the conventional explanation, which is that it has to do with the management of heat. [Sperm cannot survive long at body temperature.]
RD: And you understand the implausibility of that explanation?
JL: The evolutionary process has produced such spectacular mechanisms for managing problems that would seem to be much more difficult than coping with heat. And we have astonishing regulatory mechanisms for heat in our body already. I mean, we protect ourselves from invading microorganisms and from extremes of heat and cold.
If it just turned out that it was impossible to pass along genes at a particular body temperature, we could have evolved a different body temperature that was appropriate to that process. So overall, testicles do seem very strange to me.
RD: That’s what I would have said. But are you familiar with Zahavi’s handicap principle? It sounds really way out, but I think the problem of the vulnerable balls' is well suited to this particular explanation. Zahavi is an Israeli biologist whose idea was ridiculed when he first put it forward in 1975, but he has recently been vindicated by some clever mathematical modeling by Alan Grafen at Oxford University. Zahavi and Grafen state that in any encounter in animals where advertisement is important--and that's very, very often--an advertisement is only believed if it's validated by being costly. Translated into English, what the male is saying is, Look how powerful a male I am, because I can afford to wear my balls outside my body, in the most vulnerable position. You’d better not mess with me because I am proving my strength and my ability as a fighter.’
JL: That’s a sad thought, that advertising might overpower common sense, because of a universal mathematical principle.
RD: The reason it works is that all males, even the ones who are not strong, are forced to wear the badge of being strong, and the badge of being strong is only believed if it is genuinely costly.
JL: But, Richard, if this explanation is correct, why didn’t we come up with camouflaged
testicles or perhaps four testicles with a couple of backups inside? And why aren’t our hearts or lungs dangling in bags without any armor around them? Why wouldn’t evolution occasionally choose to advertise some other body part?
RD: Why is the bone of the skull so thick? Obviously to protect the brain. The weakness of the Zahavi explanation is that you wheel it out when you need to. When I’m asked questions like yours about testicles, the best strategy may be to refuse to answer. Because if you allow yourself to exercise your ingenuity in solving a particular question, then people come up with another one that you just cant think of an answer to. We’re not testing the ingenuity of the human mind here.
JL: Agreed. But a lot of people feel that if evolution can’t explain something, why should they accept it at all? Yet the whole theory doesn’t have to be cast into doubt if it can’t explain every particular–such as the origin of our dreaded dangling. Scientists don’t know everything. They work with utmost patience to test one idea at a time.
PT: Can we go back to foresight for a minute? If natural selection didn’t select for foresight but allows us to escape its dictates, how does it survive?
JL: My answer would be that our excess of foresight is like testicles. There are traits we can’t fully explain. It might be luck.

[AndrewL]

*Originally posted by refusal *
**There must be more to this. Why are sperm cells killed by elevated temperatures that all other cells can survive perfectly well? Is it some special characteristic of the cell that’s useful for their function (like their size or special chemical composition), or is it just a chance thing? Does being killed in hot temperatures help sperm in some way (like competition between sperm seems to weed out less healthy sperm before they can fertilise the egg)? **

It probably has something to do with the fact that sperm aren’t complete cells. They’re missing much of the normal cellular machinery needed for metabolism and reapir; like red blood cells, they have a very limited lifespan and need to be replaced frequently. Keeping them cooler would let them last longer in that case.