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Only Brussels sprouts. Oh dear.
i think they're actually on the outside because the sperm needs to be a different temperature than the rest of your body or they'll die. but that doesn't make sense because they go into a woman and can live for a while... hmmm
Gwrr.. How about putting the testicles inside the body, like women?
Temperature regulationIn boreoeutherian land mammals (but not the xenarthran or afrotherian land mammals) the testes are located outside of the body, suspended by the spermatic cord within the scrotum. It has been suggested  that the ancestor of the boreoeutherian mammals was a small mammal that required very large testes (perhaps rather like those of a hamster) for sperm competition and thus had to place its testes outside the body. This led to enzymes involved in spermatogenesis, spermatogenic DNA polymerase beta and recombinase activities evolving a unique temperature optimum, at a degree somewhat less than core body temperature (37 °C or 98.6 °F for humans). When the boreoeutherian mammals then diversified into forms that were larger and/or did not require intense sperm competition they were stuck with enzymes that operated best at cooler temperatures and had to keep their testicles outside the body. An alternative argument is that the cooler temperature of the testes allows for more efficient fertile spermatogenesis. Another argument is that it protects the testes from abdominal cavity pressure changes caused by jumping and galloping. . As external testes would increase drag many boreotherian aquatic mammals have internal testes which are kept cool by special circulatory systems that cool the arterial blood going to the testes using by placing the arteries near veins bringing cooled venous blood from the skin.The cremasteric muscle is part of the spermatic cord. When this muscle contracts, the cord is shortened and the testicle is moved closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature. When cooling is required, the cremasteric muscle relaxes and the testicle is lowered away from the warm body and is able to cool. This phenomenon is known as the cremasteric reflex. It also occurs in response to stress (the testicles rise up toward the body in an effort to protect them in a fight), and there are persistent reports that relaxation indicates approach of orgasm. There is a noticeable tendency to also retract during orgasm.The testicles can also be lifted voluntarily using the pubococcygeus muscle, which partially activates related muscles. This can sometimes be triggered by tightening or sucking in the stomach or abdomen. The testicles have a tendency to perspire profusely.Monotremes, armadillos, sloths, elephants, and rhinoceroses have low body temperatures and do not have external scrotal sacs; their testes remain within the abdomen. Marine mammals also have internal testes, but it has recently been shown (eg, for dolphins) that they use elaborate vascular networks to provide the necessary temperature lowering for proper operation.Animals other than mammals do not have externalized testicles. Birds, despite having very high core body temperatures have internal testes; it was once theorized that birds used their air sacs to cool the testes internally, but later studies revealed that birds' testes function at core body temperature.from wikipedia: http://en.wikipedia.org/wiki/Testicles