LOL. Don't tell them you have balls that hurt when kicked in the first place?
Oh and I found this chart. It features the Eutherians ('true beasts'), which includes Mammals, Monotremes, and Marsupials. All are warmblooded.Results of mapping the three character states onto a phylogeny of the Mammalia. Testicle position unordered: red, testicond; gray, descended and ascrotal; black, descended, scrotal; blue, marsupial; white, equivocal.
(Click for a bigger image)
from here: http://pharyngula.org/index/weblog/comments/descent_of_the_testicle/
Note how it shows that the primitive/original state is probably
to have the testicles descend showing that the descent of testicles really is connected to the development of endothermy. (If you can't understand that chart, think of it as a family tree. Groups on the bottom are granddads and grandmas and whatnot, groups at the top are cousins and relatives to each other)
Note how again it shows the logical flow of evolution. Red never becomes black or gray again. There are only about 3 branches which show red (testes do not descend, the scrotal sack is not present). Two are primitive branches and one are the sirenids and their allies - Golden Moles, Hyraxes Manatees, Dugongs, and Elephants. They are closely related to each other but VERY different in terms of appearance and habitats. This could actually be explained by the fact that their testes is never cooled. Meaning, the rate of mutation is faster, thus faster evolution. And yes, you heard it right, Elephants don't have balls!
Whales and allies also have a more sophisticated solution. Since their body need to be streamlined, they need to lose the scrotal sack. But they also have to keep sperm cool. Their evolutionary solution is to cool their blood on the skin (they live in mostly cool waters) and then shunt the cooled blood around their internal testes, thereby cooling it. They don't need to have balls then.
Thus we can say that whales have more highly evolved balls than humans. LOL
Most of the larger mammals (except the aquatic ones) have external balls, which means that it's been pretty effective so far, as far as survival of the fittest goes. Maybe if we can genesplice whales and humans we can produce children with internal balls... but they would only be fertile if they lived in water.
Either ways, if you want to have children, don't heat your balls or wear tight underwear. And don't let 11 year olds kick them.