I could easily just Google this question, but I want to hear what TSD has to say. Why do males have two testicles? Does one make girls and one make boys? Did girls give it to us so when they kick us in the balls it hurts more? What is their purpose?
There are all sorts of reasons, but it really just boils down to Bilateral Symmetry.
That, and redundancy: Even if one of your balls gets irreparably damaged, you can still use the other. That sort of redundancy is good, for such an essential biological function (essential from the point of view of evolution, at least).
Definitely not. X and Y bearing little swimmers are made in each testicle.
Figure out why females have two ovaries and you’ll have your answer as to why males have two testicles. They arise from the same source embryologically.
I believe redundancy is significant. As noted they tend to get injured. Having a backup increases that odds of passing on genes.
Hah I never even thought of redundancy as an explanation, bravo.
I would’ve thought that the brain, heart, liver, and digestive system are even more essential.
You would think, right?
Makes you wonder why you have 2 kidneys and one liver.
A single brain and heart kind of make sense because of the energy that would be required to duplicate the nervous and circulatory systems, almost like diminishing returns.
And even though you only have one liver, it sort of is redundant, in that you can live with a fraction of a liver, and it’s the one organ which will eventually grow back.
Meanwhile, problems with the other organs mostly tend to be slow to develop, giving you plenty of time to sleep around before the end, but problems with the testicles are often sudden and catastrophic, and even if you’re still walking, thinking, and pumping blood after that point, evolution doesn’t have much use for you any more.
Most of those are surrounded by a bony cage. Your brain is probably the best protected organ you have. Even your digestive system has to suffer a puncture or heavy trauma for a fatal injury (IANAD, so maybe I’m understating the danger here). Balls are just out there in the open.
Indeed. Further, the nature of the brain and heart are such that you really can’t have a convenient backup. Both take a lot of energy to grow and maintain, problems are usually either catastrophic to the point where no recovery is possible or very slow to develop such that it doesn’t hinder you most of your life. And if you did have a backup, it would interfere with the function of the organ’s primary role.
A second brain portion just couldn’t take over the task of the primary thought organ. (Note, however, that you can survive and function with limited brain damage, and the bilateral symmetry of the brain can help one part substitute for a damaged portion.) And the heart’s pumping mechanism would be interfered with if something else was pumping around as well.
Are there really NO organisms whatsoever that have two or more hearts?
Humanoids from Gallifrey have 2 hearts and travel in blue police boxes. 
Sure. Hagfish have four hearts.
In the 80s there was Stacey Q.
All the spare redundant back-up balls in the world aren’t going to help propagate the species if there’s only one penis that that gets mangled or lost. :eek: Where’s the intelligent design in all this?
BTW: The OP is correct, that it could be easily googled. But who cares to find the five explanations at Yahoo Answers? OTOH, there was also this:
One good kick can take out as nut. A penis is more durable due to it’s normally flaccid state.
Natural selection: the guy who makes a poor decision to masturbate with a belt sander is not afforded the opportunity to reproduce.
iirc, octopus have 3 hearts
And has that ever been tested, or are we just assuming that is the case? Science requires verification from observation. Anyone know any one testicled men who have a variety of children that actually look like them?