I’m missing something here: Why are there two testicles on males? We have two eyes for a reason, we have two ears for a reason, but why two balls? I don’t see any reason why a guy would need two when one does the job just fine.
Why do women have two ovaries? Why do nearly all people have two kidneys? Or two lungs?
Well, redundancy is a nice safety factor to have.
Why not three then?
And why not have other organs (heart, liver, pancreas) which are equally essential for living be redundant?
Isn’t Klingon phsiology like that?
I for one think three balls would be a bit uncomfortable. I have enough trouble keeping the pair sitting nicely.
I’d think the plumbing changes to have two hearts pumping blood would be fairly complex, which may have something to do with the lack of multiple hearts.
And, on the question of pairs, why two legs, two arms? Why not five limbs, or six?
Humans, like most other animals, are bilaterally symmetrical. That was established waaaay back in evolution. That’s just the way it happened for us.
hehe aeropl says “Im missing something here” and then goes on to ask why two are needed…
doesnt anyone see the humor?
As my high-school biology teacher used to say, “Do you want me to answer as myself, or do you want me to answer as God?”
It works. Birds only have one functioning ovary, and that works too.
Redundancy? Bi-lateral symmetry?
If think a more important question is why are they on the outside and not inside the body?
The classic answer to that one is that they operate best at a temperature slightly below the normal body temperature (but not too much below, which is why they get hauled in when it is cold).
However, why would it not have been possible to simply make them work best at normal body temperature, like the ovaries?
Evolution doesn’t always end up producing the most elegant solution to the problem; it has to work largely by modifying stuff that already exists; I’m struggling to explain this adequately, but imagine a fork in the road; if you turn right, you take the road to the coast, if you turn left, you end up in the mountains - after having turned toward the mountains, it may not be possible to simply branch off again and end up at the coast (especially when you have no particular destination in mind) ; you’re stuck with the legacy of a previous bifurcation.
That’s a very eloquent way of putting it, Mangetout.
Kudos.
(And I’m a gonna steal that phrase and use it as my own! :D)
aeropl,
Since you already have several serious answers to your question, would you mind if I made a light-hearted one?
The right one is for the boy sperms (Y), and the left one is for the girl sperms (X). 
Unless you want to give the ‘because God said so’ answer, the reason why anything is the way it is in terms of biology is pretty simple- the ones who didn’t do it that way didn’t survive.
One is regular milk and the other is chocolate milk, no wait, I think I screwed that up…
'Cuz “One is the loneliest number…”.
If I had three I could finally teach myself how to juggle.
LOL…my cousin really believed that was true when my aunt was breastfeeding his little brother.
Three is too many.
One’s not enough.
YiBaiYuan: Sadly, some people actually believe that.
Amp, davebear, and lieu: I laughed out loud.
Okay I realize there’s the redundancy issue, but it still doesn’t make sense to me… It’s not like evolution planned to have two in case one testicle got cancer and had to be surgically removed. I don’t see how two could evolve (except for being the result of bilateral symmetry) through natural selection. If you get hit down there, chances are it will destroy both right? How often does one fail and the other keeps working? I guess evolution has a lot of unexplainable things.
Okay, I’ll hijack my own thread with a few more questions.
- Does the human body have three of a kind of any organ for redundancy?
- What are the theories on why/how bilateral symmetry evolved?
I don’t understand the bilateral symmetry thing… why not just one ball right in the center?
Why not two penises? Now we’re talkin’ fun!