Evolution's Worst Mistake? How About External Testicles?

Evolution's Worst Mistake? How About External Testicles?
"EVOLUTION is a work in progress, so it’s hardly surprising that some of the features it has built into the human body are still far from optimal.
And of all those features, one of the hardest to explain is also one of the most conspicuous: external testicles.
There’s no good reason sperm development needs lower temperatures.
It’s just a fluke, an example of poor design.
From an evolutionary standpoint, after all, testicles are the most important thing about a man — without them, he wouldn’t exist at all.
And there they are, just sitting out in the open. 
Exposed. 
Vulnerable. 
What kind of design is this?...
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