Why Do Mice Have Longer Sperm Than Elephants?

In the animal world, if several males mate with the same female, their sperm compete to fertilize her limited supply of eggs. And longer sperm seem to have a competitive advantage, but even when it comes to sperm the size of the animals matter. The larger the animal, the more important the number of sperm is relative to sperm length. That's why elephants have smaller sperm than mice.

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