Successful fertilization requires sperm with rapid forward motility, correct oval head morphology, a single tail, and sufficient mitochondria in the mid-region.

“So the idea here is that we want the maximum number of high-quality sperm-- that is, rapidly forward, motile sperm that are of the correct morphology-- that is, shape. That's going to require a lot of mitochondria in the mid region, a well-shaped head-- so it's going to be an oval-shaped head. The tail is going to be a single tail, not multiple tails. These aren't going to be the twitcher type of-- or immotile type of sperm that are either twitching in place or aren't moving forward. All of those components are going to be essential for increasing the probability of fertilization.”