Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes

by Nathan H. Lents

Human sperm cells, you see, can’t turn left. This is due to the corkscrew nature of their propulsion system; rather than snapping their whiplike tails back and forth and side to side, sperm cells rotate their tails around in a corkscrew motion, like the way you would move your index finger to draw a circle in the air. Because most sperm whip their tails in a right-handed spiral, the rotation pushes them forward and toward the right and they end up swimming in ever-widening circles. This means that it can take as long as three days to reach the egg waiting in the fallopian tube to be fertilized. Very few of the original number get anywhere near their goal. This is one reason why human males produce sperm in such large numbers. You need about two hundred million of them to start with in order to get just one to its destination.