The author seems confused: > Sperm passage up the female tract is more like an extremely challenging military obstacle course than a standard sprint-style swim

The author seems confused: > Sperm passage up the female tract is more like an extremely challenging military obstacle course than a standard sprint-style swimming race. Sperm numbers are progressively whittled down as they migrate up the female tract, so that less than one in a million from the original ejaculate will surround the egg at the time of fertilisation. Any sperm with physical abnormalities are progressively eliminated along the way, but survivors surrounding the egg are a random sample of intact sperm. > The entrenched idea that ‘the best sperm wins’ has elicited various suggestions that some kind of selection occurs, but it is difficult to imagine how this could possibly happen. The DNA in a sperm head is tightly bound and virtually crystalline, so how could its properties be detected from outside?