The sperm race

Description:Any sperm with physical abnormalities are progressively eliminated along the way, but survivors surrounding the egg are a random sample of intact sperm. However, from the mids on, mounting evidence revealed that human sperm can survive intact for at least five days. Relatively few sperm travel directly though the womb cavity, and numbers are further reduced during entry into the oviduct. Whereas natural selection can lead to increased sperm production if males are in direct competition, it will also favour mechanisms in the female tract that constrain numbers of sperm around the egg. More powerful microscopes eventually relegated the homunculus to the dustbin of history — but in some ways not much has changed. Crossing over increases variation, the essential raw material for natural selection. The vesicles and the prostate gland together produce seminal fluid, which can coagulate to form a plug in the vagina, temporarily blocking access by other males.

Views: 2562 Date: 2018-07-27 Favorited: 37