Not many of us have won a marathon . . . hell, most of us would struggle to even finish one. But even the least competitive, most couch potato-like among us are the result of winning the most difficult of races in the most appalling of conditions: the race between sperm in an ejaculate to fertilize a female's egg.

The average human ejaculate contains around 180 million spermatozoa (the number depends on the length of "recharge" time between ejaculations). It takes between five minutes and one hour for the thrashing sperm to reach the fallopian tubes. And so hostile are the conditions in the vagina that human sperm are fertile for only 24 to 48 hours once inside.

So everyone: Congratulate yourselves, you did well to get here. Sit back on that couch and eat some more doughnuts.