Sperm Competition

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Posted by: SexOracle, on 11/13/2008 , in category "Sex and You"
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Location: United States

Abstract: After reading some very interesting research, Sex Oracle has decided to tell you about sperm competition and why it’s more than just the greatest race of your life.

Sperm competition is a phenomenon found in all animals, be they insects, fish, reptiles, amphibians, birds or mammals (that includes us). It is a part of the greater “battle of the sexes” in which male and female are constantly co-adapting to each other.

First, you need to understand a bit about Sexual Selection, especially the bit about the different investments men and women make in reproduction.

Sperm in their billions are fairly inexpensive, and eggs (only a few hundred to each woman) are energy-rich and expensive. In other words, men can reproduce easily in vast quantity (given enough women) and women can reproduce a limited amount with lifestyle and health sacrifices.

Therefore, a woman wants to have her eggs fertilized by the best man possible (genes and resource-wise), a man that will stick around to support her and the children. A man wants to spread his genes and it seems the only feasible way to do this is to pledge vast resources and lifetime protection. Now the man thinks, if I’m working so hard and giving so much to my wife and children, why not make sure they are really my children? So he engages in ‘mate-guarding’ – doing his best to prevent other men impregnating his wife. It partly explains some cultures’ need for women to remain virgins until marriage (notice that such cultures usually follow male-led religions).

Thus begins the asymmetrical war of the sexes.

From a purely biological point of view, a woman’s best option is to copulate with two or more men of superior genetic quality, during her most fertile days of the month. Multiple types of sperm then have to battle it out. Her offspring will be the result of the ‘winner’ and will carry genes for winning sperm, ensuring grandchildren. During the time a woman is less fertile and less likely to become pregnant, she wants to have a more stable partner around to support her. According to studies reviewed by Thornhill (2006), the group of males with the best genes, and the group of stable, supportive, wealthy males, don’t usually overlap.

Applied to real life, a woman who has a less attractive partner is more likely to fantasise about other men during her fertile phase, and want to be with her partner during her less fertile phase. However, if she considers her partner very attractive, she will want to copulate only with him.

Most males are unaware of the sperm tactics they apply on a regular basis. In other words, males want their sperm to win. Masturbation refreshes the supply, expelling inferior sperm and those left in the urethra from his last ejaculation. The human male has developed large genitalia (relative to most of his ape cousins). He guards his mate from other men, and when he can’t do that (for example, his wife might go away on a business trip) he produces more sperm than usual, so that he can top up the sperm community living in his partner’s uterus (guarding the precious egg from evil foreign invaders). Why? She may be around other males. This phenomenon is more manifest when he perceives that she’s been around other competitive males than when he thinks she spent her time with non-rivals, like her girlfriends or family.

How about our animal cousins? Some birds and lizards ejaculate quickly to prevent another male pushing them off. Daddy Long Legs spiders develop long legs to run fast, as the females’ policy is “first come first served”. There are creatures that manage to block their mate’s vagina after copulation, with chemicals or their own penis, while others convince a female to discard her last lover’s sperm.

This short clip explains how masturbation and oral sex is used in sperm competition, among animals!