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Can someone explain Fishers principle?
This is the explanation of why there are usually about 50 -50 male - females born in populations of say humans, but also other mammals. The principle talks about expending energy on off spring, so called parental expenditure or investment.
But it just doesn’t seem to make sense because a singe male is able to fertilise many females. So surely there would be less need of males than females?
2 Answers
- 8 years agoFavorite Answer
Basically, it costs the same amount of energy to the parent (mother especially) to produce males and females. Male offspring can, as you said, fertilize more females, so it might seem like it would be more evolutionarily favourable to have all male offspring.
But let's say that in a certain generation, the genes that favour male offspring is prevalent in the population so the generation is 95% male. Although these males would be theoretically able to fertilize many females, there are fewer females in the population for them to fertilize. Male-male competition will increase, and not all males will then reproduce. However, ALL of the females will reproduce because of the excess of females. These females are less likely to have the male-favouring gene (due to the fact that they are female), so the next generation will have a more even sex ratio.
Basically, this results in a balance between male and female in the population due to a balance in sex-preference genes.
Evolutionarily
