Why Natural Selection Allows a 50:50 Sex Ratio

2 months ago

We could say that Evolution actually has to do with reproduction but when you look at some species, not all the males contribute to the mating process that forms their next generation. For instance, in Elephant Seals popularly known as Sea Elephants, the number of males that contributes the making of the next generation is very little with 4% of the males accounting of 88% of the mating activities that give rise to the next generation but when they reproduce, they reproduce to form almost 50:50 of male to female ratio population even when it would have been more efficient to have lesser numbers of male and a higher number of females, it isn't so in almost all animal species.

When we look at biological sex of male and female (not gender), it has become so common that we have almost equal number of both and people do not really pause to look at why and this can be because most people have learned that if the male (XY) chromosomes and the female (XX) chromosome come together we would end up with an equal probability of both sex.

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When it comes to reproduction, the females use up a lot of energy to get their eggs even when you would expect that the eggs be much since we need more populations for survival and evolution purposes but nature has shown that making an egg is quite expensive compared to making sperm even when males do not do any of the caring when the newborns are around.

In Biology, if it requires the survival of the fittest to make more offspring then we are going to be saying that 96% of elephant seals are not fit but in reality they are. That's said, what would happen if we had a 1 male to 9 female population, it will mean that the male will have mating opportunities 9 times more than the female and if it was a 1 to 9 male and female ratio, then it means the male has its gene in 18 offspring if each female has 2 newborn while the females have their genes in 2 offspring.

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If we had a reverse case, and we have 9 male to 1 female, then there will be four and half times more grandchildren then when it was more females than males. then there will be more males than females in a few generation to come. If there is a mutation causing 90% male offspring to emanate, then being male will not be an advantage because the females would be lesser making it difficult. For these things not to be a problem, mutation has been able to help us get the 50:50 male and female ratio which is evolutionary stable.

Let me guess something, you think I am talking about numbers right from the beginning of the post, I suppose? Well it isn't about numbers but resources from both male and female. This 50:50 ratio is seen the male and female invest their gamate to form offspring which are either male or female. This even shows up in parental care because if females required more parental cares of males, then there will be more females than males born.

You don't get it right; a good example is the Australian Brushtail Possum. The mothers invest more resources on their daughters and when the resources are scares, the male tends to survive because they didn't have as much resources before so nothing really changed. In this 50:50 case of natural selection, there will always be exceptions in nature but nature has been able to keep this stable even in animals where the females have to die to bring forth offspring, there is still balance.