Why aren’t there more females than males in most species?


Would it not be more beneficial for a species (population wise) to have more individuals able of giving birth rather than individuals that only increase the population during reproduction?

In: 0

Just thinking logically here, not a biologist, but no, this would lead to bottlenecking over time. Everyone’s genes would start to look like everyone else’s over time, and any issue that targets certain genes would become detrimental. Even males and females probably leads to more genetic variety and more diverse survivability traits.

Let’s assume 75% of all humans were female and 25% of all humans were male. In such a world, each man would have on average 3 female partners to reproduce. Let’s say he has 4 children with each female partners. All 12 children would have 50% of the man’s genes, but only 4 children would have 50% of each mother’s genes.

That means that it’s evolutionarily beneficial to have sons. If I have a son, he will pass on my and my wife’s genes to 12 children. If I have a daughter, she will only pass our genes on to 4 children.

Now, imagine I have a mutation that increases the likelyhood of producing sons. That would be a huge evolutionary benefit for my genes. If my genes cause 50% (instead of 25%) of my children to be male, that means that those 6 sons will pass on my genes to 72 grandchildren and my 6 daughters will pass on their genes to 24 grandchildren – a total of 96. For everyone without this mutation it would be 3 sons with 36 grandchildren and 9 daughters with 36 grandchildren – a total of 72.

Thanks to my mutation, I get an extra 24 grandchildren. On top of that, I also pass on the 50%-male-children gene to half of my offspring. That means half of my offspring also has this evolutionary benefit.

Over generations, this mutation spreads throughout the population until we at some point have about 50% males and 50% females.

The same would happen with an imbalance in the other direction.

Well, it might seem like having more females would be better for making lots of babies, but it’s not always that simple.

First, it’s important to remember that not all animals give birth in the same way. Some lay eggs, and some have live babies. For animals that lay eggs, like chickens or turtles, it’s usually the females that do all the work of laying and caring for the eggs. For animals that have live babies, both males and females contribute to making the babies, but only the females can actually carry and give birth to them.

Second, having more females than males might not be the best thing for a species because it could upset the balance of the group. If there were too many females and not enough males, the males might have trouble finding mates, and that could make it harder for the group to have babies at all.

Lastly, some species have evolved to have more males or females for various reasons, such as competition for resources, survival strategies or mating behaviors. This means that having an equal number of males and females may not always be the most effective strategy for ensuring the survival of a particular species.

So, in short, having an equal number of males and females (or more females than males) may not be necessary or the most advantageous for every species, and different species have evolved different reproductive strategies to ensure their survival.