I had an idea for a humanoid species that has a significant number more female births than male births, how would this trait have provided enough of an advantage to allow the species to survive to develop civilization?
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The evolution of sexual reproduction comes at a significant cost to a species because males cannot produce offspring. Species that are all hermaphrodites are capable of producing twice as many progeny each generation as species with an equal sex ratio. This is called the two-fold cost of sex. Sexual reproduction evolved and persists however because species that routinely recombine their genes are, to put it simply, better at evolution.
So following this line of thought, you need at least some males in order to have a sexually reproducing species. But why does the cost have to be “two-fold”? Why should half the species’ population be male when a much smaller proportion of males could serve the needs of the species. In fact, a lower ratio of males would be evolutionarily optimal from the perspective of the species but it won’t occur because evolutionary game theory occurs at the individual level. It turns out that a 50-50 male/female ratio is an evolutionary stable strategy according to Fisher’s principle. Essentially, if a population has a skewed sex-ratio, then it becomes evolutionarily advantageous for individuals to produce offspring of the minor sex as they will have better reproductive opportunities. Thus the system is always self-correcting towards the evolutionarily stable strategy of 50-50 male/female.
So, having more females than males actually is an evolutionarily favorable strategy as it increases the total potential progeny of the species, but it can never persist stably because evolution is always pushing against it. If you want a population like this you need to break Fisher’s principle in some way. Check out the parasitic/symbiotic bacteria Wolbachia that change the sex of infected insects and the sex of their progeny to suit their own needs.