Males can spread their genes far and wide. They have no real limitations and therefore they are not the important ones in the area of perpetuating the species. To the females have been given that sacred task. If females do not have children of the same species as themselves, their species dies exactly that much. Females are the limiting factor in perpetuation of the species.
Females can only have a limited number of children in their lifetimes.
The more children that they have, the more of their species that will exist in the next generation. Unless, of course, they mate with a different species and thereby lessen the numbers in the next generation of their own species. These simple facts of life should not be a shock to anyone. A few moments of contemplation by any adult or even adolescent will verify what I have said as being true. In biology you will find that a species is a grouping of animals which normally interbreed amongst themselves, thereby continuing to perpetuate their common characteristics to the next generation.