yes and no. its because in society we have choice. Women can choose to be with whomever they want irrespective of their natural biology between the legs. But when we did roam around nude, as animals do still, our genitals were on display. Sexual competition was fierce. Women were receiving ejaculate from many males, and the healthier males had the advantage. What determined "healthier" and still to an extent does (altho we dont have the competition between males as we did before)? Age, fitness, penis length, girth, testicle size (the latter being a big one).
Lots of guys talking about dick size but no one mentioned testicle size, a decent determining factor in who produces more sperm, semen, testosterone etc. And also dont forget the size of the penis head, which is used for scooping.
Male anatomy is designed for competition, and if left to just male anatomy, men with bigger testicles and larger penises will win over the smaller men.
ive donated sperm in a variety of capacities and i know my big testicles produce a much higher count than men with avg or below avg sized testes, often the men seeking some sort of fertility treatment.
Of course smaller men can still reproduce. If its just them and a woman, they got plenty of time to make it happen. But if i were to ejaculate before, or same time, or after a man who is less fertile (for the above reasons) he likely will not impregnate, i will.