3 ms·

You're taking it back a step to asking "why sexual reproduction"? The original question is... assuming that we have mandatory sexual reproduction, why do we ha

• pvaldes 10y ago
  Because upper vertebrates normally can't exert influence on the sex of the offspring before birth. Your DNA will have an X chromosom at least. In principle [1], you can have either a second X or an Y. 50% probabilities. 1:1. Only reptile, amphibious, fishes and it seems that very primitive mammals also can do this. Our system to get rid of the excedent is to make males sillier, much more prone to take life-threatening risks than females. 1 [Those aren't our only options, we have the so called supermales (one X, two Y), and superfemales (XXX) but they are not common and some combinations ("1.5 X") are sterile]
  • seszett 10y ago
    > Because upper vertebrates normally can't exert influence on the sex of the offspring before birth. Your DNA will have an X chromosom at least. In principle [1], you can have either a second X or an Y. 50% probabilities. 1:1. That's not a sufficient explanation, as there could be a different ratio during the sperm cell generation process or selection during insemination or from the egg cells themselves. Y and X sperm cells could easily be handled differently at any point of the whole process.
  • digi_owl 10y ago
    I could have sworn i have read about a species of mice that do not have Y at all, but still produce males.
  • Retric 10y ago
    Humans have a ~1:1.05 F:M ratio so evolution really can alter the ratio. (Though this ratio varies by population.) https://en.wikipedia.org/wiki/Human_sex_ratio https://en.wikipedia.org/wiki/Human_sex_ratio