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1

This is just a guess, but maybe it's cheaper to masturbate than to maintain the additional machinery to quickly re-absorb or otherwise dispose of the unused/old sperm. Assuming that fresher sperm will be more likely to fertilise the egg, selection will favour those with a larger proportion of fresher sperm per ejaculation. So individuals who have recently ...


9

Very short answer: No! You should have a look to the wikipedia page on sex-determination systems. Diversity among the species that reproduce sexually Not all species that have sexual reproduction have genders. Yeasts for example have mating types but no gender. Diversity among the species that have genders Sex is determined by both genetic and ...


5

No. There are many sex-determination systems. Mammals and fruitflies use the XX/XY sex-determination system — except for the platypus, which has 10 sex chromosomes. ZW sex-determination system is used by birds and some reptiles. It's similar but with the male having two of the same chromosome (ZZ) and the female being the heterogametic sex (ZW). There's ...



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