eli5: What advantage does sexual dimorphism provide in nature?

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eli5: What advantage does sexual dimorphism provide in nature?

In: Biology
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Sexual dimorphism provides, at least in humans, one sex that is adapted to care for the offspring for a long period of time. Being that humans are helpless for most of their childhood and into their teenage years, having one sex that is adapted to put their energy not just into nourishing a fetus, but caring for the young post birth allows for the young to be more successful in a given environment.

For humans in the modern day, sexual dimorphism has less an effect on our survivability, and there are many arguments surrounding the impact of sex upon how one thinks/behaves, ranging from some claiming it having little to no effect on how we operate at all, to others claiming it is extremely influential.

It tends to lead to better genetic diversity. Species that can self-fertilize are basically just cloning themselves, so if a disease came along that one was susceptible to, all members would be equally susceptible.

Having a male and female means that the genetic “pot” is always getting stirred as different groups bring in different genes, which protects the species as a whole from getting wiped out in one fell swoop.

Females are often bigger and heavier than males (not in our species) as they have to invest more resources in producing offspring – the males contribute just sperm, which is cheap. That’s the case for a lot of mammals, some birds of prey, &c.

The sexual arms races for extraordinary characters have already been mentioned.

Other advantages of sexual dimorphism can be seen in extreme cases:

* some deep-sea fishes have big females but very tiny males living parasitically on them. The deep oceans are dark and vast and once you’ve found a mate you stick to it. Literally;

* bees and ants have practically created three “sexes” (or castes): a big solitary queen busy laying eggs, sterile workers (actually females) foraging for the queen and the larvae, and temporary males which are just vectors for the queen’s genes. A kind of natural taylorism, efficiency by specialization. 😉