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If nature has one type of gender, then after sexual reproduction only copies of the same living thing will produce with very or no variations in the new generation. So nature does not have a single gender for most of the species.

Nature have two types of gender for most of the species, so that variations can occur in new generations after sexual reproduction.

But why nature does not have more than two types of gender for each species?

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closed as off-topic by JDługosz, Aify, Hohmannfan, Mołot, Skye Oct 15 '16 at 12:44

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – JDługosz, Aify, Hohmannfan, Mołot, Skye
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Of note, most species are asexual, as far as I know. It's just that most species are also microbes. Sexual reproduction seems to mostly be useful in larger species, so our generation-to-generation variance is much larger, which combats the rapid reproductive rate of microbes that would otherwise evolve too fast for our immune systems to keep up with. $\endgroup$ – MichaelS Oct 15 '16 at 5:04
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    $\begingroup$ People might be informed on this subject at Biology. $\endgroup$ – JDługosz Oct 15 '16 at 6:40
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    $\begingroup$ But it does. Check out this crazy example: newscientist.com/article/… $\endgroup$ – Erik Oct 15 '16 at 8:26
  • $\begingroup$ Select species of snake and fish are also known to clone themselves A-Sexually, a trait that proves useful when in extreme environmental situations. $\endgroup$ – Harry David Oct 15 '16 at 11:52
  • $\begingroup$ Oh, and in nature there are in fact 63 genders... apath.org/rede/23.html $\endgroup$ – Harry David Oct 15 '16 at 11:54
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There's a bunch of questions you might be asking here, and I've explored a few:

Why don't some species require more than two individuals to mate together before producing offspring?

Because putting three gametes in the same place is a lot harder than putting two, and isn't worth the extra bit of genetic diversity.

Why don't some species have more than two sex-chromosome makeups?

It's kind of complicated to make chromosomes work with more than two; when two individuals mate, how will the chromosomes be exchanged to actually create a viable karyotype every time? It could conceivably work under processes other than meiosis, though.

Why do species not express gamete stages?

Actually, there's an awful lot of plants that do weird things with gamete stages - look up "alternation of generations."

Also, this answer is helpful: https://www.quora.com/Are-there-any-species-with-more-than-two-sexes. Apparently some species of lobster commensalist has some very complex way of reproducing, involving a lot of different genetic roles beyond just gamete and zygote etc.

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