amazons were isolated on an island? or are you saying amazon rainforests are isolated islands? Or are you asking about what would happen if men got stranded on an isolated island which climate is tropical like amazon rainforests?
the answer is sex.
Probably Amazons as in the all female group of Amazonian warriors. Not sure if it was IRL or some sort of literary work, because IIRC they appeared in Greek Mythology.
And yeah, I'd have to agree with the 'sex' bit. Like how would they devy up the captured/kidnapped/whatever women? [Huh, makes me remember an 18+ cyoa work.] Because they would have to, to increase their numbers.
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Wasn't there an episode of survivor or something where they put a group of men on one island and a group of women on another? If I recall right the guys made huts with working water in two weeks.
lol, really? Might needa watch that, but since it's a tv series/show would have to take that with a grain of salt.
Especially Since men tend to have an ego, especially around other men [a sort of superiority complex]..... Though, that may only kickstart if women are in the perimeter, as a sort of mating ritual thing.
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Anyways, think there were some literary works with an all male group, but they tend to be 'monsters', like orcs and goblins.
** The Amazonians were able to because it's the females that, tend to, carry the babies.
Don't think there are many ways for an all male group to be formed, besides raiding/pillaging--like the vikings--or taking in orphans.
Speaking of literary, reminds me of an old space anime. Forgot it, but there was an all male society and an all female one. Think it was the start for Vandread, but way too long to remember if that's the right one.