Interchangeable genres

Westerns and post-apocalyptic stories have plenty of similarities – sparsely inhabited environments, where human habitations are few and far between, lawless lands where the one with the last bullet wins, a few solitary lunatics scraping by in the utter wilderness outside of the relative law and order of small towns.

Then there's sailor/pirate stories and sci-fi, just replace ships with spaceships, islands with planets, and unfathomable and terrifying unseen sea monsters with unfathomable and terrifying unseen alien life forms. Drowning at sea and suffocating in the vacuum of space.

What other genres are there that are essentially interchangeable with each other?

Westerns and post-apocalyptic stories have plenty of similarities – sparsely inhabited environments, where human habitations are few and far between, lawless lands where the one with the last bullet wins, a few solitary lunatics scraping by in the utter wilderness outside of the relative law and order of small towns.

Then there's sailor/pirate stories and sci-fi, just replace ships with spaceships, islands with planets, and unfathomable and terrifying unseen sea monsters with unfathomable and terrifying unseen alien life forms. Drowning at sea and suffocating in the vacuum of space.

What other genres are there that are essentially interchangeable with each other?

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