The naturalistic fallacy occurs when arguers presume that if humans in their primordial state, or animals in their natural state, exhibit a certain behavior, then that behavior must be morally right. As such, it is a specific form of the is-ought fallacy.

Here is an example:

"Our ancient cave-dwelling ancestors would kill any other humans who poached on their hunting territory, so it must be okay for me to kill trespassers on my property."

The problem here is that even if the supposition about ancient humans' behavior is correct, it does not mean that this is morally commendable behavior.

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