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How does the naturalistic fallacy confuse facts about evolution with moral judgments?

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Marble bust of Aristotle with a beard and draped robe, showing detailed facial features and wavy hair, set against a dark background. — Philosophy of biology Detail of a Roman copy (2nd century bce) of a Greek alabaster portrait bust of Aristotle, c. 325 bce; in the collection of the Roman National Museum.

The naturalistic fallacy confuses facts about evolution with moral judgments by incorrectly assuming that what is "natural"—or the result of natural selection—is inherently "good" or morally right.123

This error stems from a logical leap often described as moving from an "is" to an "ought." It attempts to derive nonnatural moral properties (such as being morally right) directly from natural properties (such as the biological processes of evolution). For example, early proponents of social Darwinism argued that because the "struggle for existence" is a natural evolutionary mechanism, it should be encouraged as a moral or economic model for human society.1

Philosophers like G.E. Moore and David Hume have criticized this reasoning, noting that biological facts do not dictate moral obligations. Relying on this fallacy is ethically flawed because natural processes also produce outcomes widely considered undesirable, such as disease, predation, and aggression. Ultimately, demonstrating that a behavior has evolutionary origins does not establish that it is rational, correct, or morally justified.12