Robert Ludlow Trivers (; February 19, 1943 – March 12, 2026) was an American evolutionary biologist and sociobiologist who profoundly influenced both fields. Trivers proposed the theories of reciprocal altruism (1971), parental investment (1972), facultative sex ratio determination (1973), and parent–offspring conflict (1974). He has also contributed by explaining self-deception as an adaptive evolutionary strategy (first described in 1976) and discussing intragenomic conflict.
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