The following five sentences, labeled 1 to 5, relate to a single topic. Four of these sentences can be arranged to form a logical paragraph. Identify the sentence that does not fit with the others and enter its number as your answer.

1. The apparent paradox of altruism, wherein an individual incurs a personal fitness cost to benefit another, stands as a fundamental challenge to classical Darwinian theory primarily focused on individual reproductive success.
2. Kin selection theory elucidates this puzzle by proposing that altruistic acts are genetically favored when they enhance the reproductive success of close relatives, thereby ensuring the propagation of shared genetic material.
3. Critiques of evolutionary psychology often highlight its propensity to commit the naturalistic fallacy, conflating empirical observations of behavior with normative ethical judgments about what 'ought' to be.
4. Beyond genetic relatedness, the mechanism of reciprocal altruism explains cooperative behaviors among non-kin, contingent on the expectation of future beneficial exchanges and the establishment of trust within social groups.
5. These two robust frameworks, inclusive fitness via kin selection and direct reciprocity, collectively provide the dominant evolutionary explanations for the widespread prevalence and persistence of altruistic tendencies in various species.