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Sober: Did evolution make us psychological egoists

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Sober. Did evolution make us psychological egoists?.

In Brief

Despite the dominant thinking in the literature, there is no good reason to assume that evolution has made human beings psychological egoists. Psychological altruism is a plausible human trait.


  • Psychological Egoism: Behaviors are motivated by self-regarding preferences. Helping others is only preferred for instrumental reasons.
  • Psychological Altruism: Behaviors are motivated by other-directed preferences. Helping others is preferred as an end-in-itself.
  • Evolutionary altruism: Behaviors that benefit other organisms' fitness at the expense of your own fitness. Note that psychological altruism can exist even when evolutionary altruism does not (i.e. psychological altruism targeted at your young would actually boost your evolutionary fitness.)
  • Evolved behavior: In order for an organism to evolve a behavior, natural selection must equip it with a proximate mechanism that triggers that behavior in the appropriate circumstances.
  • Evolutionary fitness: You're more "fit" if more of your genes are passed on (i.e. you have more surviving posterity).


Question: Which proximate psychological mechanisms (altruism or egoism) are favored by natural selection in human beings?

Direct vs. Indirect Evolutionary Strategies:

Sober uses the example of the fruitfly to illustrate the distinction between direct and indirect mechanisms for implementing behavior. Keep in mind that fruitflies need to live in humid habitats.

  • Direct Strategy: The organism is able to detect the property that is evolutionarily favorable, and this detection triggers a corresponding behavior. Example: Fruitflies have humidity detectors.
  • Indirect Strategy: The organism is able to detect a property that is correlated with an evolutionarily favorable property, and this detection triggers a corresponding behavior. Example: Fruitflies have light detectors, and darkness and humidity are correlated in the flies' usual habitat.

Predicting whether direct or indirect mechanisms evolve will hinge on three considerations:

  1. Effectiveness: How well do the detected property and the evolutionarily favorable property correlate?
  2. Availability: Is the direct mechanism evolutionarily available?
  3. Side Constraints: Will a mechanism have some detrimental influence on the fitness of the organism?

Raising Offspring:

Caring for offspring involves helping others and improves the evolutionary fitness of the parent (i.e. it allows them to pass on their genes). Psychological altruism is a direct solution to the design problem of getting organisms to take care of their offspring. Psychological egoism is an indirect solution. Using the three criteria above, we can evaluate which strategy is most plausible from an evolutionary-biological point of view.

  1. Effectiveness: Altruism would be more effective than egoism, since the correlation between a parent's well-being and that of its offspring is likely to be imperfect. (Indeed, many parents will eat their young for food, or abandon their young and simply take care of themselves. A parent lacking altruism might also lack surviving posterity.)
  2. Availability: The basic belief/desire structure of the human mind makes altruism and egoism equally available. The types of mental "equipment" used when people are motivated by either other-regarding or self-regarding preferences are essentially equivalent.
  3. Side Constraints: Too little is known about the human mind to comment here.


Given the effectiveness of altruism and the mutual availability of both altruism and egoism, there is no good reason to assume that evolution has made human beings psychological egoists. Even if evolutionary egoism is true, that does not disqualify the possibility that we are psychological altruists.

Comments and Criticisms

Voting Tie-in: If psychological altruism is evolutionarily plausible, then can voting behavior be the result of other-regarding preferences?