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Related Concept Videos

Inclusive Fitness00:57

Inclusive Fitness

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Most altruistic behavior—in which one animal helps another at a cost to themselves—occurs between relatives. Scientists think these altruistic behaviors evolved because they increase the inclusive fitness of the animal providing help.
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Altruism01:03

Altruism

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Altruistic behaviors are “unselfish” behaviors—those that help another individual at the expense of the individual carrying out the behavior. Despite the negative consequences for the altruistic animal, these behaviors are thought to have evolved for several reasons.
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Natural Selection and Adaptation01:15

Natural Selection and Adaptation

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Natural selection, a fundamental concept in evolutionary biology, is the mechanism by which evolution is driven, favoring organisms that are best adapted to their environments. This process enhances their chances of survival and reproduction. Adaptation, a key outcome of this process, involves genetic modifications that optimize an organism's functionality under specific environmental challenges, such as extreme cold or thinner air at high altitudes.
Beyond physical adaptations,...
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What is Natural Selection?01:32

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Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.
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Limits to Natural Selection01:38

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Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.
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Egoism and Altruism01:55

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Voluntary behavior with the intent to help other people is called prosocial behavior. Why do people help other people? Is personal benefit such as feeling good about oneself the only reason people help one another?
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Related Experiment Video

Updated: Jun 13, 2025

Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli
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Altruism and natural selection in a variable environment.

Miguel Dos Santos1, Philip A Downing2,3, Ashleigh S Griffin1

  • 1Department of Biology, Oxford University, Oxford OX1 3SZ, United Kingdom.

Proceedings of the National Academy of Sciences of the United States of America
|September 10, 2024
PubMed
Summary
This summary is machine-generated.

Altruistic helping can evolve even without benefiting relatives, by reducing their reproductive success variance. However, this study shows variance effects are inconsistent, with mean benefits being more crucial for helping evolution.

Keywords:
bet-hedgingcooperative breedingkin selectionsocial evolution

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Area of Science:

  • Evolutionary biology
  • Behavioral ecology
  • Social evolution

Background:

  • Hamilton's rule is foundational for understanding social behavior evolution.
  • Recent theories propose 'altruistic bet-hedging' where helping benefits non-relatives by reducing reproductive variance.

Purpose of the Study:

  • To derive a comprehensive version of Hamilton's rule accounting for environmental variability.
  • To empirically test the role of variance in reproductive success on the evolution of helping behavior.

Main Methods:

  • Developed a theoretical model of Hamilton's rule incorporating environmental variability.
  • Quantified the impact of helping on reproductive success variance in 15 cooperatively breeding bird species.

Main Results:

  • Helping did not consistently decrease reproductive success variance; it often increased it.
  • The mean benefits of helping across environments were more significant than variance effects.
  • Theoretical model shows variance effects can favor or disfavor helping inconsistently.

Conclusions:

  • The impact of helping on reproductive success variance is not a consistent or strong driver for the evolution of helping.
  • Mean fitness benefits, not variance reduction, appear to be the primary factor favoring altruistic behaviors.