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Kin Selection | Theory & Examples

Devin Eichlin, Adrienne Brundage
  • Author
    Devin Eichlin

    Devin received a Bachelors of Science in Biology from Virginia Polytechnic Institute and State University. As an undergraduate she excelled in microbiology, chemistry, physics and she discovered a love for conservation while studying abroad. She has 5+ years experience working in the veterinary medicine field. Devin also taught 6th, 7th, and 8th grade science courses for Florida public schools and continues to have a love for science.

  • Instructor
    Adrienne Brundage

    Adrienne holds a Ph.D. in Entomology from Texas A&M University, M.S. in Organismal Biology from San Jose State University, and B.S. in Plant Protection Sciences from California Polytechnic State University, San Luis Obispo. She has extensive teaching experience as a university lecturer, and has instructed coursework in topics ranging from research methods, forensic sciences, botany, zoology, cell biology, human biology, microbiology, and bacteriology.

Learn about kin selection and kin selection theory. Discover why it is also known as group selection and kin altruism with kin selection examples to illustrate. Updated: 03/24/2022

What is Kin Selection Theory?

Biological imperative is the need of an organism to pass on its genetic traits through reproduction. Natural selection occurs when certain traits within a population are more advantageous, and therefore are more likely to be passed onto future generations through reproduction. In natural selection, it is generally thought that advantageous traits benefit an individual, making the individual more likely to reproduce and pass on these advantageous traits to their offspring. However, there is a unique type of natural selection called kin selection where these traits do not benefit an individual but instead may benefit their relatives. Because genes and traits are likely shared between relatives, this evolutionary strategy can help ensure that the shared traits will survive and be passed to the next generation.

So, what is kin selection? Kin selection by definition is a unique type of natural selection where the reproductive success of relatives is favored over an individual's success. In kin selection, an individual will often sacrifice themselves or their chances of reproduction to help ensure that relatives have a chance to reproduce and pass on their traits. Kin selection plays an important role in the evolution of certain species.

Kin Altruism

Altruism is a behavior that decreases the evolutionary success of the individual in order to increase the success of other individuals. Often altruism can result in the self-sacrifice of an individual for the benefit or survival of others. Kin selection can be classified as an altruistic behavior and is therefore sometimes called kin altruism. Kin selection behavior is altruistic because an organism weighs the success of its relatives as greater than its own success.

Kin selection also encourages the proliferation of altruistic traits. Because the altruistic individual has many of the same genetic traits, including altruistic behavior traits, as their relatives, the relatives are more likely to succeed and pass on the altruistic trait to offspring. One individual acting altruistically towards relatives actually helps to ensure that their own altruistic traits survive within the population.

Group Selection: Definition & Explanation

Similar to kin selection, group selection is a type of natural selection in which an organism behaves altruistically. When discussing evolutionary behavior, group selection definition is an individual behaving in ways that benefit the success of their group or population instead of simply benefiting themselves. Unlike kin selection, the group is more inclusive and does not limit the benefits to relatives but instead to a larger group that does not necessarily share the same genetic traits. Kin selection is often seen as a subtype of group selection.

Kin Recognition

Kin recognition (KR) is the ability of an organism to distinguish between relatives and nonrelatives within its species. Recognizing kin is an ability found not only in organisms with higher levels of intelligence but throughout the animal kingdom, including some microbes. KR is also being studied in plant species. Kin recognition is essential to a species' survival and evolution because it reduces inbreeding and ensures a species' success by influencing behaviors such as altruistic acts.

Various species have different ways of identifying kin from non-kin. Typically, phenotypic traits (appearance, sound, smell, taste, behaviors) are observed and identified for kin recognition. For example, the Belding's Ground Squirrel has specific glands that produce unique scents. These scents provide information about an individual's genetics and are therefore similar in smell for related organisms. Humans recognize kin differently than ground squirrels do. Because human families generally live together and within close proximity, many humans recognize their own kin through association with other family members. It is, however, possible for humans to recognize kin from phenotypic traits such as facial appearance.

Definition of Kin Selection

Family is a complicated thing, isn't it? One day you're arguing over the remote, the next you're coming together for a big dinner, and then you get to fight over who does the dishes. But what happens if someone decides to pick on your little brother? Or gossips about your sister? Or insults your mother? There is nothing that makes someone angrier than when a family member is attacked in some way. Why is that? Why can we get so frustrated with our own relatives, yet get so angry when someone outside attacks them? One explanation is kin selection.

Kin selection is a type of natural selection where individuals will sacrifice their own lives in an effort to save closely related organisms; therefore, ensuring the survival of genes that they both share.

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  • 0:00 Definition of Kin Selection
  • 0:50 Genes Want to be Passed On
  • 2:35 Altruism in Action
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Early Work on Kin Selection Theory

The first ideas about kin altruism were introduced in Charles Darwin's On the Origin of Species in 1859. Here, Darwin discussed his ideas of natural selection as the driving force of species evolution. During his research, Darwin observed that the natural selection process differs throughout species. Normally, natural selection favors the "fittest" individuals, but in some species, natural selection favors altruistic individuals that put the success of their family above their own. For example, Darwin researched honeybee colonies with a single queen that produces all the eggs and hundreds of related female worker bees that never reproduce. These worker bees exhibit kin altruism by forgoing their own ability to reproduce and instead help to raise the offspring of their queen.

This altruistic behavior left Darwin and other biologists questioning how this altruistic behavior was beneficial to the species and natural selection. Evolutionary biologists continued to work on this altruism theory, with many scientists contributing to the final production of a kin selection theory. In 1932, scientist and mathematician J.B.S. Haldane identified a mathematical component to altruistic behaviors between relatives in relation to the amount of genetic material they may have in common. Haldane is most noted for his declaration "I would lay down my life for two brothers or eight cousins."

In 1963, scientist William Hamilton researched altruistic behaviors within species and recognized that altruistic behaviors mostly occurred between related individuals and not random individuals. By encouraging the success of family members, individuals guarantee that some of their genetic material will be passed on to future generations. It was not until 1964 that evolutionary biologist John Maynard Smith officially coined the term "kin selection." J.M. Smith used the term kin selection to refer to Hamilton's research while debating the ideas of kin selection vs group selection.

Hamilton's Rule

As discussed above, William Hamilton's research was essential to the production of kin selection theory. Although not called kin selection at that point, Hamilton's research was used to compose the idea of inclusive fitness. Inclusive fitness is a theory in evolutionary biology that states that altruistic behaviors within a species are in part responsible for the species' success. Individuals that are related genetically are more likely to benefit from altruistic behaviors because even though one individual may sacrifice their ability to reproduce when helping family, many of their traits will still be passed onto the next generation when their family members reproduce. The genetics for altruistic traits are passed onto future generations because altruism benefits the species.

Hamilton developed a rule describing genes associated with altruism. This rule weighs the altruistic cost of giving up one's own chance of reproducing to the benefit of family members' reproduction success.

Hamilton's Rule can be expressed mathematically: C < B x r

  • C is the reproductive cost that the altruistic individual will have. C typically represents the amount of offspring the individual will not produce if engaging in altruistic behavior.
  • B is the reproductive benefit that the altruism-receiving individual will have. B represents the amount of offspring the recipient will be able to produce.
  • r is the genetic relatedness of the altruistic individual and the individual benefiting from altruism. Relatedness refers to how likely the relatives are to share genetic traits that can be passed on.

The more closely related two individuals are, the more likely they are to engage in altruistic behavior towards each other.

Genes Want to be Passed On

You share a lot of things with your family, but at the most basic level, you share genes. Every individual inherits his or her genetic code from his or her parents. This is true for all living things, no matter how they pass their genes on. This also means that every living thing has genes in common with its parents, its siblings, and its offspring. Have you ever noticed that you look a lot like a beloved aunt? Or your brother is the spitting image of your grandfather? Those are common genes that you all share.

Now, the whole purpose of reproduction is to pass genes on to the next generation. Scientists call this the biological imperative, or the biological drive for every living thing to reproduce and pass on genes. But have you noticed that not every single living thing on earth has the ability to pass on its genes? I'm sure you've met people who can't have children, but did you know that there are animals that have lost reproductive ability completely?

Honeybees, for example, are mostly all female, and are mostly all infertile. They live in hives with a single queen that produces eggs, while hundreds of worker bees take care of everything else. If the whole purpose of life is to pass on genes, why are worker bees willing to take care of another bee's baby? Because the worker bees and the baby bees share a mother, which means they are all related, and share the same genes. So, by caring for the new babies, the worker bees are making sure that those genes they share are going to be passed on to a new generation, without having to have offspring themselves. This caring for closely related individuals at the expense of personal fertility is known as kin selection.

Altruism in Action

Kin selection is a type of altruistic behavior. Altruistic behavior is a set of actions by an individual that benefits someone else, while often causing harm to the individual. This is a form of selflessness that helps others survive and reproduce.

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Video Transcript

Definition of Kin Selection

Family is a complicated thing, isn't it? One day you're arguing over the remote, the next you're coming together for a big dinner, and then you get to fight over who does the dishes. But what happens if someone decides to pick on your little brother? Or gossips about your sister? Or insults your mother? There is nothing that makes someone angrier than when a family member is attacked in some way. Why is that? Why can we get so frustrated with our own relatives, yet get so angry when someone outside attacks them? One explanation is kin selection.

Kin selection is a type of natural selection where individuals will sacrifice their own lives in an effort to save closely related organisms; therefore, ensuring the survival of genes that they both share.

Genes Want to be Passed On

You share a lot of things with your family, but at the most basic level, you share genes. Every individual inherits his or her genetic code from his or her parents. This is true for all living things, no matter how they pass their genes on. This also means that every living thing has genes in common with its parents, its siblings, and its offspring. Have you ever noticed that you look a lot like a beloved aunt? Or your brother is the spitting image of your grandfather? Those are common genes that you all share.

Now, the whole purpose of reproduction is to pass genes on to the next generation. Scientists call this the biological imperative, or the biological drive for every living thing to reproduce and pass on genes. But have you noticed that not every single living thing on earth has the ability to pass on its genes? I'm sure you've met people who can't have children, but did you know that there are animals that have lost reproductive ability completely?

Honeybees, for example, are mostly all female, and are mostly all infertile. They live in hives with a single queen that produces eggs, while hundreds of worker bees take care of everything else. If the whole purpose of life is to pass on genes, why are worker bees willing to take care of another bee's baby? Because the worker bees and the baby bees share a mother, which means they are all related, and share the same genes. So, by caring for the new babies, the worker bees are making sure that those genes they share are going to be passed on to a new generation, without having to have offspring themselves. This caring for closely related individuals at the expense of personal fertility is known as kin selection.

Altruism in Action

Kin selection is a type of altruistic behavior. Altruistic behavior is a set of actions by an individual that benefits someone else, while often causing harm to the individual. This is a form of selflessness that helps others survive and reproduce.

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Frequently Asked Questions

What does kin selection predict?

Kin selection can predict whether an individual will behave altruistically to benefit a family member. The more closely related two individuals are, the more likely they are to behave altruistically.

What is the purpose of kin selection?

Kin selection is a mechanism of natural selection that instead of selecting the fittest individual to thrive and reproduce, selects relatives of altruistic individuals to thrive and reproduce. This unique method ensures that many of the genes in the altruistic individual still get passed onto future generations when their relatives reproduce.

Who proposed kin selection theory?

Altruistic behaviors have been researched and noted by scientists extending back to Charles Darwin in the 1850s. Although not initially called kin selection theory, William Hamilton is largely credited with the foundation ideas of kin selection theory in his inclusive fitness theory. Hamilton also devised Hamilton's rule that mathematically compares the altruistic cost, the relative's reproductive benefit, and relatedness of the two individuals.

What is kin selection theory in psychology?

Kin selection theory states that individuals with altruistic traits will sacrifice their chances of reproduction if it will increase the chances of relatives reproducing. Examples can be seen in human behavior, with most people being more likely to behave altruistically towards relatives.

What does kin selection require?

Kin selection requires organisms to be genetically related (relatives). It also requires that individuals are able to recognize kin from non-kin.

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