Altruism in animals
Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...

is a well-documented animal behaviour
Ethology is the scientific study of animal behavior, and a sub-topic of zoology....

, which appears most obviously in kin relationships but may also be evident amongst wider social groups, in which an animal sacrifices its own well-being for the benefit of another animal.


In the science of ethology
Ethology is the scientific study of animal behavior, and a sub-topic of zoology....

 (the study of behavior), and more generally in the study of social evolution
Social evolution
Social evolution is a subdiscipline of evolutionary biology that is concerned with social behaviors that have fitness consequences for individuals other than the actor...

, on occasion, some animals do behave in ways that reduce their individual fitness but increase the fitness of other individuals in the population; this is a functional definition of altruism. Research in evolutionary theory has been applied to social behaviour, including altruism. Cases of animals helping individuals to whom they are closely related can be explained by kin selection
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...

, and are not considered true altruism. Beyond the physical exertions that mothers, and in some species fathers, undertake to protect their young, extreme examples of sacrifice may occur. One example is matriphagy (the consumption of the mother by her offspring) in the spider Stegodyphus
Stegodyphus is a genus of araneomorph spiders in the family Eresidae. The 21 species are distributed from Africa to Europe and Asia, with two species Stegodyphus is a genus of araneomorph spiders in the family Eresidae. The 21 species are distributed from Africa to Europe and Asia, with two species...

. Hamilton's rule describes the benefit of such altruism in terms of Wright's
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...

 coefficient of relationship
Coefficient of relationship
In population genetics, Sewall Wright's coefficient of relationship or coefficient of relatedness or relatedness or r is defined as 2 times the Coefficient of Inbreeding...

 to the beneficiary and the benefit granted to the beneficiary minus the cost to the sacrificer. Should this sum be greater than zero a fitness gain will result from the sacrifice.

When apparent altruism is not between kin, it may be based on reciprocity
Reciprocal altruism
In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar manner at a later time...

. A monkey will present its back to another monkey, who will pick out parasites; after a time the roles will be reversed. Such reciprocity will pay off, in evolutionary terms, as long as the costs of helping are less than the benefits of being helped and as long as animals will not gain in the long run by "cheating" – that is to say, by receiving favours without returning them. This is elaborated on in evolutionary game theory
Evolutionary game theory
Evolutionary game theory is the application of Game Theory to evolving populations of lifeforms in biology. EGT is useful in this context by defining a framework of contests, strategies and analytics into which Darwinian competition can be modelled. It originated in 1973 with John Maynard Smith...

 and specifically the prisoner's dilemma
Prisoner's dilemma
The prisoner’s dilemma is a canonical example of a game, analyzed in game theory that shows why two individuals might not cooperate, even if it appears that it is in their best interest to do so. It was originally framed by Merrill Flood and Melvin Dresher working at RAND in 1950. Albert W...

 as social theory.

Implications in evolutionary theory

Researchers on alleged altruist behaviours among animals have been ideologically opposed to the social darwinist
Social Darwinism
Social Darwinism is a term commonly used for theories of society that emerged in England and the United States in the 1870s, seeking to apply the principles of Darwinian evolution to sociology and politics...

 concept of the "survival of the fittest
Survival of the fittest
"Survival of the fittest" is a phrase originating in evolutionary theory, as an alternative description of Natural selection. The phrase is today commonly used in contexts that are incompatible with the original meaning as intended by its first two proponents: British polymath philosopher Herbert...

", under the name of "survival of the nicest" — the latter being globally compatible, however, with the theory of evolution by natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

. Insistence on such cooperative behaviours between animals was first exposed by the Russian zoologist and anarchist Peter Kropotkin
Peter Kropotkin
Prince Pyotr Alexeyevich Kropotkin was a Russian zoologist, evolutionary theorist, philosopher, economist, geographer, author and one of the world's foremost anarcho-communists. Kropotkin advocated a communist society free from central government and based on voluntary associations between...

 in his 1902 book, Mutual Aid: A Factor of Evolution
Mutual Aid: A Factor of Evolution
Mutual Aid: A Factor of Evolution is a book by Peter Kropotkin on the subject of mutual aid, written while he was living in exile in England. It was first published by William Heinemann in London in October 1902...


Recent developments in game theory
Game theory
Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...

 have provided some explanations for apparent altruism, as have traditional evolutionary analyses. Among the proposed mechanisms are:
  • Behavioural manipulation (for example, by certain parasites
    Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...

     that can alter the behavior of the host)
  • Bounded rationality
    Bounded rationality
    Bounded rationality is the idea that in decision making, rationality of individuals is limited by the information they have, the cognitive limitations of their minds, and the finite amount of time they have to make a decision...

     (for example, Herbert Simon
    Herbert Simon
    Herbert Alexander Simon was an American political scientist, economist, sociologist, and psychologist, and professor—most notably at Carnegie Mellon University—whose research ranged across the fields of cognitive psychology, cognitive science, computer science, public administration, economics,...

  • Kin selection
    Kin selection
    Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...

     including eusociality
    Eusociality is a term used for the highest level of social organization in a hierarchical classification....

     (see also "The Selfish Gene
    The Selfish Gene
    The Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...

  • Meme
    A meme is "an idea, behaviour or style that spreads from person to person within a culture."A meme acts as a unit for carrying cultural ideas, symbols or practices, which can be transmitted from one mind to another through writing, speech, gestures, rituals or other imitable phenomena...

    s (by influencing behavior to favor their own spread; see religion as a meme)
  • Reciprocal altruism
    Reciprocal altruism
    In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar manner at a later time...

    , mutual aid
  • Sexual selection
    Sexual selection
    Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...

    , in particular, the Handicap principle
    Handicap principle
    The handicap principle is a hypothesis originally proposed in 1975 by biologist Amotz Zahavi to explain how evolution may lead to "honest" or reliable signaling between animals who have an obvious motivation to bluff or deceive each other...

  • Reciprocity
    Reciprocity (social psychology)
    Reciprocity in social psychology refers to responding to a positive action with another positive action, rewarding kind actions. People categorize an action as kind by viewing its consequences and also by the person's fundamental intentions. Even if the consequences are the same, underlying...

    • Indirect reciprocity (for example, reputation
      Reputation of a social entity is an opinion about that entity, typically a result of social evaluation on a set of criteria...

    • Strong reciprocity
  • Pseudo-reciprocity

The study of altruism was the initial impetus behind George R. Price
George R. Price
George Robert Price was an American population geneticist. Originally a physical chemist and later a science journalist, he moved to London in 1967, where he worked in theoretical biology at the Galton Laboratory, making three important contributions: first, rederiving W.D...

's development of the Price equation
Price equation
The Price equation is a covariance equation which is a mathematical description of evolution and natural selection. The Price equation was derived by George R. Price, working in London to re-derive W.D. Hamilton's work on kin selection...

 which is a mathematical equation used to study genetic evolution. An interesting example of altruism is found in the cellular slime mould
Slime mould
Slime mold or mould is a broad term describing protists that use spores to reproduce. Slime molds were formerly classified as fungi, but are no longer considered part of this kingdom....

s, such as Dictyostelium
The dictyostelids are a group of cellular slime molds, or social amoebae.-Slug behavior:When food is readily available they are individual amoebae, which feed and divide normally...

. These protists live as individual amoeba
Amoeba is a genus of Protozoa.History=The amoeba was first discovered by August Johann Rösel von Rosenhof in 1757. Early naturalists referred to Amoeba as the Proteus animalcule after the Greek god Proteus, who could change his shape...

e until starved, at which point they aggregate and form a multicellular fruiting body in which some cells sacrifice themselves to promote the survival of other cells in the fruiting body. Social behavior and altruism share many similarities to the interactions between the many parts (cells, genes) of an organism, but are distinguished by the ability of each individual to reproduce indefinitely without an absolute requirement for its neighbors.

Jorge Moll and Jordan Grafman, neuroscientists at the National Institutes of Health
National Institutes of Health
The National Institutes of Health are an agency of the United States Department of Health and Human Services and are the primary agency of the United States government responsible for biomedical and health-related research. Its science and engineering counterpart is the National Science Foundation...

 and LABS-D'Or Hospital Network (J.M.) provided the first evidence for the neural bases of altruistic giving in normal healthy volunteers, using functional magnetic resonance imaging
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...

. In their research, published in the Proceedings of the National Academy of Sciences
Proceedings of the National Academy of Sciences
The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences...

 USA in October, 2006, they showed that both pure monetary rewards and charitable donations activated the mesolimbic
Mesolimbic pathway
The mesolimbic pathway is one of the dopaminergic pathways in the brain. The pathway begins in the ventral tegmental area of the midbrain and connects to the limbic system via the nucleus accumbens, the amygdala, and the hippocampus as well as to the medial prefrontal cortex...

 reward pathway, a primitive part of the brain that usually lights up in response to food and sex. However, when volunteers generously placed their interests of others before their own by making charitable donations, another brain circuit was selectively activated: the subgenual cortex/septal region. These structures are intimately related to social attachment and bonding in other species. Altruism, the experiment suggested, was not a superior moral faculty that suppresses basic selfish urges but rather was basic to the brain, hard-wired and pleasurable.

A new study by Samuel Bowles
Samuel Bowles (economist)
Samuel Bowles is an American economist and Professor Emeritus at the University of Massachusetts, Amherst where he taught courses on microeconomics and the theory of institutions.- Biography :...

 at the Santa Fe Institute
Santa Fe Institute
The Santa Fe Institute is an independent, nonprofit theoretical research institute located in Santa Fe and dedicated to the multidisciplinary study of the fundamental principles of complex adaptive systems, including physical, computational, biological, and social systems.The Institute houses a...

 in New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

, US, is seen by some as breathing new life into the model of group selection
Group selection
In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....

 for altruism, known as "Survival of the nicest". Bowles conducted a genetic analysis of contemporary foraging groups, including Australian aboriginals, native Siberian Inuit
The Inuit are a group of culturally similar indigenous peoples inhabiting the Arctic regions of Canada , Denmark , Russia and the United States . Inuit means “the people” in the Inuktitut language...

 populations and indigenous tribal groups in Africa. It was found that hunter-gatherer
A hunter-gatherer or forage society is one in which most or all food is obtained from wild plants and animals, in contrast to agricultural societies which rely mainly on domesticated species. Hunting and gathering was the ancestral subsistence mode of Homo, and all modern humans were...

 bands of up to 30 individuals were considerably more closely related than was previously thought. Under these conditions, thought to be similar to those of the middle and upper Paleolithic
The Paleolithic Age, Era or Period, is a prehistoric period of human history distinguished by the development of the most primitive stone tools discovered , and covers roughly 99% of human technological prehistory...

, altruism towards other group-members would improve the overall fitness of the group.

If an individual defended the group but was killed, any genes that the individual shared with the overall group would still be passed on. Early customs such as food sharing or monogamy
Monogamy /Gr. μονός+γάμος - one+marriage/ a form of marriage in which an individual has only one spouse at any one time. In current usage monogamy often refers to having one sexual partner irrespective of marriage or reproduction...

 could have levelled out the "cost" of altruistic behaviour, in the same way that income taxes redistribute income in society. He assembled genetic, climactic, archaeological, ethnographic and experimental data to examine the cost-benefit relationship of human cooperation in ancient populations. In his model, members of a group bearing genes for altruistic behaviour pay a "tax" by limiting their reproductive opportunities to benefit from sharing food and information, thereby increasing the average fitness of the group as well as their inter-relatedness. Bands of altruistic humans would then act together to gain resources from other groups at this challenging time in history.

Altruist theories in evolutionary biology were contested by Amotz Zahavi
Amotz Zahavi
Amotz Zahavi is an Israeli evolutionary biologist, a Professor Emeritus at the Zoology Department of Tel Aviv University, and one of the founders of the Society for the Protection of Nature in Israel...

, the inventor of the signalling theory
Signalling theory
Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals. The central question is when organisms with conflicting interests should be expected to communicate "honestly"...

 and its correlative, the handicap principle
Handicap principle
The handicap principle is a hypothesis originally proposed in 1975 by biologist Amotz Zahavi to explain how evolution may lead to "honest" or reliable signaling between animals who have an obvious motivation to bluff or deceive each other...

, based mainly on his observations of the Arabian Babbler
Arabian Babbler
The Arabian Babbler is a passerine bird belonging to the genus Turdoides, a genus of Old World babblers.It is 26–29 cm long with a wingspan of 31-33.5 cm and a weight of 64-83 grams. It has a fairly long curved bill, a long tail, rounded wings and strong legs and feet. The plumage...

, a bird commonly known for its surprising (alleged) altruistic behaviours.

Researchers in Switzerland have developed an algorithm based on Hamilton's rule of kin selection. The algorithm shows how altruism in a swarm
Swarm behaviour, or swarming, is a collective behaviour exhibited by animals of similar size which aggregate together, perhaps milling about the same spot or perhaps moving en masse or migrating in some direction. As a term, swarming is applied particularly to insects, but can also be applied to...

 of entities can, over time, evolve and result in more effective swarm behaviour.

Examples of animal altruism

  • Dogs often adopt orphaned cats, squirrels, ducks and even tigers.
  • Dolphin
    Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

    s support sick or injured animals, swimming under them for hours at a time and pushing them to the surface so they can breathe.
  • Wolves and wild dogs
    The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

     bring meat back to members of the pack not present at the kill.
  • Male baboon
    Baboons are African and Arabian Old World monkeys belonging to the genus Papio, part of the subfamily Cercopithecinae. There are five species, which are some of the largest non-hominoid members of the primate order; only the mandrill and the drill are larger...

    s threaten predators and cover the rear as the troop retreats.
  • Gibbon
    Gibbons are apes in the family Hylobatidae . The family is divided into four genera based on their diploid chromosome number: Hylobates , Hoolock , Nomascus , and Symphalangus . The extinct Bunopithecus sericus is a gibbon or gibbon-like ape which, until recently, was thought to be closely related...

    s and chimpanzee
    Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...

    s with food will, in response to a gesture, share their food with others of the group. Chimpanzees will help humans and conspecifics
    Conspecificity is a concept in biology. Two or more individual organisms, populations, or taxa are conspecific if they belong to the same species....

     without any reward in return.
  • Bonobo
    The bonobo , Pan paniscus, previously called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee, is a great ape and one of the two species making up the genus Pan. The other species in genus Pan is Pan troglodytes, or the common chimpanzee...

    s have been observed aiding injured or handicapped bonobos.
  • Vampire bats commonly regurgitate blood to share with unlucky or sick roost mates that have been unable to find a meal, often forming a buddy system
    Buddy system
    The buddy system is a procedure in which two people, the "buddies", operate together as a single unit so that they are able to monitor and help each other.-Advantages:...

  • Raccoon
    Procyon is a genus of nocturnal mammals, comprising three species commonly known as raccoons, in the family Procyonidae. The most familiar species, the common raccoon , is often known simply as "the" raccoon, as the two other raccoon species in the genus are native only to the tropics and are...

    s inform conspecifics
    Conspecificity is a concept in biology. Two or more individual organisms, populations, or taxa are conspecific if they belong to the same species....

     about feeding grounds by droppings left on commonly shared latrines. A similar information system has been observed to be used by common raven
    Common Raven
    The Common Raven , also known as the Northern Raven, is a large, all-black passerine bird. Found across the northern hemisphere, it is the most widely distributed of all corvids...

  • In numerous bird species, a breeding pair receives support in raising its young from other "helper" birds, including help with the feeding of its fledglings. Some will even go as far as protecting an unrelated bird's young from predators
  • Most mammal carnivores like wolves or dogs have a habit of not harming pack members below certain age, of opposite sex or in surrendering position (in case of some animals, the behavior exists within entire species rather than one pack).
  • Vervet Monkey
    Vervet Monkey
    The vervet monkey , or simply vervet, is an Old World monkey of the family Cercopithecidae native to Africa. The term "vervet" is also used to refer to all the members of the genus Chlorocebus....

    s give alarm calls to warn fellow monkeys of the presence of predators, even though in doing so they attract attention to themselves, increasing their personal chance of being attacked.
  • Walrus
    The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

    es have been seen adopting orphans who lost their parents to predators.
  • Some termites
    Globitermes sulphureus
    Globitermes sulphureus is a species of termite that is very common in Central and Southern Vietnam and also present in other areas of South East Asia, including Malaysia. They live in nests made of earth that can be up to 1.5m tall and can contain tens of thousands of individuals...

     and ants
    Camponotus saundersi
    Camponotus saundersi is a species of ant found in Malaysia and Brunei, belonging to the genus of Carpenter ants. Workers can explode suicidally as an ultimate act of defense, an ability it has in common with several other species in this genus and a few other insects...

     release a sticky secretion by fatally rupturing a specialized gland. This autothysis
    Autothysis is the process where an animal destroys itself via an internal rupturing or explosion of an organ which ruptures the skin. The term was proposed by Maschwitz and Maschwitz in 1974 to describe the defensive mechanism of the carpenter ant . It is caused by a contraction of muscles around a...

     altruistically aids the colony
    Ant colony
    An ant colony is an underground lair where ants live, eat and mate. Colonies consist of a series of underground chambers, connected to each other and the surface of the earth by small tunnels. There are rooms for nurseries, food storage, and mating...

     at the expense of the individual insect. For example, defending against invading ants by creating a tar baby
    Tar baby
    The Tar-Baby is a doll made of tar and turpentine used to entrap Br'er Rabbit in the second of the Uncle Remus stories. The more that Br'er Rabbit fights the Tar-Baby, the more entangled he becomes...

  • Meerkats often have one standing guard to warn whilst the rest feed in case of predators attack.
  • African buffalo
    African Buffalo
    The African buffalo, affalo, nyati, Mbogo or Cape buffalo is a large African bovine. It is not closely related to the slightly larger wild Asian water buffalo, but its ancestry remains unclear...

     will rescue a member of the herd captured by predators.
  • Lemurs of all ages and of both sexes will take care of infants unrelated to them

See also

  • Cheating (biology)
    Cheating (biology)
    Cheating is a metaphor commonly used in behavioral ecology to describe organisms that receive a benefit at the cost of others. Cheating is common in many mutualistic and altruistic relationships. Natural selection favors cheating, but there are mechanisms to regulate cheating.- Theoretical Models...

  • Evolutionarily stable strategy
    Evolutionarily stable strategy
    In game theory and behavioural ecology, an evolutionarily stable strategy , which is sometimes also called an evolutionary stable strategy, is a strategy which, if adopted by a population of players, cannot be invaded by any alternative strategy that is initially rare. An ESS is an equilibrium...

  • Gene-centered view of evolution
    Gene-centered view of evolution
    The gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution occurs through the differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation, with gene defined as...

  • Sociobiology
    Sociobiology is a field of scientific study which is based on the assumption that social behavior has resulted from evolution and attempts to explain and examine social behavior within that context. Often considered a branch of biology and sociology, it also draws from ethology, anthropology,...

  • Evolution of morality
    Evolution of morality
    The evolution of morality refers to the emergence of human moral behavior over the course of human evolution. Morality can be defined as a system of ideas about right and wrong conduct. In everyday life, morality is typically associated with human behavior and not much thought is given to the...

  • Evolutionary ethics
    Evolutionary ethics
    Evolutionary ethics could be either a form of descriptive ethics or normative ethics.Descriptive evolutionary ethics consists of biological approaches to ethics based on the role of evolution in shaping human psychology and behavior...

External links

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