Altruism among Animals – Definition and Evolution

What is Altruism?

  • Altruism, a concept deeply rooted in human nature, refers to the act of selflessly benefiting others without expecting anything in return. It encompasses various forms of positive actions, such as sharing resources, providing assistance, offering advice, or even sacrificing one’s own well-being for the greater good. While altruistic acts may seem to come naturally to some individuals, they often involve a certain cost, whether it be time, effort, or personal sacrifice.
  • From a genetic perspective, altruistic behavior can be understood as a phenomenon that increases the fitness or survival chances of another individual while potentially decreasing one’s own fitness. To illustrate this, let us consider a hypothetical population of animals with two different alleles: X and X’. The X allele promotes behavior that benefits other members of the species, such as saving them from predators, while the X’ allele favors non-involvement and self-preservation. In this scenario, individuals possessing the X’ allele are more likely to live longer and reproduce more compared to those with the X allele, which promotes altruism. Consequently, over time, the frequency of the X allele in the population is likely to decline.
  • It is important to note that altruism is not limited to genetic or biological contexts. Humans, with their complex cognitive abilities and social structures, often engage in altruistic behavior that goes beyond mere genetic predispositions. Empathy, compassion, and a sense of morality play significant roles in motivating altruistic actions among individuals.
  • Altruism manifests in various ways across different cultures and societies. Acts of charity, volunteering, and philanthropy are prominent examples of altruistic behavior in human society. These actions demonstrate the willingness to assist others in need, support social causes, or contribute to the well-being of communities. Altruism can also be observed in everyday interactions, such as holding the door for someone, offering a helping hand to a stranger, or comforting a friend in distress.
  • Although there may be an inherent cost or sacrifice associated with altruism, the benefits it brings are immeasurable. Altruistic acts not only benefit the recipients directly but also foster a sense of connection and cooperation within communities. They contribute to the development of empathy, trust, and social cohesion, ultimately enhancing the overall well-being of individuals and society as a whole.
  • In conclusion, altruism is the selfless act of benefiting others without expecting anything in return. While genetic factors can influence the presence or decline of altruistic traits, human altruism extends beyond biological motivations. It encompasses a wide range of actions driven by empathy, compassion, and moral values. Altruism plays a crucial role in strengthening social bonds, promoting cooperation, and creating a more compassionate and harmonious world.

Evolution of Altruism

The evolution of altruism has been a subject of fascination for socio-biologists, as seemingly selfless behavior can be observed in various animals, including humans. Over the past two decades, researchers have put forth three explanations to shed light on the evolution of altruistic behavior.

The first explanation revolves around selfish behavior, where an individual’s actions benefit themselves, albeit others in the group may also reap some benefits. This notion of selfish behavior has been discussed in detail previously.


The second explanation is known as kin selection, proposed by W. D. Hamilton in 1963. Kin selection suggests that altruistic behavior can evolve even if it reduces an individual’s own fitness. This concept emphasizes the importance of genetic relatedness among individuals. When an individual helps or supports genetically related kin, they are indirectly promoting the survival and reproduction of shared genes, which may enhance the overall fitness of the family or group.

The third explanation involves eusociality, which is evident in certain insect species such as termites, ants, bees, and wasps. The evolution of sterile castes within these species is believed to be a result of kin selection. In eusocial colonies, the majority of members exhibit what can be seen as the pinnacle of altruism. These individuals forgo their own reproductive fitness entirely and dedicate themselves to the welfare of the colony as a whole.


But how can an individual worker ant, bee, or wasp ensure the transmission of her genetic traits to the next generation? This can be best explained through the concept of haplodiploidy, as depicted in Figure 5.36. A female individual in hymenopteran societies can either reproduce and produce offspring or assist her sisters. Due to haplodiploidy, a female hymenopteran can maximize her evolutionary success by caring for her sisters, as they share 75% of her genes. In contrast, her own offspring would only inherit 50% of her genes.

In certain bird species that live in social groups and occupy territories, only one female lays eggs, and one male fertilizes them, while the remaining birds help in feeding younger siblings and defending the nest against predators. When either the dominant male or female dies, one of the helpers takes their place.


Studies conducted by K. Rabenold in 1984 on tropical wrens revealed that pairs or trios of birds rarely managed to raise any young successfully. However, pairs with two helpers raised four times as many young, and groups of six or eight raised twice as many as quartets. The key factor contributing to improved nesting success was better defense against predators.

In the case of helper wrens, they have the ability to form pairs independently, but they choose to be helpers, investing their time and energy while risking predation, without gaining any direct genetic benefits. However, they contribute to the reproductive success of their siblings who share 50% of their genes. Thus, genes that favor helping behaviors are being passed along.


Cooperative breeding, where individuals assist in raising offspring that are not their own, is also observed in many other vertebrates. This behavior often arises due to factors such as predation or the lack of available habitats for independent reproduction. Consequently, helping behavior can increase the fitness of individuals.

Reciprocal altruism, proposed by W. D. Hamilton in 1963, addresses the question of how altruistic behavior can evolve among individuals who are not genetically related. It suggests that altruism can be favored when there is a system of exchanging altruistic acts between individuals. This can be likened to the concept of “you scratch my back, and I’ll scratch yours.”


In conclusion, the evolution of altruism has been explored through various explanations, including selfish behavior, kin selection, eusociality, and reciprocal altruism. These concepts highlight the complex interplay between genetic relatedness, social structures, and the exchange of beneficial actions. Through these mechanisms, altruistic behavior has evolved and continues to shape the dynamics of various species, including humans.

Hamilton’s rule and inclusive fitness with suitable examples

Hamilton’s rule and inclusive fitness are concepts that help explain the evolution of altruistic behavior based on genetic relatedness within a population. Let’s delve into these concepts and explore examples that illustrate their application.


Hamilton’s Rule: Hamilton’s rule, formulated by W. D. Hamilton, states that altruistic behavior is more likely to evolve when the benefit to the recipient, multiplied by the degree of genetic relatedness between the actor and the recipient, exceeds the cost to the actor. Mathematically, it can be expressed as:

rb > c

Where: r = Coefficient of relatedness (the probability that a gene present in one individual is also present in the other due to common descent) b = Benefit to the recipient c = Cost to the actor

Inclusive Fitness: Inclusive fitness is a measure that combines an individual’s own reproductive success (direct fitness) with the reproductive success of relatives that share similar genes (indirect fitness). It encompasses both personal reproduction and the reproduction facilitated by altruistic acts towards kin. Inclusive fitness can be seen as the sum of an individual’s direct fitness and indirect fitness.

Example 1: Alarm Calls in Ground Squirrels Ground squirrels are social animals that live in colonies and are susceptible to predation. When a predator approaches, an individual squirrel may emit an alarm call, warning others of the danger. This behavior incurs a cost to the caller, as it may attract the predator’s attention. However, it benefits the other squirrels by increasing their chances of survival. The alarm call behavior can be explained using Hamilton’s rule and inclusive fitness. The caller incurs a cost (c) but enhances the survival (benefit, b) of close relatives who share a portion of its genes (high coefficient of relatedness, r). Therefore, the inclusive fitness gained by protecting genetically related individuals outweighs the cost, leading to the evolution of alarm calls.

Example 2: Cooperative Breeding in Meerkats Meerkats, small mammals that live in family groups, exhibit cooperative breeding behavior. In a meerkat group, only the dominant pair typically reproduces, while other members assist in raising their offspring by providing food, protection, and other forms of care. This cooperative behavior incurs costs for the helpers, as they invest time and energy without directly reproducing. However, their assistance enhances the survival and reproductive success of their close relatives, increasing the inclusive fitness of the helpers. The coefficient of relatedness between siblings or other kin within the group is high, reinforcing the evolution of cooperative breeding.

Example 3: Social Insects (Bees, Ants, Termites) Social insect colonies, such as those of bees, ants, and termites, exemplify the ultimate form of altruistic behavior. Within these colonies, there is a division of labor, with some individuals (workers) sacrificing their reproductive potential to support the reproduction of a few individuals (queens). The sterile workers engage in tasks such as foraging, caring for the young, and defending the colony, while the queens are responsible for reproduction. This social structure is driven by kin selection and the relatedness between colony members. The workers, who are typically closely related sisters, enhance the inclusive fitness of their genes by helping the reproductive success of the queens, who share a significant portion of their genetic material.

In these examples, Hamilton’s rule and inclusive fitness help explain the evolution of altruistic behavior. The costs incurred by the actors are outweighed by the benefits gained by genetically related individuals, resulting in the propagation of altruistic traits within a population.


What is altruism among animals?

Altruism among animals refers to selfless behaviors exhibited by individuals that benefit others at a cost to themselves.

Why do animals exhibit altruistic behavior?

Altruistic behavior in animals can be driven by factors such as genetic relatedness, cooperative breeding, reciprocal altruism, or eusociality.

How is altruism related to genetic relatedness in animals?

Altruistic behavior is often more likely to occur among closely related individuals because helping kin promotes the survival and reproduction of shared genes.

What is cooperative breeding, and how does it relate to altruism?

Cooperative breeding is a form of altruistic behavior where individuals assist in raising offspring that are not their own. This behavior can increase the inclusive fitness of individuals and benefit their genetic relatives.

Can animals exhibit reciprocal altruism?

Yes, reciprocal altruism is observed in some animal species. It involves individuals providing assistance to others with the expectation of receiving help in return at a later time.

Are there any examples of altruistic behavior in social insect colonies?

Yes, social insects like bees, ants, and termites exhibit altruistic behavior within their colonies. Sterile workers sacrifice their own reproduction to support the reproductive success of a few individuals (queens) through tasks like foraging, nest defense, and brood care.

How do researchers study altruism in animals?

Researchers use various methods such as observation, experiments, genetic analysis, and mathematical modeling to study altruistic behavior among animals.

Can altruistic behavior be learned or is it instinctual in animals?

Altruistic behavior in animals can be a combination of innate predispositions and learned behaviors. Some aspects of altruism may be instinctual, while others may be shaped by social learning and environmental factors.

Do animals show different levels of altruism within and across species?

Yes, the extent of altruism can vary both within and across animal species. Some species may exhibit high levels of altruistic behavior, while others may show limited or no altruism.

Is there a direct evolutionary advantage to altruistic behavior in animals?

While altruistic behavior may involve costs for the individual performing the behavior, it can confer indirect benefits through increased inclusive fitness or enhanced survival and reproduction of genetically related individuals, contributing to the evolutionary success of certain traits or social structures.

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