Altruism is ecologically defined as the act of an individual that increases the biological fitness (survival and/or reproduction) of another individual while decreasing the same of themself. In principle, it is the practice of expressing concern for the betterment of other human beings or other animals. This affects the actor’s own quality of life both materialistically and spiritually. It can also be defined as the synonym of selflessness, in an extreme case.


The genetic evolution of altruism really confused biologists. This is because the concept seemed paradoxical in a Darwinian world, where every organism struggles to improve its own biological fitness and only the fittest organism eventually survives.

In early 1960s, W. D. Hamilton explained that this interaction can actually be favoured by the alleles for altruism when the interacting individuals are genetically related. He even mathematically derived his claim, which is known as Hamilton’s rule. The rationale is that these alleles are carried by individuals who have a higher probability of interacting with other individuals who also carry the alleles for altruism than any random individual in the population. This is called “kin selection.”

The mathematical relation that explains when natural selection favours altruism is,

rb c > 0

(Hamilton’s rule)

where c is the average effect of the altruism-inducing allele on the fitness of its bearer, b is the average effect on the fitness of recipients, and r is the genetic relatedness between the actor and the recipients.

More recently, a considerable number of supposedly alternative pathways to altruism have been studied and reported. These have risen serious questions over explanations for the evolution of altruism.

Five Interesting Examples of Altruism

1. Shiga toxin-producing Escherichia coli (STEC)

Recently, in 2011, a hypothesis was proposed independently by two research groups that STEC may benefit from Shiga toxin production due to the toxin-dependent killing of eukaryotic cells (like, unicellular predators or human leukocytes), which can increase its probability of living. However, this hypothesis could only be considered as an example of “bacterial altruism” if we assume that the production of the toxin is limited only in a small fraction of bacterial cells, thus, killing only a few members of the population for the overall benefit of the population.

2. T4 bacteriophage and Escherichia coli

Some strains of Escherichia coli contain some specific genes that can trigger cell death when infected by bacteriophage T4. This will kill both the infected bacteria and the virus inside them. Therefore, as the bacterial population gets saved, this can be considered a classic example of altruism.

3. Human beings

Altruism can exist in a whole range of forms in human beings. However, to understand this we can consider a specific example. Infants, even as young as 14 to 18 months of age, can help others to attain their goals like fetch out-of-reach objects or opening cabinets. They do this irrespective of any reward from adults, therefore, setting up a nice example of altruism.

4. Plants

A specific example of corn reproduction can also explain altruistic behaviour. They reproduce via double fertilization, that is, when the two pollen grains come in contact with an individual silk, they produce a seed containing an embryo and endosperm. It was observed that the embryos with the same mother and father as the endosperm in their seed weighed significantly more than embryos with the same mother but a different father. This means that the embryos with a different father were not handed over as much food as the ones with the same father, thus suggesting an altruistic behaviour.

5. Insects

Altruistic behaviour is most widely explained with the example of sterile worker castes which are found in the colonies of social insects. These workers invest in a variety of cooperative behaviours from brood care and colony defence to forming bivouacs and tending fungus gardens, instead of attempting to reproduce. In some extreme cases, workers even become morphologically specialized to perform these tasks.

Read Also:


  • The evolution of altruism and the serial rediscovery of the role of relatedness Tomas Kay, Laurent Keller, Laurent Lehmann Proceedings of the National Academy of Sciences Nov 2020, 117 (46) 28894-28898; DOI: 10.1073/pnas.2013596117
  • Łoś, J. M., Łoś, M., Węgrzyn, A., & Węgrzyn, G. (2013). Altruism of Shiga toxin-producing Escherichia coli: recent hypothesis versus experimental results. Frontiers in Cellular and Infection Microbiology, 2. doi:10.3389/fcimb.2012.00166
  •  Shub, D. A. (1994). Bacterial Viruses: Bacterial altruism? Current Biology, 4(6), 555–556. doi:10.1016/s0960-9822(00)00124-x
  • Warneken, F., & Tomasello, M. (2009). The roots of human altruism. British Journal of Psychology, 100(3), 455–471. doi:10.1348/000712608×379061
  • University of Colorado at Boulder. (2013, February 1). Some plants are altruistic, too, new study suggests. ScienceDaily. Retrieved June 13, 2021 from
  • Downing, P. A., Cornwallis, C. K., & Griffin, A. S. (2016). How to make a sterile helper. BioEssays, 39(1), e201600136. doi:10.1002/bies.201600136

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