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Part II - Cases of altruism in the animal kingdom

Charity cases in nature - when are animals more likely to be altruistic?

With the understanding that true altruism never benefits an individual, let’s explore some of these interesting cases of altruism in nature.

In my last post we explored why true altruism is uncommon in the animal kingdom (Part I). The presence of altruism in nature is a contradiction to Darwin’s theory of natural selection; a behavior that doesn’t increase one’s fitness should eventually disappear from a population. As a result, altruism is an exciting field for animal behavior theory and experimentation. The most common altruistic behaviors fall into two categories: kin selection and reciprocal altruism.

Kin Selection

One explanation for altruism is that individuals that are more closely related are more likely to perform altruistic behaviors. In a roundabout way, helping your parents, siblings, and even cousins means that you can increase the chances that some of your shared DNA will be passed on to their offspring.

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Fig.1 Left: A queen bee (marked with red) surrounded by worker bees (photo by Samuel Huang). Right: Green ants form a bridge so other worker ants can move between the foliage and a concrete surface (photo by Lian Guo).

Eusocial insect colonies, like ants, are a classic example of kin selection [1]. In these colonies, there is a queen and many worker insects. When biological success is measured by the number of offspring you produce, it seems odd to have a system where only the queen and a few male insects reproduce in a colony of hundreds or even millions of insects. Worker ants are sterile and perform all other tasks within a colony, like gathering food, feeding offspring, building the nest, etc; AKA the best housemates you could ever have! It would appear that these insects are altruistic, giving their entire lives to help the queen reproduce successfully. However, all workers are related to their queen. Therefore when the queen reproduces successfully, the genes of the worker ants are also passed on to offspring. Because all members of the community are able to increase their fitness through this method, this social strategy persisted and evolved in several insect classes, as well as in some African mole rats [2].

Another example of kin selection is when animals produce alarm calls. Upon detecting a predator, an individual will begin alarm calling to warn others in their living group of nearby danger. Emitting a warning call endangers the caller by potentially attracting the attention of the predator to that individual. As a result, alarm calls can be considered an altruistic behavior (shown in Fig. 2). A living group, or coterie, of black tailed prairie dogs typically consists of highly-related females, their offspring, and nomadic males. When researchers exposed a coterie of black tailed prairie dogs to a stuffed American badger, they found that the number of times an alarm call was issued doubled when the “predator” was moved within a coterie’s territory compared to being run through an adjacent territory [3]. Researchers found that alarm calls were produced at a higher frequency when there were signs of danger in the presence of closely-related kin [4]. Again, an apparently altruistic behavior is performed more frequently when relatives are present, improving kin fitness and therefore one’s own fitness.

Fig.2 Black tailed prairie dogs spend about one-third of their time standing watch for predators. When alarmed, they emit loud and repetitive antipredator calls that can be echoed by others in the coterie.

Reciprocal Altruism

Since there are also occurrences of altruism between unrelated individuals, scientists began looking for an alternative explanation for altruistic behaviors. Researchers found that when altruistic behaviors are likely to be reciprocated, altruistic behaviors can develop into a strategy for survival.

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Fig.3 An olive baboon baby clings to its mother’s back (photo by Ray Morris).

This was found to be the case for an observational study on olive baboons in Tanzania [5]. Male baboons would “solicit” help from another male baboon to threaten an opponent male, often when that opponent is consorting with an oestrous female. The soliciting male and helping male were able to threaten or fight the opponent, resulting in the soliciting male mating with the oestrous female, with no apparent benefit to the helping male. While this appears to be an altruistic and potentially costly behavior (if injured from fight), researchers found that males which most frequently gave help were also the ones to most frequently receive help, often from the same individual that they helped. Furthermore, adult males were unresponsive to solicitations from juvenile baboons, potentially because juveniles are unlikely to be useful in a confrontation with other adult males. While male baboons do engage in what is considered an altruistic behavior, it occurs more readily when there is high likelihood that there will be reciprocation of that behavior.

These are just a few examples of altruism in the animal kingdom. For more examples, check out this article. It appears that in nature, altruism is much like karma—what you do is what you get!

References:

[1] Queller, David C., and Joan E. Strassmann. “Kin selection and social insects.” Bioscience 48, no. 3 (1998): 165-175.

[2] Plowes, Nicola. “An Introduction to Eusociality.” Nature Education Knowledge 3, no. 10 (2010): 7. http://www.nature.com/scitable/knowledge/library/an-introduction-to-eusociality-15788128

[3] Hoogland, John L. The black-tailed prairie dog: social life of a burrowing mammal. University of Chicago Press, 1995.

[4] Hoogland, John L. “Nepotism and alarm calling in the black-tailed prairie dog (Cynomys ludovicianus).” Animal Behaviour 31, no. 2 (1983): 472-479.

[5] Packer, Craig. “Reciprocal altruism in Papio anubis.” (1977): 441-443. http://www.nature.com.silk.library.umass.edu/nature/journal/v265/n5593/pdf/265441a0.pdf

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