What is altruism?
Altruistic behaviors are known to be those actions that are beneficial to others, but seemigly not to the individual performing the behavior. In humans, this could be something such as donating to charity or volunteering in order to help those in need. This behavior is also seen across many different animal species, and has a surprising evolutionary background.
Fairy Wren: A Complex Example
Take, for example, the Australian bird species, the superb fairy wren. It has been found that only some of these birds exhibit altruistic behaviors by taking part in “cooperative feeding.” In other words, the males of a female’s previous brood (as well as unrelated males) will help in feeding the female’s new chicks. The interesting fact about this altruistic behavior, however, is that there does not appear to be any long-term survival benefit to these baby birds recieving food from helpers. And, besides this, it may appear to be counterproductive for these helper birds in terms of evolutionary fitness. It is not the siblings/ unrelated chicks that the helper birds are benefiting, however. It was previously beleived that the mother bird was the one benefiting— with helper birds around (the birds exhibiting altruism), the mother appeared to be healthier due to the fact that she had spent less energy feeding her chicks. More recent studies have discovered that not only does kin-selection play a role in the evolution of this behavior, but so do mechanisms that involve future-direct benefits for the helper birds.
Direct and Indirect Selection
In the case of altruism for the purpose of kin selection, helper birds feed chicks that are fully or partially related to them in order to increase the survival of related future-breeders, and therefore some of the helpers’ genes. Intrestingly, however, some fairy wrens are altruistic towards unrelated chicks. This appeared to be due to the fact that this altruistic behavior can aid the helper birds in acquiring a breeding position within their particular territory in the future. In fact, the chances of unrelated helper birds taking part in cooperative feeding was increased when the liklihood of inheriting that breeding territory was higher.
How does this behavior have an evolutionary basis, though? In other words, how does it increase fitness? Fitness, overall, has to do with getting ones’ genes into the next generation’s gene pool. But it is important to realize that there is both direct fitness, and indirect fitness. Direct fitness has to do with personal reproduction, and therefore one’s own offspring, while indirect fitness involves the related individuals that are able to survive and reproduce (due to to an altruistic behavior). This indirect fitness, then, is due to indirect selection– natural selection for traits that increase the reproductive success of one’s relatives. Both direct and indirect fitness are beneficial to an individual because, even in the case of closely related relatives surviving and reproducing, genes similar to one’s own are passed down.
If we were to use the fairy wren as an example, indirect selection is seen in the case of helper birds taking part in cooperative feeding of related birds. Indirect selection (kin-selection) then leads to indirect fitness in the altruist individual (the number of relatives, in this case the baby birds, the altruist helps to survive and reproduce). Direct selection is also at play here, although it may not appear obvious at first. This occurs even when the altruist is taking part in cooperative feeding of unrelated birds– the helper birds take part in this behavior in order to increase their liklihood of inheriting breeding territory, as well as increase the number of their own future helpers (the birds which they are helping to raise). Thus, by inheriting breeding territory and securing a set of future helper birds, these altruist fairy wren are increasing their own direct fitness.
Kingma, S., Hall, M., Peters, A., Associate Editor: Anna Qvarnström, & Editor: Judith L. Bronstein. (2011). Multiple Benefits Drive Helping Behavior in a Cooperatively Breeding Bird: An Integrated Analysis. The American Naturalist, 177(4), 486-495. doi:10.1086/658989
Monash University. “Fairy wrens are accountants of the animal kingdom, not altruistic as previously thought.” ScienceDaily. ScienceDaily, 20 March 2011. <www.sciencedaily.com/releases/2011/03/110318102252.htm>.
Featured image: “Male and Female Superb Fairy Wren” via wikicommons under CC SA-BY 3.0