Albert’s Fun Fact Science Corner: Kin Selection

Photo Courtesy of Badlands National Park

Photo Courtesy of Badlands National Park

In the sun-dried, endless plains of Badlands National Park, a black-tailed prairie dog looks up. Its tan fur blending in with the cracked earth as a black speck spirals closer and closer, silhouetted against a powder-blue sky. As the shadow nears, growing and taking shape, the prairie dog recognizes it as a ferruginous hawk, just on the verge of discovering and attacking the colony. The prairie dog does not run, it does not hide, it does not arm itself for battle. Instead, the prairie dog launches itself onto its two hind feet, exposing its fuzzy little belly and raising its round black eyes to sky, screaming to the heavens. It draws the attention of the predator, but also alerts its neighboring prairie dogs to the hawk’s presence. It has brought itself that much closer to dismemberment and digestion, but has allowed its colony a few extra moments to take shelter and survive the deadly visit. A beautiful and stunning display of altruism at work in the animal kingdom.

Altruism truly is a tricky topic. Darwin’s “On the Origin of Species” let us all know that nature prizes fitness above all. Lifetime Reproductive Fitness (LRF) is the number of viable offspring an individual has in their lifetime, and it has historically been the gold standard for understanding selective pressures in evolutionary biology. If a certain trait or behaviour can increase an individual’s LRF and that trait or behaviour is heritable, then that trait or behaviour will proliferate and become more common. The noble black-tailed prairie dog, however, seems to contradict this “gold standard” of natural selection. It springs to its hind legs, purposefully risks its LRF in a dance with death, and laughs in the face of traditional evolutionary biology. Is this really unaccounted for by nature? Did familial love and caring overcome the animal kingdom’s most basic evolutionary drives? Has biology evolved its way out of selfishness and into altruism?

In his 1964 paper “The Genetical Evolution of Social Behavior,” Evolutionary Biologist W.D. Hamilton proposed a new method of understanding fitness. His approach was to look not at the fitness of the individual, but the fitness of the genetic information they carry. Closely related organisms share much of the same genetic information — siblings share about half of their genetic information with each other, first cousins share one-eighth. If we look not just at the LRF of an individual, but how much of their own genetic information they can ensure is passed on to the next generation cumulatively, we can understand how it is “worth it” evolutionarily for an individual to sacrifice their own LRF for that of their relatives. Thankfully, Hamilton’s formula for this is very simple. Let C be the expected cost to the LRF of an individual, let r be the relatedness, or fraction of genetic material shared, with an individual being benefited by the behaviour, and let B be the expected benefit in LRF to the related individual. We can then propose that when C < ∑rB, the seemingly “altruistic” behaviour is actually an evolutionarily advantageous gamble. For example, if the alarm-calling prairie dog expects to have two more offspring in its lifetime and it expects that by alarm-calling it will have a 50% chance of being eaten, C = 1. If there are 4 prairie dogs nearby whose chances of being eaten will be decreased by 25% by the alarm call, and they will each have 4 additional offspring if saved, then B = 1 for each prairie dog. If each prairie dog nearby is a sibling of the alarm-calling prairie dog, they each share ½ of their genetic material with the alarm-calling prairie dog and r=½. The rB for each prairie dog is ½ and for all 4 prairie dogs together it is 2, and because 1<2, the alarm calling behaviour is evolutionarily advantageous.

This poses a problem for our dream of altruistic prairie dogs. It seems something is lost when we can explain their behaviour in terms of an evolutionary mechanism. What was once a miniscule rodent laughing in the face of biology is now simply a cog in a machine of genes and memes trying to proliferate. Just a mechanism for a selfish and self-reproducing DNA molecule to continue its march towards an ultimate dissolution into the chaos of the universe. A pattern that wants to stay that way. A particularly tricky molecule for entropy to stamp out.

But perhaps, there is another way to look at this. Perhaps the black-footed prairie dog and its eusocial entourage of seemingly altruistic animals — including bees and shrimp and naked mole rats — have a point. Perhaps it is not evolution which has bent their rodent ways of life to conform to some model of fitness. Instead, with their ever growing teeth and powerful cries to the endless skies above, prairie dogs have carved their own path into the hostile and unloving universe we live in. Perhaps they have bent the hand of evolutionary biology to accommodate their communal and selfless lifestyle. They have found a way to be altruistic and loving against the wishes of an environment so antithetical to the concept of sacrifice that the existence of fitness beyond the traditional LRF was baffling and groundbreaking when it was first made note of in journals.

Often it can feel depressing and reductive to pick apart behaviour we love and participate in under the microscope of evolutionary biology, but it is important to remember that biological concepts and formulae are not etched into the fabric of the universe: they are created by people to better understand the phenomena around us. Instead of seeing ourselves as reduced to simply the mechanisms of molecules and trends, maybe it is healthier to think of ourselves as some of the greatest obstacles the universe has to description and prediction. We and the nature around us are some of the most complex systems in the cosmos. So much about you and I is so vastly unknown and so poorly understood. What confusing and sublime altruism will we see fit to create? When we stand up and bear ourselves to the heavens, what will we cry that will bewilder all those who listen?

About the Author

Recent Stories
Notify of

Inline Feedbacks
View all comments