altruism fitness animal behavior

Part I - Why true altruism is a rare behavior in the animal kingdom

Being selfish means staying alive

When I say altruism, you probably think of giving to others. As humans, we admire when someone acts altruistic and consider altruism to be a good personality trait. Why then, is true altruism in the animal kingdom rare?

When I say altruism, you probably think of giving to others. As humans, we admire when someone acts altruistic and consider altruism to be a good personality trait. Why then, is true altruism in the animal kingdom rare? Let’s start with some definitions 1.


1: unselfish regard for or devotion to the welfare of others

2: behavior by an animal that is not beneficial to or may be harmful to itself but that benefits others of its species”

The first definition is what we typically use when discussing altruism, like charity and volunteering. The second definition refers to biological altruism, or when an animal performs a behavior that benefits another animal at a loss to themselves. Specifically, this loss is a cost to fitness.

In biology, fitness isn’t about working out and eating healthily (stuff grad students wish they had time for). Fitness is a measure of the reproductive success of an individual. The number of offspring you have, as well as how many grandchildren and great-grandchildren (and so on) you have, factor into your fitness. Fitness depends greatly on your ability to survive to sexual maturity and obtain enough resources to produce healthy young. A given individual will generally have higher fitness when they have the traits that are best suited to their environment (e.g. feed efficiently, evade predators, attract mates, provide for offspring). It’s essential to understand fitness in order to appreciate why true altruism is actually a detrimental strategy to an animal. Today, you will meet Bashar and Billy Joe, two photogenic dogs that will help us explore fitness and altruism (Fig 1).

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Fig 1. Bashar (top) and Billy Joe (bottom) contemplate how to increase their fitness—a YMCA membership perhaps? (photos by Ryan McGuire).

(Note: these situations are completely made up!)

Bashar eats well and has no problem finding a mate (he’s a good dancer). He has a litter of puppies every other year and is very good at providing food for his kids. Almost all of his offspring use their own amazing dance moves to find mates of their own and start new families, giving Bashar plenty of grandkids to be proud of.

Billy Joe is an overly picky eater and can only sometimes find a mate (he only knows the stanky leg). He’s lazy so whenever he does have kids, he feeds them when he feels like it. Due to starvation and picky eating habits, only some of his pups survive to adulthood and even less end up having pups of their own.

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Fig 2. Bashar’s good health, plentiful mates, and good parenting leads to many pups and grandpups. Billy Joe, in poor health, lacking in mates, and apathetic parenting, has fewer pups and grandpups. (Made by Lian Guo).

Between these two, who do you think has higher fitness? That’s right, Bashar is succeeding at the game of life, whereas Billy Joe is not (Fig 2). The result is more little Bashars in the world than Billy Joes, reflecting that Bashar had traits that increased his fitness compared to Billy Joe.

Now let’s get back to altruism. True altruism in the animal kingdom is actually super weird, because everything animals do is to increase their fitness. Why feed yourself and avoid predators? So you can live long enough to have babies! Why have an ornate courtship dance? So you can attract a mate to have babies! Why protect and care for your offspring? So your babies can survive and have more babies! True altruism goes completely against this goal of increasing one’s fitness.

To give a concrete example, true altruism would be like if Bashar took half of the food he collected for his pups and gave them to Billy Joe’s pups. Giving Billy Joe food that Bashar’s own pups could have eaten decreases Bashar’s fitness because he is lowering the chances that his own offspring will survive (Fig 3). Bashar’s lowered number of offspring leads to a lower likelihood he would have any grandpups. If Bashar’s offspring also inherit his penchant for altruism, his descendants will continue to have lower fitness until his genes virtually exit the gene pool.

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Fig 3. Bashar is feeling altruistic and gives half of the food he collects to Billy Joe’s pups. The result is less food for his own pups, meaning less of them survive to produce their own offspring. Billy Joe is pretty happy though! (Made by Lian Guo).

Essentially, truly altruistic behaviors will not succeed in a population because they lead to decreased fitness, so we’d expect altruistic individuals to eventually disappear from a population. The result is a low occurrence of true altruism in the animal kingdom. Moral of the story: stay selfish Bashar!

There are certain situations where altruistic behaviors can be beneficial. Stay tuned for Part II of this post, where I will illustrate several types of altruism that are more commonly found in the animal kingdom.

For more, check out this “quick guide” to altruism.



[2] West, Stuart A., Andy Gardner, and Ashleigh S. Griffin. “Altruism.” Current Biology 16, no. 13 (2006): R482-R483. (

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