Tap to Read ➤

Evolution of Altruism in Animals

Mrunal Belvalkar
Altruism is a kind of social behavior that benefits the recipient at the cost of the altruistic individual. If such is the nature of altruism that it does not fit within the frame of 'survival of the fittest', why did animals evolve to behave altruistically? Read on.
There are so many instances in everyday life when we wish someone would cooperate with us a little more in order for us to do something, or in order for our relationship with that person to work out better.
You wish your kid sister would understand how busy you have been and how tired you are and hence cooperate with you in keeping your room clean. You wish your teacher would cooperate and agree to give you after class lessons because you are finding something rather difficult to understand.
In all these instances, what you are expecting is for the person to do something for you, to help you out. We expect this only - or mostly - from people we know, people we are in some way related to; and other people who are related to us expect the same from us as well.

What is Altruism?

In terms of evolutionary biology, a social behavior is broadly defined as an act or deed that has consequences on the actor as well as the recipient of the act or deed.
Hence, altruism is defined as a social behavior that benefits the recipient but not the actor; the actor is then said to behaved altruistically.
Your sister, your teacher are the altruistic individuals in the given example, and you are a recipient of their altruism. They do something for you, without their act or deed benefiting themselves as such. They use their resources (time, effort, energy) for your benefit.
One can get to see abundant examples of altruism in nature, especially in animals, if one looks keenly enough...
  • Birds such as the scrub jay often receive help from other birds, sometimes even those that are unrelated to scrub jays, in raising their fledglings and in their protection.
  • When a cat climbs up a tree, only one of the birds sitting on that tree begins to chirp noisily. In doing so, the bird is in fact revealing its location rather than hiding it and is attracting the cat to itself. 
But in the process, the bird succeeds in alerting other members of its flock so that they will hide and not make a noise. The bird thus sacrifices its life in saving that of others, a purely altruistic act.
  • Vervet monkeys are also seen to engage in similar behavior when they are posed by a predator. They give a warning call to other individuals of the group and alert them to the presence of a predator, so that they can save themselves.
  • Autothysis is another example of altruism at work. Autothysis is when an organism sacrifices its life by internally rupturing an organ in its body which helps other members of the group in some ways. Autothysis in ants helps them to release a sticky substance which helps trap invading ants or other insects and prevent them from getting closer to the colony.
  • Queen bees are the only reproductive individuals in a beehive. Yet the drones (male bees) and the workers (non-laying female bees) all help the queen and tend to the needs of the queen and the laid eggs and growing larvae.
  • Vampire bats are known to regurgitate blood and feed other vampire bats that have not been able to go out hunting.
  • Many animals have been shown to share their food or bring back the kill for its mate (wolves). Some even adopt abandoned young ones (dogs, walruses), often of different species as well. Dogs are known to adopt orphaned cats, squirrels, etc.

The Problem with Altruism

In terms of evolutionary biology, altruism is difficult to understand as it clashes with Charles Darwin's theory of natural selection, which states that nature 'selects' those who are fit to survive, or life evolves by the rule of 'survival of the fittest'.
If individuals are engaging in altruistic behavior, they are in fact sacrificing their resources for benefit of others of their kind; in other words, they are reducing their 'fitness' for others' benefit. But still they do it.
How did such a behavior evolve in life? The answer to the question lies in the previous sentence. Have you figured it out? "If individuals are engaging in altruistic behavior, they are in fact sacrificing their resources for benefit of others of their kind." That is the key to evolution of altruism in animals.
Altruism is always showered by actors on those who are related - genetically related, to be more specific - to themselves. Why? Because if it weren't so, the species of the altruist would be at the mercy of selfish individuals, and could well go extinct! How? Read on...

Hamilton's Rule: Altruism is Directed Towards Kin!

We all know that as there are altruistic individuals in a population, so are there the selfish individuals; who do not help others, but want all the benefit they can get from others. In terms of evolutionary biology, such individuals have a better chance for survival, as they do not sacrifice their fitness for anyone and yet reap all benefits.
Suppose an altruistic individual bears a cost 'C' for its altruism. The recipient attains a benefit 'B' out of it. Now, if the recipient is selfish, then it will take all the benefit without having to pay any cost.
If all the individuals in a species are altruists, then that species is at the risk of resource exhaustion because of selfish individuals, and in due course of time could go extinct.
Now imagine a case where an altruist can selectively direct its altruism towards only and only another altruist... well, there is a theory that may work, isn't it? That is exactly how altruism works - you scratch my back, and I'll scratch yours.
It is all a case of reciprocity. But how can you be sure that the recipient of altruism is another altruistic individual only? Hamilton's rule helps us in understanding this.
Mathematically, the Hamilton's rule is expressed as -

rB - C > 0

where, r = relatedness; B = benefit of altruism to recipient, C = cost of altruism to actor.
What the equation implies is - if the benefit of altruism received by an individual is greater than the cost that the altruistic individual has to bear, then and then only is an act of altruism justified. How is this possible? If the recipient is also an altruist.
When is that possible? If the recipient is genetically related to the altruist. How? Because then the recipient would also have the tendency of being altruistic, and would hence in turn help other individuals of the species.
The species as a whole, would hence benefit out of being altruistic. This is what makes altruism an evolutionarily stable theory; i.e. a theory that cannot be invaded by cheating or selfish individuals. 'r' can be easily calculated.
For a concerned individual, its 'r' with its siblings and also with its offspring is 0.5 (because 'half' of the genes would be similar), with its grand-offspring is 0.25 (because only a quarter of the genes would be similar), and so on.
Altruism is observed in humans as well. But altruism is not so easy to understand in humans, for the simple reason that we have something called 'thinking'. We have the power to 'think' about our actions, to 'make a choice', to choose to help or not help someone; and we do it consciously.
We are aware of an instance when we are making a choice. We hesitate before extending our cooperation to someone who hasn't helped us out or 'been nice' to us.
In animals however, altruism is more 'natural'. This kind of behavior makes us wonder if our 'thinking' ability has really benefited us, or is it only making us more spiteful. But cheating and being selfish never goes unchecked or unnoticed, even among animals. Vengeful behavior has been studied in chimpanzees.