Altruism (biology)

Altruism (biology) refers to behavior by an individual that increases the fitness of another individual while decreasing the fitness of the actor. In simpler terms, it's when an organism acts in a way that benefits others at a cost to itself. This cost and benefit are measured in terms of reproductive success, or expected number of offspring.

At first glance, altruism presents an evolutionary paradox. Natural selection favors traits that enhance an individual's own survival and reproduction. Why would an organism perform an action that reduces its own chances of propagating its genes?

Several mechanisms have been proposed to explain the evolution of altruism:

• Kin Selection: This is perhaps the most well-understood explanation. Kin selection suggests that altruism can evolve if the beneficiaries of altruistic acts are related to the actor. This is because relatives share genes. By helping relatives reproduce, an individual is indirectly promoting the propagation of its own genes, even if it comes at a personal cost. The concept of "inclusive fitness" describes this combined reproductive success of an individual plus the reproductive success of its relatives, weighted by their degree of relatedness. Hamilton's rule (rB > C) provides a mathematical framework, where r is the coefficient of relatedness between actor and recipient, B is the benefit to the recipient, and C is the cost to the actor. Altruism is favored when the benefit to the recipient, devalued by the coefficient of relatedness, exceeds the cost to the actor.

• Reciprocal Altruism: This mechanism explains altruism between unrelated individuals. It proposes that altruistic acts can evolve if there is a reasonable expectation that the favor will be returned in the future. In other words, "you scratch my back, and I'll scratch yours." For reciprocal altruism to work, individuals must be able to recognize each other, remember past interactions, and punish cheaters who fail to reciprocate. This is more likely to evolve in species with stable social groups and long lifespans.

• Group Selection: This is a more controversial explanation. Group selection suggests that altruism can evolve because groups with altruistic individuals are more likely to survive and reproduce than groups with selfish individuals. This perspective emphasizes the benefits of altruism at the group level, even if it may be costly at the individual level. However, the relative importance of group selection compared to kin selection and reciprocal altruism is still debated among evolutionary biologists.

• Indirect Reciprocity: In this scenario, altruistic acts are directed towards individuals who have helped others in the past. Individuals gain a reputation for being helpful, which then increases their chances of receiving help from others in the future. This is sometimes phrased as "I'll help you, because someone else helped someone else."

It's important to note that these mechanisms are not mutually exclusive, and altruistic behavior in many species may be driven by a combination of factors. Understanding the evolutionary basis of altruism provides crucial insights into the complex social interactions and cooperative behaviors observed in the natural world.