BIOLOGY Volume 2 - A Guide to General Biology - 2004

17. ANIMAL COORDINATION AND REGULATION

17.8. Innate Behavior

17.8.10. Altruistic Behavior

One aspect of social behavior that remains not fully understood is that some individuals expend their time and energy caring for conspecifics. This phenomenon is known as altruism, and in its most extreme forms, it involves actions that benefit others at a cost or even direct risk to the individual performing them.

When it comes to mating and parental care, altruism is entirely explicable, as it obviously concerns passing on genes to subsequent generations and ensuring the survival of the species as a whole. For instance, a female baboon carries her infants constantly for nearly six years, while most birds feed and protect their nestlings until they can forage for themselves. What is less obvious is why certain individuals help not only their own offspring, but also, say, warn any group members of impending danger or raise someone else's young.

Some light is shed on this by The behavior of eusocial insects characterized by a caste system, such as ants, certain wasps, and bees. Here, the advantages to the species associated with a division of labor and a social hierarchy are clear, yet it remains unclear how such an Organization arose in the course of evolutionary history.

Sterile females of social insects by definition produce no offspring, yet they sacrifice their lives for the sake of their brothers and sisters. Chromosomal Analysis of the queen, drones, and worker bees shows that sisters (the queen and the workers) are more genetically close to one another than a mother is to her offspring. This is explained by the fact that the fertile queen, like the workers, is diploid, whereas the drone (male) is haploid. Consequently, by helping their own mother reproduce, the workers actually increase the presence of their own genes in the population (via their sisters) more effectively than by producing offspring of their own. Thus, the transition to sterility and altruism in the majority of individuals does not lead to the loss of hereditary traits essential for the species' survival (including purely altruistic ones), and a single sister—the queen—is quite sufficient to transmit them to the next generation.

Altruistic behavior is widespread among primates, ranging from joint defense against predators (in guenons) through mutual grooming and food-sharing tendencies (in apes) to the willingness to lay down one's life for family and country (in humans). The scale of altruism appears to correlate with the genetic relatedness of individuals; that is, it is most pronounced among kin—parents and offspring, and siblings—who share a relatively high percentage of common alleles. Consequently, the adaptive outcome of such behavior must be an increase in the population of the frequency of alleles shared by the "donor" and the "recipient" of the altruistic acts. This behavior is called kin Selection and is maintained across generations because it promotes the survival and reproduction of the bearers of altruistic genes, even when these individuals act purely as "recipients" of such acts.

For situations where altruism extends beyond kin to virtually all members of one's species, a similar mechanism has been postulated. In principle, any biological species originates from changes within a population that spread through the establishment of kinship ties; consequently, altruistic genes will persist even after some of their carriers sacrifice themselves for the survival of the rest. However, the initial correlation between its expression and the degree of relatedness must be preserved. This Conclusion is supported by field observations: altruistic acts are much more frequently observed in animals that live in stable family groups (e.g., zebras) than in those that form massive, mixed-composition herds (e.g., wildebeests).

Similar Examples of altruistic behavior are characteristic of human society, with altruism overall being most noticeably manifested among close relatives with a high proportion of shared alleles.