Final answer:
Kin selection is a form of natural selection explaining altruism among relatives sharing common genes. Altruism is a behavior where one individual decreases its own fitness to increase another's. Kin selection and altruism are related as such behaviors may propagate the altruist's genes indirectly through relatives, while unrelated individuals may act altruistically based on reciprocal benefits.
Step-by-step explanation:
What is kin selection and altruism? Kin selection is a form of natural selection that explains how behavior that seems altruistic is actually advantageous in terms of genetics. It occurs when an individual's actions may decrease their own chance of survival or reproduction, but benefit the reproductive success of relatives who share many common genes. This in turn can lead to a greater representation of the altruist's genes in the next generation.
Altruism, in a biological sense, is a behavior that reduces an individual's own fitness in order to increase the fitness of another individual. These behaviors can range from feeding offspring to more subtle forms, such as warning calls that put the caller at risk but protect the community. Kin selection is a major explanation for altruistic behaviors, especially when these behaviors benefit relatives that share a genetic lineage with the altruist. Essentially, the "selfless" act of altruism is not so selfless when viewed through the lens of genetic survival and inclusive fitness.
Where the lines blur is in the observation that sometimes unrelated individuals also exhibit altruistic behaviors towards each other. This is often explained by reciprocal altruism, where individuals benefit mutually over time through cooperative behaviors, enhancing each other's fitness with the expectation of future reciprocation. While kin selection and altruism are deeply interconnected, understanding these concepts requires considering both the genetic relationships involved and the broader social dynamics of the species in question.