Final answer:
The greenbeard effect (option A) is a theoretical model explaining altruistic behavior among non-kin individuals in a population, which relies on recognition of a shared trait that is linked to an allele promoting altruism towards those who share that trait.
Step-by-step explanation:
The theoretical model of an allele for altruistic behavior that could spread through a population via recognition of similar traits, without involving kin selection or reciprocal altruism, is known as the greenbeard effect. This concept was introduced by Richard Dawkins in his book 'The Selfish Gene'. It describes a scenario where an allele causes three distinct effects – the presence of a recognizable trait (the 'greenbeard'), the ability to recognize this trait in others, and a tendency to act altruistically towards those with the same trait.
The greenbeard effect can lead to the increase of frequency of this allele in a population as individuals with the 'greenbeard' trait selectively assist each other, enhancing each other's fitness.
While kin selection explains altruistic behaviors towards relatives sharing genes and reciprocal altruism involves a mutual exchange of benefits over time, the greenbeard effect represents an alternative means by which altruism can evolve among non-kin that share a specific trait or allele. However, this concept remains largely theoretical and actual examples in nature are rare.