Green-beard effect

The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication. A gene for altruism can be favored by selection if the altruism is primarily directed at other individuals who share the same gene (kin selection).

A green-beard effect gene (or linked genes) produces three phenotypic effects: (1) a perceptible trait &mdash; the hypothetical green beard; (2) recognition of this trait in others; and (3) preferential treatment to those recognized. So, this gene is directly recognizing copies of itself, regardless of average relatedness.

Green-beard altruism could, strictly speaking, increase the presence of green-beard phenotypes in a population even if genes are assisting other genes that are not exact copies of themselves in a molecular sense: all that is required is that they produce the three phenotypic characteristics described above. Green beard genes are vulnerable to mutant genes arising that produce the perceptible trait without the helping behaviour.

The idea of a green-beard gene was proposed by William D. Hamilton in his landmark article of 1964 and named by Richard Dawkins in his classic book The Selfish Gene of 1976. But only in 1998 was the first green-beard gene actually found in nature, most specifically in the Red imported fire ant (Solenopsis invicta).