The armpit effect in biology is a hypothesis that an individual learns to identify closely related individuals by their odor, comparing it to its own smell for phenotype matching. The animal is able to identify subtle genetic distinctions in odor, and this behavior enables an animal to distinguish between kin and non-kin. The theory was proposed by Richard Dawkins who hypothesized that it would be advantageous to an animal to be able to recognize its kin in this way so as to increase its fitness and reproductive success, an example being a mother's ability to feed her own offspring rather than those of another individual.