pheromones

pheromones any of a variety of substances, secreted by many animal species, that alter the behavior of individuals of the same species. Sex attractant pheromones, secreted by a male or female to attract the opposite sex, are widespread among insects. The pheromones produced by males include a substance produced by cockroaches that attracts females and orients them in the correct mating positions and a substance elaborated by the desert locust that accelerates sexual maturation in adults of both sexes. Male-attracting pheromones have been discovered in the females of many species of beetles, bees, and moths. The polyphemus moth will not mate unless red oak leaves are present; it has been found that the leaves give off a volatile aldehyde that stimulates the female to release a male-attracting pheromone. Attempts are being made to use pheromones in insect control, e.g., as bait to attract males to field traps or, in very high concentrations, to disorient insects and prevent mating.

pheromones like hormones, are secretions that act as chemical signals. While hormones change the behaviour of target cells elsewhere in the body, pheromones are odours that ‘carry stimulation’ (from the Greek phero and horma) and change the behaviour of other creatures of the same species that pick up the scent. Pheromones are widespread in the animal world, from the single-celled amoeba to human beings. A classic example is the pheromone emitted by female gypsy moths, which can be detected by sensory receptors on the antennae of a male moth 1 Km or more away, enabling it to home in on the female. Unspayed female dogs can attract males from a similar distance. Ants have a ‘lexicon’ of different pheromones, which they use to elicit attacks on or flight from predators, to mark trails, and so on. Territorial mammals often mark their territory with pheromones in their urine, or rubbed on to ‘scenting posts’ from glands in their skin. There seems to be genetically determined variation of pheromones among individuals of some species, enabling them to recognize mates, offspring or intruders on their territory. Although humans appear to have lost much of the olfactory sensitivity of their mammalian ancestors, recent research suggests that body odours, not necessarily consciously perceived, play an important role in social interaction. Human sweat acquires a distinctive odour at puberty, but urine, as well as genital secretions, may also contain pheromones. The well-known synchronization of the menstrual cycles of nuns and girls at boarding school is probably mediated by odour, and there is evidence that smell enables mothers to distinguish their own children's clothing from that worn by others. Sexual preference is certainly influenced by smell: love may indeed be largely a matter of ‘chemistry’.

Colin Blakemore

pheromone Substance secreted externally by certain animals that influences the behaviour of members of the same species. Common in mammals and insects, these substances are often sexual attractants. They may be a component of body products such as urine, or secreted by specific glands.