pheromones

Meaning: A pheromone is a chemical released into the environment by one animal that changes the behavior or physiology of another animal of the same species. Examples include sex attractants, alarm signals, and trail markers in insects. The molecules bind receptors in the olfactory epithelium. Many animals also have a vomeronasal organ, which sends signals toward the amygdala and hypothalamus, regions tied to emotion, mating, and hormone release. This pathway is one reason pheromone responses can look automatic and instinctive.

On the MCAT: Pheromones appear in the sensation and perception material on olfaction, a chemical sense. A passage may describe an animal behavior, such as mate attraction or alarm responses, and ask you to decide whether a chemical signal could explain it. Another passage may describe a human study, such as the claim that women who live together have menstrual cycles that synchronize (the McClintock effect). Expect questions on controls, confounds, and whether the data support a causal chemical signal. Human evidence is mixed, so a well-supported conclusion should be stated cautiously.

Common confusion: Pheromones are not hormones. A hormone travels in the blood and acts within the body that made it. A pheromone leaves the body, travels through air or water, and acts on a different individual. Also, an ordinary smell is not automatically a pheromone, because the term requires a species-specific signal that changes the receiver's behavior or physiology.