Why Snakes Have Forked Tongues

The forked tongue of snakes has intrigued people for millennia, inspiring many hypotheses. In many cultures and religions, the forked tongue symbolizes malevolence and deceit. The first person known to inquire about the functional significance of the forked tongue was Aristotle; he suggested that it would double the pleasure of sensations of taste. By the beginning of the twentieth century, the consensus was that the snake’s tongue is a tactile organ, that is, the snake uses it to tap the group much as a blind person uses a cane.

In 1920, Broman suggested what seemed to be a winning hypothesis: When the snake retracts its tongue, the tips (or tines) of the forked tongue are inserted into openings on both sides of the roof of the mouth, through these openings chemical stimuli reach special organs that help snakes detect smells – the vemeronasal organs (VNO). These organs are highly developed in snakes, lizards, and many mammals. They are a second system for detecting smells that appear to have evolved specifically to detect pheromones, the chemical signals that animals secrete as messages to other animals of their species. Broman suggested that forked tongue flicks out, picking up chemical signals, and then delivers these to the VNO. This hypothesis was widely accepted into the 1980s. Then X-ray movie studies of tongue flicks in snakes and lizards with forked tongue disproved the hypothesis; they showed that when the tongue is withdrawn into the mouth, it enters a sheath and the tips do not go into the openings to the VNO. Instead, the chemical molecules are deposited on pads at the bottom of the mouth, and closing the mouth presses the pads and molecules against the opening.

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