NATURE: THE ETHOLOGISTS

In contrast, ethology—a discipline that developed in Europe but that now dominates United States studies as well—holds that much of what animals know is innate (instinctive). A particular species of digger wasp, for example, finds and captures only honey bees. With no previous experience a female wasp will excavate an elaborate burrow, find a bee, paralyze it with a careful and precise sting to the neck, navigate back to her inconspicuous home, and, when the larder has been stocked with the correct number of bees, lay an egg on one of them and seal the chamber. The female wasp’s entire behavior is designed so that she can function in a single specialized way. Ethologists believe that this entire behavioral sequence has been programmed into the wasp by its genes at birth and that, in varying degrees, such patterns of innate guidance may be seen throughout the animal world. Extreme ethologists have even held that all novel behaviors result from maturation—flying in birds, for example, which requires no learning but is delayed until the chick is strong enough—or imprinting, a kind of automatic memorization discussed below.
The three Nobel Prize-winning founders of ethology—Konrad Lorenz of Austria, Nikolaas Tinbergen of the Netherlands, and Karl von Frisch of West Germany (now part of the united Federal Republic of Germany)—uncovered four basic strategies by which genetic programming helps direct the lives of animals: sign stimuli (frequently called releasers), motor programs, drive, and programmed learning (including imprinting).

Sign Stimuli (Releasers)
Sign stimuli are cues that enable animals to recognize important objects or individuals when they encounter them for the first time. Baby herring gulls, for example, must know from the outset to whom they should direct their begging calls and pecks in order to be fed. An adult returning to the nest with food holds its bill downward and swings it back and forth in front of the chicks. The baby gulls peck at the red spot on the tip of the bill, causing the parent to regurgitate a meal. The young chick’s recognition of a parent is based entirely on the sign stimulus of the bill’s vertical line and red spot moving horizontally. A wooden model of the bill works as well as the real parent; a knitting needle with a spot is more effective than either in getting the chicks to respond.
Sign stimuli need not be visual. The begging call that a chick produces is a releaser for its parents’ feeding behavior. The special scent, or pheromone, emitted by female moths is a sign stimulus that attracts males. Tactile (touch) and even electrical sign stimuli are also known.
The most widespread uses of sign stimuli in the animal world are in communication, hunting, and predator avoidance. The young of most species of snake-hunting birds, for instance, innately recognize and avoid deadly coral snakes; young fowl and ducklings are born able to recognize and flee from the silhouette of hawks. Similar sign stimuli are often used in food gathering. The bee-hunting wasp recognizes honey bees by means of a series of releasers: The odor of the bee attracts the wasp upwind; the sight of any small, dark object guides it to the attack; and, finally, the odor of the object as the wasp prepares to sting determines whether the attack will be completed.
This use of a series of releasers, one after the other, greatly increases the specificity of what are individually crude and schematic cues; it is a strategy frequently employed in communication. Most animal species are solitary except when courting and rearing young. To avoid confusion, the signals that identify the sex and species of an animal’s potential mate must be clear and unambiguous. For example, a minnowlike fish called the stickleback uses a system of interlocking releasers to orchestrate its mating. When its breeding season arrives, the underside of each male turns bright red. This color attracts females but also provokes attacks by other males; red objects of almost any description will trigger male stickleback aggression. A female responds to the male’s red signal with a curious approach posture that displays her swollen belly full of eggs. This incites the male to perform a zigzag dance that leads the female to the tunnel-like nest he has built. The female struggles into the nest, whereupon the male touches her tail with his nose and quivers. The resulting vibration causes the female to release her eggs for the male to fertilize. If the male fails to perform the last part of the ballet, the female will not lay her eggs; vibrating the female with a pencil, however, which she can plainly see is not a male stickleback, works perfectly well, although the male in this case, not having gone through the last stage of the ritual, refuses to fertilize the eggs and eats them instead.