A new-born baby grips your finger without ever being taught; a moth flies into a flame; a dog learns to sit for a treat; geese fly south every winter. All of these are behaviour — the responses of an animal to its environment. Some are built into the genes, some are learned through experience, and every one of them helps the animal survive.
Behaviour is the response of an organism to a stimulus (a change in its internal or external environment). It is the visible, co-ordinated activity an animal carries out — moving, feeding, escaping, courting, signalling — in answer to what it senses. Behaviour is the meeting point of the nervous system, the sense organs, the muscles and the endocrine (hormone) system, all working together.
Behaviour is studied because it has clear survival value: it lets an animal find food, avoid being eaten, escape harmful conditions, find a mate and care for its young. Anything that improves these chances of survival and reproduction is favoured by natural selection, so behaviour — like any other adaptation — evolves.
Biologists divide behaviour into two great classes by its origin: innate (inherited) behaviour, which is genetically programmed, and learned behaviour, which is modified by experience. In real animals the two blend, but the distinction is the backbone of this chapter.
Innate behaviour is behaviour an animal is born with — it is inherited in the genes, performed correctly the first time without being learned, and is essentially the same in every member of the species. Because it does not depend on practice, it is reliable and fast — ideal for situations where there is no time to learn, such as escaping a predator.
| Feature of innate behaviour | Meaning |
|---|---|
| Inherited | Coded by genes, passed from parents to offspring |
| Stereotyped | The same fixed pattern in all individuals of the species |
| Not learned | Performed correctly the first time, without experience |
| Independent of teaching | Appears even in animals reared in isolation |
Its main forms — reflexes, kinesis, taxis, instinct, fixed action patterns, orientation and migration — are described below.
A reflex is the simplest unit of innate behaviour: a rapid, automatic, involuntary response to a stimulus, carried by a fixed nerve pathway called the reflex arc (receptor → sensory neuron → relay neuron in spinal cord → motor neuron → effector). Examples: pulling your hand off a hot plate, blinking when something nears the eye, the knee-jerk, a baby's grasping and sucking reflexes. Reflexes protect the body and need no thought.
Kinesis is a non-directional response in which the animal changes its rate of movement (speed or turning) according to the intensity of a stimulus — but does not move straight toward or away from it. A classic example is the woodlouse: in dry air it moves fast and turns a lot; in damp air it slows down and stops. The result is that it spends most time in damp places, even though it never "aims" for them. Kinesis keeps animals in favourable conditions without needing a sense of direction.
Taxis is a directional movement of the whole animal toward or away from a stimulus. It is named by the stimulus, and by whether the animal approaches (positive) or retreats (negative):
Instinct is a complex, inborn behaviour pattern that is more elaborate than a single reflex — a whole chain of stereotyped actions, performed without learning, such as a spider spinning its web, a bird building a nest, or a bee's waggle dance.
A fixed action pattern (FAP) is the unit of instinct: a stereotyped sequence of actions, triggered by a specific stimulus (the sign stimulus or releaser), that runs to completion once started — even if the stimulus is removed partway. The classic example is the greylag goose retrieving an egg that has rolled from the nest: once it starts the rolling movement with its beak, it completes the whole motion even if the egg is taken away. The egg shape is the sign stimulus that releases the FAP.
Orientation is the way an animal positions or arranges itself in relation to a stimulus — to gravity, light, or its surroundings — so that it is correctly placed to behave or to navigate. Taxes and kineses are forms of orientation in movement; more broadly, orientation lets an animal keep the right posture and find its way, using cues such as the Sun, stars or the Earth's magnetic field.
Migration is the regular, two-way, seasonal movement of animals between two areas, usually to find food, better climate or breeding grounds, returning later. It is largely innate but uses orientation cues to navigate. Examples: birds (swallows, geese) flying to warmer regions for winter; salmon returning from the sea to the river where they hatched to spawn; the long migrations of whales and monarch butterflies. Migration is highly adaptive — it lets animals exploit seasonal resources and breed where conditions are best.
Learned behaviour is behaviour that is modified by experience — it is acquired during the animal's lifetime, can change with circumstances, and is not identical in every individual. Learning lets an animal adjust to a changing environment rather than relying only on fixed responses; it is most developed in animals with complex brains. The main types are habituation, imprinting, classical conditioning, operant conditioning, and insight/latent learning.
Habituation is the simplest form of learning: an animal gradually stops responding to a repeated, harmless stimulus. A snail withdraws into its shell when touched, but if touched again and again with no harm, it stops withdrawing. Birds at first flee a scarecrow but soon ignore it. Habituation is adaptive because it stops the animal wasting energy reacting to stimuli that do not matter.
Imprinting is a special, rapid form of learning that occurs only during a brief, fixed critical (sensitive) period early in life, and is then permanent. The young animal forms a strong attachment to the first large moving object it sees — normally its mother — and follows it. Konrad Lorenz showed that newly hatched greylag goslings would imprint on him and follow him as if he were their parent. Imprinting is adaptive: it keeps the young close to a protector and teaches them what their own species looks like (important later for choosing a mate).
Classical conditioning is learning to give an existing reflex response to a new stimulus by association. The Russian physiologist Ivan Pavlov demonstrated it with dogs:
The key is that a previously meaningless stimulus comes to trigger a reflex because it has been repeatedly paired with the natural stimulus. If the bell is then rung many times without food, the response fades — this is extinction.
Operant conditioning is trial-and-error learning: an animal learns to repeat an action that brings a reward, and to avoid one that brings punishment. The behaviour comes first, by chance, and its consequences shape whether it happens again. B. F. Skinner studied this with a rat in a "Skinner box": exploring at random, the rat happens to press a lever and food appears (a reward / positive reinforcement). After several lucky presses, the rat learns to press the lever deliberately to get food. A reward that strengthens a behaviour is a reinforcement; an unpleasant consequence (a punishment) weakens it. This is how a dog learns to "sit" for a treat.
Insight learning is the highest form of learning: solving a new problem suddenly, by reasoning, using past experience — without trial and error. The classic study is Wolfgang Köhler's chimpanzees, which, after a pause, stacked boxes or joined sticks to reach a banana hung out of reach — a flash of "insight". Insight is best developed in primates and other intelligent mammals.
Latent (hidden) learning is learning that happens without any obvious reward and is not shown until it is useful. A rat allowed to explore a maze freely seems to learn nothing, but when food is later placed in the maze it finds its way far faster than an untrained rat — it had silently built a "map". Latent learning shows that animals can store information for future use.
Social behaviour is the interaction between members of the same species living together — co-operating to feed, defend, breed and rear young. Living in groups (a herd, flock, shoal, colony or pack) is adaptive: it gives safety in numbers, shared care of the young, co-operative hunting and defence. Many social animals show a social hierarchy (a "pecking order") and territorial behaviour, which reduce constant fighting.
Social life depends on communication — passing information between individuals through signals. Animals communicate by:
Behaviour ties together everything else in the syllabus — the nervous system, sense organs, hormones and evolution. An animal's body equips it to act, but its behaviour decides whether it survives the next minute, finds the next meal, or leaves any offspring at all. Innate responses give speed and certainty where there is no time to learn; learned and social behaviours give the flexibility to thrive in a changing world. Together they are among the most powerful adaptations life has evolved.