The biological meaning of intelligence

In chapter 15 we introduced the notion of "intelligent behaviour". We describe behaviour as "intelligent" if it is capable of being is flexible and novel, allowing the animal to respond successfully even when it receives inadequate stimulus information. What kinds of animals have this quality?

  • Intelligent behaviour requires a range of sensory input channels, some or all of which must have high capacity. The more ways the animal has of sensing its surroundings - in other words, the greater the range of stimuli it can perceive - the greater its capacity for behavioural novelty.
  • The more ways in which the animal can respond to changes in its surroundings, the greater its capacity for flexible behaviour. So intelligent behaviour also requires a wide range of outputs.
  • If the animal's behavioural outputs and sensory inputs are varied and of high capacity, then it is a very complicated task to select, sort and integrate the flow of information involved. Therefore, intelligent behaviour requires a large brain that can sort, integrate and correlate vast amounts of information quickly.
  • Brain size alone is not sufficient. The more routes there are between stimulus and output, and the more indirect and cross-connected these routes become, the greater the flexibility and novelty of behaviour. Therefore, the brain of an animal that can behave intelligently has enormous numbers of indirect, cross-connected routes between inputs and outputs.

For an animal to make full use of a large brain with numerous cross-connections between multiple high-capacity input and output channels, there are at least two other requirements:-

  • It must be able to store memories of past situations and behaviours, so the present situation can be compared with previous experience and the best course of action selected or devised.
  • It must be capable of learning; i.e. distinguishing responses that are appropriate in a given situation from responses that are not. Observation of adult behaviour is important for learning by the young; the young remember and emulate what their elders do. Intelligent animals therefore tend to be social and to protect and "instruct" their young.

An animal's behaviour need not be "intelligent" just because the animal has a brain. The main functions of the brain are to control the animal's internal physiological activities and its responses to environmental stimuli. The second function is relevant to behaviour (intelligent or otherwise). To fulfil this function, the brain has to integrate all currently relevant sensory information. It must use this integrated information to create an internal representation or "model" of the environment, and of the animal's body in relation to that environment. Then it must direct the body's responses in accordance with this model.

Overall, animals behave in ways that ensure their survival and reproduction. They do this by responding moment by moment to changes in the environment and to signals from their bodies (for instance, perceived danger is avoided; food is sought when an animal is hungry). All behaviour, not least intelligent behaviour, is therefore targeted or goal-seeking. When an animal behaves "intelligently", memory and learning are crucially involved and most behaviour is generated internally, in the brain. Intelligent behaviour is modulated by stimuli from the environment, but does not usually arise directly from such stimuli. It appears rational, or creative, a matter of choice rather than reflex or instinct. Perception is an active process, seeking and selecting sensory stimuli in accordance with the animal's needs.

Primate (especially human) brains are tremendously complicated, but they are made of cells like any other organ; and each cell conforms to the "living state" model that we summarised in chapter 10. Cells in the brain exchange information with one another, as in the rest of the body. The cells that carry sensory information to the brain, process it and cause responses are nerve cells or neurones. Circuits of neurones relate sensory input to response (output) and do the work of learning and remembering. To understand "intelligent behaviour", therefore, the first step is to explore how neurones work. The second step is to explore how the junctions between neurones, synapses, perform their role.

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