Sunday, November 24, 2002		Nature

Learning modes of animals
Nutan Shukla

BEHAVIOUR in animals describes the way that an animal is related to the environment, and much of the interaction between the phenotype and the environment occurs through the medium of behaviour.

All behaviour is hereditary in the sense that it is an expression of genetic information coded in the genes.

As the nervous system develops in the embryo, definite behaviour patterns are provided for in its structure.

Insects and spiders exhibit this nervous organisation to a high degree; it is also found to be well developed in fish, birds and other animals. In some vertebrates (particularly mammals), in some molluscs (soft-bodied unsegmented animals usually having a hard shell) and in various other groups, the structure of the nervous system makes allowance for flexible responses and learning. But this does not mean an animal’s behaviour is either completely fixed in pattern or completely flexible; mammals, in addition to intelligence, also possess instincts’ perhaps for more than has been suspected: similarly insects, despite their repertory of stereotyped instincts, can learn some things.

Behaviour can be either innate, or, to varying extents, learned. In practice, it is difficult to draw a line between innate (inborn) and learned behaviour — the problem is that since innate behaviour develops as a result of the interaction of internal environmental influences, it is, like learned behaviour, to some extent determined by the environment. For this reason, the distinction is not clear-cut and the term unlearned is often preferred to the terms innate and inborn.

The best example of innate behaviour is provided by birds. In fact, the discovery of extensive and varied innate behaviour in birds has literally revolutionised the attitude of scientists towards their behaviour. It is now recognised, for example, that hawks, gulls, ducks and most of the familiar passerine birds (perching birds) will defend a certain area shortly before mating and while being mated. This territory-defence behaviour appears to be a trait inherited from the lizards, from which birds descended.

The characteristic bird song serves notice to others of the same species that a certain piece of territory is claimed. This is the message conveyed when one male bird, whether wood thrush or barnyard cock, answers another. To a female, the song may indicate a male and a possible mate.

The actual song in some species is inherited, and this has been demonstrated by rearing the birds by hand in the complete absence of others of the species. It was also found that male canaries so raised will sing a typical, although somewhat simple, canary song; for the development of the flourishes, apparently, the example of other males is necessary. Females canaries injected with the male sex hormone will sing as long as the hormone lasts.

Scientists studying the behaviour of birds have found that in defending their territory against intruding males of the same species, male birds respond to definite features that are characteristic of their rivals — even when these features are combined in some object only slightly resembling a rival bird. Thus male bluebirds will attack a ball of blue and reddish feathers. When male birds attack their own images in windowpanes or mirrors they are usually trying to defend a breeding territory against intruding males.

The building of nests is also under the control of instinctive responses. Captive birds that have been reared out of nests for several generations will construct the proper kind of nest, which they have never seen, when they mature and are provided with necessary materials.

There are three different ways of learning; by trial and error, by imitation and by instruction. The trial and error method is found in all animals that can learn and is the sole means of learning in invertebrates. Compared with other methods, it takes a long time and can be dangerous. It is the method usually referred to in discussions of learning and in experiments for testing learning ability.

For example, rats can learn to find their ways through a maze by trial and error so long as a reward is offered. Learning by trial and error, however, reaches its highest development in mammals.

Imitation is a short-cut to learned behaviour, but is a speedier and much more sophisticated means of building up behaviour patterns. It depends on the ability of an animal to recognise and copy another member of its species, usually its mother.

Instruction is, of course, a uniquely human way of creating behaviour patterns, for it involves conscious thought and intent.