Evolutionary biologists are interested in explaining how a state of affairs observed today (such as the behaviour typical of a certain species) is likely to have come about as a result of evolution by natural selection. To account for the establishment of a particular genetic trait, they imagine a time before the trait existed. Then they postulate that a rare gene arises in an individual, or arises with an immigrant, and that individuals carrying the gene exhibit the trait. They then ask what circumstances will favour the spread of the gene through the population. If a gene is favoured by natural selection, then individuals with genotypes incorporating the gene will have increased fitness. The gene may be said to have invaded the population. To become established a gene must not only compete with the existing members of the gene pool, but must also resist invasion by other mutant genes. It is as if genes develop a strategy to increase their numbers at the expense of other genes. Thus an evolutionary strategy is a passive result of natural selection that gives the appearance of a ploy employed by genes to increase their numbers at the expense of other genes. So an evolutionary strategy is not a strategy in the cognitive sense, but a theoretical tool employed by evolutionary biologists.

The most important events include juvenile development, the age of sexual maturity, the timing of reproductive events, the number and size of offspring, the level of parental investment, and the lifespan that is typical of the species. For a given individual, the resources that can be allocated to these events are finite. The time and energy devoted to one event diminishes the time and energy available for the others.

Of prime importance is the notion of reproductive value, the expected contribution to the population by current and future reproduction. Animal species that live in unpredictable or unstable environments usually reproduce quickly (i.e. have a short generation period). There is little advantage in adaptations that permit competition with other animals, since the environment is likely to change. They tend to invest in numerous, inexpensive offspring that disperse widely. For species that inhabit stable and predictable environments competition with other animals is an important factor. Such species tend to have a long generation period and few well-cared-for offspring. Examples include elephants, whales, and humans. The majority of animals fall between these two extremes. Indeed we can look at the situation as a life-history spectrum. The implication of this line of thinking is that it is in the nature of individual humans (i.e. their characteristic life-history strategy) to care not only for their personal lifestyle, but also for that of their offspring and relatives. You may think this a bit far-fetched, but consider the following.

The experimental physiologist Michel Cabanac (a name to remember) asked his subjects (students) to adopt a certain posture and to hold this posture for as long as they could. It was a sitting posture, back against a wall but with nothing to sit on. After a short while holding this posture becomes painful. In a series of experiments Cabanac paid the subjects differing amounts (per session) per second for holding the posture for as long as they could. He found that, within limits, the greater the rate of pay, the longer the subjects would hold the painful posture. This experiment was repeated in Oxford, but with a difference. In some sessions, the money went, not to the subject, but to a named relative of the subject. In other words, the subject was told before the session that today the money would be sent to their aunt, or cousin, and so on. The subjects had previously been asked for details of their relatives. The amounts of money sent out were rather small, usually about £1. The experiment was then repeated in London, and in South Africa where the subjects were Zulus from both urban and rural backgrounds (in the latter case the payment was made in food).¹ In all cases it was found that the subjects would hold the posture for longer the more closely related (in terms of their coefficient of relatedness) they were to the recipients of the money/food. In other words, the subjects were putting up with pain, not for their own benefit, but for that of a relative. Apart from the biological implications of these results (see below) there are economic implications. They suggest that a person’s economic aspirations are likely to include benefits to relatives, albeit implicitly.

Altruistic behaviour benefits other animals at some cost to the donor. In evolutionary biology, altruism is defined by reference to its effects on survival prospects without reference to any motivation or intention that may be involved. The possibility that animals may have altruistic or selfish intentions is, of course, of interest, but it is not relevant to consideration of altruism from an evolutionary point of view. This distinction is sometimes forgotten.

As we have seen, the age at which an animal should ideally become sexually mature and capable of reproduction is a matter of evolutionary life-history strategy. In unpredictable environments natural selection usually favours early maturity and large numbers of offspring which are left to fend for themselves. In more stable environments it is a better strategy to mature late and have few offspring which are well cared for. In general, the more time and energy a parent expends upon a particular offspring, the fitter that offspring will be. There is often an inverse relationship between the total number of offspring produced and their average fitness. An animal’s individual fitness is a measure of its ability to leave viable offspring. The process of natural selection determines which characteristics of the animal confer greater fitness. However, the effectiveness of natural selection depends upon the mixture of genotypes in the population. Thus, the relative fitness of a genotype depends upon the other genotypes present in the population, as well as upon other environmental conditions.

The concept of fitness can be applied to individual genes by considering the survival of particular genes in the gene pool from one generation to another. A gene that can enhance the reproductive success of the animal carrying it will thereby increase its representation in the gene pool. It could do this by influencing the animal’s morphology or physiology, making it more likely to survive climatic and other hazards, or by influencing its behaviour, making the animal more successful in courtship or raising young. A gene that influences parental behaviour will probably be represented in the offspring so that by facilitating parental care, the gene itself is likely to appear in other individuals. Indeed, a situation could arise in which the gene could have a deleterious effect upon the animal carrying it but increase its probability of survival in the offspring. An obvious example is a gene that leads the parent to endanger its own life in attempts to preserve the lives of its progeny. This is a form of altruism.

By the mid 20th century, biologists had realized that the fitness of an individual gene could be increased as a result of altruistic behaviour on the part of animals carrying the gene. However, William Hamilton (1964) was the first to enunciate the general principle that natural selection tends to maximize not individual fitness but inclusive fitness; that is, an animal’s fitness depends upon not only its own reproductive success but also that of its kin. The inclusive fitness of an individual depends upon the survival of its descendants and of its collateral relatives. Thus even if an animal has no offspring its inclusive fitness may not be zero, because its genes will be passed on by nieces, nephews, and cousins.²

It is possible that cheating could be countered if individuals were altruistic only toward other individuals that were likely to reciprocate. For example, when a female olive baboon (Papio anubis) comes into oestrus, a male forms a consort relationship with her. He follows her around, waiting for an opportunity to mate, and guards the female from the attentions of other males. However, a rival male may sometimes solicit the help of a third male in an attempt to gain access to the female. While the solicited male challenges the consort male to a fight, the rival male gains access to the female. The altruism shown by the solicited male is often reciprocated. Those males that most often gave aid were those that most frequently received such aid.³

This type of reciprocal altruism obviously provides scope for cheating. An individual that receives aid may refuse to reciprocate at a later date. However, if opportunities for reciprocal altruism arise sufficiently often, and if the individuals involved are known to each other, then a non-cooperative individual can be identified easily and discriminated against. Thus, for natural selection to favour reciprocal altruism, the individuals must have sufficient opportunities for reciprocation, they must be able to recognize each other individually and remember their obligations, and they must be motivated to reciprocate. These conditions are found in primitive human societies, and reciprocal altruism has played an important role in human evolution.⁴

Sensitive periods of learning occur in the early life of many animals. During such periods they often learn from their parents. For example, the white crowned sparrow will remember its parents’ song provided it hears it during the sensitive period between 10 and 50 days old. Individuals prevented from hearing the song of their own species during this period never produce a proper white crowned sparrow song during later life. Whereas the juvenile white crowned sparrow will not learn songs that are much different from the song of its own species, other birds, such as the bullfinch, will learn the song of a completely different species. Thus a juvenile bullfinch fostered by a canary will adopt canary song. The tendency to copy the song of the parents leads to regional variations even among species that will learn only songs similar to that of their own species. In the region of San Francisco, for example, populations of white crowned sparrows separated by only a few miles have distinct dialects.⁵

Animal dialects represent an elementary form of tradition. Juvenile white crowned sparrows are inevitably exposed to the song dialect characteristic of the locality in which they are born, because their sensitive period of learning occurs before they are mobile. Other forms of traditional behaviour include the migration routes of some mammals and birds. Geese, ducks, and swans migrate in flocks composed of mixed juveniles and adults. The juveniles learn the route that is characteristic of their population, stopping at traditional rest places and breeding and over-wintering localities.⁶ There are many other examples. Reindeer also show fidelity to traditional migration routes and calving grounds. Migratory salmon hatch in freshwater streams and migrate to the sea. The juveniles become imprinted on the odour of their native stream and return to the same stream as adults to spawn in the traditional places. Some game trails of deer and other mammals are known to have been used for centuries. In parts of Britain and Germany, where roads have been built across the traditional migratory routes of toads, conservationists stand guard during the breeding season to prevent the toads from being run over by motorists.

Simple forms of traditional behaviour do not require any special learning abilities, or any special teaching. They arise as an inevitable consequence of the circumstances in which the young are raised and of the tendency of juvenile animals to become imprinted upon their habitat, their parents, and their peers. In some animals, however, more complex forms of learning are involved. For example, tool use in primates can spread through a population, as a result of imitative learning.

Imitation is not always what it seems. Animals may copy each other as a result of simple social facilitation. Many animals eat more when fed in groups than when fed alone. This has been demonstrated experimentally in chickens, puppies, fish, and opossums. If a chicken is allowed to eat until completely satiated, and is then introduced to others that are still feeding, the satiated bird will resume eating. Domestic chicks also have a tendency to peck when others peck, even if there is no food available. Chicks tend to peck at the same type of food-like particle as the mother hen. The tendency to concentrate on the type of food being eaten by others has also been demonstrated in sparrows and chaffinches.⁷

Avoidance of noxious food can also be socially facilitated. Attempts to kill large flocks of the common crow in the United States, by providing poisoned bait, were not successful because the majority avoided the bait after a few individuals had been poisoned. Similarly, the reaction of just one rat to novel food may be sufficient to determine the reactions of other rats in the group. If one rat eats the food, then others will join in, but if that rat sniffs the food and rejects it, the others will reject it. Sometimes, the pioneer rat urina...