Some years ago, Professor Robert Havighurst of the University of Chicago, USA, proposed that stages in human development can best be thought of in terms of the developmental ‘tasks’ that are part of the normal transition. He identified ten developmental tasks associated with the adolescent transition. Each of the Havighurst tasks can also be seen as elements of the overall sense of self that adolescents carry with them as they move towards and into young adulthood. Adolescents do not progress through these multiple developmental tasks separately; at any given time they may be dealing with several.

The adolescent must adjust to a new physical sense of self. At no other time since birth does an individual undergo such profound physical changes as during early adolescence. Puberty is marked by sudden rapid growth in height and weight. Also, the young person experiences the emergence and accentuation of those physical traits that make the person a boy or a girl. The young person looks less like a child and more like a physically mature adult. The effect of this rapid change is that mid-adolescents are body-conscious, and their concerns are directed towards their opposite-sexed peers.

The adolescent must adjust to new intellectual abilities. In addition to a sudden spurt in physical growth, adolescents experience a sudden increase in their ability to think about their world. As a normal part of maturity, they are able to think more things. However, they are also able to conceive of their world with awareness. Before adolescence, children's thinking is dominated by a concrete example for any problem that they solve; their thinking is constrained to what is real and physical. During adolescence, young people begin to recognise and understand abstractions. The growth in ability to deal with abstractions accelerates during the middle stages of adolescence.

The adolescent must adjust to increased cognitive demands at school. Adults see high school in part as a place where adolescents prepare for adult roles and responsibilities and in part as preparatory for further education. School curricula are frequently dominated by the inclusion of more abstract, demanding material, regardless of whether the adolescents have achieved formal thought. Since not all adolescents make the intellectual transition at the same rate, demands for abstract thinking prior to the achievement of that ability may be frustrating.

The adolescent must adopt a personal value system. During adolescence, as teens develop increasingly complex knowledge systems, they also adopt an integrated set of values and morals. During the early stages of moral development, parents provide their child with a structured set of rules of what is right and wrong, what is acceptable and unacceptable. Eventually the adolescent must assess the parent's values as they come into conflict with values expressed by peers and other segments of society. To reconcile differences, the adolescent restructures those beliefs into a personal ideology.

The adolescent must develop expanded verbal skills to accommodate more complex concepts and tasks. Their limited language of childhood is no longer adequate. As their conceptual development may outstrip their verbal development, adolescents may appear less competent than they really are.

The adolescent must establish adult vocational goals. As part of the process of establishing a personal identity, the adolescent must also begin the process of focusing on the question, 'What do you plan to be when you grow up?1 Mid-adolescents must identify, at least at a preliminary level, what their adult vocational goals are and how they intend to achieve them.

The adolescent must develop a personal sense of identity. Prior to adolescence, one's identity is an extension of one's parents' identity. During the early adolescent years a young person begins to recognise their uniqueness and to establish themselves as separate individuals, independent of their parents. As such, one must reconsider the answer to the question, ‘what does it mean to be me?' or "who am l?"

The adolescent must establish emotional and psychological independence from his or her parents, childhood is marked by strong dependence on one's parents. Adolescents may yearn to keep that safe, secure, supportive, dependent relationship. Yet, to be an adult implies a sense of independence, of autonomy, of being one's own person. In an attempt to assert their need for independence and individuality, adolescents may respond with what appears to be hostility and lack of cooperation.

The adolescent must develop stable and productive peer relationships. Although peer interaction is not unique to adolescence, it seems to hit a peak of importance during early adolescence. Certainly by late adolescence or early adulthood the need for peer approval has diminished. This degree to which an adolescent is able to make friends and have an accepting peer group, though, is a major indicator of how well the adolescent will adjust in other areas of social and psychological development. Early adolescence is also a period of intense conformity to peers.” Fitting in' not being different, and being accepted seem somehow pressing to this age group. The worst possibility, from the view of the young teen, is to be seen by peers as different.

The adolescent must develop increased impulse control and behavioural maturity. In their shift to adulthood, most young people engage in one or more behaviours that place them at physical, social, or educational risk. Risky behaviours are sufficiently pervasive among adolescents to suggest that risk-taking may be a normal developmental process of middle adolescence. Gradually adolescents develop a set of behavioural self-controls through which they assess which behaviours are acceptable and adult-like.

A Sometime in the early Cretaceous period of the Earth's history, hunting wasps of a certain type became bees by adopting a vegetarian diet: they began to rely more and more on the pollen of plants as a source of protein for themselves and their offspring, as an alternative to insects. In so doing, they accidentally transported pollen on their bodies to other plants of the same species, bringing about pollination. The stage was thus set for a succession of ever-closer mutual adaptations of bees and flowering plants. In particular, flowers began to reward bees for their unwitting role in their reproduction by providing richer sources of pollen and another source of nutrition, nectar.

B Today about 15 per cent of our diet consists of crops which are pollinated by bees. The meat and other animal products we consume are ultimately derived from bee- pollinated forage crops, and account for another 15 per cent. It follows that around one third of our food is directly or indirectly dependent on the pollinating services of bees. On a global basis, the annual value of agricultural crops dependent on the pollination services of bees is estimated at £1,000 million (US$1,590 million). Much of this pollination is due to honey bees, and in monetary terms it exceeds the value of the annual honey crop by a factor of fifty.

C But the apparently harmonious relationship between bees and plants conceals a conflict of interests. Although flowers need bees and vice versa, it pays each partner to minimise its costs and maximise its profits. This may sound like an extreme case of attributing human qualities to non-human species, but using the marketplace and the principles of double-entry book keeping as metaphors may give US some insights into what is really going on between bees and flowering plants. In the real world, both flower and bee operate in a competitive marketplace. A community of retailers, the flowers, seek to attract more or less discriminating consumers, the bees. Each flower has to juggle the costs and benefits of investing in advertising, by colour and scent, and providing rewards, nectar and pollen, clearly a species which depends on cross-pollination is on a knife-edge: it must provide sufficient nectar to attract the interest of a bee, but not enough to satisfy all of its needs in one visit. A satiated bee would return to its nest rather than visit another flower. The bee, on the other hand, is out to get the maximum amount of pollen and nectar. It must assess the quality and quantity of rewards which are on offer and juggle its energy costs so that it makes a calorific profit on each foraging trip. The apparent harmony between plants and bees is therefore not all that it seems. Instead, it is an equilibrium based on compromises between the competing interests of the protagonists.

D This sounds remarkably like the ideas of the 18th-century economist Adam Smith. In his book, The Wealth of Nations, Smith postulated that in human society the competitive interactions of different ‘economic units' eventually resulted in a balanced, or ‘harmonious’ society. One might predict, therefore, that economists would find the relationships between bees and plants of some interest. This is the case in Israel, where economists are collaborating with botanists and entomologists in a long-term study of the pollination biology of the native flora, in an attempt to understand the dynamics of the relationship between communities of bees and plants.

E This sort of study is of more than passing academic interest. It is important that authorities understand the dynamic relationships between plants and their pollinators. This is especially true when, say, devising conservation policies. A good example comes from the forests of tropical South America. Here, as in all rainforests, there is a high diversity of tree species. There may be more than 120 per acre, but in a given acre there may only be one or two individuals of any one species: These trees are pollinated by large, fast-flying bees. There is evidence that certain types of bees learn the distribution of these scattered trees and forage regularly along the same routes. This is called ‘trap-lining’ and the bees forage for up to 23 km from their nests. The bees are therefore acting as long distance pollinators.

F An issue of current concern in tropical forest conservation is that of trying to estimate the minimum sustainable size of islands' of forest reserve in areas where large-scale felling is taking place. There is much discussion on seed dispersal distances. But this is only one half of the equation, so far as the reproduction of trees is concerned. There is another question that must be addressed in order to calculate whether proposed forest reserves are close enough to the nearest large tract of forest: ‘what is the flight range of these long-distance foragers?' We need to know much more about bees and their relationships with plants before this question can be answered.

G Bees, then, are vital to our survival. Furthermore, much of the visual impact of human environments derives from vegetation, and most vegetation is dependent on bees for pollination. Thus, as pollinators of crops and natural vegetation, bees occupy key positions in the web of relationships which sustain the living architecture of our planet.