Early development

1 What is development?

In this unit we begin to look at the human being in the context of an individual life cycle, examining some of the processes that contribute to the formation of a new person. This is the first time that many of you will have encountered this level of biological detail; we would ask that you take the time to understand it fully at this stage. We hope to show you that, far from being a dry academic subject, the study of biology allows us to glimpse a dimension of dynamic sophistication and elegance that underpins all the richness and variety of life.

Development can be defined as the collection of processes that produce a whole new individual. From this definition you might surmise that development is a life-long process, as we never stop ‘developing’; however, for now we shall confine our discussion to the early steps of the story, beginning with the production of sex cells – eggs and sperm – which have the capacity to fuse together to form a new, unique being. The study of development has a relatively short history. Until the late 17th century it was believed that a new individual was entirely preformed in the sex cells of its male parent. Indeed, some scientists of the day claimed that by using microscopes, invented in the early 17th century, they could actually see tiny preformed people – called homunculi – in sperm cells (Figure 1a). The female was thought to act only as an oven in which the baby could grow (Figure 1b) until it was large enough to survive birth.

Figure 1(a), Homunculi claimed to be visible in sperm.

Figure 1(b), Pregnancy simplified. (From late 17th century illustrations)

However, the advent of better microscopes did not substantiate these claims, and gradually it became clear that both sperm and an egg, produced by the mother, were needed to make a baby.

Why should we want to make babies? One view is that babies are noisy, disruptive, smelly, exhausting and expensive. They are a large drain on physical resources, especially those of their mothers. Parental input into rearing babies and children lasts a long time – until recent years, with people generally living longer than they used to, parenting was literally a lifetime's work. And yet parents generally find their children rewarding (at least sometimes). They are usually precious to them, and even the most mild-mannered parents will physically fight to protect their child. From an evolutionary point of view, it is important that we should keep on reproducing, otherwise our numbers would dwindle and our species might risk extinction. But few people, if any, embark on baby-making with this thought uppermost in their minds. Fortunately, our conscious behaviour is not dictated by this kind of evolutionary imperative: most of us have some freedom of choice, and our decisions are made by taking account of many factors in our lives, some of which may be subconscious, others overwhelmingly practical.

Many babies, of course, just ‘come along’: the urge for sexual intercourse is very strong, and, in our society at least, has become separated from the urge to reproduce. But for those of us who have the choice of whether or not to reproduce, a majority – recently quoted as 80% of British adults – chooses to have at least one child. The reasons for this are many.

Q Can you think of some?

A People like babies, and want one of their own. Other family members are generally keen for young couples to have families. It is a socially acceptable thing to do. It may help to cement a relationship. People enjoy living in large families.

No doubt you thought of many other reasons.

Q Make a list of the factors affecting your decision whether or not to have one or more children. Ask at least one other person to do the same, and then compare your answers. Note the points of similarity and difference between your answers. Are there any factors which are positive for one person and negative for another? Why do you think this is the case?

The factors listed by you and your friends may have included such items as not wanting to take on added responsibilities, wanting the stability of family life, not being able to afford giving up work, one's (or one's partner's) age, being in an unstable relationship, and doubtless many others. It is likely that many of the reasons given will be social rather than biological: this emphasizes our role as social, highly interactive beings with the ability to adapt our behaviour to suit our environments.

We shall now go on to consider some of these reasons in more detail, and look at how people can choose whether to have a child.