The Ascent of Man (37 page)

Here is a second pair; it might be of the same kind as the first, or of the opposite kind; and it might face either way. We stack it over the first pair and turn it through thirty-six degrees. Here is a third pair, to which we do the same thing. And so on.

These treads are a code which will tell the cell step by step how to make the proteins necessary to life. The gene is forming visibly in front of our eyes, and the handrails of sugars and phosphates hold the spiral staircase rigid on each side. The spiral DNA molecule is a gene, a gene in action, and the treads are the steps by which it acts.

On 2 April 1953 James Watson and Francis Crick sent
to
Nature
the paper which describes this structure in DNA on which they had worked for only eighteen months. In the words of Jacques Monod, of the Pasteur Institute in Paris and the Salk Institute in California,

The fundamental biological invariant is DNA. That is why Mendel’s defining of the gene as the unvarying bearer of hereditary traits, its chemical identification by Avery (confirmed by
Hershey), and the elucidation by Watson and Crick of the structural basis of its replicative invariance, without any doubt constitute the most important discoveries ever made in biology. To which of course must be added the theory of natural selection, whose certainty and full significance were established only by those later discoveries.

The model of DNA patently lends itself to the process
of replication which is fundamental to life even before sex. When a cell divides, the two spirals separate. Each base fixes opposite to it the other member of the pair to which it belongs. This is the point of the redundancy in the double helix: because each half carries the whole message or instruction, when a cell divides the same gene is reproduced. The magic number two here is the means by which
a cell passes on its genetic identity when it divides.

The DNA spiral is not a monument. It is an instruction, a living mobile to tell the cell how to carry out the processes of life step by step. Life follows a time-table, and the treads of the DNA spiral encode and signal the sequence in which the time-table must go. The machinery of the cell reads off the treads in order, one after another.
A sequence of three treads acts as a signal to the cell to make one amino acid. As the amino acids are formed in order, they line up and assemble in the cell as proteins. And the proteins are the agents and building blocks of life in the cell.

Every cell in the body carries the complete potential to make the whole animal, except only the sperm and egg cells. The sperm and the egg are incomplete,
and essentially they are half cells: they carry half the total number of genes. Then when the egg is fertilised by the sperm, the genes from each come together in pairs as Mendel foresaw, and the total of instructions is assembled again. The fertilised egg is then a complete cell, and it is the model of every cell in the body. For every cell is formed by division of the fertilised egg, and is
therefore identical with it in its genetic make-up. Like a chick embryo, the animal has the legacy of the fertilised egg all through life.

As the embryo develops the cells differentiate. Along the primitive streak the beginnings of the nervous system are laid down. Clumps of cells on either side will form the backbone. The cells specialise: nerve cells, muscle cells, connective tissue (the ligaments
and tendons), blood cells, blood vessels. The cells specialise because they have accepted the DNA instructions to make the proteins that are appropriate to the functioning of that cell and no other. This is the DNA in action.

The baby is an individual from birth. The coupling of genes from both parents stirred the pool of diversity. The child inherits gifts from both parents, and chance has now
combined these gifts in a new and original arrangement. The child is not a prisoner of its inheritance; it holds its inheritance as a new creation which its future actions will unfold.

The child is an individual. The bee is not, because the drone bee is one of a series of identical replicas. In any hive the queen is the only fertile female. When she mates with a drone in mid-air, she goes on
hoarding his sperms; the drone dies. If the queen now releases a sperm with an egg she lays, she makes a worker bee, a female. If she lays an egg but releases no sperm with it, a drone bee is made, a male, in a sort of virgin birth. It is a totalitarian paradise, for ever loyal, for ever fixed, because it has shut itself off from the adventure of diversity that drives and changes the higher animals
and man.

A world as rigid as the bee’s could be created among higher animals, even among men, by cloning: that is, by growing a colony or clone of identical animals from cells of a single parent. Begin with a mixed population of an amphibian, the axolod. Suppose we decided to fix on one type, the speckled axolotl. We take some eggs from a speckled female and grow an embryo which is destined to
be speckled. Now we tease out from the embryo a number of cells. Wherever in the embryo we take them from, they are identical in their genetic makeup, and each cell is capable of growing into a complete animal – our procedure will prove that.

We are going to grow identical animals, one from each cell. We need a carrier in which to grow the cells: any axolotl carrier will do – she can be white.
We take unfertilised eggs from the carrier and destroy the nucleus in
each egg. And into it we insert one of the single identical cells of the speckled parent of the clone. These eggs will now grow into speckled axolotls.

The clone of identical eggs made in this way are all grown at the same time. Each egg divides at the same moment – divides once, divides twice, and goes on dividing. All that
is normal, exactly as in any egg. At the next stage, single cell divisions are no longer visible. Each egg has turned into a kind of tennis ball, and begins to turn itself inside out – or it would be more literal to say, outside in. Still all the eggs are in step. Each egg folds over to form the animal, always in step: a regimented world in which the units obey every command identically at the identical
moment, except (we see) one unfortunate that has been deprived and is falling behind. And finally we have the clone of individual axolotls, each of them an identical copy of the parent, and each of them a virgin birth like the drone bee.

Should we make clones of human beings – copies of a beautiful mother, perhaps, or of a clever father? Of course not. My view is that diversity is the breath
of life, and we must not abandon that for any single form which happens to catch our fancy – even our genetic fancy. Cloning is the stabilisation of one form, and that runs against the whole current of creation – of human creation above all. Evolution is founded in variety and creates diversity; and of all animals, man is most creative because he carries and expresses the largest store of variety.
Every attempt to make us uniform, biologically, emotionally, or intellectually, is a betrayal of the evolutionary thrust that has made man its apex.

Yet it is odd that the myths of creation in human cultures seem almost to yearn back for an ancestral clone. There is a strange suppression of sex in the ancient stories of origins. Eve is cloned from Adam’s rib, and there is a preference for virgin
birth.

Happily we are not frozen into identical copies. In the human species sex is highly developed. The female is receptive at all times, she has permanent breasts, she takes an active part in sexual selection. Eve’s apple, as it were, fertilises mankind; or at least spurs it to its ageless preoccupation.

It is obvious that sex has a very special character for human beings. It has a special
biological character. Let us take one simple, down-to-earth criterion for that: we are the only species in which the female has orgasms. That is remarkable, but it is so. It is a mark of the fact that in general there is much less difference between men and women (in the biological sense and in sexual behaviour) than there is in other species. That may seem a strange thing to say. But to the gorilla
and the chimpanzee, where there are enormous differences between male and female, it would be obvious. In the language of biology, sexual dimorphism is small in the human species.

So much for biology. But there is a point on the borderline between biology and culture which really marks the symmetry in sexual behaviour, I think, very strikingly. It is an obvious one. We are the only species that
copulates face to face, and this is universal in all cultures. To my mind, it is an expression of a general equality which has been important in the evolution of man, I think, right back to the time of
Australopithecus
and the first tool-makers.

Why do I say that? Well, we have something to explain. We have to explain the speed of human evolution over a matter of one, three, let us say five million
years at most. That is terribly fast. Natural selection simply does not act as fast as that on animal species. We, the hominids, must have supplied a form of selection of our own; and the obvious choice is sexual selection. There is evidence now that women marry men who are intellectually like them, and men marry women who are intellectually like them. And if that preference really goes back
over some million of years, then it means that selection for skills has always been important on the part of both sexes.

I believe that as soon as the forerunners of man began to be nimble with their hands in making tools and clever with their brains in planning them, the nimble and clever enjoyed a
selective advantage. They were able to get more mates and to beget and feed more children than the rest. If my speculation about this is right, it explains how the nimble-fingered and quick-witted were able to dominate the biological evolution of man, and take it ahead so fast. And it shows that even in his biological evolution, man has been nudged and driven by a cultural talent, the ability to make
tools and communal plans. I think that is still expressed in the care that kindred and community take in all cultures, and only in human cultures, to arrange what is revealingly called a good match.

Yet if that had been the only selective factor then, of course, we should be much more homogeneous than we are. What keeps alive the variety among human beings? That is a cultural point. In every
culture there are also special safeguards to make for variety. The most striking of them is the universal prohibition of incest (for the man in the street – it does not always apply to royal families). The prohibition of incest-only has a meaning if it is designed to prevent older males dominating a group of females, as they do in (let us say) ape groups.

The preoccupation with the choice of
a mate both by male and female I regard as a continuing echo of the major selective force by which we have evolved. All that tenderness, the postponement of marriage, the preparations and preliminaries that are found in all cultures, are an expression of the weight that we give to the hidden qualities in a mate. Universals that stretch across all cultures are rare and tell-tale. Ours is a cultural
species, and I believe that our unique attention to sexual choice has helped to mould it.

Most of the world’s literature, most of the world’s art, is preoccupied with the theme of boy meets girl. We tend to think of this as being a sexual preoccupation that needs no explanation. But I think that is a mistake. On the contrary, it expresses the deeper fact that we are uncommonly careful in the
choice, not of whom we take to bed, but by whom we are to beget children. Sex was invented as a biological instrument by (say) the green algae. But as an instrument in the ascent of man which is basic to his cultural evolution, it was invented by man himself

Spiritual and carnal love are inseparable. A poem by John Donne says that; he called it
The Extasie
, and I quote eight lines from almost
eighty.

All day, the same our postures were,