Modern Mind

a single species of hominid that was different to, and the ancestor of, many others. 24 This species, which they named
Australopithecus afarensis,
they said was fully bipedal and showed marked sexual dimorphism (the males were much bigger than the females), though even the males wereno more than four feet six. Their brains were in the chimpanzee range and their faces pronounced, like the apes; their teeth were halfway between those of the apes and humans. Most controversially, Johanson and White claimed that
A. afarensis
was the ancestor of both the
Australopithecus
and the
Homo
genus, ‘which therefore must have diverged some time after three million years ago.’ 25
    At the beginning it had been Johanson and White’s intention to include Mary Leakey as a coauthor, but Mary was unhappy with the label
Australopithecus
being attached to the fossils she had discovered. The convention in science is for the discoverer to have the first ‘say’ in publishing the fossils that he or she finds, and to name them. After that, of course, other scientists are free to agree or disagree. By including Mary’s discoveries in their paper, Johanson and White were not only breaking with tradition; they knew by then that they were specifically going against her own interpretation. But they were anxious to claim for
A. afarensis
the tide of common ancestor of almost all known hominid fossils and so went ahead anyway. This caused a bitter feud that has never healed. 26
    Beyond the personal dimension, however,
A. afarensis
has provoked much rethinking. 27 At the time it was given its name, the predominant view was that bipedalism and tool using were related: early man walked on two feet so as to free his hands for tools. But according to Johanson and White, early man was bipedal at least half a million years before tool using came in. The latest thinking puts bipedalism alongside a period of drying in Africa, when the forest retreated and open savannah grasslands spread. In such an environment, upright walking would have offered certain selective advantages – upright early man would have been faster, his body would have cooled more quickly, and he could have roamed over greater distances, with his hands free to carry food home, or back to his offspring. So although the bitterness was personally unpleasant, it did provoke useful new ideas about man’s origins. 28
    Since the discovery of the helical structure of DNA in 1953, the next theoretical advance had come in 1961, when Francis Crick and Sidney Brenner in Cambridge had shown that the amino acids that make up the proteins of life are actually coded by a triplet of base pairs on DNA strands. That is, of the four bases – (a)denine, (c)ytosine, (g)uanine, and (t)hymine – three, in certain arrangements, such as CGT or ATG, code for specific acids. But more practical advances involved two ways of manipulating DNA that proved integral to the process of what became known as genetic engineering. The first was cloning, the second, gene sequencing.
    In November 1972 Stanley Cohen heard a lecture in Hawaii delivered by Herbert Boyer, a microbiologist from the University of California at San Francisco. Boyer’s lecture was about certain substances known as ‘restriction enzymes.’ These were substances which, when they came across a certain pattern of DNA bases, cut them in two. For example, every time they came across a T(hymine) followed by an A(denine), one restriction enzyme (of which there are several) would sever the DNA at that point. However, as Boyer told the meeting, restriction enzymes did more than this. When they cut, they didnot form a blunt end, with both strands of the double helix stopping at the same point; instead they formed jagged or steplike ends, one part jutting out, slightly longer than the other. Because of this, the ends were what scientists labelled ‘sticky,’ in that the flaps attracted complementary bases. 29 At the time he attended Boyer’s lecture, Cohen was himself working on plasmids, microscopic loops of DNA that lurk outside a bacterium’s chromosome and reproduce independently. As Cohen took in what Boyer was saying, he saw an immediate – and revolutionary – link to his own work. Because plasmids were loops, if they were cut with one of Boyer’s restriction enzymes, they would become like broken rings, the two broken ends being mirror images of each other. Therefore, strips of DNA from other animals, and it didn’t matter which (a lion,