Evolution: swing power

Darwin was correct that we evolved from simple creatures. But he was wrong, I believe, about the causes. We did not somehow become naturally smart enough to invent the technology upon which we rely. Instead, the technology evolved us.

The dawn of the technological era over 2.5m years ago is signalled archaeologically by the first chipped stone artefact. After that, the process of natural selection and survival of the fittest was undermined; intelligent humans with weapons could kill animals stronger than them. That our evolutionary ancestors started out far from the top of the food chain is illustrated by the Taung child fossil, the remains of an infant hominin who, some 2.6m years ago, was probably eviscerated and carried off by an eagle. How did these ancestors emerge from apedom into civilisation, discarding their massive canines and huge body mass, while surviving in such a harsh environment?

The answer was a radical new technology: the baby sling, a smarter solution for carrying infants than holding them in our arms. This, I have concluded, allowed the radical expansion in our ancestors’ brain size that began some 2m years ago.

The use of stone tools had, before this, already conferred some intellectual advantage upon our ancestors, reducing the need for physical strength and allowing more energy to be expended on developing intelligence. But walking on two legs—which first freed hominins’ hands—also had a contradictory effect on intellectual development, thanks to the fact that it demanded a narrow pelvis to act as a stable platform for an upright spine. This, in turn, set a natural upper limit on head size at birth. So although a sort of interactive intelligence—smartness in the hands—was encouraged, any related expansion of the brain posed a major problem.

Darwin argued that females would have valued more intelligent mates, driving the ascent from ape to Homo through sexual selection. But females would have been experiencing increasingly dangerous birth (thanks to the conflicting demands of a smaller pelvis and bigger baby heads). In evolutionary terms, the human brain is a liability: an expensive-to-maintain feature that is energy-inefficient and vulnerable.

Our ancestors’ upright gait would have made it harder for newborns to cling to mothers—as would the fact that they are likely to have had considerably less body hair than their ape-like ancestors—so pressure on early bipeds to come up with a baby-carrying solution would have been intense. Using a carrying device is a concept comprehensible to chimpanzees, only requiring a little more intelligence than theirs—or a stroke of luck—to be invented. It is likely that slings, both for launching projectiles and for carrying babies, could have been invented in the period of the first chipped stone technology—which means they predate (and likely enabled) the emergence of the larger brains that characterise the appearance of the human genus, Homo. We know, after all, that rocks were used for meat butchery 3.2m years ago, and that by 2.6m they were being deliberately shaped into tools rather than simply picked up and used. This signals not just the start of tools being created according to standard designs for particular purposes, but also “entailment”: where technology becomes interlinked, with one tool being manufactured to create another.

The implications of sling technology are immense. Slings enable the fetal stage to be extended after birth—marsupial style—allowing brains to continue expanding outside the womb, and in an increasingly cultural environment. After this, the rapid development of further technology for early humans may well have been driven by aggressive competition between different technology-using groups.

In terms of human brain size, the high water mark was passed some 40,000 years ago. The pressure on that organ has been off ever since we started outsourcing intelligence in the form of language, writing and, now, machines. Today, our technology is becoming so sophisticated that what will emerge in future may no longer even be controlled by our own volition.

This may be a good thing. It is the unexpected side effects of technology that often turn out to have the most potential. Indeed, the very idea of our humanity existing in opposition to our technology is wrong. As the philosopher John Gray once argued, “it may be in their capacity for consciousness that humans and the machines they are now devising are most alike.” Technology has a capacity to elide time and endure in physical form indefinitely. It could also destroy our planet. But there is no back-to-nature solution. There never has been for the artificial ape.