Why Darwin’s Unfinished Symphony?

We humans possess an extraordinary capacity for cultural production, from the arts and language to science and technology. Yet a scientific understanding of how the human mind and culture evolved from their roots in animal behavior remains elusive.  This challenge to understand the origins of human intelligence, technology and culture is what I call Darwin’s Unfinished Symphony. As a scientist, I have studied this intriguing problem for 30 years, and this book draws on our findings to present a new theory of human cognitive evolution.

What is distinctive about your book?

The book emphasizes how we humans are creatures of our own making. The truly unique characteristics of our species—such as our intelligence, language, teaching, and cooperation—are not adaptive responses to external conditions such as climate, predators or disease. Rather, the learned and transmitted activities of our ancestors shaped our intellects through accelerating cycles of evolutionary feedback. Culture is not just the magnificent end product of an evolutionary process—it was also the key driving force behind that evolution.

How do you explain the evolution of the human mind?

I begin by describing how animals invent new behavior, and copy the good ideas of others, and then depict how this innovation and social learning was the driving force behind the evolution of the large primate brain, and the advanced cognition, language and cooperation of humans. In the process, I explain the evolution of the capabilities underlying modern humans’ ability to design iPhones, dance the tango, and send astronauts into space. I also depict the science behind the research: the key experiments, the false leads, and the scientific breakthroughs that eventually led us to the key insight that culture transformed human evolution.

What does this book have to say about animal intelligence?

Our research into animal behavior has established that mammals, birds, fishes and insects all acquire knowledge and skills through social learning. Mostly animals copy useful things, such as how to find and process food, but social learning can generate extraordinary habits. For instance, capuchin monkeys possess habits of sucking of each other’s body parts, whilst some chickens have a taste for cannibalism. Animals can be highly innovative. For instance, apes have contrived clever means of extracting palm hearts from trees with vicious spines, whilst gulls have devised the habit of catching rabbits and killing them by dropping them onto rocks. From these foundations, human culture evolved through a runaway autocatalytic process in which innovation, social learning, tool use, and brain expansion fed back on each other.

Animals can be smart, but humans are clearly far more intelligent. Why is that?

Studies of how the brain evolved in primates suggests a key role for a “cultural drive” mechanism, whereby natural selection favored more and more accurate and efficient copying, leading to the evolution of complex tool use and foraging, broader diets, longer lifespans with periods of infant dependence when novel skills are learned, greater innovativeness and better perceptual and learning abilities. While cultural drive may have operated in birds and whales too, in primates there were unique opportunities for social, ecological and technical forms of intelligence to feed back upon each other. The result was a runaway process that climaxed with the awesome computational power of the human mind.

How did language evolve? And do other animals have languages of their own?

Animals possess rich forms of communication, but nothing with the complex syntax and flexibility of human language. However, the origins of language reside not in ancient forms of communication but, rather, in social learning and teaching. We alone possess language because we alone created a world sufficiently rich and rapidly changing to require it.  As the number of food types, foraging skills, processing methods, and gestures that our ancestors had to learn increased, teaching this knowledge became vital. Our studies used mathematical models to explore when it pays to teach others, and found that complex cumulative cultural traditions created the rare circumstances in which teaching could evolve. Only then could language be favored by natural selection, as a cheap, accurate and flexible means to teach.

Does that mean that cultural activities affected human biological evolution?

There is now strong evidence that genes and culture have coevolved. For example, human societies differ substantially in their diets, which vary with local cultural traditions. Eating particular foods modifies how natural selection acts on the population, to favor genes that allow that diet to be broken down. Genes involved in the metabolism of proteins, carbohydrates, lipids, phosphates, dairy products and alcohol all show signs of recent selection in response to human culture. Our agricultural practices and aggregation into towns and cities inadvertently propagated crowd- and animal-borne diseases, such as malaria and tuberculosis, generating strong selection for genes that confer resistance to these diseases.

Did gene-culture coevolution affect our brains too?

Yes. Gene-culture coevolution may even be the dominant factor in human evolution, strongly influencing brain size, complexity and development, and massively upgrading our capacity for learning and computation, with knock on consequences for the ability to communicate and cooperate. Culture took human populations down novel evolutionary pathways, generated an evolved psychology—including a motivation to teach, speak, imitate, emulate, and share the goals and intentions of others—entirely different from that observed in any other animal.

You talk about culture. Does your book have anything to say about the arts?

Yes. Evolutionary biology can shed light on the origins of the psychological, neurological and physiological attributes necessary for culture to come into existence. I illustrate this with the example of the evolution of dance, which explains, for instance, why humans are capable of moving in time to music, how we are able to synchronize our actions with others, and how we can learn long sequences of movements. Far from destroying culture, our understanding of the underlying science feeds back to make the historical analysis richer and less mysterious.