Book review: The Secret of our Success: how culture is driving human evolution, domesticating our species and making us smarter
Jo Henrich starts the book with a thought provoking question: How come we, as a species, have come to spread and flourish in so many diverse environments, but as individuals, would usually be unable to survive on our own? His main contention is that from a million or so years ago, we began learning from each other, memorising and spreading tool making and use, languages, social motivations and values. These have accumulated over time to give cultural practices that have assured our survival in groups, and dominance over other life forms in all new environments we have moved into, but this is socially shared knowledge, and beyond the abilities of one individual to know and practice individually.
In examining how we got from where we were to where we are now, he first approaches the question of “why us?”, say, rather than the dominant megafauna that were around before the spread of humans. He shows through experimental evidence that we are not innately smarter or quicker at tool use or cognitive problem solving than our nearest relative the chimp, but we are uniquely expert, by now, at social learning/imitation from others; much of our attention is paid to this, and, what's more, we start this development very early in our lives.
So, how has this specialism evolved to become such an important differentiation from other species? He shows that through the process of greater social dependence due to the dangers of predation as we moved from the forest environment, we had tended to discover and build up knowledge of tool use, cooking and hunting techniques. Over many generations, natural and sexual selection will have increasingly favoured better cultural learners over those endowed with simple strength and brute force e.g. Neanderthals. Homo Sapiens thus eventually emerged as the first culturally dependent species, through the accumulation of packages of survival “know how” that could be adapted to new environments as population density accelerated and bands spread out. Though hard to prove such a hypothesis, the evidence of deferred mylination of neurons in humans suggests that this is an adaptation that maximises cultural learning in the young; over many generations, individuals have tended to best succeed when they have spent longer acquiring cultural practices.
Archaeological evidence suggests that cutting, preparing and cooking food, using tools and fire, was one of the first and most central of these culturally evolved techniques; not only has it has altered the physiology of our digestive system fundamentally, also enabled and fuelled our rapid brain growth. Evidence such as this, and the study of other genetically identifiable traits such as lactose intolerance, eye colour and alcohol tolerance show us that culture has differentially affected the genomes of different populations, giving evidence of gene-culture co-evolution.
Cognitive adaptation to learning cultural practices has also led to increasing complexity in how hominids reasoned and made decisions. Culturally learned practices often become a matter of faith – the complex routines of preparing, for instance, plants foods that contain a lot of toxins, are often not understood by the individuals that perform them, yet the belief/faith that what is the custom is the right way to do it is deeply held, even to the point of extraneous, unnecessary aspects of rituals being perpetuated in a sort of “over-imitation”.
This aspect of learning has been further refined into even more effective social learning/imitation – beyond learning the norms of behaviour (as above), we have also developed preferential learning from prestigious individuals. What makes some people more successful than others overall in life is often hard to assess, exactly what qualities make for successful hunting for instance. So we developed a 'secondary' quality to our social learning – pay attention to the individuals that others learn from, and adopt a wide range of behaviours from those models; many of them will probably be at least tangentially related to their observed success – not just movement and posture, but also their beliefs (e.g. praying) and motivations. Thus reputation evolved to become a tangible social asset in that it builds and maintains prestige; dominance has also played a part in our social status evaluation for social learning, but this has not become so much a part of our social structure as it has in other primates, for instance chimpanzees.
Continuing on the theme of how learned social behaviour has become increasingly “ingrained” in our psyche, JH goes on to examine incest taboos, marital relationships and rituals. Bearing in mind that human groups have adopted different strategies around mating over a long time, nevertheless they have generally all developed ways of encouraging 'pair bonding'. Thus, though it may involve some polygamy, virtually all human groups have developed some kind of marriage ritual with ongoing obligations, openly performed in a social situation. The presence of onlookers reinforces the marriage obligation; future behaviour is acknowledged as being the business of kin and friends, who will be guaranteed to witness and gossip about their misdemeanours; reputation is then again at stake.
In this way, cultural norms are established that will tend to make the social group stable and self-sustaining, through the internalisation of these unspoken 'rules' of conduct, as individuals weigh up the costs and benefits of various actions within the group. The involvement of, and growing importance of in-law relationships and of other, more distant relationships, has not only added support for family life, but it has also helped ingrain family oriented values as cultural norms which in turn have helped to broaden community cohesion, and hold together bands and tribes as tight cohesive units. This marks the stage of becoming a truly cultural species, where we had come to respond in self, and mutually “policing” ways against behaviours that 'defect' from group norms, in such ways that they have come to structure virtually all our decisions.
This process of norm establishment within groups leading to greater cohesion also become a key factor in a further stage of social evolution, through inter-group competition. Inter-group competition has led to expansion of territory and influence for more successful groups not only through violent dominance and takeover, but also through differential reproduction and survival rates of more successful groups, and adoption of the cultural practices by less successful local groups, including sometimes large scale migration into them. This process of growth in group size became even more exaggerated as the cultural practices of animal domestication and agriculture made some already successful groups even more successful. In the areas where this lifestyle was possible it also meant that the cultural practices became more complex and lengthy to learn or adopt.
These social developments that enabled and encouraged coalition into bigger groups also led to increased technological innovation, as larger groups came to be more socially well connected. Social learning works best when we have more models to imitate and greater opportunity for the best imitators to get prestige and be copied most accurately. Innovation happens, not by the intervention of 'Great Inventors' generally, but through the steady accretion of modifications by diligent copiers who add a little bit themselves. This tendency has led to greater specialisation within groups, eventually in historical times, leading to the formation of guilds, schools, universities, etc.
This cohesion into very stable social units is also the stage where epigenetic evolutionary mechanisms (developmental changes in a lifetime that are not genetically inherited) become more important than genetic adaptations; biological developmental changes that enable greater sharing and learning become more important than fixed traits. Thus, there isn't a 'gene' for language, but as we evolved language as another cultural 'tool', it recruited already formed organs and brain regions, and through usage for this purpose, affected their developmental trajectory. Communicating to other conspecifics has evolved slowly through stages of gesture, sign and whistle languages towards 'spoken' languages, and it has developed very differently in different regions, depending on many local factors, including the density and interconnectedness of groups, and the strength of establishment of social norms of behaviour and tool use.
Illustrating the point about this stage being a 'co-evolution' of culture and genes, he shows that developing language use has changed some of the physiology of our sensory equipment and larynx, but even more so the psychological connectivity of our brains, particularly in more complex cognitive functioning. He further illustrates this with reference to the evolution of writing systems, expertise in spatial orientation, complex mate choice strategies and moral behaviour.
Concluding this chronology, he returns to the reason why this has all happened to us as a species, starting with becoming a terrestial ape, he emphasises that it was the dynamic of all the previously specified factors happening in sequence that enabled our rapid evolution, rather than any particular breakthrough. We have tended to spread, survive and thrive in difficult environments, through creating 'Niches', changing the micro-environments with our technological know how and transmitted cultural practices. Thus, the rapid economic, social and cultural acceleration of the past few hundred years is an extension of this trend, and our evolutionary trajectory still continues, developing yet more complex social institutions (eg: democracy) for managing even larger groupings of people, more complex ways of resource management, and more complex psychological functioning.
Altogether the book is, in my opinion, to date, the most comprehensive chronology of the our evolution. Much of it is backed up with plausible evidence, and where he has speculated, this is well justified and compared to the direction of research from other authors. What I feel he captures particularly well is the interaction of climate, habitat and changing selection pressures that have brought us to this point in our evolution. On a personal level, I would have liked to see more of a projection forward of possible futures from his chronology, as I believe the same influences of cultural learning and following social norms does not prepare us, as a species, to face the difficulties that resource depletion and climate change are starting to bring to us. Though that, of course, is more likely to be the subject of a book yet to be written.
Steve Heigham. March 2017.