Nothing in Behaviour Makes Sense Except in the Light of Evolution
And Why We Need A Selectionist View
The story of behaviour goes all the way back to the very first life forms. Those initial life forms, prokaryotes, emerged with certain physical traits—they were single-celled, microscopic, with few internal or external structures. There were variations in those traits, some of which were more adaptive than others in the organisms’ environmental conditions, and were thus passed down to subsequent generations. Variation, selection, replication. Every trait in every living organism who descended from those primordial life forms (yes, us included) resulted from these fundamental processes, and are still bound by them.
Evolution in a Nutshell
Consider these three environments and three species of birds that inhabit them, all of which descended from a common ancestor. Each species has come to possess traits uniquely adapted to their environment. The greater roadrunner has a brown plumage (great for camouflaging), excretes excess salt through a special gland near their eye (loses less water than urine), flutters the unfeathered area beneath the chin (dissipates heat), and drastically reduces metabolism at night (conserves energy and reduces heat loss). The ptarmigan has brown feathers in summer and white feathers in winter (great for camouflaging), possesses large fat reserves (provides energy and insulation), and has feathers around its nostrils (warms the air it breathes) and on its soles (insulates against the cold ground). The black-capped lory has a strong, hooked beak (perfect for cracking open seeds and nuts), hair-like structures on its tongue (maximises nectar uptake), and sturdy feet (excellent for perching on trees). Like many other tropical birds, it is also strikingly coloured. As to why, if you wonder, possible explanations include in a highly biodiverse environment, there is a greater need to stand out, and the more favourable climate and greater availability of food allows greater investment of energy into colourful plumages.
The discovery of the processes of variation, selection, and replication, are attributed to Charles Darwin (and to a lesser extent Alfred Wallace), who as a young naturalist and geologist, embarked on a multiyear voyage around the globe beginning 1831 aboard the HMS Beagle. On the expedition, he collected flora and fauna specimens and meticulously documented his observations of similarities and differences between the wildlife he encountered. From his systematic observations, Darwin acquired an insight into how species change over time, which he developed into a theory of evolution through natural selection, culminating in his seminal work On the Origin of Species, published in 1859.
Evolution theory continued to develop and gain acceptance, bolstered by the discovery of genes and DNA. By the 1970s, evolution theory had reached the apex of biology as a grand unifying theory to explain all biological phenomena, leading the geneticist Theodosius Dobzhansky to declare that nothing in biology makes sense except in the light of evolution. At the time, the en vogue train of evolution thought was a gene-centric view, best exemplified by the (still) influential work by Richard Dawkins, The Selfish Gene. The gene-centred view, as eloquently argued in The Selfish Gene, posits that variation, selection, and replication occurs solely at the level of the genes. Organisms exist to as vessels for genes to replicate. A chicken is an egg’s way of making another egg. In other words, whatever we think, feel, or do, is determined by our genes for this sole purpose.
From Genes to Behaviour
Evaluating the truthfulness of a gene-centric view would require a whole article on its own. For now, let us refocus our attention on the organism. Organisms do not just possess physical traits. They also interact with their environment, operate upon it. In other words, they behave. Our behavioural traits are subject to the same selection processes of variation, selection, and replication. In our evolutionary history, behavioural traits varied. In our ancestors, adaptive traits such as languaging and social behaviours were selected for and replicated. Non-adaptive traits were not replicated, and traits that previously were but have ceased to be adaptive such as tree climbing ceased to be replicated (just don’t tell this guy).
Certain behaviours are so critically adaptive in our evolutionary history that they are innately wired in us. We come preloaded with them, so to speak. We flinch when an object moves rapidly towards our face. We salivate when we smell food. We display a preference towards food, sex, warmth, social affiliation. These innate repertoires of behaviours require no learning and are largely stable throughout our lifespans, although modifiable to some extent (individuals from different cultures can react very differently to a whiff of fermented shark meat or durian).
However, the vast majority of behaviours in adult human repertoires (and many other species) are learnt within our lifespans in response to environmental events. To understand why, let us consider two games—tic-tac-toe (or noughts and crosses), and Go. In the former, the game is relatively simple. With a few programmed rules, the game is essentially solved and you can never lose. Similarly, in a theoretically simple environment, organisms can successfully thrive with a few pre-programmed behaviours. Go, on the other hand, is an exceedingly complex game, with the number of possible moves thought to surpass the number of atoms in the universe by many orders of magnitude. Unlike tic-tac-toe, it is impossible to programme rules for every single position in Go. In fact, it was widely believed mastery of the game required human intuition, and that computers could never defeat a professional Go player. Incidentally, in 2016, the computer programme AlphaGo developed by Google DeepMind managed to do so, defeating one of the game’s GOATs, Lee Sedol. The match was captured in a beautiful documentary (watch it, it will be the best use of your time this week). The complexity of our environments is analogous to a game of Go, except at random intervals, the board size changes, pieces are removed, positions are swapped, new opponents are substituted in, and new rules are added.
Complexity demands dynamic and highly sophisticated levels of adaptability. By the time children are a few years old, their acquired repertoire of behaviours will have vastly exceeded their innate repertoire. Consider again the three environments earlier, to which we add a fourth, familiar to many of you. These environments exert very different selection pressures on the humans living in them. What sort of behaviours and products of behaviours are required to survive in each environment?
Unsurprisingly, we see very different behavioural repertoires emerge that are uniquely adapted to each environmental context. More importantly, these behavioural repertoires are dynamic rather than static. Take a white-collar executive from urban, tropical Singapore and place him in the Arctic tundra, and we will observe near-instantaneous, dramatic shifts in his behaviour, or a quick death. In his book The Secret of Our Success: How Culture is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter, evolutionary biologist Joseph Henrich recounts the fate of early European explorers who found themselves stranded in inhospitable environments, including tundras, deserts, and swamps. Many perished, but a few survived, made possible only through great adaptations in their behaviours to their new environments. It is important to also note that the survivors were often aided in no small part by indigenous populations and their vast stores of cultural knowledge (more on this in the future), who not only survived, but thrived in those environments. Inhospitable, as it turns out, just means pre-adaption.
A Selectionist View of the World
In contrast to the gene-centric view, here we have evidence of behavioural selection at the unit of the individual organism (selection can occur still on other levels, a concept known as multilevel selection—again, more of this in the future). Behavioural selection was studied extensively in animal models, then with humans beginning with the pioneering work of Edward Thorndike, John B. Watson, and later, B. F. Skinner. The study of variation, selection, and replication of behaviour in response to environmental conditions, also known as operant learning, coalesced into a natural science discipline in the behavioural sciences, known today as behaviour analysis. The core tenet of behaviour analysis is simple—the outcomes (or consequences) of our behaviours select for our behaviours, powerfully so. When a behaviour leads to a desirable outcome, it is more readily expressed. When it leads to an undesirable outcome, it is less readily expressed. The influence of these consequences can be attenuated by physiological processes such as sensitisation, habituation, or attentional constraints, but make no mistake—just about everything we think, feel, do, is bound by the same selection processes, often beneath conscious awareness. To understand any given behaviour, we need to understand the conditions which select for it, both in the organism’s present and its past.
Although Thorndike and his mentor William James were very much influenced by evolutionary thought, behaviour analysis was largely separated from evolution theory in its early development. Later in his career, a growing realisation of the consilience between behaviour analysis and evolution theory led Skinner to publish perhaps his most influential paper Selection by Consequences in 1981, integrating the principles of behaviour with a selectionist view. At this point, it is important to disabuse the reader of an idea that has taken hold in some—that while our great capacity for such dynamic, sophisticated adaptions was selected for in our evolutionary history, it has given rise to systems of knowledge and practices that now allow us to transcend evolution in some way. We haven’t. If anything, these continually advancing systems of knowledge and practices (evidence of continued selection) gives us some slight hope for the survival of our species against the many extinction-event selection pressures that will certainly come our way.
What promise does a selectionist view hold in our curious world? At this moment, Simone Biles is (again) living her Olympic dream at the ripe old age (for a gymnast) of 27; other dreams are being crushed in conflict zones; groups of people are arguing about climate change action, or whether climate change is real at all; some countries are grappling with soaring obesity rates; others are still grappling with malnutrition. It is the hope of this newsletter to persuade you that these outcomes of actions by individuals or groups of individuals can be better understood if we adopt a selectionist view.
As evolutionary biologist David Sloan Wilson repeatedly puts it, the theory decides what we can observe. By extension, the tool decides what we can change. Both are needed. A chisel is no more useful in the hands of a baker, than yeast and flour in the hands of a sculptor. In this newsletter, we will review theories (all nested within the grand unifying theory of evolution) and tools to understand and change behaviours. These theories and tools have withstood the great selection pressures of vigorous scientific research. They are necessary, but by no means sufficient to solve many of the complex challenges great or small mankind grapples with. My hope is that they serve you well (if not, in keeping with a selectionist view, discard them) as you navigate the intricacies of human behaviour in whichever direction you endeavour. Stay tuned.
Excellent article. Looking forward to subsequent posts.