Comment on Humans – The Species that Changed Earth
Erle Ellis, both in this Social Evolution Forum article and his monograph (Ellis, 2015), impressively synthesises ideas regarding cultural evolution, niche construction, multi-level selection and non-genetic inheritance to grapple with a key question: why the Anthropocene, and not, say, the Panthropocene, the Ceteacocene, or the Corvocene? Why have humans transformed the planet to such a huge degree, and not chimpanzees, killer whales, or crows? This is not just an academic question. As Ellis notes, by better understanding how we, as a species, got to this point, we might be better able to change course and avoid what appear to be looming ecological disasters such as global climate change or anthropogenic mass extinction.
There is not much that I disagree with in Ellis’ answer (e.g. see Mesoudi, 2011a, 2016). Individual humans are smart, but not that smart, at least compared to chimps, cetaceans or corvids. What marks us out is what Michael Tomasello and colleagues have called our ‘cultural intelligence’ (Herrmann et al, 2007): our ability to acquire vast quantities of knowledge from others via social learning. More precisely, a person can learn from someone else something that they could never have invented or discovered alone. This is Tomasello’s ‘ratchet effect’, or what Robert Boyd and Peter Richerson have called ‘cumulative culture’ (Boyd & Richerson, 1996). While the individuals of many species can learn useful things from conspecifics, such as chimpanzee nut-cracking or dolphin sponge-feeding, these never go beyond what a single chimp or dolphin could plausibly invent on their own. Who among us, in contrast, could have single-handedly invented from scratch differential calculus, glass-blowing, vaccination, the steam engine or industrial nitrogen-fixation? History tells us that these inventions or discoveries required the accumulated wisdom of many, many generations of inventors each making incremental modifications to what had been discovered previously. They did not spring forth fully formed from a single genius’ mind, despite popular conceptions to the contrary.
This idea of cumulative culture is key, I think. It turns human culture into a truly evolutionary process: in Darwin’s terms, a process of ‘descent with modification’. Beneficial modifications – either clever insights or serendipitous accidents – are preserved and recombined over successive generations, or even within generations. As Ellis points out, cultural evolution is often faster than genetic evolution (see also Perreault, 2012). This is because it is cumulative: each generation need not rediscover basic principles and can go straight to innovation or recombination. This even allows knowledge in some domains, such as science and technology, to increase exponentially, either because there is ever-more knowledge to recombine (Youn et al., 2015), or because some discoveries (e.g. telescopes, microscopes or computers) themselves make further discoveries more likely (Mesoudi, 2011b). Perhaps this exponential accumulation is part of the problem. Political opinion, and indeed political will, is often much slower. By the time a consensus is reached that, say, fossil fuels should be abandoned due to their environmental harm, carbon-based industrialisation has already gone full steam ahead. The short-termism inherent in political decision-making, created by 4 or 5 year election cycles, is not well matched to the speed of cumulative technological evolution.
Cumulative cultural evolution, combined with the idea of niche construction, also alters our understanding of ‘the environment’. Erle states that “A key prediction of the EES [Extended Evolutionary Synthesis] is that when environments vary rapidly, within the span of a single generation, this tends to favor adaptive traits that are inherited horizontally and obliquely, like cultural traits”. This is not entirely accurate. Evolutionary models show that rapid environmental change actually favours individual (or asocial) learning, not social learning (Aoki, Wakano, & Feldman, 2005). This is because when environments change rapidly, then the things you can copy from others have a high chance of being out of date. It is more adaptive, in rapidly changing environments, to sample the environment directly.
Yet this assumes that ‘the environment’ is external to the individuals doing the learning, and that purely individual/asocial learning is a viable alternative to social learning. Once culture goes cumulative, however, this no longer holds. ‘The environment’ becomes the accumulated knowledge that we acquire from others, and the niche-constructed environments that we create using that accumulated knowledge: cities, mass-produced food, the internet, mass transit and the like. It is not possible any more to ‘directly sample the environment’. Social learning is adaptive because of cumulative culture (Boyd & Richerson, 1996). Rapid (anthropogenic) environmental change is the consequence, not the cause, of this.
So what makes culture cumulative? And why do only humans have it? This is currently unknown (Dean et al., 2014). Many suggestions revolve around the fidelity of social learning: we have some cognitive mechanism(s) that makes knowledge more accurately copied and more likely to be preserved and accumulated. Candidate mechanisms include imitation (copying others’ actions, rather than the outcomes of their actions), over-imitation (copying others’ actions even when the outcome is unclear or arbitrary), payoff-biased social learning (preferentially copying successful people or traits, rather than copying at random), teaching (modifying one’s behaviour at some cost to allow someone else to more easily copy it), theory of mind (understanding what someone else needs to learn, to help them learn it) or language, both spoken and written. Other suggestions concern demography, such as living in large enough groups such that accumulated knowledge is not lost when, say, the only expert basket maker or quantum physicist accidentally falls off a cliff. Yet all of these factors are arguably found in other species to some degree: other species imitate, teach, live in large groups, etc. Maybe more than one of them are needed. Maybe all of them. Maybe this explains why cumulative culture only emerged once, relatively recently, in an otherwise unremarkable ape.
There is not much psychology in Ellis’ (admittedly already wide-ranging) article. Yet understanding human psychology seems crucial for understanding the human activity that led us to this point, as well as for potentially altering current and future behaviour for the positive. What does a cultural evolution perspective say about human psychology? First, it suggests that we should not expect to find domain-specific, genetically-evolved mental modules that are matched to specific aspects of ancestral environments, as proposed by some evolutionary psychologists (sometimes called the “Stone Age Mind” hypothesis). As noted above, once culture is cumulative, the relevant adaptive environment constitutes the constantly changing and accumulating pool of socially learned knowledge that can be found in other people’s heads.
That’s not to say we should adopt a blank slate theory of human cognition. Cognitive anthropologists (e.g. Sperber, 1996) convincingly show that some ideas are more cognitively attractive than others, such as those that fit with our folk intuitions about psychology, biology or physics. This is important, and can account for certain regularities across different societies, such as the cross-cultural historical prevalence of blood-letting medical practices (Miton, Claidière, & Mercier, 2015). But this cannot be the whole story. Blood-letting was eventually abandoned in favor of modern medicine, which is often highly unintuitive. Vaccination or germ theory are prime examples of cognitively unintuitive ideas that have nonetheless spread because of their efficacy via cultural selection. Another example is the theory of evolution itself. Evolutionary theory, with its focus on within-population variation and gradual change over long time periods, is deeply unintuitive to our essentialist minds (Shtulman & Schulz, 2008). This is why creationism is so common and evolution must be explicitly taught. Evolutionary theory is the result of multiple accumulated modifications, some intentional and some accidental, with a subsequent dose of payoff-biased social learning as evolutionary theory came to explain numerous observations about the natural world. In short, cognitively attractive (but false) ideas can often be overcome by content-neutral cultural selection.
I think that this is an encouraging conclusion. As Ellis notes, cultural evolution, like biological evolution, has no inherent or inevitable progressive direction, beyond local, historically-contingent adaptation. In his words, it is “a process, not a destiny”. And human minds are not fixed to repeat the same errors over and over again, or hard-wired to behave as if they were in a mismatched ancestral environment. In my opinion, and I think in Ellis’ too, the many methods of cultural evolution – mathematical models, lab experiments, ethnographic field studies, and comparative and historical cultural phylogenetics, all linked within a unified evolutionary framework (Mesoudi, 2011a) – provide the best chance of understanding how human psychology permits and constrains the human activity which links, at multiple levels (Waring et al., 2015), to the large-scale cultural (‘anthropogenic’) change that has led us into the Anthropocene.
Aoki, K., Wakano, J. Y., & Feldman, M. W. (2005). The emergence of social learning in a temporally changing environment. Current Anthropology, 46, 334–340.
Boyd, R., & Richerson, P. J. (1996). Why culture is common, but cultural evolution is rare. Proceedings of The British Academy, 88, 77–93.
Dean, L. G., Vale, G. L., Laland, K. N., Flynn, E., & Kendal, R. L. (2014). Human cumulative culture: a comparative perspective. Biological Reviews, 89, 284–301.
Ellis, E. C. (2015). Ecology in an anthropogenic biosphere. Ecological Monographs, 85(3), 287–331.
Herrmann, E., Call, J., Hernandez-Lloreda, M. V., Hare, B., & Tomasello, M. (2007). Humans have evolved specialized skills of social cognition: The cultural intelligence hypothesis. Science, 317, 1360–1366.
Mesoudi, A. (2011a). Cultural evolution. Chicago, IL: Univ. Chicago Press.
Mesoudi, A. (2011b). Variable cultural acquisition costs constrain cumulative cultural evolution. PLOS One, 6, e18239.
Mesoudi, A. (2016). Cultural evolution: Integrating psychology, evolution and culture. Current Opinion in Psychology, 7, 17–22.
Miton, H., Claidière, N., & Mercier, H. (2015). Universal cognitive mechanisms explain the cultural success of bloodletting. Evolution and Human Behavior, 36, 303–312.
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Youn, H., Strumsky, D., Bettencourt, L. M. A., & Lobo, J. (2015). Invention as a combinatorial process: evidence from US patents. Journal of The Royal Society Interface, 12, 20150272.