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What began as a small increase in the fidelity of social learning may have made all the difference in human evolution

Darwin’s Unfinished Symphony: How Culture Made the Human Mind

Kevin N. Laland
Princeton University Press
464 pp.
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Despite ardently defending his theory of natural selection, Alfred Russel Wallace felt that evolution alone could not account for our species’ unique features, including our big brains, mental abilities and moral sentiments. To explain humanity, he challenged, demands, “some power, distinct from that which has guided the development of the lower animals” (1).

In the past decade, a new hypothesis has matured that suggests that another “power” may indeed have helped drive natural selection in humans, although it is rather different from the one Wallace imagined. In Darwin’s Unfinished Symphony, Kevin Laland makes a powerful case that culture drove much of our species’ genetic evolution over the past few million years.

Here’s the idea: The social learning abilities of our apelike ancestors became sufficiently high fidelity that knowledge about tool-making, cooking, and food-finding began to accumulate over generations. Soon, this accumulating body of nongenetic information generated a variety of new genetic selection pressures. Knives and cooking, for example, created selection pressures that shaped our hands, teeth, and dexterity.

Similarly, the availability of adaptive know-how created selection pressures that honed our brains, making them better at acquiring, processing, storing, and retransmitting an ever-expanding body of culture. The better our brains got at tapping the knowledge distributed across our social networks, the more rapidly and effectively cultural evolution generated sophisticated tools and techniques. This autocatalytic interaction between genes and culture may explain not only our brain’s rapid expansion but also our species’ extended childhoods, prosocial inclinations, longer memories, sharper visual acuity, and enhanced ability to infer the beliefs and desires of others.


What began as a small increase in the fidelity of social learning may have precipitated the emergence of culture.

Narrating his own scientific career as a detective story, Laland weaves together a rich body of research that includes meticulous laboratory studies of social learning in fish and rodents, comparative analyses of brain size and innovation based on field studies, and intuitive descriptions of a variety of mathematical culture-gene coevolutionary models. His authoritative tour of the literature on animal learning reveals how profoundly natural selection has sculpted these abilities across diverse taxa.

By combining this work with analyses of primate behavior, Laland shows how social learning transmits some amount of culture, which can beget larger brains, higher intelligence, and greater innovation in many species. However, unlike all other species, only human social learning has given rise to significant cumulative cultural evolution. This, he argues, makes all the difference.

By this account, the divide between humans and other animals began as a small quantitative increase in the fidelity of social learning. Such an increase can be the difference between cultural stasis and a gradually improving package of tools, strategies, and know-how. Laland persuasively argues that cumulative cultural evolution fostered the genetic evolution of teaching, which is otherwise rare and scattered in the natural world. In boosting the fidelity of social learning, teaching further catalyzed cumulative cultural evolution and thus drove more rapid gene-culture coevolution. To facilitate teaching, Laland argues that natural selection favored the evolution of language. That is, language is for teaching and is essential for transmitting social norms.

Although this account largely converges with my own (2), I worry that it may overestimate the centrality of teaching and language for social learning, especially early in human evolution. My concern arises from the fact that, although teaching—broadly defined—does exist in some form across diverse societies, most of the research on pedagogy, parenting, and socialization derives from populations that are Western, educated, industrialized, rich, and democratic (WEIRD).

In contrast to small-scale societies, WEIRD people rely heavily on intense verbal tuition, positive feedback, and active instructional interventions (3). This bias may skew our understanding of the role played by direct tuition and verbal scaffolding in cultural transmission. Further, numerous social norms, rituals, and technical skills are culturally transmitted without teaching or language (4), especially in small-scale societies. I offer this as fuel for further research, because I firmly agree that teaching and language do play an important role in human culture-gene coevolution.

Like natural selection in the time of Wallace and Darwin, the idea that culture provides the central driving force in human evolution has come of age (2, 5). Orchestrated by one of the field’s leading researchers, Darwin’s Unfinished Symphony makes a compelling case that elegantly seats humans within the natural world, while at the same time explaining our peculiar uniqueness.


  1. A. R. Wallace, Contributions to the Theory of Natural Selection (Macmillan, 1870).

  2. J. Henrich, The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smart (Princeton Univ. Press, 2016).

  3. D. Lancy, The Anthropology of Childhood: Cherubs, Chattel, Changelings (Cambridge Univ. Press, 2009).

  4. G. D. Salali, M. Juda, J. Henrich, Evol. Hum. Behav. 36, 86 (2015).

  5. R. Boyd, A Different Kind of Animal: How Culture Transformed Our Species (Princeton Univ. Press, 2017).

About the author

The reviewer is at the Department of Human Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.