The extension of biology through culture.

Biology is the study of life. How our understanding of the nature and evolution of living systems is being enriched and extended through new discoveries about social learning and culture in human and nonhuman animals is the subject of the collection of articles we introduce here. Recent decades have revealed that social learning and the transmission of cultural traditions are much more widespread in the animal kingdom than earlier suspected, affecting numerous forms of functional behavior and creating a secondary form of evolution, built onto the better-known primary, genetically based form. New scientific approaches to the study of human cultural evolution have also emerged and become productive. However, these developments in the study of cultural phenomena in both human and nonhuman animals have yet to be seriously integrated into mainstream evolutionary biology. Here we offer an introductory overview of the background and scope of a collection of articles that report recent progress in these fields, and outline their proposed significance for biology at large. The theoretical backbone of the life sciences, its central organizing principle, is of course evolution, by now rich in both theory and empirical support (1–3). The great synthesis of Darwin’s and Wallace’s evolutionary insights and early 20th century understanding of genetics that became known as the “Modern Synthesis” was achieved by a brilliant set of biologists mainly in the period 1938–1946 (4), and its principles have provided the core of evolutionary theory since that time (5). Thus, contemporary texts on “evolution” focus on such topics as mutation, genetically based inheritance, population genetics, genomics, and the natural and sexual selection pressures that shape gene frequencies, genotypes, and phenotypes (1, 2, 6, 7). Genes and their role in inheritance have come to be celebrated as the pivotal elements in evolution (8). However, a second form of evolution was also recognized long ago, in the ways that cultural phenomena have changed in the course of human history, through a different form of inheritance: that in which people learn from others (social learning), including from previous generations. Darwin himself recognized the parallels between the evolution of culturally inherited languages and organic evolution (9, 10); indeed, evolutionary family trees of languages proposed by philologists long predated the Origin of Species, although they were further spurred by its publication (11–13). During the 1970s and 1980s, first by Cavalli-Sforza and Feldman (14–16) and then Boyd and Richerson (17), the implications of the existence of the two forms of evolution, organic and cultural, was at last explored systematically and formally, through conceptual and mathematical modeling that formed a foundation for later empirical investigations. The present collection of papers opens with a contribution by Creanza et al. (18) that offers an overview of both the foundational studies in (human) cultural evolution and major developments in the period since. The early body of 20th century work laid out some of the ways in which cultural evolution: (i ) echoes many core principles of organic evolution, yet (ii ) also differs from it in dramatic ways that change evolutionary dynamics, and (iii) interacts with the genetically based phenomena to create new complexities (“gene–culture coevolution”). We return to discuss these further, below. From a somewhat different perspective MaynardSmith and Szathmary (19) distinguished a series of major transitions in the nature of evolution, such as the emergence of multicellularity and of sex, the most recent major transition being the emergence of (human) culture; and Dawkins (20) gave a name to cultural elements suggested to be the analogs of genetic replicators—“memes”—which has been assimilated into popular culture. Other authors suggested “semes” (21), echoing semiotics, the study of signs and symbols. We shall discuss such developments and subsequent related scientific progress further below, but for