The authors deliver a decisive blow to the idea of unidirectional behavioural and cognitive evolution in this tightly argued account of why the bow and arrow was invented and then possibly laid aside by Middle Stone Age communities in southern Africa. Finding that all are modern humans (Homo sapiens), they paint a picture of diverse strategies for survival and development from 75 000 years ago onwards. It is one in which material inventions can come and go, human societies negotiating their own paths through a rugged mental landscape of opportunity.

Over the last quarter century, the dominant tendency in comparative cognitive psychology has been to emphasize the similarities between human and nonhuman minds and to downplay the differences as “one of degree and not of kind” (Darwin 1871). In the present target article, we argue that Darwin was mistaken: the profound biological continuity between human and nonhuman animals masks an equally profound discontinuity between human and nonhuman minds. To wit, there is a significant discontinuity in the degree to which human and nonhuman animals are able to approximate the higher-order, systematic, relational capabilities of a physical symbol system (PSS) (Newell 1980). We show that this symbolic-relational discontinuity pervades nearly every domain of cognition and runs much deeper than even the spectacular scaffolding provided by language or culture alone can explain. We propose a representational-level specification as to where human and nonhuman animals' abilities to approximate a PSS are similar and where they differ. We conclude by suggesting that recent symbolic-connectionist models of cognition shed new light on the mechanisms that underlie the gap between human and nonhuman minds.