Abstract This study seeks to make a contribution to evolutionary science. It shows how the Natural Semantic Metalanguage (NSM) system of semantic–conceptual representation, developed for modern humans, can be “reverse engineered” to produce a plausible model of cognitive evolution from the time of the Last Common Ancestor (LCA) of humans and chimpanzees. We posit six stages of cognitive development, each with its own distinct repertoire of conceptual primes. The progression between the stages is seen as driven by natural selection in the service of enhanced cognitive operations for biological problem solving under changing anatomical, behavioural, environmental and social conditions. The paper draws on a range of evidence and leading ideas from archaeology, paleoanthropology and primatology.