Misunderstandings often develop when scientists from different backgrounds use the same words (e.g., “selection”) when they mean different things by them. Theorists must therefore choose and define their terms carefully. In addition, proponents of “new” theories need to demonstrate empirically that theirs are more powerful than the existing theories they wish to supplant. Wilson & Sober have not yet done this.

Humans appear to be possible candidates for group selection because they are often said to live in bands, clans, and tribes. These terms, however, are only names for conceptual categories of people. They do not designate enduring bounded gatherings of people that might be “vehicles of selection.” Hence, group selection has probably not been a major force in human evolution.

Wilson & Sober's discussion of group selection is marred by the absence of plausible examples of human group-level behavioral adaptation. The trait of authoritarianism is one possible example of such an adaptation. It reduces within-group variance in reproductive success, manifests itself more strongly in response to group-level threat, and is found in a variety of cultures.

Many neo-Darwinists treat natural selection of genes and individual organisms as broadly equivalent. This enables Wilson & Sober (W&S) to propose a multilevel group selection model by drawing parallels between individuals and groups. The notion of gene/individual equivalence is a profound misconception. Its elimination negates W&S's current approach but offers the best way forward for both life and behavioural sciences.

The six commentaries raise five issues about multi-level selection theory that we attempt to address: (1) replicators without vehicles, (2) group selection and movement between groups, (3) absolute versus relative fitness, (4) group-level psychological adaptions, and (5) multi-level selection as a predictive theory.

The hypothesized brain evolution and preconditions for language may have allowed for the emergence of musicality either simultaneously with or before the emergence of language. Music and language are parallel in their hierarchical, temporally organized structure, and the evolution of hierarchical representation in hominids may have provided the basis for musical representation. Because music could have been produced manually or vocally before the production of spoken language, it remains possible that language emerged from music and that music thus served as a communicative precursor to language.

The problem of how certain structure–function composites of high complexity could have evolved gradually and by natural selection has been with us at least since Charles Darwin admitted how difficult it was to explain, “his” theory, the origins of “organs of extreme perfection and complication” – such as the eyes of higher animals. Human language capacity is another evolutionary achievement of extraordinary perfection and complexity. Like other skilled human activities, it involves both central (neural) and peripheral (vocal and respiratory) complexes. The reduction of these to simpler building stones to which evolutionary principles may be applied is staggeringly difficult.

Wilkins & Wakefield (1995) provide a thoughtful contribution to our understanding of language origins. In this commentary I attempt to define the relationship between object-manipulation and primate brain function further by reviewing research on aimed throwing and the production and use of stone tools by tufted capuchin monkeys (Cebtis apella). I propose that examining the relation between brain function and object-manipulation in Cebus will provide insight into the preconditions of language in our hominid ancestors.

This response to continuing commentary addresses brain-hand relationships in Cebus apella (as introduced in West-ergaard's commentary), the evolutionary and acquisition parallels between music and language (suggested by Lynch), and the potential behavioral linguistic consequences of the evolutionary neurobiology in Australopithecus africanus and Homo habilis (discussed by Tobias). Finally, we reiterate the importance of well informed, multidisciplinary approaches to the study of the emergence of human species-specific cognition, especially linguistic capacity.