Understanding the origins of evil behaviour is one of our most important intellectual tasks. A distinction can perhaps be drawn between overt sadistic cruelty and the lack of empathy to suffering that is a hallmark of evil. There is increasing data available on the prevalence, proximal psychobiological underpinnings, and distal evolutionary basis for these contrasting phenomena.

The nature of children's early environment has profound long-term consequences. We are beginning to understand the underlying molecular programming of the stress-response system, which may mediate the destructive long-term effects of cruelty to children, explain the evolutionary stability of cruelty, and provide opportunities for its reversal of early trauma.

It is difficult to fully account for (1) cruelty in modern society and (2) female cruelty, referring only to a cruelty-satiation association. Instead it seems likely that cruelty acquires its reinforcing value via association with a range of reinforcers. In addition, when one's goal is violence prevention, it is important to identify causes that can be manipulated.

A Rousseauist bias towards the study of human aggression has treated it as a regrettable anomaly rather than a volatile reflection of important forces in human evolution. Intrepidly, Nell displays the arc of connection between predation in humans and other animals and the neurophysiological factors that underlie chronic interest in accident, death, and harsh force.

Two areas of research for testing Nell's theory are suggested. One is cruelty's seemingly negative correlation with age, which would confirm its linkage with testosterone, sex, and dominance. The other is the special field of leisure activity called thanatourism, that is, the transformation of loci of human horror into tourist attractions.

I ask four questions: (1) Why should we think that our hominid ancestor's predation is not just a causal influence but the main causal factor responsible for human cruelty? (2) Why not think of human cruelty as a necessary part of a syndrome in which other phenomena are necessarily involved? (3) What definitions of cruelty does Nell propose that we operate with? And (4) what about the meaning of cruelty for human beings?

This response deals with seven of the major challenges the commentators have raised to the target article. First, I show that the historical-anecdotal method I have followed has its roots in sociology, and that there is a strong case for the development of a psychology of history. Next, the observational data suggesting that intentional cruelty cannot be restricted to humans is rebutted on the grounds that cruelty requires not only an intention to inflict pain, but to do so because that pain would cause the victim to sufferwhich requires a theory of mind. Third, in the light of the commentaries, I recognise that not only predation but also intraspecific aggression contributes to the development of cruelty. Fourth, I contrast nativists and environmentalists, the former regarding cruelty as a universal human capacity and the latter holding the view that cruelty is acquired through social learning, and argue that there is an otherworldly quality to the environmentalist view. I then show (the fifth challenge) that the target article does generate testable hypotheses. Sixth is a consideration of the implications of the target article for the re-admission of the concept of evil to the psychological lexicon; and seventh, a consideration of the commentaries which note that the cultivation of compassion is a tool for the prevention of cruelty. The last section of the response replies to questions of detail and rebuts some misrepresentations of my argument.

It has long been claimed that Homo sapiens is the only species that has language, but only recently has it been recognized that humans also have an unusual pattern of growth and development. Social mammals have two stages of pre-adult development: infancy and juvenility. Humans have two additional prolonged and pronounced life history stages: childhood, an interval of four years extending between infancy and the juvenile period that follows, and adolescence, a stage of about eight years that stretches from juvenility to adulthood. We begin by reviewing the primary biological and linguistic changes occurring in each of the four pre-adult ontogenetic stages in human life history. Then we attempt to trace the evolution of childhood and juvenility in our hominin ancestors. We propose that several different forms of selection applied in infancy and childhood; and that, in adolescence, elaborated vocal behaviors played a role in courtship and intrasexual competition, enhancing fitness and ultimately integrating performative and pragmatic skills with linguistic knowledge in a broad faculty of language. A theoretical consequence of our proposal is that fossil evidence of the uniquely human stages may be used, with other findings, to date the emergence of language. If important aspects of language cannot appear until sexual maturity, as we propose, then a second consequence is that the development of language requires the whole of modern human ontogeny. Our life history model thus offers new ways of investigating, and thinking about, the evolution, development, and ultimately the nature of human language.

The ethnographic description of story-telling and narrative transmission of cultural facts is an aspect of Locke & Bogin's (L&B's) article that should be amplified. Innate shared gene patrimony is biased by the kinship structure of particular societies and interacts with the transmission of narratives. Trance experiences are another interesting aspect of verbal and agonistic performances.

That both language and novel life-history stages are unique to humans is an interesting datum. But failure to distinguish between language and language use results in an exaggeration of the language acquisition period, which in turn vitiates claims that new developmental stages were causative factors in language evolution.

Aspects of cognitive immaturity may serve both to adapt children to their immediate environment and to prepare them for future ones. Language may have evolved in children's groups in the context of play. Developmental plasticity provides variability upon which natural selection operates, and such plasticity, that likely played an important role in the evolution of language, characterizes human children today.

One way of dealing with the proliferation of conjectures that accompany the diverse study of the evolution of language is to develop precise and testable models which reveal otherwise latent implications. We suggest how verbal theories of the role of individual development in language evolution can benefit from formal modeling, and vice versa.

Life history shaped language as, cascading in time, social strategies became more verbal. Although the insight is important, Locke & Bogin (L&B) also advocate a code model of language. Rejecting this input-output view, I emphasize the interpersonal dynamics of dialogue. From this perspective, childish minds as well as language could be derived from the selective advantages of a total interactional history.

Locke & Bogin (L&B) rightly point to the absence of ontogeny in theories of language evolution. However, they overly rely upon ontogenetic data to isolate components of the language faculty. Only an adaptationist analysis, of the sort seen in evolutionary psychology, can carve language at its joints and lead to testable predictions about how language works.

Language and life history can be related functionally through the study of human ontogeny, thus usefully informing our understanding of several unique aspects of the evolution of species. The operational principles outlined by Locke & Bogin (L&B) demonstrate that the present can provide a useful framework for understanding the past.

A realistic developmental view of language acquisition recognizes vocabulary and pragmatics as well as grammar with a lengthy period of growth in a favorable environment. Cross-fostering is a tool of behavioral biology for studying the interaction between genetic endowment and developmental environment. Sign language studies of cross-fostered chimpanzees measure development in a nearly human environment.

Locke & Bogin (L&B) suggest that theoretical principles of ontogenetic development apply to language evolution. If this is the case, then evolutionary theory should utilize epigenetic theories of development to theorize, model, and elucidate the evolution of language wherever possible. In this commentary, I evoke principles of dynamic systems theory to evaluate the evolutionary phenomena presented in the target article.

We focus on two problems with the evolutionary scenario proposed: (1) It bypasses the question of the origins of the communicative and semiotic features that make language distinct from, say, pleasant but meaningless sounds. (2) It does little to explain the absence of language in, for example, chimpanzees: Most of the selection pressures invoked apply just as strongly to chimps. We suggest how these problems could possibly be amended.

The proposition that selective advantages of linguistic skills have contributed to shifts in ontogenetic landmarks of human life histories in early Homo sapiens is weakened by neglecting alternative mechanisms of life history evolution. Moreover, arguments about biological continuity through sweeping comparisons with nonhuman primates do not support various assumptions of this scenario.

Ontogeny, specifically the role of language in the human family now and in prehistory, is central to Locke & Bogin's (L&B's) thesis in a compelling way. The unique life-history stages of childhood and adolescence, however, must be interpreted not only against an exceptionally high quality human infancy but also in light of the evolution of co-constructed, emotionally based communication in ape, hominid, and human infancy.