I welcome the arguments of Evans & Levinson (E&L) and offer only some supplementary remarks perhaps relevant to the future elaboration of their case. I strongly agree that, given the shared properties of the world we live in, our appeals to innate concepts and structures should be a last resort. My primary recommendation is that they expand their model from two tracks to three, so that they can deal with the ways in which biological and cultural evolution must necessarily interact with the evolution of an individual's language repertories in ontogeny. I also comment on the relevance of the argument from the poverty of the stimulus, and I offer a caveat, based on analogous issues in biology, on the metaphor of language as a container of meanings or other content. I have elsewhere addressed related issues, including the primacy of behavior in shaping brain structure (Catania Reference Catania2008), the interpretation of learning in terms of selection rather than in terms of associations (Catania Reference Catania1995; Reference Catania2003; Catania & Shimoff Reference Catania and Shimoff1998), and the distinction between language structure and function and its implications (Catania Reference Catania1973; Reference Catania1990; Reference Catania and Gyori2001; Reference Catania2004; Catania & Cerutti Reference Catania, Cerutti, Thompson and Zeiler1986).

E&L make a persuasive case for the interaction of biological and cultural evolution. But languages can survive only if acquired and maintained by individuals who then pass them on. This acquisition and maintenance involves a third variety of selection operating on individual behavior, at every level: from the shaping of complex vocalizations as the child masters phonetic structures, through the semantic and syntactic details of those languages, to the sophisticated social interactions of mature speakers. Without selection at the level of individual language repertories, those linguistic and social practices cannot last long enough to be transmitted across successive generations. For this to work, by the way, ontogenetic and cultural selection must operate upon similar kinds of linguistic units; what is acquired in learning must share dimensions with what is culturally transmitted.

Adequate scenarios for language evolution must take into account these three varieties of selection. Each requires variations among the units upon which it operates; each entails different mechanisms by which environments select surviving variants. Biological contingencies must select requisite physiological attributes (e.g., vocal tract structure, neural organization). Ontogenetic contingencies must maintain the features of languages acquired by individuals. Cultural selection must perpetuate language practices across generations. E&L's discussion of language diversity nicely accommodates these processes, because it allows for substantial ranges of variation while still showing how languages can be maintained within and across generations.

These different varieties of selection often complement one another, but selection at one level may oppose selection at another. For example, behavior selected through ontogenetic processes during an individual's lifetime may reduce the individual's reproductive fitness at the phylogenetic level (consider substance abuse or sexual behavior involving partners at risk for AIDS).

Although they do so sparingly, and typically only implicitly, E&L sometimes discuss language as a container of meanings or of other content expressed in words and sentences. The conduit metaphor of language is pervasive but too often misleading (Reddy Reference Reddy and Ortony1979). Assuming that language expresses or contains something transmitted from one individual to another raises some of the same difficulties as the assumption that genetic materials transmit information. Dawkins (Reference Dawkins1982) made that point when distinguishing between blueprints and recipes in characterizing genetic materials, which do not contain body plans or other information about the organism that will be their product. Rather than blueprints, they are recipes for development; the relevant information is not about past selective environments or about the way mature organisms will interact with their environments. A parallel distinction is relevant to language and has implications for language evolution. Words are not carriers of meanings or schemas or other information relevant to the selective environments that engendered them; we should look at words not in terms of what they contain but rather in terms of what they do (Catania Reference Catania1987). Of all that they can do, one irreducible function of language is providing a mechanism by which one individual can change the behavior of others. This alone may be a sufficient basis for the origins of language. Other functions of language (e.g., communication, calculation, narrative, truth) may then be its derivatives.

I was surprised that E&L did not mention Chomsky's argument from the poverty of the stimulus (Chomsky Reference Chomsky1965), because claims that the relevant structures cannot be found in the environmental contingencies justify the reification and internalization of language universals. The argument that children learn grammatical structures even in the absence of examples of negative instances seems to assume that learning any distinction requires exposure to all possible negative exemplars. But, for example, a bird raised in monochromatic light does not discriminate among wavelengths. Yet after learning to discriminate between the original wavelength and just a single new one not seen before, the bird responds in an orderly way to wavelengths across the entire visual spectrum (Terrace Reference Terrace1975). Similarly, any verbal environment including contrasts between several grammatical structures provides the differences on which learning can be based: for example, both active and passive voice are grammatical but provide a contrast that may enable later discrimination of grammatical versus ungrammatical.

Of course, these outcomes tell us about the structure of the underlying continua (the orderliness of the color continuum could be described as its universal grammar). But with regard to grammatical dimensions, those structures are so highly variable across languages, as E&L so aptly argue, that it would be as reasonable to assume that they are driven by language cultures within lifetimes in social environments as that they are driven by brain structures evolved over biological time (Catania Reference Catania2008; Moerk Reference Moerk1992). This is consistent with evidence that rich verbal environments in which parents spend lots of time interacting verbally with their children make vast and lasting differences in their verbal competence, as measured by vocabulary growth rate, school performance, and IQ scores (Hart & Risley Reference Hart and Risley1995). Verbal environments matter.