The hypothesis that excessive early infant crying evolved to reduce the risk of withdrawal of parental care is disputed on the grounds that excessive infant crying is irritating and imposes fitness losses rather than gains. Alternative explanations for the early crying curve that take into account development on the part of the infant and the emerging infant-caregiver bond are proposed.

The majority of the commentaries focused on excessive crying and colic and included two major themes: the consideration of proximate physiological mechanisms, and challenges to my interpretation of the signal functions of early infant crying amount. I initially concluded that none of the competing signaling hypotheses enjoyed strong support, but I nevertheless favored the signaling vigor hypothesis above the signaling need and manipulation hypotheses. Consideration of the neurobiological causation of the n-shaped crying curve and further evidence and argumentation concerning the potential signal functions, however, do not allow for the elevation of any one of these hypotheses above the others, and it remains the case that none are strongly supported. Taken together, however, the target article and commentary do provide a solid foundation for further research. In the target article, I also proposed a model of how infant cry acoustics can influence patterns of care and abuse. Commentary has enriched this model by including the consideration of developmental changes in cry acoustics across early infancy, and by further integrating the cry signal with other modalities of communication and with later development. I trust that the foregoing will show that the joint pursuit of the proximate mechanisms and the potential signal functions of early infant cry amount and cry acoustics should prove fruitful. Before embarking on my reevaluation, however, I begin this response by addressing the issue of consciousness in evolutionary accounts of signaling.

In order to formulate hypotheses about the evolutionary underpinnings that preceded the first glimmerings of language, mother-infant gestural and vocal interactions are compared in chimpanzees and humans and used to model those of early hominins. These data, along with paleoanthropological evidence, suggest that prelinguistic vocal substrates for protolanguage that had prosodic features similar to contemporary motherese evolved as the trend for enlarging brains in late australopithecines/early Homo progressively increased the difficulty of parturition, thus causing a selective shift toward females that gave birth to relatively undeveloped neonates. It is hypothesized that hominin mothers adopted new foraging strategies that entailed maternal silencing, reassuring, and controlling of the behaviors of physically removed infants (i.e., that shared human babies' inability to cling to their mothers' bodies). As mothers increasingly used prosodic and gestural markings to encourage juveniles to behave and to follow, the meanings of certain utterances (words) became conventionalized. This hypothesis is based on the premises that hominin mothers that attended vigilantly to infants were strongly selected for, and that such mothers had genetically based potentials for consciously modifying vocalizations and gestures to control infants, both of which receive support from the literature.

In early hominins, there possibly was high selective pressure for the development of reciprocal mother and child vocalizations such as proposed by Falk. In this context, temporoparietal-prefrontal networks that participate in tasks such as working memory and imitation may have been strongly selected for. These networks may have become the precursors of the future language areas of the human brain.

Falk has much of interest to say on the evolution of mothering, but she fails to address the core issue of language evolution: how symbolism or structure evolved. Control of infants does not require either, and Falk provides neither evidence nor arguments supporting referential symbolism as a component of mother-infant interactions.

Although motherese may facilitate language acquisition, recent findings indicate that not all aspects of motherese are necessary for word recognition and speech segmentation, the building blocks of language learning. Rather, exposure to input that has prosodic, phonological, and statistical consistencies is sufficient to jump-start the learning process. In light of this, the infant-directedness of the input might be considered superfluous, at least insofar as language acquisition is concerned.

Falk's hypothesis is attractive and seems to be supported by data from primatology and language acquisition literature. However, this etiological narrative presents a fairly low degree of plausibility, the result of two epistemological fallacies: an implicit reliance on a unilinear model of causality and the explicit belief that ontogeny is homologous to phylogeny. Although this attempt to retrace the early emergence of prelinguistic capacities in hominins falls short of producing a compelling argument, it does call attention to an aspect of linguistic behavior which may indeed have evolved under the pressure of nurturing constraints.

Bipedalism in the earliest hominid specimens is always accompanied by the reduction of projecting canine teeth. Body size is smaller than chimpanzees or humans, but molar teeth are markedly larger. Use of a pointed stick for defensive purposes on the one hand, and digging for USOs on the other, may be why bipedalism was selected for. Passing such learned behavior to the next generation may have played a role in selecting for language.

Falk's hominin mother-infant model presupposes an emerging infant capacity to perceive and learn from afforded gestures and vocalizations. Unlike back-riding offspring of other primates, who were in no need to decenter their own body-centered perspective, a mirror neurons system may have been adapted in hominin infants to subserve the kind of (m)other-centered mirroring we now see manifested by human infants soon after birth.

Prosody, in motherese as in all forms of language, has a very different form and a very different use than the central lexical, phonological, and syntactic components of language. Whereas the prosodic aspects of motherese probably derive from primate vocalization, this does not help us to understand how the more distinctive parts of language emerged.

Falk's argument takes for granted that “protolanguage” used a genetic propensity for producing word-forms. Using developmental evidence, I dispute this assumption and, instead, reframe the argument in terms of behavioral ecology. Viewed as niche-construction, putting the baby down can help clarify not only the origins of talk but also the capacity to modify what we are saying as we speak.

Falk's contribution to a continuity theory of the origins of language would be complemented by an account of the origins of displaced reference, a key characteristic distinguishing human language from animal signaling systems. Because deception is one situation in which nonhumans may use signals in the absence of their referents, deception may have been the starting point for displaced reference.

Dean Falk has strategically explored “mother-infant gestural and vocal interactions . . . in chimpanzees and humans” in order to offer hypotheses “about the evolutionary underpinnings that preceded the first glimmerings of language.” Though she offers compelling evidence for many interesting hypotheses as to the epigenesis of language, other possibilities have yet to be explored. Here we explore the role of gestural communication among deaf signers and the neural correlates associated with this type of communication.

Visual (facial), tactile, and gestural, as well as vocal, elements of mother-infant interactions are each formalizations, repetitions, exaggerations, and elaborations of ordinary adult communicative signals of affiliation – suggesting ritualization. They are temporally organized and enable emotional coordination of the interacting pair. This larger view of motherese supports Falk's claim that the social-emotional elements of language are primary and suggests that language and music have common evolutionary foundations.

Modeling the evolution of human behavior, including language, is a complex but important undertaking. The over-reliance on chimpanzees as models to assess basal hominin patterns and the implicit assumption that hominin mothers did not have significant assistance in caring for young weaken this model for the emergence of language from mother-infant vocal interactions.

Human language is a peculiar primate communication tool because of its large neocortical substrate, comparable to the structural substrates of cognitive systems. Although monkey calls and human language rely on different structures, neural substrate for human language emotional coding, prosody, and intonation is already part of nonhuman primate vocalization circuitry. Motherese could be an aspect of language at the crossing or at the origin of communicative and cognitive content.

Our starting point for the origins of language goes beyond prosody or infant-directed speech to highlight the affective, multimodal, and co-constructed nature of meaning-making that was likely present before the split between African great apes and hominins. Analysis of vocal and gestural caregiving practices in hominins, and of meaning-making via gestural interaction in African great apes, supports our thesis.

Falk claims that human language took a step forward when infants lost their ability to cling and were placed on the ground, increasing their fears, which mothers assuaged prosodically. This claim, which is unsupported by anthropological and psychological evidence, would have done little for the syllabic and segmental structure of language, and ignores infants' own contribution to the process.

In this commentary we raise three issues: (1) Is it motherese or song that sets the stage for very early mother-infant interaction? (2) Does the infant play a pivotal role in the complex temporal structure of social interaction? (3) Is the vocal channel primordial or do other modalities play an equally important role in social interaction?

Words denoting “mother” in baby talk and in languages usually include nasal sounds, supporting Falk's suggestion that infant nasalized demand vocalizations might have motivated a first word. The linguistic contrast between maternal terms and paternal terms, which favor oral consonants, and the simple phonetic patterns of parental terms in both baby talk and languages also suggest parental terms could have been first words.