Motherese is a form of affective prosody injected automatically into speech during caregiving solicitude. Affective prosody is the aspect of language that conveys emotion by changes in tone, rhythm, and emphasis during speech. It is a neocortical function that allows graded, highly varied vocal emotional expression. Other mammals have only rigid, species-specific, limbic vocalizations. Thus, encephalization with corticalization is necessary for the evolution of progressively complex vocal emotional displays.

The definition of motherese is extended to infant-directed vocalizations in non-hominin mammals. In many species, vocal interactions between mothers and their infants are common. The neural substrates mediating these interactions include the rostral limbic cortex of the frontal lobe. Spoken language may have arisen from hominin females vocalizing to their infants.

A converging pattern of evidence from laughter, tickling, and motherese suggests that bipedal locomotion plays a critical and unanticipated role in vocal evolution. Bipedalism frees the thorax of its support role during quadrupedal locomotion, which permits the uncoupling of breathing and striding necessary for the subsequent selection for vocal virtuosity and speech.

Based on the motor theory of language, which asserts an evolution from gestures along several stages to today's speech and language, we suggest that speech ontogeny may partly reflect speech phylogeny, in that perception of prosodic contours is an intermediary stage between a manual communication system and a fully developed language faculty.

Two arguments are critiqued here. The first is that hominin mothers “parked” their offspring; the evidence does not support that position. The second is that motherese developed to control the behavior of nonambulatory infants. However, Falk's case is stronger if we apply it to children who are already walking and more likely to be influenced by verbal information.

We believe that “caching” a baby would have been too great a danger in human prehistory, and thus could not serve as the context for prelinguistic vocalization. Rather, infants were most likely carried at all times. Thus, the question arises of why the cry of an infant is such a loud vocalization.

Falk's paper provides a nice cross-species perspective and an interesting background to formulate a theory of the evolution of human language. However, the author does not provide a complete overview and analysis of the origins of language and takes for granted the “continuity hypothesis.” Also her “infant parking theory” is questionable, as it is not well supported by observations.

The interests of mother and infants do not exactly coincide. Further, infants are not merely objects of attempted control by mothers, but the sources of attempts to control what mothers do. Taking account of the ways in which this is so suggests an enriched perspective on mother-infant interaction and on the beginnings of conventionalized signaling.

The hypothesis that language began as a multimodal, gestural complex finds support in data from spoken languages on the connection between intonation and gesture, as well as from the process by which intonation becomes codified into grammar. Also, data from signed languages show a similar process at work, in which gestural elements become incorporated as intonation and conventionalized as grammatical markers.

My responses to the observations and criticisms of 26 commentaries focus on the coregulated and affective nature of initial mother/infant interactions, the relationship between motherese and emergent linguistic skills and its implication for hominin evolution, the plausibility of the “putting the baby down” hypothesis, and details about specific neurological substrates that may have formed the basis for the evolution of prelinguistic behaviors and, eventually, protolanguage.

The transfer of food among group members is a ubiquitous feature of small-scale forager and forager-agricultural populations. The uniqueness of pervasive sharing among humans, especially among unrelated individuals, has led researchers to evaluate numerous hypotheses about the adaptive functions and patterns of sharing in different ecologies. This article attempts to organize available cross-cultural evidence pertaining to several contentious evolutionary models: kin selection, reciprocal altruism, tolerated scrounging, and costly signaling. Debates about the relevance of these models focus primarily on the extent to which individuals exert control over the distribution of foods they acquire, and the extent to which donors receive food or other fitness-enhancing benefits in return for shares given away. Each model can explain some of the variance in sharing patterns within groups, and so generalizations that ignore or deny the importance of any one model may be misleading. Careful multivariate analyses and cross-cultural comparisons of food transfer patterns are therefore necessary tools for assessing aspects of the sexual division of labor, human life history evolution, and the evolution of the family. This article also introduces a framework for better understanding variation in sharing behavior across small-scale traditional societies. I discuss the importance of resource ecology and the degree of coordination in acquisition activities as a key feature that influences sharing behavior.

High producers are motivated to hunt in spite of high levels of sharing because the transfers come from absolutely larger amounts of resource. In the context of a generalized cooperative subsistence strategy, stinginess could provoke the withdrawal of cooperative partners and result in a loss of income. Good producers could have more to lose by not sharing than poor producers would.

Individuals give for two reasons. One is to get a benefit back. The other is to avoid a cost. “Cooperation” theories stress mutual benefits. “Conflict” theories stress costs. Hunters may give up part of their hunt because they get favors back, or because the recipients are stronger than they are and the hunting isn't as good anywhere else.

Gurven suggests that the tolerated scrounging model has limited relevance for explaining patterns of food transfers in human populations. However, this conclusion is based on a restricted interpretation of the tolerated scrounging model proposed originally by Blurton Jones (1987). Examples of food transfers in nonhuman primates illustrate that the assumptions of Gurven's tolerated scrounging model are open to question.

Gurven discusses three key features of food sharing, specifically producer control, need, and contingency. I make two general points regarding the use of these variables in tests of food-sharing hypotheses. First, that these variables are relative, not absolute concepts; and second, that the predictions generated from these variables overlap significantly. In addition, I suggest frequency of sharing as a measure of contingency for the RA hypothesis.

Can evolutionary models explain food sharing in traditional human societies? Gurven's analysis cannot rule out any of the models (kin selection, reciprocal altruism, tolerated scrounging, costly signaling, or by-product mutualism), and quantitative partitioning of relative importance is not feasible. For now, the hypotheses seem like the proverbial blind men examining the elephant: each was partly in the right, and all were in the wrong!

In his state-of-the-art review, Gurven compares evolutionary theories of food transfers in ethnographic settings. Although this is useful, I suggest that one must first try to determine the utility of food transfers before making predictions about which parties ought to receive food. In addition, I argue that tests of kin selection theory present a special problem in food transfers.

In this comment, I describe how the processes of free giving can be simulated with the help of the Reflexive Intentional Model of the Subject (RIMS). This simulation demonstrates that there are two essential factors affecting the size of a share given to others: limits accepted by the society as “normal,” and the individual's subjective estimation of a mean share donated by other members of the society.

Emphasis on cross-cultural testing, multiple currencies, multivariate analyses, and levels of explanation makes this an important paper. However, it does not distinguish current function from evolutionary origin; it lacks history. Rather than distinct alternatives, tolerated scrounging (TS), costly signaling (CS), and reciprocal altruism (RA) are likely to be sequentially evolved components of a single integrated system (and kin selection (KS) important only among very close relatives).

Although an excellent review, the target article displays a bias in favor of reciprocity-based explanations and against alternatives. Tolerated scrounging is more subtle and pervasive than portrayed here. Costly signaling need not be limited to public displays and generalized sharing. The theoretical basis for extensive sharing and other forms of collective action remains unresolved, and standard reciprocity-based explanations are insufficient.