Unedited preprint of a submitted but not yet refereed commentary on Falk, D. (forthcoming) 'Prelinguistic evolution in early hominins: Whence motherese?' to appear in Behavioral and Brain Sciences.
School of Psychology
University of Natal
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 suggest an enriched perspective on mother-infant interaction, and on the beginnings of conventionalized signaling.
Falks proposal, while promising, underplays the role of the infant. Both of the fundamental premises of the putting down the baby hypothesis concern the mother - one suggesting that hominin mothers that attended vigilantly to their infants would have a selective advantage, and the other that such mothers would have had a genetically based potential for the gestural and vocal demands of the distal comforting and control required in the absence of direct touch (3.2.1 of the target article). Two reasons for placing greater emphasis on the contribution of the infant strike us as especially significant.
In the first place, the interests of mothers and infants, despite the considerable genetic material and energetic investment of the former in the latter, do not completely coincide. Mothers must determine an appropriate trade-off between their own survival requirements and the demands of rearing, and also between the requirements of other actual or possible offspring and those of any single infant. This begins before birth (Haig 1993). Under conditions of severe scarcity, or when the relative viability of different infants varies significantly, the costs of getting the trade-off wrong could be high. Conversely, any given infant embodies interests that from its own perspective trump those of siblings and its mother, and stands to gain, within limits, from maximizing its share of maternal resources at their expense (Trivers 1974).
This non-coincidence of interests is important because as well as being the subjects of maternal attempts at comfort and control, infants are the producers of various affective displays that co-regulate maternal behavior. The attempts of mothers to exploit ways of calming their infants, that is, sometimes take place in competition with infant behaviors such as crying or smiling that influence maternal affective state (Wiesenfeld & Klorman 1978) and can motivate actions such as feeding and holding. Falk suggests that mothers who were good at vocal comforting may have been freed to forage more effectively, but it is also possible that infants whose cries were more effective at eliciting maternal care over and above distal comforting could have been fed more. Both parties, that is, stand to gain from producing more compelling vocalizations, and from better ability to appraise those of the other. The appraisal in question is complex, because neither participant is able to rely on any invariably effective behavior- feeding or holding do not always calm an agitated infant, any more than a crying one always secures immediate maternal attention. Factors such as fatigue, fear, hunger, and habituation to a recently repeated vocal action help explain why this is so.
The above considerations could apply (and do apply in the case of modern humans) even where the signalling currency is provided by relatively universal indicators of approval, disapproval, etc (Fernald 1992, Ekman 1972). What of situations where one is imagining the early construction of semi-conventional proto-language? This brings us to our second major point.
The earliest indications of contingent, partly conventionalized signaling between mother and infant in contemporary humans can be seen in at around three months. By the time a modern human infant is fourteen weeks old mutual gaze, shared facial expression and prosodic vocalizations between it and its mother sustain pleasurable bouts of co-ordinated interaction between them. Many investigators make the mother-infant dyad their object of analysis, and focus on dyadic properties such as attunement and co-ordination, phenomena where the individual actions of either partner are best accounted for if they are seen as contingent responses to the anticipated activity of the other (e.g. Stern 1977). That is, just as caregivers effectively attuning with their offspring learn to anticipate and creatively exploit their infants activity and responsiveness in particular expressive contexts, so infants interacting with caregivers learn to do the same. Both can learn creatively to exploit the patterns of activity and responsiveness in the other for their own interests.
Examples of non-universal signals that we have observed at this age include maternal requests for infant behaviors such as being quiet, or slightly later proto-requests from the infant, for example for being lifted. (At this stage the signals are often multi-modal, including vocal and gestural components.) The fact that these signals are not universal suggests that they have been constructed in interaction, either as local inventions peculiar to the dyad, or as culturally contingent patterns introduced by the mother. A conventionalised mother to infant command that can be obeyed (some of the time) can also be disobeyed. An infant vocalisation or gesture that has come to be treated as a distinctive request cannot only be granted, it can also be refused. Proto-conventional signals, that is, can be seen as new tools in the ongoing battle for occasional control of the other described above. Innovations from either party in attempts to exploit or control the other lead to more sophisticated patterns, setting the stage for further innovation.
The sorts of innovation we have in mind can be described in
terms of attaching more refined conditional probabilities for the
success of this or that signaling strategy given an increasingly
sophisticated command of relevant contextual details. Laboratory
chimpanzees that point towards inaccessible but visible food only
when humans are present and in a position to give it to them
(Leavens & Hopkins 1998) show this sort of attention to
context. So do mothers that shift from direct comforting to an
attempt to distract a distressed infant when comforting seems
ineffective. We are familiar with attempts at parental
manipulation in modern humans by older, speaking children who
pave the way for requests they suspect would not be granted with
bouts of generous cooperativeness. We suggest that these are
different in degree but not kind from the earliest forms of
infant innovation in signaling, and that granting a more active
role to the infant could enrich Falks account of
contemporary mother-infant interaction, and perhaps his proposal
regarding the evolution of motherese.
Ekman, P. (1972) Universals and cultural differences in facial expressions of emotion. In J. Cole (Ed.), Nebraska symposium on motivation. University of Nebraska Press.
Fernald, A. (1992) Maternal Vocalizations to Infants as Biologically Relevant Signals: An Evolutionary Perspective. In Jerome H. Barkow, Leda Cosmides and John Tooby (Eds.) The Adapted Mind. Oxford University Press.
Haig, D. (1993) Genetic conflicts in human pregnancy, Quarterly Review of Biology 68:495-531.
Leavens, D. A. & Hopkins, W. D. (1998) Intentional communication by chimpanzees: A cross-sectional study of the use of referential gestures. Developmental Psychology 34:813-22.
Stern, D. (1977) The First Relationship. Fontana.
Trivers, R. L. (1974) Parent-offspring conflict. American Zoologist 14:249-64.
Wiesenfeld, A. R. & Klorman, R. (1978) The mothers psychophysiological reactions to contrasting affective expressions by her own and an unfamiliar infant. Developmental Psychology 14: 294-304.