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The signal functions of early infant crying

Published online by Cambridge University Press:  14 February 2005

Joseph Soltis
Joseph Soltis*
Affiliation:
Unit of Developmental Neuroethology, Laboratory of Comparative Ethology, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Poolesville, MD20837
*
[email protected]
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Abstract:

In this article I evaluate recent attempts to illuminate the human infant cry from an evolutionary perspective. Infants are born into an uncertain parenting environment, which can range from indulgent care of offspring to infanticide. Infant cries are in large part adaptations that maintain proximity to and elicit care from caregivers. Although there is not strong evidence for acoustically distinct cry types, infant cries may function as a graded signal. During pain-induced autonomic nervous system arousal, for example, neural input to the vocal cords increases cry pitch. Caregivers may use this acoustic information, together with other cues, to guide caregiving behavior. Serious pathology, on the other hand, results in chronically and severely abnormal cry acoustics. Such abnormal crying may be a proximate cause of adaptive infant maltreatment, in circumstances in which parents cut their losses and reduce or withdraw investment from infants with low survival chances. An increase in the amount of crying during the first few months of life is a human universal, and excessive crying, or colic, represents the upper end of this normal increase. Potential signal functions of excessive crying include manipulation of parents to acquire additional resources, honest signaling of need, and honest signaling of vigor. Current evidence does not strongly support any one of these hypotheses, but the evidence is most consistent with the hypothesis that excessive early infant crying is a signal of vigor that evolved to reduce the risk of a reduction or withdrawal of parental care.

Keywords

coliccryingearly infant cryinghonest signalinginfanticideparental careparent-offspring conflictseparation callvocalization
Type
Research Article
Information
Behavioral and Brain Sciences , Volume 27 , Issue 4 , August 2004 , pp. 443 - 458
Copyright
Copyright © Cambridge University Press 2004

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References

Notes

The author of this target article is employed by a government agency and as such this target article is considered a work of the U.S. government and not subject to copyright within the United States.

1. Throughout the paper I emphasize cross-cultural ethnography. The way of life in traditional societies, in particular in huntergatherer societies, is the best extant representation of the environment in which most of human evolutionary history unfolded, the so-called environment of evolutionary adaptedness, or EEA (Barkow et al. 1992; Bowlby 1969/1982). This is not to say that traditional societies of modern times are perfect representations of all earlier human societies. The concept of the EEA has been criticized for painting a too-homogeneous picture of the 2 million years that it spans and for not recognizing the possibility of more recent evolutionary change in humans (Irons 1998). Nevertheless, a cross-cultural approach offers the most inclusive view of the human condition, including that of our evolutionary past, and I follow that approach here.

2. In the condition-dependent handicap described in the text, low quality infants simply cannot produce the signal, or cannot produce it as conspicuously, as high quality infants. In the related strategic choice handicap, low and high quality infants can produce any level of the signal, but the marginal cost at the same level of signal is higher for low quality infants than it is for high quality infants. For a low quality infant, then, the marginal cost of producing a certain level of signal may be higher than the marginal benefit of reducing the probability of infanticide, and so no increase in the signal level would be favored. For a higher quality infant, on the other hand, the marginal cost of producing the same level of signal may be less than the marginal benefit of reducing the probability of infanticide, and an increase in signaling would be favored (see Grafen 1990a). In both scenarios, parents can use the signal to evaluate infant quality. Additionally, there can still be some cheating in “honest”-signaling systems, as emphasized in the manipulation models described in the text, but signaling is reliable if most signals are honest (Johnstone 1997; Johnstone & Grafen 1993).

3. According to this view, children develop secure attachments when mothers are available, responsive, and accepting, and they develop (possibly different forms of) insecure attachment when mothers are not, although child temperament may also contribute to the attachment process. These different forms of attachment may themselves be adaptive responses to specific rearing environments (Chisholm 1996; Hrdy 1999; Lamb et al. 1985; Zeifman 2001).

4. Infant crying that mimics need in the absence of autonomic arousal could be a manipulative signal to gain extra parental care or attention. The role of acute and chronic stress in determining early infant cry acoustics dominates the empirical literature, however, so it is unclear what amount of variation in infant cry acoustics, if any, remains unexplained by such autonomic arousal.