Summary

Crying and tears may be favored by natural selection because they bring about helping behaviour by the spectator. This helping behaviour is explained by the assumption that crying and tears “imitate” some of the perceivable characteristics of a baby that has just been born (e.g., wet face, facial expressions, respiratory sounds). If human parents and people in general are “programmed” by evolution to feel the need to help and protect when they see (and hear) newborns, then when nonneonates are in need, the appearance and the behavior that together show resemblance to the neonate may have survival value at some essential points during phylogeny and, thus, may spread in the human species.

In ontogeny, the fact that the shedding of tears usually occurs for the first time not until weeks or months after birth is not an argument against this view but, rather, supports it.

Some Theories Regarding the Function of Emotional Tears.

In The Expression of Emotions in Man and Animals, Charles Darwin listed three reasons for the secretion of tears: “The primary function of the secretion of tears, with some mucus, is to lubricate the surface of the eye, and a secondary one, as some believe, is to keep the nostrils damp, so that the inhaled air may be moist, and likewise to favour the power of smelling. But another, and at least equally important function of tears is to wash out particles of dust or other minute objects which may get into the eyes” (Darwin, 1872: 169). In Darwin’s view, the excretion of emotional tears was related to the first function.

In more recent years, A. Montagu (1959) offered another explanation of emotional tears: The intake and expulsion of air that occurs in sobbing would cause the sensitive mucous membranes of the nasopharynx to dry out quickly if tears did not keep them moist, and as a result, the risk of infection would increase. This explanation was criticized by W.H. Frey (1982:9) who wrote: “Humans do not excrete tears while running or performing other exercise where breathing is increased.” He hypothesized that, like urinating, defecating, and exhaling, emotional tearing may be involved in the removing of waste products or toxic substances from the body. Perhaps people feel better after crying because as they shed tears, they also shed, in those tears, chemicals that build up during emotional stress.

These explanations are essentially physiological, and Darwin made explicit that he assumed no other, more fundamental reason for weeping. He wrote: “…we must look at weeping as an incidental result, as purposeless as the secretion of tears from a blow outside the eye, or as a sneeze from the retina being affected by a bright light, …” (Darwin, 1872: 176-177). In his view, the sole effect of weeping or crying is to give relief to individuals who are experiencing the agony of pain.

In contrast to Darwin’s point of view, the explanation that follows directly links crying and the secretion of tears to evolutionary theory. Crying and the emotional secretion of tears are considered here to be messages that contain a request for help, and humans have the ability to cry and to shed tears because these messages have proven to be effective.

An Evolutionary Explanation of Crying and Tears.

This explanation is based on three assumptions.

A. In many species of animals, the stimuli emitted by newborns bring about parental care. In fact, the newborns of many species require parental care. Because a newborn has little else to offer than its own appearance and behaviour, it is logical that it is exactly these factors that elicit the parental care. Parents who do not react in the appropriate way to the appearance and behaviour of newborns reduce the fitness of their offspring and, therefore, the likelihood of the occurrence of behaviour resembling their own in the next generation. Consequently, parental behaviour that responds to the stimuli emitted by newborns is favored by natural selection in the species in which newborns need such parental care.

B. Behaviour of older offspring that “copies’ some of the newborn’s stimuli may also be favored by natural selection. As can be observed in many species of birds, juvenile offspring sometimes behave like helpless newborns. For instance, a young hungry sparrow that is perfectly capable of flying will, in the presence of a parent, helplessly shake its wings, thus “begging” for food. By “imitating” the first, awkward wing movements of a newly hatched bird, the juvenile induces the parent to behave like a parent and give food. If juveniles that behave in such a manner are better fed than juveniles that do not show such behaviour, then the behaviour that imitates newly hatched birds would become a mechanism that increases the fitness of individuals and, thus, could become common in a species as a result of natural selection.

C. The crying behaviour of humans is favored by natural selection because the behaviour resembles or causes resemblance to some of the stimuli emitted by newborns and, therefore, induces helping behaviour.

Some aspects of this resemblance are as follows:

1. The wetting of the face with tears – compared to the face of the newborn, which is wet with amniotic fluid.

2. The jerking, almost spasmodic respiration of a crying person – compared to the first respiratory efforts of a newborn.

3. The screaming of a crying person – compared to the first screams of a newborn.

4. The closed eyes, the wrinkled skin around the eyes, the spotted coloration of the facial skin, and the open mouth – all are very much alike in a newborn and in a nonneonate who cries.

These similarities between the appearance and behaviour of crying persons and the appearance and behaviour of newborns suggest the explanation mentioned in assumption C. That is, the crying behaviour of humans is favored by natural selection because it resembles or causes resemblance to some of the stimuli emitted by newborns, stimuli that induce the spectator to help the crying person.

This explanation is not contradicted by the fact that the shedding of tears usually takes place for the first time weeks or months after birth. It is not a wild speculation to assume that in the evolution of the shedding of tears, the distribution of scarce food was a major selective factor. However, the influence of the receiving of food on the phylogeny of crying would apply to nonneonates only. The reason is that young babies were nourished solely by means of breast-feeding, and mothers, it is assumed, normally would attempt to feed their newborns. Either a mother was able to provide milk, or, perhaps as a result of severe food shortages, she was not able to do so. In neither case would the shedding of tears make a difference with regard to the baby’s access to milk. Therefore, in the first weeks or months after birth, natural selection would not have favored the shedding of tears.

Literature:

Alexander, R. (1979) Darwinism and Human Affairs. University of Washington Press.

Blom, L. (1984). Een structuur in literatuur over huilen. Unpublished doct. Thesis, University of Amsterdam.

Darwin, C. (1872). The Expression of Emotions in Man and Animals. London: Julian Friedman Publishers (1979).

Frey, W.H. (1980). Not so idle tears. Psychology Today, 13: 91-2.

Frey, W.H. (1982). Crying Behaviour in the Human Adult. Presented August 23 to the Am. Psych. Ass. for symposium Grief and Crying.

Montagu, A. (1959). Natural selection and the Origin and Evolution of Weeping in Man. Science, 139: 1572-3.

Roes, F.L. (1985). Wetten in de Sociale Wetenschappen. Assen / Maastricht: Van Gorcum. (The Netherlands).

This article is based on a section in Roes 1985. I am indebted to Leendert Blom for helping me with literature and for providing suggestions. I presented similar ideas in: "Crying and tears mimic the neonate". Open peer commentary on Soltis, J. "The signal functions of early infant crying", Behavioral and Brain Sciences (2004), 27, 443-490, page 472.

Home