The nature and function of the smile – indeed, of any facial expression – is of interest not only in psychology and the neurosciences, but also in ethology, which is the study of behavior, especially that exhibited in similar form cross-species and which can be explained by Darwinian natural selection (e.g., Andrew Reference Andrew1963; Bolwig Reference Bolwig1964; Eibl-Eibesfeldt Reference Eibl-Eibesfeldt1971).
For example, Morton (Reference Morton1977) showed that avian and mammalian threat and non-threat (appeasement, submission) vocalizations use fundamental frequency (F0) in remarkably similar ways: threat vocalizations have low F0, whereas non-threat vocalizations have high F0. A dog's low-pitched threatening growl and its high-pitched submissive yelp are familiar examples. Morton argued that the modification of F0 conveys to the perceiver an estimate of the body size or maturity of the vocalizer and thus the degree of threat because, other things being equal, body size and maturity are correlated with the mass of the vibrating membrane (vocal cords or syringeal membranes). These deceptions benefit both parties by averting injury (or worse) resulting from actual combat.
I demonstrated that this “frequency code” applies to human speech as well: the degree of perceived dominance is inversely correlated with voice F0 (Ohala Reference Ohala1984). Furthermore, this accounts for well-documented common cross-linguistic pattern (some would say “universal”) that questions, uncertainty, and pleading are marked by a high F0 somewhere in the utterance (when these intentions are not indicated by lexical, morphological, or syntactic means). In addition, I hypothesized that the frequency code helps to resolves a long-standing puzzle about the mouth shapes accompanying threat and non-threat displays in species having plastic (i.e., movable) facial masks: canids and primates, including humans. An open-mouth and retracted lip corners is found in non-threat displays, as opposed to more protruded, rounded lip shape in threat displays. Why in non-threat should more teeth – potential weapons – be displayed in contrast to fewer teeth showing in a threat display (Izard Reference Izard1971)? The frequency code explains these dichotomous facial expressions, too: These different lip configurations will modify the resulting resonances of an accompanying vocalization in a way to convey to the perceiver an impression of a vocalizer with shorter or longer vocal tract This, I argue, is the origin of the smile. Via the well-known process of ritualization, the smile can be given without an accompanying vocalization or even with a closed mouth. This analysis meets the condition of coherence and generality in ethological explanations advocated by Darwin (Reference Darwin1872, p.18): “whether the same principle by which one expression can, as it appears, be explained, is applicable in other allied cases; and especially, whether the same general principles can be applied with satisfactory results, both to man and the lower animals.” Thus, consider a case most of us are familiar with: a submissive dog. The vocalization has a high F0, high resonances (due to mouth corner retraction), ears flattened, no bristling of the hair on the back, tail between the legs, crouching posture – the latter elements all designed to make the animal seem as small as possible. A dog's threat display is just the opposite.
That modification of the vocal anatomy is important in conveying an impression of size is reinforced by the fact that, besides the plastic modification of the vocal structures, there are implastic modifications evident in the sexual dimorphism in the adult vocal tract. The mature human male has a longer vocal tract than the female (by some 15 to 17%) – this is accomplished by the familiar descent of the larynx starting at puberty – and the male's vocal cords become fully 50% longer – but probably 100% more massive than the female's. The first modification accounts for the quantitatively different resonances of the “same” vowels as spoken by adult males and females. The latter modification accounts for the typical one octave difference in males' and females' average speaking F0. The longer vocal cords, by the way, are bought at the cost of enlargement of the laryngeal cartilages in the male, resulting in a prominent “Adam's apple.”
Numerous other species – from whooping cranes, geese, and the howler monkey – show sexually dimorphic aspects of the vocal anatomy which testify to the importance of vocalization in agonistic encounters, in sexual selection, and so on. Thus, enhancement of various aspects of adult males, human and nonhuman, gives rise to such sexually dimorphic aspects as the human male's beard, the male lion's mane, and the size dimorphism between male and female elephant seals, and the like. Size does matter.
What does all this imply for the target article by Niedenthal et al.? Just this: If, as I have argued, a smile is intended by the smiler to induce a reaction or response in the perceiver that is favorable to the smiler, then the authors' contention that “observers of smiles sometimes construct an embodied simulation of the nuanced affective state conveyed by the smile” (introduction, para. 3) is undermined. My view is similar to that espoused by the “functionalist” approach to the analysis of the outwardly visible states – call them “emotions” if one will (Campos et al. Reference Campos, Mumme, Kermoian and Campos1994). One must differentiate between (a) inner neurophysiologic states – which, to further the interests of the one experiencing these states, often would be best kept secret – although in some cases uncontrollable cues to such states may inadvertently “leak out,” for example., sweating, tremor, blushing, sexual arousal; and (b) signals such as smiles, frowns, threatening looks, and vocalizations, which are made in order to induce a targeted reaction/response in the perceiver – that is, a response favorable to the one emitting the signal. Ethology teaches us: stereotyped behavior – and this includes signaling – is generally done to benefit the individual or group exhibiting it. Such signals are not, strictly speaking, cooperative.
The nature and function of the smile – indeed, of any facial expression – is of interest not only in psychology and the neurosciences, but also in ethology, which is the study of behavior, especially that exhibited in similar form cross-species and which can be explained by Darwinian natural selection (e.g., Andrew Reference Andrew1963; Bolwig Reference Bolwig1964; Eibl-Eibesfeldt Reference Eibl-Eibesfeldt1971).
For example, Morton (Reference Morton1977) showed that avian and mammalian threat and non-threat (appeasement, submission) vocalizations use fundamental frequency (F0) in remarkably similar ways: threat vocalizations have low F0, whereas non-threat vocalizations have high F0. A dog's low-pitched threatening growl and its high-pitched submissive yelp are familiar examples. Morton argued that the modification of F0 conveys to the perceiver an estimate of the body size or maturity of the vocalizer and thus the degree of threat because, other things being equal, body size and maturity are correlated with the mass of the vibrating membrane (vocal cords or syringeal membranes). These deceptions benefit both parties by averting injury (or worse) resulting from actual combat.
I demonstrated that this “frequency code” applies to human speech as well: the degree of perceived dominance is inversely correlated with voice F0 (Ohala Reference Ohala1984). Furthermore, this accounts for well-documented common cross-linguistic pattern (some would say “universal”) that questions, uncertainty, and pleading are marked by a high F0 somewhere in the utterance (when these intentions are not indicated by lexical, morphological, or syntactic means). In addition, I hypothesized that the frequency code helps to resolves a long-standing puzzle about the mouth shapes accompanying threat and non-threat displays in species having plastic (i.e., movable) facial masks: canids and primates, including humans. An open-mouth and retracted lip corners is found in non-threat displays, as opposed to more protruded, rounded lip shape in threat displays. Why in non-threat should more teeth – potential weapons – be displayed in contrast to fewer teeth showing in a threat display (Izard Reference Izard1971)? The frequency code explains these dichotomous facial expressions, too: These different lip configurations will modify the resulting resonances of an accompanying vocalization in a way to convey to the perceiver an impression of a vocalizer with shorter or longer vocal tract This, I argue, is the origin of the smile. Via the well-known process of ritualization, the smile can be given without an accompanying vocalization or even with a closed mouth. This analysis meets the condition of coherence and generality in ethological explanations advocated by Darwin (Reference Darwin1872, p.18): “whether the same principle by which one expression can, as it appears, be explained, is applicable in other allied cases; and especially, whether the same general principles can be applied with satisfactory results, both to man and the lower animals.” Thus, consider a case most of us are familiar with: a submissive dog. The vocalization has a high F0, high resonances (due to mouth corner retraction), ears flattened, no bristling of the hair on the back, tail between the legs, crouching posture – the latter elements all designed to make the animal seem as small as possible. A dog's threat display is just the opposite.
That modification of the vocal anatomy is important in conveying an impression of size is reinforced by the fact that, besides the plastic modification of the vocal structures, there are implastic modifications evident in the sexual dimorphism in the adult vocal tract. The mature human male has a longer vocal tract than the female (by some 15 to 17%) – this is accomplished by the familiar descent of the larynx starting at puberty – and the male's vocal cords become fully 50% longer – but probably 100% more massive than the female's. The first modification accounts for the quantitatively different resonances of the “same” vowels as spoken by adult males and females. The latter modification accounts for the typical one octave difference in males' and females' average speaking F0. The longer vocal cords, by the way, are bought at the cost of enlargement of the laryngeal cartilages in the male, resulting in a prominent “Adam's apple.”
Numerous other species – from whooping cranes, geese, and the howler monkey – show sexually dimorphic aspects of the vocal anatomy which testify to the importance of vocalization in agonistic encounters, in sexual selection, and so on. Thus, enhancement of various aspects of adult males, human and nonhuman, gives rise to such sexually dimorphic aspects as the human male's beard, the male lion's mane, and the size dimorphism between male and female elephant seals, and the like. Size does matter.
What does all this imply for the target article by Niedenthal et al.? Just this: If, as I have argued, a smile is intended by the smiler to induce a reaction or response in the perceiver that is favorable to the smiler, then the authors' contention that “observers of smiles sometimes construct an embodied simulation of the nuanced affective state conveyed by the smile” (introduction, para. 3) is undermined. My view is similar to that espoused by the “functionalist” approach to the analysis of the outwardly visible states – call them “emotions” if one will (Campos et al. Reference Campos, Mumme, Kermoian and Campos1994). One must differentiate between (a) inner neurophysiologic states – which, to further the interests of the one experiencing these states, often would be best kept secret – although in some cases uncontrollable cues to such states may inadvertently “leak out,” for example., sweating, tremor, blushing, sexual arousal; and (b) signals such as smiles, frowns, threatening looks, and vocalizations, which are made in order to induce a targeted reaction/response in the perceiver – that is, a response favorable to the one emitting the signal. Ethology teaches us: stereotyped behavior – and this includes signaling – is generally done to benefit the individual or group exhibiting it. Such signals are not, strictly speaking, cooperative.