“Humanity is another corporeity”: The evolution of human bodily appearance and sociality

Abstract

Some accounts of human distinctiveness focus on anatomical features, such as bipedalism and brain size. Others focus on cognitive abilities, such as tool use and manufacture, language, and social cognition. Embodied approaches to cognition highlight the internal relations between these two groups of characteristics, arguing that cognition is rooted in and shaped by embodiment. This paper complements existing embodied approaches by focusing on an underappreciated aspect of embodiment: the appearance of the human body as condition of human sociality and cognition. I approach this issue through Merleau-Ponty’s understanding of the animate body as an intertwining of perceiving and perceivable aspects. The eye is both an animal’s embodied, perceptual openness onto the world, and the means by which that experiential openness can be perceived by others. The morphology and appearance of its embodiment condition how an animal comes to understand others and itself as animate subjects. I interpret the perceivable appearance of the human eye and skin in comparison with those of other animals. An underappreciated dimension of human distinctiveness, I argue, is the way the human sense organs render human perceiving comparatively more perceivable to conspecifics.

1 Introduction

A survey of discussions of the human species’ uniqueness and evolution will turn up a handful of common motifs. Classically, Aristotle and the tradition he inaugurated viewed the human being as the rational animal, a determination echoed with slight variation in Linnaeus’ official baptism of the species as Homo sapiens. A closely associated group of views, espoused in various forms by such prominent thinkers as Heidegger (1982) and Chomsky (Berwick & Chomsky, 2015), sees language or symbolism as the core of human cognition and distinctiveness. Material culture and its corelated cognition are part of the story, too, with Bergson (2022), McLuhan (1994), and, more recently, Malafouris (2013) all contributing to the human self-portrait as an animal capable not only of tool use, manufacture, and meta-use, but also of self-transformation through its instruments. Meanwhile, in recent decades, the emphasis has shifted to seeing distinctively human forms of sociocultural cognition as providing the foundation for all of the above determinations (Dunbar, 2016; Dunbar et al., 2014; Gamble et al., 2014; Tomasello, 2014, 2019). According to these views, it was the demands of developing a complex, cooperative sociality that drove developments in hominin brain size, social cognition, and social behavior, in contrast to the more competitive sociality of chimpanzees.

Ever since Darwin’s The Descent of Man (1871) placed the human being in an evolutionary context, paleoanthropology has offered an increasingly detailed account of the development of the anatomy of Homo sapiens and its hominin ancestors since speciation from the last common ancestor with other great apes. Hominins developed bipedalism, a fully opposable thumb, a descended larynx, a proportionately large brain, and a more gracile form. But what is the relationship between these two parallel understandings of human distinctiveness, the anatomical and the psychological? Advocates of the cognitive and cultural accounts of human distinctiveness tend to regard these physical characteristics as being of secondary importance. Dunbar, for example, views anatomical distinctiveness as the least interesting of the differences between human beings and other great apes (2016, p. 17). At best they are necessary conditions for the development of a distinctively human mind. On an intellectualist understanding of language, for example, the physiology of speech is merely the mechanism of execution for an intellectual ability that is intrinsically independent of its exercise. The motor performance of speech does not itself constitute part of cognition. Surely, the intellectualists say, we miss the point of human distinctiveness if we attempt to define the human as a “featherless biped,” to revive Diogenes of Sinope’s old joke (Diogenes Laertius, 2018, p. 279). Even Merleau-Ponty, a strong proponent of an embodied approach to the mind, will grant that “humanity is not produced as an effect through our articulations or through the way our eyes are implanted in us” (2007, p. 355).

I will argue, however, that there is a more intimate connection between what at first glance may look like mere anatomical curiosities and characteristically human cognitive capacities. Of course, the praise of the human hand as an exemplary organ of thought dates back at least to Aristotle. And with the rise of 4e approaches to cognition, the recognition of the importance of embodiment for understanding human cognitive evolution has increased (Barrett, 2018; Barrett et al., 2021; e.g., Gallagher, 2017b ch. 9; Wynn et al., 2021). But while recent approaches emphasize the role of the body in perceiving and acting insofar as these condition or constitute cognition, my emphasis is different. I will focus on distinctive characteristics of the human body insofar as it is perceived, acted with and acted upon. These characteristics are central to our ways of perceiving and acting, mediating the circuit of perceiving-and-acting-together whose distinctive structures and pervasiveness in human life are characteristic of the species. I am interested in the human body, then, not as it is experienced in the first person, but as it is given in the second and third person, the expressive morphology and appearance of the human social body. It is this body that serves as the interface of human culture and sociality, and the orientation point of cognition, experience, and behavior. The appearance of the human body mediates everything else that we think of as distinctively human. But the adaptiveness of its distinctive characteristics for this purpose has not been fully appreciated.

The oversight is all the more striking when we consider just how curious the appearance of the human animal is. Comparatively fatty and proportionately feeble among the great apes, posed precariously on two limbs, naked and defenseless by nature (as the Prometheus myth portrays it), but compensating with an almost endless array of motley adornments and imaginative prostheses, this creature is truly a sight to behold – for all who have eyes to see and hands to hold.

To get the distinctive morphology and appearance of the human social body into view, we require a suitable framework for its interpretation. I propose that a sketch for such a framework can be found in a late lecture course of Merleau-Ponty (2003). In it, he outlined an approach to the comparative and evolutionary understanding of the human body that he called esthesiology. I begin by elaborating this approach (Sect. 2). I then apply it to distinctive characteristics of the human eye and skin (Sects. 3 and 4). These morphological characteristics would not serve their social function, however, if human behavior was not also driven by distinctive motivations (Sect. 5). I close by considering some consequences of the esthesiological approach and how it can be further developed (Sect. 6).

2 The morphology of humanity: Merleau-Ponty on esthesiology and evolution

In “Eye and Mind,”¹ Merleau-Ponty writes,

If our eyes were made in such a way as to prevent our seeing any part of our body, or if some diabolical contraption were to let us move our hands over things while preventing us from touching our own body—or if, like certain animals, we had lateral eyes with no intersection of visual fields, this body, which would not reflect itself, would not sense itself, this nearly adamantine body, which would not be entirely flesh, would not be a human body, and there would be no humanity. (EM 355)

Merleau-Ponty is here alluding to analyses of embodiment and the experience of others that he and other phenomenologists have elsewhere developed in greater detail.² Our bodies have both an experiential, “interior,” first-personal aspect; and a thing-like, “exterior,” third-personal aspect. My body is that singular locus where my experience discloses the world, the opening of my seeing and touching onto the world, others, and myself. At the very same time, my body is also a thing in the world, in some respects on a par with other objects and other animate bodies I can perceive. My body is a sensing thing, a space of perceptual, kinesthetic, and affective sensation; and it is a sensible thing, a possible object of sensation for others’ sensing, made up of the same sensible stuff as the rest of the sensible world. It is a sensing-sensible, and in animal embodiment these two aspects are intimately intertwined.

Unlike the imagined variations on animal embodiment entertained in the passage just cited, in a typical human body there is reflexivity of the sensing upon the sensible: I can touch and see my own sensing-sensible body. I can even perform a sort of Gestalt switch of its sensing and sensible aspects. At one moment, I can sense the world through my left hand, touching some object with it. In the next moment, I can touch my left hand with my right and experience it – myself – as sensed, as a sensible thing in the world like others. I can thus establish a sort of visual, tactile, and kinesthetic map of the coordinates of the sensing and sensible aspects of my body. The reflexivity of the sensing and the sensible aspects of my own body allows me to discover their reversibility: My hand is in one moment an organ of experiencing (something sensing), in the next an organ experienced (something sensible).

According to Merleau-Ponty, it is because of this reflexivity and reversibility of my own sensing-sensible bodily self that I can experience others as animate, sensing creatures like me. This constitutes the most basic, “esthesiological” (Merleau-Ponty, 1964b, p. 168) mode of what phenomenologists call empathy, or what is sometimes now called direct social perception (Krueger, 2018). I immediately perceive the expressive appearance, the sensible aspect of the other’s body. But because that body is so much like my own, and because of the intimate intertwining and association of the sensing and the sensible that I am familiar with in my own body, I experience the other’s sensible body as likewise lined by a sensing aspect. I perceive the sensible hand of the other, so much like my own, also as an organ of sensing. In Husserl’s (1960) terminology, there is a perceptual-analogical “pairing” of my own body with the other’s that elicits empathy, my feeling into (Einfühlen) the other, at least on this minimal, esthesiological, pre-reflective level of experiencing the other as a sensing, self-moving, animate being like myself. The reflexivity and reversibility of my own sensing-sensible body thus allows me to experience the bodies of others as having the same characteristics as mine. I experience their bodies and my own as involved in a matrix of intercorporeity, a shared space in which our sensing bodies open onto one another and a shared world. This basic level of social perception of others is precocious and presumably widely distributed among at least the higher animals. Among humans, it is the foundation for a distinctively intersubjective, interpersonal form of life.³

The precise nature of this basic, direct, bodily experience of the other, and its relation to other modes of social understanding, is much debated in contemporary scholarship on empathy and social cognition (Gallagher, 2017a; Krueger, 2018; Maibom, 2022; Zahavi, 2014). I will accept for present purposes that this account of esthesiological empathy is more or less correct. Still, the passage quoted above from “Eye and Mind” calls for further elaboration. For while Merleau-Ponty maintains that this reflexivity of the sensing-sensible body is a necessary condition for humanity, his description certainly falls short of providing sufficient conditions for humanity and distinguishing the human body among other animal bodies. For the bodies of many other animals also exhibit this reflexivity and reversibility. The visual fields of their two eyes converge, and they can see and touch their own sensing-sensible bodies. Yet presumably they do not participate in “humanity,” whatever that may mean in this context.

Merleau-Ponty is aware of the problem. He insists that humanity “is not produced as an effect through our articulations, or through the way our eyes are implanted in us” (EM 355). What, then, does distinguish the human body from nonhuman animal bodies? Merleau-Ponty’s answer in “Eye and Mind” is the following:

A human body is present when, between seeing and visible, between touching and touched, [i.e., between sensing and sensible], between one eye and the other, between the hand and the hand a kind of crossover is made, when the spark of the sensing-sensible is lit, when the fire starts to burn that will not stop burning until some accident of the body unmakes what no accident would have sufficed to make....⁴

This statement goes beyond the previous one in suggesting a sufficient condition for a human body (“A human body is present when”). Yet its description of that condition is poetic rather than literal. In the absence of a further elaboration of the “kind of crossover” at issue here, or of the “spark of the sensing-sensible,” we are left wondering why exactly Merleau-Ponty claims to be describing a specifically human body rather than just animate, reflexive bodies more generally.

Fortunately, we can locate further resources in Merleau-Ponty for pursuing this question. Just prior to his work on “Eye and Mind” in the summer of 1960, Merleau-Ponty delivered a lecture course in the 1959–1960 academic year at the Collège de France titled “Nature and Logos: The Human Body” (N 200 ff.; cf. 1970, p. 124–131). In this course, Merleau-Ponty attempts to understand the distinctiveness of the human body within the family of higher animals more generally, which he had discussed in a preceding course (N 123 ff.). He may have had the efforts of “Nature and Logos” in mind when writing the passages quoted above from “Eye and Mind.”

Merleau-Ponty states that the goal of “Nature and Logos” is to understand humanity by focusing on the evolutionary emergence of the human body (N 208). Classical approaches in philosophy have neglected the importance of humanity’s inherence in a natural, animal body by centering and grounding their accounts on consciousness, freedom, thought, language, rationality, and the like. To some extent, this statement also applies to certain tendencies of classical authors in the phenomenological tradition, such as Husserl and Sartre, and perhaps even to those of Merleau-Ponty’s own earlier writings. Merleau-Ponty worries that such approaches neglect a fundamental characteristic of our human being and hence risk misleading us in our quest for self-understanding (2008, p. 52 f.). By contrast, he emphasizes that “human being is not animality (in the sense of mechanism) + reason.—And this is why we are concerned with the human body: before being reason, humanity is another corporeity.”⁵ The approach Merleau-Ponty proposes for understanding this “other corporeity” is through the study of the evolution of the human body insofar as the body implies and conditions the mind. We must attempt to see the gradual emergence, as though through the backside of a sheet of paper⁶, of the human variation on animal embodiment and experience.

To this end, “Nature and Logos” proposes an esthesiology (Kee, 2023). Merleau-Ponty describes this variously as “the study of this miracle that is a sense organ” (N 209) or the “study of the body as a perceiving animal” (1970, p. 128). While Merleau-Ponty does not elaborate his notion of esthesiology in detail, we can reconstruct the framework from the context of “Nature and Logos” and surrounding texts. To begin, the esthesiological study of the body views the body as an intertwining of sensing and sensible aspects. As discussed above, my eye is both a sensible, visible thing within the world, while it is also my sensing, seeing openness onto the world and other things. These two aspects of embodiment are intimately interwoven. At the same time, precisely because it is the intertwining of sensing and sensible, a sense organ is the locus of the intertwining of something sensible and something that in principle cannot be sensed by everyone. Strictly speaking, I do not see the other’s seeing when I look into her eyes in the same way that she herself experiences her seeing, or in the same way that I see her eyes. In a more classical idiom, one that Merleau-Ponty will attempt to problematize, we might say that the sensible eye is on the “outside,” while the seeing occurs in an “inner,” mental space. Nonetheless, there is a sense in which the other’s seeing is visible to me. Her eyes and overall bodily comportment exhibit (albeit imperfectly and fallibly) that and what she is seeing. And because of the tight association of the sensible and sensing aspects within my own body, in my empathic, intercorporeal experience of another animate body, the other’s sensing is also experienced. The other’s seeing is “appresented,” or “co-given,” as Husserl would put it, in my perception of her visible eye as an organ of vision. As Merleau-Ponty puts it, the sensible body of another sensing being, its sense organs, provide the “original presentability of what is as such not originally presented.”⁷ Or, in the preferred terminology of his late writing, the body offers us the visibility of something invisible (N 209) through this intimate entangling of the sensible and the sensing, the inner and the outer. For present purposes, I will refer to this intertwining in an animate body of the inner and the outer, the invisible and the visible, the sensing and the sensible, with Merleau-Ponty’s term of art: flesh. Esthesiology is the study of the flesh.⁸

Esthesiology, and phenomenological accounts of empathy more broadly, thus conflicts with accounts that emphasize theorizing, inference, or explicit simulation (Gallagher, 2007; Zahavi, 2014), while the relationship with accounts that emphasize bodily resonance, motor mimicry, or “mirror neurons” is up for debate (Fuchs, 2018; Fuchs & de Jaegher, 2009). In later sections of this paper, I will draw on empirical studies from researchers who endorse alternative theoretical perspectives and terminologies. Where I do, I will rephrase their findings in the terminology of esthesiology.

It is crucial to Merleau-Ponty’s esthesiology that our animate, perceiving bodies are open onto one another as animate, perceiving bodies. This is true of all sentient animal bodies, as we will see in the following sections. However, given the human being’s high degree of sociality and its extraordinary dependence upon conspecifics and culture⁹, it would seem likely that our bodies have evolved to be cooperative, communicative, and prosocial in exemplary ways and to a correspondingly high degree. Here we may consider Merleau-Ponty’s attention to Adolph Portmann’s studies of the appearance of animal bodies (N 186–190; Portmann, 1967). Portmann stresses that the outer aspect of animal bodies does not merely serve basic functions of vital preservation (e.g., protection, thermoregulation), but also serves a communicative, expressive role that is equally important for an animal’s intra- and interspecies social relations. The animal’s appearance contains “a reference to a possible eye” (N 187). For example, the leopard’s spots camouflage it in its environment to the dichromatic vision of its prey (though not as effectively to human trichromatic vision). And animals that are capable of detecting polarized light, such as cephalopods, emit polarized light signals from their bodies to communicate with one another (Marshall et al., 2019). Merleau-Ponty draws the following insights from Portmann’s studies:

We do not have the right to consider the species as a sum of individuals exterior to one another. There are as many relations among animals of one species as there are internal relations among every part of the body of each animal. The fact that there is a relation between the exterior aspect of the animal and its capacity for vision seems to prove it: the animal sees according to whether it is visible. […] [There is] a specular relation between animals: each is the mirror of the other. […] What exists are not separated animals, but an inter-animality. (N 189)

Merleau-Ponty applies Portmann’s insights into animal bodies in general to his investigations into the human body. He emphasizes that the human body, too, is an “organ of the for-other” (N 210, 218), an “organ of communication” (225), or an “organ to be seen/of being seen [organ à être vu]” (273).

Incorporating his interpretation of Portmann into his esthesiology, Merleau-Ponty has a powerful theoretical framework for executing his project of understanding the human species as having evolved “another corporeity.” However, in the surviving sketches of “Nature and Logos,” Merleau-Ponty in fact offers little discussion of concrete details of human sense organs to realize the programmatic promise of his esthesiology. We do not have a fully preserved transcript of the “Nature and Logos” lectures, so we cannot know for certain how far Merleau-Ponty was able to develop his esthesiology there. His untimely death the following year meant that he did not conduct this line of thinking further. In any case, in comparison to the present day, research in evolutionary anthropology, and comparative studies of the bodily appearance, social behavior, and sensory capabilities of human and nonhuman animals was still in its early stages in Merleau-Ponty’s time. We now have a greater number of relevant studies of human and nonhuman animals. In the following sections, I will interpret and integrate some of these findings through Merleau-Ponty’s esthesiology. This will allow us to further develop and potentially corroborate Merleau-Ponty’s approach, and to see how fruitful it proves for integrating and interpreting findings from the relevant disciplines and suggesting new paths of inquiry.

3 The eye and dehiscence: human vision and its visibility

Let us begin our concrete esthesiological investigation by focusing on the human eye, in both its seeing and seeable aspects (cf. Kee, 2023).

Human daytime vision is unmatched among mammals and among the best in the animal kingdom (Caves et al., 2018; Land, 2014). Only birds of prey have significantly better daytime acuity, though with a significantly narrower binocular field.¹⁰ Trichromatic vision is also rare among mammals, but several primate species including humans enjoy it (a not insignificant fact for interpreting the evolution and function of visible human skin, as we will see in the following section).

But our remarkable powers for seeing would not contribute to the interspecular relations between human beings if that seeing were not also exceptionally seeable to other seers. In this respect, too, the human eye is distinctive. To understand how, let us extend Merleau-Ponty’s thought experiment from “Eye and Mind,” where he imagined variations on the morphology of the esthesiological body. We might imagine that the morphology of human vision was such that our faces were covered by a one-way mirror, allowing us to see but not for our eyes to be seen. Or again, if we had the compound eyes of invertebrates, our eyes would appear as matrixed screens, offering little more information about our visual orientation than our ears offer concerning auditory orientation. Would humans have the way of life we are familiar with if such eyes were typical of the species?

In contrast to such possible variants, the human eye is an “organ of the for-other.” Its external appearance renders vision visible. The human eye exhibits starker chromatic contrasts than those of other mammals, including those of our closest relatives, between pupil, iris, sclera, and the surrounding skin. Human eyes protrude more from the skull and the orifices are more horizontally elongated. The placement within the skull is more horizontal than in other primate species, while still being firmly frontally placed, allowing both for a wide binocular field of vision and for the two eyes to be visible simultaneously from a broad frontal field. These visible features facilitate eye-tracking, which humans rely on in nonverbal communication and which infants use to support first language acquisition. The cooperative eye hypothesis (Kano, 2023; Kano et al., 2022; Kobayashi & Kohshima, 1997, 2001; Tomasello et al., 2007) proposes that the morphology of the human eye has evolved under selective pressure to facilitate cooperative social engagements. By contrast, chimpanzees rely primarily on head movements. It has been hypothesized that their more occluded eye morphology conceals gaze direction and evolved under selective pressure of a more competitive social environment (but cf. Clark et al., 2023). While the human eye is not the only cooperative eye in the animal kingdom (Ueda et al., 2014), it is communicative to an exemplary degree. Its visible morphology facilitates communication and cooperation by rendering human seeing more seeable than other possible and actual animal eyes would.

The morphology and movements of the human eye exhibit not only our perceptual directedness. They also communicate something about our affective and even cognitive state. Changes in pupil size correlate with changes in emotion, mood, and attention (cf. Portmann, 1967, p. 194 f.). Fearful eyes can be identified from the contrast between iris, sclera, and surrounding skin alone, even in the absence of further visual clues (Jessen & Grossmann, 2014). More complex emotions can be differentiated from the eyes, eyebrows, and surrounding facial muscles alone (Baron-Cohen et al., 2001). The absence of fur or dense hair on the skin surrounding the eyes (apart from the eyebrows, which also facilitate communication) is also unusual among mammals and serves communication, a point to which we will return below. The human eye even has a means of turning something of its literal inside out to express emotion: crying (Vingerhoets, 2013).¹¹

Returning to the central concepts of our esthesiology, then, we can see that the human eye is the locus of an internal relationship between sensible (visible, touchable) and sensing (vision) aspects of the flesh. Insofar as this sensing is in one sense visible (as the gaze of the communicative eye) and in another sense invisible (strictly speaking, no one else can access my seeing in the same way that I do), this organ is at the same time the locus of an internal relationship between something visible and outer, and something invisible and inner. While this is true, strictly speaking, of the visual organ of other animals, the human visual organ is remarkable in the extent to which its sensible aspect overtly manifests its invisible, sensing aspect.

To borrow an image that Merleau-Ponty will employ elsewhere, we can say that the human visual organ is exemplarily dehiscent.¹² In botany, dehiscence is the splitting or bursting open of an exterior structure (e.g., a seed pod) allowing that structure’s internal contents (e.g., seeds) to be dispersed. In medicine, dehiscence is the reopening of a closed wound. In the sense in which I am currently using the term, dehiscence refers to the exposure of a sensible-sensing organ such that what is typically understood to be on the “inside” and hence invisible (i.e., sensing) is exhibited on the visible, sensible “outside” surface of an animal body. Through the intertwining of the sensing and sensible in the body, sensing is dehiscent, bursting forth and presenting itself within the sensible world. The same is true of the bodily displays and expressions of affectivity (e.g., tears, cries, blushes), and, to a lesser extent, of our cognitive life. This dehiscence is a necessary condition for the reflexivity of the body discussed in the previous section. If my sensing were not sensibly manifest, it could not close its own open circuit back upon itself.

Human beings’ highly social, interdependent, cultural mode of life requires that we form strong social bonds, coordinate our flexible, complex behaviors, and impart cultural knowledge to one another to be viable as a species. Achieving all of this throughout different stages of ontogeny requires that our bodies be adapted to display our sensorimotor intentions and emotional states to one another. The need would have been all the greater if, as many researchers believe, there were significant periods of human evolution during which complex social coordination and communication occurred without language, and if language itself first evolved in the visual-manual modality before being transferred to speech. The morphology of the human eye is a glaring example of how well adapted the outward appearance of our body is to our species’ need for social, interspecular relations. The cooperative eye hypothesis provides a good starting point for esthesiology, since it has been extensively studied and there is some consensus (though not without some controversy and disagreement about details – see Kano, 2023; Clark et al., 2023) that this trait evolved under selective pressure to facilitate social communication and cooperation. The esthesiological framework allows us to interpret and integrate the various above observations concerning the sensible appearance of the human eye, understood as an organ of the for-other. It would be strange, however, if the morphology of the eye was the only feature of our bodily appearance upon which this selective pressure to facilitate cooperation has operated – if we had only cooperative eyes and not cooperative bodies more generally. Strangely, though, in the twenty years since the initial proposal of the cooperative eye hypothesis, thinking about the cooperative body has remained sequestered in ocularcentrism.¹³ As we will see in the following section, the esthesiological framework can be applied to other sense organs as well, where it might suggest further novel interpretations and hypotheses.

4 The naked ape: the cooperative skin hypothesis

The discussion in the previous section of the dehiscent, expressive, sensing-sensible human eye already began to expand beyond the ocular sense organ to encompass the visibility of the surrounding facial features (skin, muscles, eyebrows). These are also sensible aspects of our body that exhibit something of our inner, sensing life. If we are convinced that the outward appearance of the human eye has evolved to be a more dehiscent anatomical structure, then we might also venture by analogy that this is true of other sense organs, sensible features of the body, and, indeed, of the human body as a whole. Thus, esthesiology predicts that the skin, for example, has evolved to serve a social, communicative purpose, to render its sensing more sensibly apparent and available to conspecifics. Call this the cooperative skin hypothesis. When we consider morphologically, esthesiologically distinctive features of the human skin, the first and most conspicuous trait to consider is the comparative nudity and exposure to vision and touch of the furless human skin. The human being is a naked ape. Where the insect has its exoskeleton, the fish and reptile their scales, the bird its feathers, and (most) other mammals their pelts, the human body stands out for its near nudity. In skin as in eye, the human body is exemplarily dehiscent.

We must stress at the outset that the cooperative skin hypothesis is not mutually inconsistent with other proposed explanations of human furlessness, such as the thermoregulation hypothesis, which is supported by considerable evidence and a degree of consensus.¹⁴ Further, the cooperative skin hypothesis comes in varying strengths. Its strongest versions hold that social factors were (among) the strongest selective pressures influencing the loss of hominin body hair and other specific morphological features of the skin. Its weakest version holds simply that, whatever the factors that initially led to fur loss, this and other skin traits were later coopted for their social potential. In between are moderate versions of the hypothesis, which hold that social factors were among the selective pressure shaping human skin morphology, though perhaps not the original or strongest ones. Further, one may endorse stronger or weaker versions of the hypothesis with a greater or lesser degree of conviction. Given that, to my knowledge, the cooperative skin hypothesis has not previously been advanced, I consider it a reasonable goal in the present context if I can convince a reader with the relevant background knowledge in human evolution that a moderate version of the cooperative skin hypothesis is plausible and worthy of further consideration, and that the esthesiological framework proposes original, testable hypotheses for its investigation.

The considerations I will offer in support of the cooperative skin hypothesis concern the visible and touchable characteristics of the human skin. While I believe the visible characteristics of the skin may be significant for understanding the evolution of hominin sociality, the skin’s touchable features probably provide the stronger evidence.

4.1 Visible skin

Before considering more direct support for the cooperative skin hypothesis within the hominin lineage, however, let us take one last sideways glance to the primate taxon as a whole. Here we find at least one striking example of the efficacy of social sensing abilities to shape the dehiscent, sensible appearance of skin and hair. There is a strong correlation among primate species between trichromatic color vision and loss of facial fur (and sometimes rump fur) (Changizi et al., 2006). Primate species with trichromatic vision are highly unusual among mammals in this respect, but not all primates are trichromats. Many are dichromats, like most other mammals. Further, the chromatic sensitivity of the three color-sensitive cells in primate eyes is not equally distributed, as it is in many other tri- and tetrachromatic animals (Hiramatsu et al., 2017) and as would seem most effective for general color vision. Instead, the specific sensitivity of primate trichromatic vision is nearly optimally tuned to detect variations in blood oxygen and saturation levels in the skin. The leading hypothesis for explaining this is that primate color vision evolved, or has been fine-tuned, to be especially sensitive to social signals exhibited in the skin of conspecifics. These modifications are regulated by blood in the face and may indicate an animal’s mood or state (e.g., blushing in humans, or displays of anger or sexual receptivity in nonhuman primates). Having acquired the visual ability to detect such modifications in the skin, trichromat primates may have lost the fur on their faces or rumps to further exploit this visual ability.¹⁵,¹⁶

We say of a person who openly expresses their emotions that they wear their heart on their sleeve. They put what is usually on the inside on the outside. They make their sensing sensible to others. Where the combination of dehiscent skin and primate color vision is concerned, the metaphor is almost literal. We show our hearts on our skin, in the affective dehiscence of primate flesh. Furless skin reveals something of what the blood and heart beneath are doing, and this indicates something of an animal’s underlying physiological and affective state.

Extending this line of thinking we may ask, if some primate species lost some hair to facilitate sociality, might not ancestral hominins have lost even more fur for the same general purpose, as the stronger version of the cooperative skin hypothesis suggests? To further motivate this suggestion, we must consider the various ways in which the visible and touchable characteristics of furless skin might have been more conducive than furred skin to the epistemic and affective demands of complex, cooperative hominin sociality.

Consider the importance of being able to discern the detail and intention of conspecifics’ actions for the human cultural and social lifeform. Throughout our lifespans, but especially in early development, human beings learn by seeing and imitating. Indeed, not only can we discern to a high degree what another human being is up to on a basic, sensorimotor level through simply observing their body in action. We can sometimes even determine what someone’s distal action intention is just from observing an initial action. For example, an observer can tell if an object was grasped with the intention to eat it, throw it, or hand it to someone else, just by observing the initial grasping approach of the hand and arm (Ansuini et al., 2014; Becchio et al., 2018). Though we do not entirely understand how it is achieved, this ability presumably depends on the specific visibility of the body, especially the important kinematic markers of the joints of the fingers, hand, wrist, and elbow. Animal bodies are kinetically dehiscent, exhibiting their internal, kinesthetic sensing on their visible, kinematic exterior. We also rely on the visible articulations of the human body to discern the signs of the deliberately communicative body. Our bodies are deictic (e.g., pointing), iconic (pantomime), and symbolic (sign language) signing systems (to follow Peirce’s (1868) classification of signs, as Tomasello (2008, 2014) does). But these signs are only as useful as their visibility for the vision that sees them.

I am not aware of any comparative kinematic studies that corroborate the cooperative skin hypothesis, and designing a study that was not species-biased would no doubt be a challenge. Nonetheless, it seems at least highly plausible that the morphological peculiarities of the comparatively furless human body facilitate our ability to read bodily affects, actions, intentions, and signs, and that these traits may well have evolved or been refined under selective pressure to facilitate such cooperative sociality. Indeed, it may not only be furlessness as such that contributes to this dehiscence of the human skin, but even the specific pigmentation patterns of the human hands and fingernails. Humans are unusual among primates in having little or no pigmentation on the palms of the hands and soles of the feet, and unique in having unpigmented finger- and toenails in adulthood.¹⁷ The result is an amplified contrast of the articulations of the hands, making them more visible against the rest of the body¹⁸, against dark backgrounds, and in dim lighting (e.g., firelight) conditions. This allows us to see the hands and their movements clearly, which facilitates seeing what others are doing, the cultural transmission of fine manual skills such as tool use and manufacture, and manual communication. The effect is something like a natural version of point-light biological displays, in which lights attached to kinematic landmarks of the human body such as major joints are used to generate a black-and-white still or moving “dot-person” image. Perception of the dot image evokes a strong experience of perceiving an animate human body. Nature, it appears, outfitted our ancestors with kinematic accentuation of fingernails, palms, and fingers that allow these crucial areas of human fine motor skill to be more readily perceived. Animal bodies may be kinetically dehiscent to greater or lesser degrees, and the human body appears in this respect as well to be extraordinarily dehiscent. ¹⁹

These points are all the more forceful if, as many researchers believe, hominin sociality was becoming increasingly complex prior to conventional language, communication first evolved as bodily-visual deictic and iconic signs, and conventional language itself first emerged in the visual modality (Tomasello, 2014; Zlatev et al., 2020). During these phases of hominin social evolution, referential communication and imitative cultural transmission would have occurred almost exclusively through vision, without the support of spoken conventional language. At some point, firelight also became an important condition of hominin vision, as working and social hours were extended but under poor lighting conditions (Dunbar & Gowlett, 2014; Hewes, 1983). We must imagine that the selective pressure operating on hominin social vision and visibility during these stages of evolution would have been immense.

There are numerous other respects in which being furless renders the human body more visibly dehiscent and more amenable to a complexly cooperative, social way of life. The callouses, scars, and wrinkles of our bodies, our very posture, bear witness to what nature, others, culture, and dauntless old time have done to our bodies, and to what we have done through those bodies. The furless body is also arguably more amenable to individual and cultural expression through adornments such as jewelry and clothing as well as through body modification practices such as scarification, tattooing, and piercing. Indeed, the suitability for cultural expression can be seen also in that one part of the body where humans typically have the most hair, the scalp. Human head hair is unique in the curious lengths to which it can grow if not cultured. This characteristic provides humans of all cultures an opportunity to stylize and express themselves, or to be stylized and expressed by others. And whether it is blushing, strenuously exerting itself, or being subjected to torture, the affective surface through which the human body interfaces with the world is bared for all to see.

4.2 Touchable skin

But to fully appreciate the social significance of bared skin, it is not enough to look at it; we must feel it. Here it is worth recalling that the skin is not only an organ of exteroception and the place where our kinetic and communicative intent is exposed. It is also an organ of affectivity and interoception, sensing aspects of the internal state of the organism, such as temperature, pleasure, and pain. This information is crucial for maintaining homeostasis and ultimately for survival (Crucianelli & Ehrsson, 2022). The skin’s sensible accessibility to vision and touch thus provides arguably the most direct access to the inner life of another organism. And this access is not only epistemic, as when I see what another is looking at, touching, or doing. Through the direct skin-to-skin contact of social touch (affective touch), we can also affect one another’s invisible, sensing states. Social touch soothes stress and negative affect, generates trust and goodwill, creates and maintains social bonds, plays a critical role in normal development, and is associated with a host of positive health benefits (Schirmer et al., 2022). Exploiting its potential may have been of utmost significance as hominin group sizes increased. Some of the greatest pressures on primate groups are the internal conflicts and emotional strains that come with group living and the need to solidify group bonds (Gamble et al., 2014), and these factors constrain the upper size limit of primate groups. Social primates use bodily contact to respond to these challenges. Most people know from personal experience the tremendous power of social touch, and a considerable literature has emerged over the past three decades investigating its physiological, psychological, and sociocultural dimensions (McGlone et al., 2014; Morrison, 2016).

At this point, our casual talk of human “furlessness” requires greater precision. Hominins did not lose their fur entirely, and modern humans still have a comparable number of hair follicles per skin area to our chimpanzee and bonobo cousins. Hominin body hair underwent diminution. Specifically, the coarse terminal hairs that make up the visible outer layer of most mammals’ pelts are considerably reduced in humans. This left humans with more, and more exposed, finer vellus hairs, or “peach fuzz.” Vellus hair covers our body, except for the glabrous skin of the palms of the hands and soles of the feet, the lips, and the eyelids. It protects the skin and helps with thermoregulation. Unlike terminal hairs, vellus hairs appear to be innervated by the C-tactile fibers that have been most closely associated with social touch.²⁰

Of course, other, furrier primates, have their equivalent to human social touch. Social grooming serves not only a hygienic function for primates, but also establishes and maintains social bonds. Some primates spend up to 20% of their waking hours engaged in social grooming (Dunbar, 1991). Indeed, the time required for social grooming is a considerable constraint on primate time budgets. As Dunbar (2016) has argued, early hominins’ daily time budgets for foraging, feeding, moving, resting, and socializing would have been stretched to the max, putting considerable demand on them to find more efficient methods of maintaining social ties. Grandi (2016) has proposed that there may have been an evolutionary trajectory from social grooming “as a utilitarian action with affiliative meaning among monkeys, to the caress as a purely affective gesture associated with humans”. If this is so, then I would submit as a corollary of the cooperative skin hypothesis that the specific morphology of human skin and body hair evolved under selective pressure to facilitate social touch. We lost our terminal body hair, we let our guard (hairs) down, in part to be more dehiscent, to be physically, neurophysiologically, and emotionally closer to one another. Here again, further comparative research is needed to confirm whether furless human flesh does in fact facilitate social touch in the way I have proposed. But esthesiology already proves its worth as a research program for suggesting this line of inquiry.

But even this finer-grained look at the sensing-sensible skin-hair flesh only begins to brush the surface of the complex social, emotional, and even cognitive function of our largest, most visible, and yet most overlooked organ. I close this section by mentioning a recent direction of research amenable to esthesiology that could provide further support for the cooperative skin hypothesis. In recent years, some proponents of 4e cognition have challenged the supposed primacy and autonomy of the brain for human cognition (e.g., Thompson & Cosmelli, 2011). Meanwhile, researchers have begun to appreciate the intimate connections between brain and skin (Weiglein et al., 2022). Denda et al. (2018) have hypothesized that hominin hair loss and the baring of skin may have stimulated increase in brain size. There are several comparative examples where augmented sensing capacity of the skin appears to have influenced brain growth, such as in the octopus, in Cetaceans, and in the remarkable electric fish of the genus Gnathonemus.²¹ In vertebrates, the epidermis and central nervous system share a common ontogenetic origin in the embryonic ectoderm. In the adult organism, the epidermis retains a “full suite of neuro mechanisms that are traditionally associated with nervous tissues” (p. 2). This includes neurotransmitters and neurohormones such as dopamine, serotonin, GABA, opioids, and oxytocin. These compounds are usually associated with higher cognitive function of the central nervous system, and some are associated with empathy and social bonding. While the function of these so-called “orphan receptors” in the skin is not entirely understood, they have been implicated in sensory responses to light, sound, and chemical stimulation. The loss of pelage on the hominin body would have led to an “urgent need for central processing” (p. 2) of the novel sensory stimuli that hairless skin would have received, possibly stimulating an increase in brain size. From our esthesiological perspective, we can add that it would not only be the new possibilities of external stimulation, but also the heightened reflexivity of the body, the possibility of integrating its multimodal network of sensations, and the requirement of correlating these with other bodies through pairing (see above, Sect. 2), that may have stimulated the increase in hominin brain size. Reciprocally, the new possibilities for sociality opened by hair diminution and increases in brain size may have increased selective pressure for further hair diminution or refinement of the sensing-sensible hair-skin morphology through a sort of coevolutionary, autocatalytic process.

Though this research is still in a nascent phase, the implication of the skin in the nervous system and in human sociality lends further plausibility to the cooperative skin hypothesis and suggests some very concrete mechanisms through which bared skin might facilitate sociality. In both classical modern philosophy and much of contemporary cognitive science, the problem of social cognition has been construed as a matter of how one mind, whether a solipsistic Cartesian consciousness or a skull-bound brain, can be justified in inferring beyond its enclosure to the existence and state of another mind. But conceiving sociality in terms of dehiscent flesh paints a very different picture. As the once rigid boundaries between outside and inside, body and mind, behavior and cognition, begin to crumble, the exterior of the body ceases to be the façade and wall that separates one mind from another, and instead becomes the genuine interface and porous membrane where minds see and touch one another.

5 From the Esthesiological to the affective body

Of course, the characteristics of the human body I have mentioned in the previous two sections in and of themselves by no means provide sufficient conditions for the evolution of humanity. Taken separately, they are not even necessary conditions, without further qualification, for humanity. The numerous variations on normal human sensorimotor capacities seem to prove this. To quote again and at greater length from Merleau-Ponty,

[H]umanity is not produced as an effect through our articulations or through the way our eyes are implanted in us […]. These contingencies and others like them, without which there would be no human being, do not by simple summation bring it about that there is one sole human being. The body’s animation is not the assemblage or juxtaposition of its parts.²²

I propose that we read Merleau-Ponty here as saying that some such contingencies of the kind that I have been discussing in this paper (namely, contingencies that augment the dehiscence, reflexivity, and reversibility of the sensing-sensible body) are necessary conditions for humanity as we know it. Though the specific features we have discussed may not be strictly necessary for a human form of life, it is necessary that there be some such features. This also allows us to avoid any sort of essentialism about these characteristics such that one could say that a person who does not exhibit some of them was in any simple and clearly definable way deficient in their humanity. So far, all that is required is that many or most humans have a highly dehiscent, reflexive flesh that somehow, typically in multiple ways, opens their sensing-sensible bodies onto one another and the world.

But if with this we begin to define a very loose necessary and insufficient condition for humanity, we now return to the question broached above: What would need to be added to provide sufficient conditions? Recall the continuation of the passage under discussion from “Eye and Mind”:

A human body is present when, between seeing and visible, between touching and touched, between one eye and the other, between the hand and the hand a kind of crossover is made, when the spark of the sensing-sensible is lit, when the fire starts to burn that will not stop burning until some accident of the body unmakes what no accident would have sufficed to make... (EM 355)

Now Merleau-Ponty adds to the dehiscence and reflexivity of the body a special “kind of crossover,” a lighting of the “spark of the sensing-sensible,” which he seems to take as a sufficient condition for a human body (“A human body is present when” – emphasis added). This language is poetic, and in the context in which it occurs Merleau-Ponty has other intentions than exploring my current question. As such, the passage trails off in an ellipsis and Merleau-Ponty does not return to the topic in “Eye and Mind.” However, here again reading “Eye and Mind” against the background of “Nature and Logos” may provide a clue. If our discussion thus far has focused on the esthesiological body, we must now consider what Merleau-Ponty there refers to as the libidinal, or erotic, implication of esthesiology, but which for present purposes we may understand as the affective component of esthesiology.²³

“Einfühlung [empathy],” Merleau-Ponty writes, “is already desire” (N 210). This is so because our empathic perception of the other already implies the motivation to live vicariously in and through the other. Indeed, the mere ability to understand others through social perception would count for little if we did not also have an implicit desire to actualize this capacity. This is evident in developmental conditions in which social cognition is disrupted, where an early sign of the condition is often a lack of normal motivation to engage in typical human sociality, such as eye contact with caretakers and joint attention.

Following the strategy of inquiry we have pursued thus far, then, we might propose as a corollary to our understanding of the human being as “another way of being body” the claim that human being is also another form of desiring. And perhaps this other way of desiring is the “spark” that makes of a dehiscent and reflexive body (common to many animals, even if the human body is arguably dehiscent and reflexive to a higher degree) a typically human body. Let us consider two examples of typical, uniquely human “erotic” behaviors that are entailed by our esthesiology, appear early in development, and are crucial for the acquisition of the social, cultural, and cognitive life that we typically think of as distinctively human.

The first example is proto-conversation, face-to-face interactions between infants and caretakers. These play a critical developmental role in early infancy, a stage sometimes referred to as primary intersubjectivity (Trevarthen, 1979) when infant social interaction is primarily dyadic between infant and caretaker. Proto-conversations involve eye-gazing and reciprocal exchanges of facial expressions, gestures, and pre-linguistic vocalizations. In the classic still-face experimental paradigm, experimenters observe infant responses when caretakers break off contingent interaction. Typically, the infant will exhibit confusion or distress and make efforts to solicit a response from the caretaker. A lack of interest in or avoidance of eye contact, and not reciprocating smiles, by contrast, are two predictors of autism spectrum disorder in early infancy.

While it is debatable what cognitive and perceptual capacities are implied by primary intersubjectivity, one thing that seems uncontroversial is the role of emotion and motivation. Whatever else infants engaging in proto-conversation are capable of, typically they clearly desire to participate in and maintain the exchange and the social connection between themselves and their caretakers. And this strong motivational component ensures that they will have rich and ample experiences of primary intersubjectivity that allow them to develop their social perception and cognition, and that scaffold the acquisition of higher cultural, cognitive, and linguistic abilities. Primary intersubjectivity is now widely regarded as a uniquely human mode of precocious sociality (Moll et al., 2021).

We see that primary intersubjectivity clearly relies upon the dehiscence of the human body in the sensible expressivity of the eyes, face, and voice. That is, it relies upon the morphologically distinctive characteristics of the human body described by esthesiology. At the same time, it takes these up through a unique mode of desiring, through a keen and native interest in participating in affective social exchanges. The esthesiological body is an affective, desiring body. At the same time, this esthesiological-affective body is the foundation for the acquisition of higher social-cognitive skills distinctive of the human being.

A second example of affective-esthesiological behavior in early development is declarative pointing (Kee, 2019; Tomasello, 2008, 2019). Infants typically acquire the pointing gesture towards the end of the first year. Pointing is a form of secondary intersubjectivity, in which the self-other dyad of primary intersubjectivity is expanded to include a third term, a referent of joint attention shared by infant and caretaker. In the case of pointing, the referent is the object indicated by the pointing gesture. Pointing is not entirely unique to humans. Some nonhuman primates raised in captivity acquire the pointing gesture. There is even evidence that some corvids use deictic gestures to signal objects of interest to one another (Pika & Bugnyar, 2011). However, humans are certainly the most prolific pointers in the animal kingdom. Furthermore, they also point with motivations that are species unique. While a chimpanzee raised in captivity may use an imperative pointing gesture to make a command or indicate a wish to a caretaker, humans also use pointing gestures with a purely declarative motivation. We point not just to inform or to request, but also, it appears, simply in order to establish common ground and share the world with one another. This is evident in many infants who, having acquired the pointing gesture, begin pointing at anything and everything. We can infer that these gestures have genuinely communicative intent, as the infant will often direct its gaze from referent, to caretaker, and back, or use vocalizations to attract the caretaker’s attention to ensure that joint attention has truly been established. However, the intention does not seem to be to make a request from or provide information to the caretaker. Rather, the motivation seems to be “declarative.” But while declarative pointing and showing more generally do not serve an immediate practical end, they play an important role in allowing infants to generate the rich, targeted information from caretakers about the world, including linguistic input, that will help them grow into the human cultural and symbolic world. That is, relying on the esthesiological, dehiscent human body as a source of perceptual, deictic, and emotional information about the world from mature, enculturated humans plays an important role in infants becoming enculturated humans themselves. And this process is driven in part by a distinctive way of desiring, rather than a unique cognitive (in the narrow sense) capacity. Here again, where these motivations and behaviors are atypical, there are often disruptions in other aspects of sociality and cognition.²⁴

6 Conclusion

I have attempted to develop the esthesiological program outlined in Merleau-Ponty’s late work. I have conducted some initial comparative esthesiological investigations into human and nonhuman animal bodies considering facts about those bodies unknown in Merleau-Ponty’s time. I have argued that the phenomenological-esthesiological framework for understanding social perception as rooted in the flesh, the sensing-sensible body, gives us a powerful tool for interpreting and integrating a wide range of findings concerning human and nonhuman animal bodies to develop a composite picture of the emergence of a distinctively human variation on animality as “another manner of being a body” (N 208). These variations on animal embodiment, I have suggested, were likely critical for the development of a distinctively human social and symbolic form of life.

This approach, then, is on course to fill in the gap announced in the Introduction of this paper between approaches to human distinctiveness that focus on bodily features and those that focus on cognitive features (cf. Kee, 2024). There are still some further steps to be made, however, to complete this task. In closing, I will indicate some further aspects of the project Merleau-Ponty envisaged in “Nature and Logos” that I have not been able to explore in detail. These concern animality, language, and ontology.

Already in the course prior to “Nature and Logos,” Merleau-Ponty had approached the question of animality and its place in nature, providing interpretations of the works of Lorenz, von Uexküll, and Portmann, among others (N 123 ff.). “Nature and Logos” no doubt regards the emergence of the human within the animal kingdom as a highly distinctive variation on animality. That being said, in the conceptual space of possible understandings of anthropological difference, the account offered by esthesiology tends to emphasize continuities to a greater degree than some other approaches do. In my rendering of the story of human distinctiveness, I have foregrounded the role of comparatively minor divergences in the appearance and morphology of the human body, and the animation of these traits through new motivations. I have downplayed the role of modes of cognition that are different in kind as such. This is not necessarily to deny that they exist, of course. Rather, it is to seek a deeper origin and account of them. It is an account that sees humanity as a variation on animality rather than something other than animality. In the outline for “Nature and Logos,” Merleau-Ponty planned to address “the Ineinander of animality-humanity = grasped in other living beings as variants” (N 208). In the sketches, he expresses again the idea that human being is not in the first place what it is by the external superposition of some additional faculty (e.g., reason, or language), but rather as “another manner of being a body” that retains an Ineinander and “strange kinship” with animality (214). We should note that while the esthesiological framework was first proposed by Merleau-Ponty and is here developed towards the end of understanding the distinctively human mode of embodiment, it is in fact a framework suitable for developing a phenomenological zoology or ethology more generally. While there has been much insightful research motivated by Merleau-Ponty’s thinking on animality (Toadvine, 2007, 2009; Trigg, 2020; Westling, 2014), to my knowledge the esthesiological framework has not yet been adopted to help reconstruct the socio-sensory worlds of nonhuman animals. Doing so could shed light on the thorny question of the nature of nonhuman animals’ social cognition, thus providing a welcome theoretical alternative to an increasingly embattled theory of mind paradigm.²⁵

The discussions of the esthesiological and “libidinal” (affective) body in “Nature and Logos” should shed light on the nature of logos and language. Merleau-Ponty’s outline for the course suggests that after the study of the affective body, we should come to understand “How the Logos is introduced—perceiving and speaking” (N 208). In the sketches for the course, the issue is raised under the heading “the body and symbolism” (211, 219, 226), an aspect of the body that Merleau-Ponty suggests follows directly from the studies of the esthesiological-affective body. The communicative and expressive dimensions of the body that I have discussed in the previous section could shed some light on this connection with symbolism. But there is more at stake than this. In the context of the series of Nature lectures and his late philosophy more broadly, Merleau-Ponty is attempting to understand the relationship between nature and logos. He proposes a continuity between the “logos of the natural world” (which presumably includes the natural symbolism of the perceiving, sensorimotor body, the “language before language” – 219) and the conventional symbolism of instituted languages (which are like a “second body” – 211 – or “second nature” – 227). These dense passages are some of the most provocative and profound in Merleau-Ponty’s discussions of language and warrant further discussion with respect to his late philosophy of language.

Indeed, the sketches for “Nature and Logos” indicate that Merleau-Ponty viewed the route through nature and esthesiology as a viable way of approaching the central ontological themes of his late philosophy as a whole. The Introduction to “Nature and Logos” states that this path through the ontology of nature is a preferable propaedeutic to ontology as such (N 204). And the outline for the course indicates that the final section (following the one on symbolism, logos, and language) should discuss the “properly philosophical problematic: the visible and the invisible” (208). Indeed, one thing that comes out more clearly in “Nature and Logos” than in other late writings on the topic is that the locus of the entire dialectic of the visible and the invisible is found in the intertwining of these two elemental aspects within my body, the sensing and the sensible, and that this body is itself inherent in the same nature and being that it interrogates. This approach to the problem of the visible and the invisible through sensing-sensible embodiment could be more accessible than the presentations in other late texts, which offer a philosophy that is, as one commentator’s understated remark has it, “rather difficult to think” (Hass, 2008, p. 197). For Merleau-Ponty scholars, then, the path through Nature pursued here is thus an alternative entry point into Merleau-Ponty’s late thought and could shed light on puzzles left open from “Eye and Mind” and The Visible and the Invisible.

Even without this thicker philosophical and ontological dimension, however, the esthesiology outlined in this paper offers a promising approach for conceiving human and nonhuman animal embodiment for researchers in the human and life sciences.²⁶