Note to readers: Biological Expositions is a series of blog-posts each of which is equivalent in content to a book chapter. If bio-bullets are likened to a starter, blog-posts could be seen as a light lunch and Biological Expositions as a three course meal. We look forward to your comments on this series.
The human ear lobe may be Nature’s first body part which has evolved only to be custom-tooled.
Robin: Welcome, Human Ear Lobe, to our interview series here at Exploring the Bio-edge.
Human Ear Lobe: Thank you.
The Honey Badger: You feel that, as an anatomical feature, you’re underrated?
Human Ear Lobe: Yes, I’m a unique aspect of the human species, hiding in plain sight.
Robin (smiling): You certainly look pretty plain. What’s special about you?
Human Ear Lobe: I may seem ordinary, but it’s what I represent: the first bionic organ ever evolved on Earth.
The Honey Badger: That’s an extraordinary claim. Could you elaborate?
Human Ear Lobe: I’m in a category of my own that’s been overlooked by evolutionary biologists. I requested this interview to point out what’s right under, or should I say to the left and right of, experts’ noses.
Robin: Well, we’ve done the usual preparation: Wikipedia, Google Scholar, biological dictionaries, etc. What little is written just confirms that you have hardly any known function.
Human Ear Lobe: Even experts sometimes assume that a biological feature is redundant just because no function springs to mind. But just think about it: how could I have evolved without paying my way?
The Honey Badger: Well, you didn’t exactly evolve, did you? I mean, surely you’re just another example of a vestigial body part, a shred of tissue hanging on from an evolutionary past?
Human Ear Lobe: That’s dubious. If I’m a shred, it’s not of pre-human ancestry. I’m a label of neither primates in general, nor anthropoids, nor apes. Instead I’m a human tag, evolved for the first time in Homo, which would make me novel rather than vestigial. If so, I distinguish the most technological and possibly most intelligent animal of all.
Robin: You’re categorically distinctive of humans?
Human Ear Lobe: Possibly.
Robin: Many listeners may assume that you’re just a reduced version of something found in apes. For example, the chimpanzee has an ear that’s large but otherwise similar to the human ear. In which ways does the human ear differ from those of the closest relatives?
Human Ear Lobe: Have you taken a careful look at a photo of Jane Goodall next to a chimpanzee? It looks like she possesses me but the chimpanzee lacks me.
Figure 1. Jane Goodall with chimpanzee, showing ear lobe in human only [photo by M. Neugebauer, available from www.wildchimpanzees.org].
Figure 2. Chimpanzee juvenile, showing absence of ear lobe owing to extension of helical cartilage to lower edge of ear [photo by Tambako The Jaguar under Creative Commons licence 2.0].
The Honey Badger: And other species of apes?
Human Ear Lobe: The external ear has a fairly consistent form among apes but its conspicuousness varies. The chimpanzee has proportionately the largest ear, while small ears characterise the gorilla and especially the orangutan. In the bonobo, orangutan and gibbons, the ears are hidden behind head hair, and in the mature male orangutan the ear is additionally hidden behind the cheek-flange. But I think you’ll find that, strictly speaking, none of these species have an ear lobe.
Robin: The distinction you’re making isn’t obvious. Maybe we have different ideas of what an ear lobe is in the first place?
Human Ear Lobe: Okay, let me define myself within the primates. The ear lobe is that part of the external ear that has no cartilage, i.e. no skeleton. I’m odd – perhaps unique – in having two epidermal surfaces on a single dermal layer, making me a bilateral section of skin tissue. If you skewer an ear lobe, you enter skin and then exit from skin; I’m not covered by skin, I am skin tissue alone. Because it contains a thin layer of cartilage, what looks superficially like an ear lobe in the chimpanzee is not as stretchy and resilient as me.
The Honey Badger: How can you have evolved beyond the level of evolution of the rest of the human ear? That seems incongruous although – as a mammal with a particularly reduced auricle – I admittedly have a poor eye for ears.
Human Ear Lobe: Primates have advanced brains but in fact they’ve preserved an ancient, original form of the external ear that’s poorly supplied with muscles. In most ways humans retain a remarkably primitive auricle. A close look at the ears of tree shrews, which approximate the ancestors of primates, will show the resemblance to miniature prototypes for the human ear. So the evolutionary line leading from early mammals to humans, over a period of more than fifty million years, has kept the same basic design of the external ear from tree shrew all the way to chimpanzee.
Figure 3. Tree shrew and human, showing similarity of human ear shape to that of a primitive relative of primates [left photo © D. Daniels, right photo © Robin and the Honey Badger].
Robin: Are you suggesting that the human ear is almost like a living fossil except for the novelty of the ear lobe?
Human Ear Lobe: Yes, tree shrews may appear to have an ear lobe, but the difference is that, as in apes, the lowermost part of their external ear is reinforced by cartilage. My self-concept is that only in humans has an ear lobe evolved by virtue of the loss of the skeletal structure of this part of the external ear.
The Honey Badger: Are humans the only primates to modify the basic primate prototype of the external ear by losing some of the cartilage without reducing the size of the ear?
Human Ear Lobe: No, they’re not. Nocturnal primates such as galagos have ears with so little cartilage and so many small muscles that these ears can swivel like radar dishes and fold like origami.
The Honey Badger: Okay, but even if humans are the only primates to produce you, a true ear lobe, how does that make you bionic?
Human Ear Lobe: I see myself as having little function but to be accessorised. I’m most alive when I have some artefact or other attached to me, and that extension may as well be my biological purpose. There’s no other animal on Earth that has evolved a body part dedicated to such augmentation.
Robin: By accessorisation, do you mean adornment? Surely humans adorn lots of different parts of their bodies?
Human Ear Lobe: Modern decoration of the human ears may be misleading because traditional ear lobe artefacts announce social status and technical progress rather than just being aesthetic. And necklaces, brooches, bangles, anklets and finger rings differ in a way. Sure, you can accessorise various body parts, but which other organ in any animal is like the ear lobe in being technically modified – first pierced and stretched and then accessorised – as its main use?
The Honey Badger: But surely augmenting you necessitates disfiguring you?
Human Ear Lobe: Well, yes, it may seem odd that I feel most fulfilled when I’m pierced and stretched on purpose. But this is not mutilation, because I’m not harmed in any real sense; and it would also be misleading to call this cosmetic surgery because the operation may be fashionable but it’s not frivolous. My very nature tends to preclude ‘mutilation’, because as skin devoid of cartilage I heal quickly and can last a lifetime even if I’m first pierced in infancy. It’s much easier to hang an artefact from the ear by piercing me than by leaving me intact. And only when I’m stretched into a wide loop can a substantial artefact be hung from me or framed within me.
Figure 4. Examples of ear lobe artefacts worn by humans [photos of Hmong (top) and Karen (bottom) women in the public domain and Maasai woman (right) by W. Warby under CC licence 2.0].
Figure 5. Human adult, showing pierced and stretched ear lobe draped over ear when not accessorised [photo by The.Rohit under Creative Commons licence 2.0].
Robin: So are you saying that the human ear lobe doesn’t really perform its main function until it’s been the object of surgery?
Human Ear Lobe: Yes, human ears go hand in hand with tools. And, anatomically, I suspect that I’m more distinctive of humans than the opposable thumb – which various other primates possess to various degrees.
The Honey Badger: Speaking of the human hand: that can be made into a fist, something possessed by no other mammal. Men have always been able to harden the fist by clutching a stone within it, and who knows how long they’ve worn the artefacts called knuckledusters? How is that kind of augmentation by means of tools inferior to what you’re claiming for yourself?
Human Ear Lobe: I agree that the use of tools to augment the fist is distinctively human. The difference is that fist-fighting isn’t the main use of the human hand. Whereas a fist is just a hand in a certain posture, I’m a body part in my own right. And of course there’s the difference that I’m as useful in women as in men.
Robin: Let’s sum up so far. You first evolved within the genus Homo? And, although you evolved by ‘natural selection’, you can’t fulfil your function until ‘initiated’ on the receiving end of a sharp instrument?
Human Ear Lobe: That’s about right. As human ancestors evolved a combination of bipedality, nakedness and technology, my evolution came to make sense: an organ that can’t be used properly without being tooled. Where else in Nature can you find such a development?
The Honey Badger: I don’t want to seem facetious, but why didn’t you evolve to have a ready-made hole in you?
Human Ear Lobe: Because the selective pressure wasn’t for that. It was for an organ amenable to being custom-tooled.
Robin: Well, that is an original concept for biologists to ponder. But let’s just go back to basics for a minute. Surely another adaptive explanation is that you could serve as a radiator of body heat as in elephants and other mammals with big ears?
Human Ear Lobe: In theory, yes, but I don’t engorge enough with blood during heat stress to make that plausible as my main use. Humans have instead evolved – to a greater degree than in any ape – perspiration. And although humans originated in the tropics, they’ve long inhabited climates so cold that the ear lobe risks frostbite much of the time. So the idea that I evolved for regulation of body temperature doesn’t really hold up.
The Honey Badger: Well . . . what about a function in signalling embarrassment by means of blushing?
Human Ear Lobe: Okay, the external ear can go red emotionally, but I can’t say I do so especially. Maybe sceptical listeners could pay detailed attention next time their ‘ears are burning’: the upper part of the ear certainly feels hot, but does the ear lobe? Not in my experience. Anyway, blushing is hardly visible if the natural complexion is dark.
Robin: Another thing, I’ve seen the ear lobes of naughty children being grabbed by adults as a form of discipline …
The Honey Badger: … and I know when I grab my own offspring by the loose skin of the nape, they become passive and manageable in a reflexive way, allowing me to carry them to safety. Could parental discipline be your real function?
Human Ear Lobe: Sure, I can provide a good handle on children because pulling me triggers submission without risking real injury. But an adult is more likely to grab a whole ear than just an ear lobe. And discipline doesn’t explain why I get bigger, not smaller, through life. Nobody repays a grandparent by pulling an earring like a bull’s nose-ring. Or even by assisting the grandparent along gently by means of the ear lobes.
The Honey Badger: True, humans are surprisingly delicate except for their fists … What about sexual selection? Aren’t you an erogenous zone?
Human Ear Lobe: Yes, but not primarily. Do the ears of men and women differ in shape in any way? For that matter, do men or women ever ogle me in my naked state, whether intact or pierced and stretched?
The Honey Badger: Well, I couldn’t say. I’m on a different wavelength when it comes to allure.
Human Ear Lobe (chuckling): A lover’s gaze lingers on the eyes, nose, lips, teeth, cheeks, chin, hair, neck … and ear lobe accessories can certainly enhance a good-looking face. But the ear itself is perhaps the most sexually neutral part of the face to look at. Who applies make-up to an ear lobe in preference to wearing an accessory? I bet some honeymoon couples would go embarrassedly blank if you put them on the spot to recall the unaltered shape of each other’s ear lobes.
Robin: So none of the direct adaptive explanations adds up?
Human Ear Lobe: Not in my experience. I don’t think biologists would be convinced that my existence is explained by the various functions you’ve listed.
The Honey Badger: Returning to a point you made earlier about the large ear of the chimpanzee. My hardly discernible external ears suit me fine, so I’m puzzled by this size. Given that neither apes nor humans can really move the ears by muscular contraction, does the chimpanzee hear particularly well?
Human Ear Lobe: I look forward to primatologists studying whether the chimpanzee can locate sounds better than other apes can. But there’s more to ear size than just hearing. In both the chimpanzee and true baboons, the disproportionately large ears of infants seem to be used as flags for protection from macho violence. At birth, the ears are also pink in contrast to the black hair.
Robin: And how is that relevant for you, the Human Ear Lobe?
Human Ear Lobe: Well, humans have a quite different pattern: there’s nothing striking about the ear of a human baby. But, instead of advertising youth and vulnerability as chimpanzee and baboons do, humans use the ear to advertise maturity. My interpretation is that humans may have inherited the flagging of social status from ancestral primates but they’ve turned this theme on its head in an evolutionary sense.
Figure 6. Hamadryas baboon, showing conspicuousness of ear in infant, particularly compared with mature male [photos by J. Milich and C. King under Creative Commons licence 2.0].
Figure 7: Baboon infant, showing large ear and tonal contrast with head hair [photos by R. Mensen under Creative Commons licence 2.0].
The Honey Badger: Are you suggesting that the ear actually gets bigger and more conspicuous as humans age?
Human Ear Lobe: Yes, I think that most of your listeners will accept that the ear is largest in elderly people. The human skull shrinks while the ear is one of the few body parts that keeps on growing into old age – particularly the ear lobe, which consists purely of double-sided skin.
The Honey Badger: One way to interpret humans is as a juvenified form of primate. You know, bulging forehead, large brain, flat face, small jaws, and other features associated with infant apes. Are the external ears a part of that?
Human Ear Lobe: If you found that the newborns of, say, the bonobo possess an ear lobe that is lost in adulthood, maybe you could explain me in terms of juvenification. But I don’t think anyone’s thought to look.
Robin: So, getting back to your self-interpretation: your view is that humans differ from other anthropoid primates in that the ear is used to signify mature, not infantile, status in society?
Human Ear Lobe: Yes. Part of my beauty is that I don’t wear out with age as a label of social standing via ear lobe artefacts of various sorts.
The Honey Badger: I begin to understand your hypothetical significance in human evolution as the first body part to evolve bionically. But what do you mean by social standing?
Human Ear Lobe: Well, I mean the various aspects of position or power in society, such as class, clan, and caste. Also rank, profession, wealth, gender, religion and political allegiance.
Robin: Many parts of the human face and head show racial variation, and race can affect status. It’s obvious that ethnic groups may use different artefacts, but does the unaltered shape of the ear lobe conform to other facial features in reflecting genetic differences among races?
Human Ear Lobe: No, strangely enough it doesn’t. One of the noteworthy things about me is that I show little racial variation even though the texture of ear wax is certainly variable along racial lines.
The Honey Badger: So the unaltered form of the ear lobe varies individually without showing either sexuality or raciality as such?
Human Ear Lobe: That about sums it up. I’m genetically variable enough in any population to have allowed rapid natural selection, but for whatever reason this has not led to the racial differentiation seen in so many other features of the face and head.
Robin: … which is consistent with your interpretation that you signify status within societies?
Human Ear Lobe: Yes. In a science-fiction world, one race might have a pendulous ear lobe, a second a tightly attached ear lobe, a third a fatty, dimpled ear lobe, and a fourth a hair-tasselled ear lobe. And individuals everywhere obviously vary in the shape of the ear and ear lobe, so racial variation could, hypothetically, have arisen in me. But the only hint of this – apart from skin colour of course – is that Africans, particularly the Khoi people, seem to have the smallest ears. In general, I’m ‘colour-blind’, supporting the idea that surgery plus accessorisation of the ear lobe have made individual variation in my shape irrelevant from the point of view of further natural selection.
The Honey Badger: And by accessories you mean symbolic rather than utilitarian artefacts?
Human Ear Lobe: Yes, ear lobe rings, plugs, coils, spools and tubes, some of which can be much larger than the ears themselves. And hand-made of wood, bone, ivory, stone, glass, metal, feathers, ceramics, a wide variety of materials and designs depending on the situation, but representing status rather than being useful gadgets in themselves.
Robin: But surely not all human societies in history have accessorised the ear lobe?
Human Ear Lobe: Accessorising me may not be a human universal to the degree that marriage is, but the practice has been widespread for thousands of years and may have originated up to one hundred thousand years ago. Ancient Chinese, Babylonians, Egyptians, Greeks, Romans, Renaissance; in the Western Hemisphere, Mayans, Aztecs and Incas. The archaeological evidence could fill several books.
The Honey Badger: And the various traditions signify social status in all its diverse aspects?
Human Ear Lobe: That’s the idea. My impression is that ear lobe artefacts seem to be relatively elaborate at a certain stage of technological progress where, because of constraints on transport and storage, metal is used but material possessions are few.
Robin: Which culture in the modern world retains that way of life?
Human Ear Lobe: Well, several, but the Maasai and Fulani might be high-profile examples.
Robin: Can we call traditional ear lobe artefacts ‘jewellery’?
Figure 8. Mask of Aztec god Xipe Totec, showing pierced ear lobes in a divine image [photo in the public domain].
Figure 9. Human adult, showing ear lobe accessory next to skull in European grave from 550-650 AD [photo by Albärt under Creative Commons licence 3.0].
Human Ear Lobe: Well, if jewellery is defined as ornamentation using valuable commodities, the best example is ear lobe artefacts made of gold and silver. In the case of nomadic people such as the Fulani who lacked fixed safes or banks, wearing these materials on the ear has been a way of signifying wealth at the same time as protecting that wealth.
The Honey Badger: Gold and silver are so heavy that wearing them in any quantity must really stretch the ear lobes. And surely such advertising of precious metals just invites crime?
Human Ear Lobe: The stretch does look painful but I can take the strain. And, perversely, this exposure of wealth can deter theft in traditional societies because to violate a woman’s body by ripping the ear lobes would treble – by adding assault and physical injury – the crime of robbery.
The Honey Badger: Okay, you’ve made a good case that a body part in primates was earmarked for technological augmentation. But some would associate the most ostentatious of ear lobe artefacts mainly with primitive cultures. Have modern humans already transcended the utility of the ear lobe?
Human Ear Lobe: In one sense, yes. In modern cities, ear lobe artefacts have devolved towards mere adornment. Accessorisation of the ear lobes tends to be downplayed with increasing technological sophistication.
The Honey Badger: Humans today can admittedly use dozens of metallic, plastic and electronic devices, so it may be redundant to advertise a technological edge indirectly by means of the original symbols. But perhaps among the last of the nomadic pastoralists the ear lobe might still provide one of the few opportunities to show social currency.
Human Ear Lobe: I agree. Although today, in 2012, mobile phones are changing that as we speak.
Robin: So has natural selection of the ear lobe already been suspended?
Human Ear Lobe: I do suspect that I’m already becoming obsolete for the human species as a whole. If I really am the first example of bionic natural selection, perhaps I’m also the last. But my historical significance will remain as a ‘thin end of a wedge’ in human evolution.
Robin: Are you implying some kind of evolutionary threshold?
Human Ear Lobe: The moment that line was crossed where an organism – the genus Homo – dedicated a piece of skin to being pierced constructively for the embodiment of an artefact, things would never be the same again. But because of how far technology has now advanced, Homo sapiens has, overall, already outgrown the need for a special body part like me. Ear lobe accessories are largely redundant for the most powerful people today, as bionics blur technology with anatomy to new depths.
The Honey Badger: I take it you refer to appliances from contact lenses through breast implants and hip replacements to various electronics inside the human body, including cardiac pacemakers, cochlear implants, and tracking devices?
Human Ear Lobe: Yes, the evolution of the human organism into a mix of animate and inanimate seems like the way of the future because every year brings progress in the melding of flesh and bones with various medical and robotic devices.
Robin: So, for those listeners sceptical of a long-term transition from natural organs to a combination of body and contrivance, you see your history as a pointer to an evolutionary path beyond natural selection?
Human Ear Lobe: Yes, however limited my evolutionary future in a Darwinian sense, I may – in retrospect – have a lasting significance in the book of human history.
Robin: Well, perhaps listeners will share their own insights and interpretations. Regardless, you’ve brought just the kind of subject we love to explore here at the Bio-edge. I for one will certainly keep my ear to the ground for information refuting or supporting your ideas.
The Honey Badger: Yes, thanks for stretching our imaginations today and for giving us a new framework on which to hang our thoughts as we observe the ears around us.
Acknowledgements:
We thank Friderun Ankel-Simons for her generous discussion during the writing of this essay.
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LOBULATED EARS: NATURAL SELECTION GONE BIONIC?