Spare Parts Page 9

  Two muscles work the ossicles. The first is the tensor tympani, which stretches from the auditory canal to the tympanum. When you hear a loud noise—or the sound of your own teeth colliding as you chew your food—this muscle tightens the tympanum, lowering the sound that reaches your inner ear. Just as some modern imaging techniques such as a PET scan can show parts of your brain lighting up when you even think about food, the tensor tympanum may actually begin to contract if you even think about loud noises. The second muscle in the middle ear, the stapedius, is the smallest muscle in your whole body. It moves the ossicles, and sometimes it overreacts, creating a high-pitch ticking sound. On the other hand, when the stapedius is immobilized, as may happen in people with Bell’s palsy, a form of facial paralysis, it may change the perception of loud noise in one ear or both.12, 13

  The fish from whom we lifted our early gill-like structures do not have ears, but they do have grooves along the head and body lined with hair cells that sense differences in water pressure, making it possible for the animal to swim this way and that without bumping into an opposing current or, more to the point, a larger, possibly hostile fish. We have something similar, nerve cells in our inner ear semicircular canals that are sensitive to the motions of liquid and behave like a gyroscope, helping you to keep your balance when you move your head from side to side or up and down.

  Now having followed the energy of sound waves as they move from the concha to the organ of corti, let’s go back to Darwin’s target, the outer ear.

  PICTURING THE PINNA

  The Outer Ear, Gray’s anatomy, 20th edition (1918)

  The most obvious characteristic of the outer ear is its shape, which is determined and maintained by the helix, its stiff, cartilaginous rim. About one-third of the way down from the top of the helix, some of us have a thickened spot familiarly known as Darwin’s tubercule or Darwin’s point. This bump is common among apes. In humans it is a congenital condition that studies have found to occur in about one in ten Spanish adults, four in ten Indian adults, and nearly six in ten Swedish schoolchildren. It may show up on one ear or both. It may or may not run in families and may or may not be linked to one particular gene. One study of 264 pairs of twins found 26 pairs in which one twin had the point on one or both ears and the other did not. But here’s one definite: Darwin’s tubercule is definitely more common among men than among women.14

  Darwin himself called this bump the Woolnerian Tip in honor of British sculptor Thomas Woolner, who, he wrote, in The Descent of Man, “informs me of one little peculiarity in the external ear, which he has often observed both in men and women, and of which he perceived the full signification…. The peculiarity consists in a little blunt point, projecting from the inwardly folded margin, or helix. Mr. Woolner made an exact model of one such case, and has sent me the accompanying drawing. These points not only project inwards, but often a little outwards, so that they are visible when the head is viewed from directly in front or behind. They are variable in size and somewhat in position, standing either a little higher or lower; and they sometimes occur on one ear and not on the other. Now the meaning of these projections is not, I think, doubtful; but it may be thought that they offer too trifling a character to be worth notice. This thought, however, is as false as it is natural. Every character, however slight, must be the result of some definite cause; and if it occurs in many individuals deserves consideration. The helix obviously consists of the extreme margin of the ear folded inwards; and this folding appears to be in some manner connected with the whole external ear being permanently pressed backwards.”15, 16

  At the bottom of the helix is the lobule, a.k.a. your earlobe, the only part of the outer ear with no cartilage, which is why it is so soft and floppy. “It has been asserted,” Darwin wrote, “that the ear of man alone possesses a lobule; but a rudiment of it is found in the gorilla.” And then, citing William Thierry Preyer, the English-born director of the Physiology Institute at the University of Jena (Germany) and father of the Preyer Reflex (an animal’s pricking up its ears in response to a sudden loud noise), Darwin slipped casually into nineteenth-century scientific racism: “… as I hear from Prof. Preyer, it is not rarely absent in the negro.”17

  Most of us have “free” earlobes, that is, lobes separated from the side of the head. Some of us have “attached” lobes that are connected to the side of the head. A smaller group of us have earlobes that are in between, sort of joined and sort of free. All three types are genetically determined and may run in families, but because the trait is governed by more than one gene, what you get may not be what your parents got. A slew of serious no-nonsense studies of earlobes show varying conclusions about the importance of earlobe heredity. The first two appeared in 1922, one in the genetics journal Hereditas and the second in Zeitschrift für Induktive Abstammungs- und Vererbungslehre (Magazine for Inductive Descent Apprenticeships and Genetics), both concluding, absolutely, that attached earlobes were a dominant trait.18 Fifteen years later, in 1937, a different researcher got different results, this time proving, absolutely, that attached earlobes were a recessive trait. Absolutely, that is, until later that year when a third group of investigators sort of gave up. Dividing earlobes into an “arbitrary classification [of] two sharply defined types,” they said, “… gives a false picture, since all gradations between the two extremes are encountered.”19

  In 1966, a team of Indian researchers proposed that the state of the earlobe depends not on one dominant or one recessive gene, but on a group of genes, a neat way to explain why a child’s lobe might not match his parents’.20 More than thirty years later, still intrigued with what they called a “very important tool to study population variances,” members of the original team published data to show that free earlobes are more common than attached earlobes in both men and women.21 And that remains today’s prevailing wisdom: more often free than attached, more commonly free among men, most likely due to more than one gene, and so long as they are in place right there at the bottom of your ear, just fine.

  Of course, the state of your earlobes isn’t the only occasionally odd feature of the human outer ear. Some of us are born with incomplete or abnormally small auricles, a condition known as microtia from the Greek mikros meaning small and otos meaning ear, with –ia meaning condition tacked on at the end. Others like the actor Will Smith, Barack Obama, and Britain’s Prince Charles come into the world with ears that are larger than normal, a condition known as macrotia, the obvious etymological opposite of microtia. And a very unusual few arrive with incomplete outer ears or none at all (anotia, from the Greek an- meaning without). Your ears may be shaped like cups or bent over like a rabbit’s, the latter known as “lop ear” after the Holland Lop, a breed of rabbits first found in the Netherlands. They may be attached to the cheek rather than the side of the head (melotia from the Greek melon meaning cheek) or set lower on the head than we are used to seeing, one of the defects associated with the chromosomal abnormality Trisomy 18/Edwards syndrome.22, 23 Or the top of the ear may be pointed.

  In the animal kingdom, the list of those with pointy ears includes the blood-sucking vampire bat (Desmodus rotundus), civets, red pandas, African bush pigs, and, as Darwin wrote, many monkeys, whose upper ear “is slightly pointed … [as] could actually be observed in a specimen of the Ateles beelzebuth [white-bellied spider monkey] in the Zoological Gardens [the London Zoo]; and we may safely conclude that it is a similar structure—a vestige of formerly pointed ears—which occasionally reappears in man.”24, 25 Doctors call this an “elfin ear,” a nickname for Stahl’s Ear Deformity, one of several anomalies that may be linked to pressure on the ear exerted by the auricular muscles while the infant is in utero.26 The deformity, which can be corrected with surgery, looks like the ear on the familiar image of an elf-like Jack Frost.

  Like tails, pointed ears also appear in human myth and magic as far back as the Greek god Pan, whose most prominent features were his lower body (a goat’s) and his horns, but whose pictures
also show ears to rival Dr. Spock’s. As for Spock himself, his were so famous that beginning in the 1980s, many Trekkies handed their ears over to “body modifiers,” nonphysicians who cut the cartilage at the top of the helix and sewed it back together in a point, a practice plastic surgeons call both risky and, unlike body piercing, irreversible.

  But does the shape of a healthy ear really matter to anyone other than the person on whose head it hangs? Maybe—but not the way you might think it might.

  Like other physical characteristics, the ears have occasionally been regarded as a guide to the human personality. In 1900, Oxfordian Mary Anne Ellis published The Human ear: Its Identification and Physiognomy. Ellis seems to have been a fan of phrenology, the then-popular “science” predicting personality based on bumps on the head. In her preface she writes that “[t]he following chapters contain a method of classifying portraits of the human ear, by which reference for the purpose of identification is made possible and convenient. They also show the value of identification among ‘non-criminals,’ by means of a minute division of the shapes of the rim of the ear. The subject of heredity, as shown by the shape of the ear, is illustrated by nature-prints from members of several families. No one has hitherto investigated this branch of the subject. A concise account, from original sources, of ancient and modern writers upon Ears is given, ending with a fall analysis of … tentative efforts in that direction … there has been no systematic scientific investigation of the peculiarities of the forms of the ear and their important place in physiognomy, except the very recent examination of criminals’ ears alone. The ‘non-criminal’ classes have a still more distinctive and better-developed ear. Nature-printing from the ear was invented by me, for the purpose of having permanent portraits of ears of the exact size and shape of the originals, by which means they could be compared and collated. The illustrations have been reduced uniformly in size, the proportions being kept the same. M. A. E. Oxford, 1900”27

  Mark Nixon, a computer scientist at the University of Southampton (England) School of Electronics and Computer Science, makes a more pragmatic 21st-century case. He thinks that modern technology called image ray transform might make the ear an even more effective identification tool than the fingerprint. Here’s how it works: Light rays are shined on the ear to make thousands of images of the way the light reflects back. A computer program analyzes the reflections and turns them into numbers that classify the ear as one among millions. Nixon’s test run of 250 human ears was 99.6% accurate in linking an ear to its owner. Nothing’s perfect, of course. Unlike fingerprints, which are engraved in the womb and never change, even after death, your ears, like other parts of your body, shift shape as you grow older, growing about 1/5 of a millimeter/0.007 inches every year, eventually stretching to an average 72 mm/2.8 inches in women older than 70 and 78 mm/3 inches for men at the same age.28 Thus, an image developed at age 20 may not be useful in identifying someone at age 60. Nonetheless, don’t be surprised if a gumshoe in some future detective novel demands, “Show me your ears.”29

  MUSCLE MECHANICS

  There are more than six hundred muscles in the human body, including the nine auriculares.30 The muscles inside the auricle are called intrinsic (interior) muscles; the outsiders are called extrinsic (exterior) muscles. The intrinsics are the end points of the group of muscles that enables our facial expressions; their job is to move small parts of the outer ear such as the tragus. The extrinsic muscles are designed to move the outer ear itself.

  Animals have many more ear muscles than we do. For example, a horse has ten extrinsic auriculares and six intrinsic ones, all of which he can muster to express emotion or step up his ability to hear and identify sound. Normally, the equine ear muscles are relaxed and so are the ears, but when horse is curious about a sound, he will move his ears back and forth to catch it, and when fearful he will flatten his ears against his head. We, on the other hand, have only three outside muscles: the auricularis superior muscle on top meant to lift the ear up; the auricularis anterior in front to pull it forward; and the auricularis posterior, which, as its name implies, sits on the back rim, to pull the ear backwards. Inside we have the helicis major, helicis minor, tragicus, antitragicus, transverse auricular, and oblique auriculares. If all these muscles worked as well as a horse’s sixteen or the astounding group of thirty-two muscles that move a cat’s ear, three outside and six inside should be enough for us to swing our ears around at will.

  But they don’t. So we can’t. And we’re not alone.

  The keepers in the Zoological Gardens, the antecedent of London’s Zoo, assured Darwin that our closest relatives, chimpanzees and orangutans, couldn’t move their ears, either. “It may be,” Darwin wrote, “that owing to their arboreal habits and great strength they were but little exposed to danger, and so during a lengthened period moved their ears but little, and thus gradually lost the power of moving them. This would be a parallel case with that of those large and heavy birds, which, from inhabiting oceanic islands, have not been exposed to the attacks of beasts of prey, and have consequently lost the power of using their wings for flight.”31

  That’s interesting, but modern science has a more precise neurophysiological explanation. “The mechanism behind ear movements is sophisticated,” says Bastiaan Coen Ter Meulen, a researcher scientist at Erasmus MC (medical center) in Rotterdam. Our external ear muscles and those of our closest relatives, the apes, are controlled by a specific area in the brainstem, and he says, “[c]ompared to animals, especially bats and cats, this nucleus is rather small in humans.” (As an aside, while performing the first EEG to document the brain waves of a woman whose ears moved repeatedly while she was unconscious, Ter Meulen found that one of the muscles that moves our eyes also slightly moves our ears, which is why, he explains, when we look to one side or the other, our ears pull back a bit.)32

  Given the difference between our ear muscles and those of most of the nonprimate animal kingdom, Darwin’s disdain for the auriculares was more solidly based than his dismissal of the auricle itself. But his proclamation of total vestigiality was a step too far if for no other reason than that the shape of the ear itself is strongly influenced by where the intrinsic and extrinsic muscles fit into the tissues.

  It’s true that most of us cannot move our ears at will, at least not without a serious amount of effort and training, but it’s also true that Darwin himself had seen one man who could perform a whole set of exercises with his “useless” ear muscles and conceded that with practice others might also be able to do likewise. Darwin was right when he said that our inability to move our ears about as though we were bats, cats, horses, or dogs, who move their ears to locate the source of a sound, is “compensated by the freedom with which [humans] can move the head in a horizontal plane, so as to catch sounds from all directions.” But modern studies plus the inevitable anecdotal reports suggest that as many as 20 percent of the human race, one in five of us, are actually natural ear wigglers.33 This privileged group includes the late Leonard Nimoy, Sean Connery, Stephen Colbert, and not-quite-human Elmo, all of whom may or may not be able to perform the other most difficult human muscle maneuvers: touching the nose or chin with your tongue, lifting one eyebrow (Nimoy again), twitching the nose like Bewitched’s Elizabeth Montgomery, curling the tongue into a tube, tickling one’s own self, or sneezing with the eyes open. Some people add touching your elbow with your tongue to that list, but the U.S. Records Management Team at Guinness World Records says no, that trick’s not all that hard to do.34 In short, some people are born ear wigglers, others can be taught, and still others wish they couldn’t: moving ear syndrome, a type of muscle disorder like a twitch, leads to involuntary ear movements that can be remedied with Botox injections.35

  The last word on the importance of the auriculares might belong to neurologists treating patients who are recovering from stroke or facial paralysis. Because wiggling your ears requires complicated coordination of multiple muscles, learning more about how this happens
may lead to a better understanding of disorders of the facial muscles such as the paralytic Bell’s Palsy. And better yet, learning more about how some of us are able to control our ear muscles may have something to teach us about the body’s primary control center, the brain. Jerome J. Miller is a Research Fellow of the National Trauma Research Institute, Monash Alfred Psychiatry Research Centre of the Alfred & Monash University Central Clinical School in Melbourne (Australia). In 2014, he published an article in the journal Medical Hypotheses whose central proposition he summarized this way: “[r]esearch has shown that activation of higher-order cognitive processes create larger gains in recovery than repetitive tasks, most likely due to neuroplasticity. That is, neuroplasticity is promoted by task complexity. Ear wiggling is a rare skill among humans yet may activate and promote advanced recovery after a brain injury. Increased cognitive complexity of learning a new task could allow insights into plasticity in learning new motor tasks and the role of cognitive complexity in learning that task. This paper focuses on a hypothesis relating to white matter pathways dormant in most people (such as those related to ear wiggling). If these pathways can be triggered by electrical/magnetic stimulation and/or higher-order thought into becoming consciously controllable, then it is possible that activation of a dormant, complex skill may assist in re-growth or repair of brain-damaged pathways. The broader potential impact of the proposed hypothesis is that ear wiggling could be used for improving the recovery of TBI or stroke subjects via neuroplasticity processes.”36

  Imagine that. Until now, our external ear muscles may have seemed pretty much useless except for performing party tricks, but this new possibility of a serious medical value suggests that absent some extraordinarily dramatic mutation affecting our entire species, they are unlikely to disappear anytime soon.