Spare Parts Read online

  As for a human tail, embryologists now know that a gene named Wnt-3a oversees the process of tail growing in mice, and that we actually have this gene that produces the “tail” on the human embryo whose cells normally disappear as a natural result of apoptosis (programmed cell death). But—and it’s an important but—we use these genes for other parts of the body, rather than to grow a real, living tail like some other mammals. On the rare occasion when a mistake happens and a mutation occurs, Bingo! A baby with a true tail.30

  While different authors may cite different studies, the common wisdom is that there have been about one hundred infants born with tails who were documented in medical journals and papers, some reputable, some not so much. But in reality what looks like a newborn human’s tail may be something else entirely. Perhaps it is a coccygeal process or coccygeal projection, that atavistic tail left over from the embryonic extension of the spine containing one or more vertebrae. The second, more common “tail” is a caudal (tail-like) appendage, a soft structure containing blood vessels, nerves, and muscle tissue, but no vertebrae. It may be attached at the base of the spine or higher up on the spinal column. As a 1982 report in the New England Journal of Medicine noted, this tissue differs from the tail of other vertebrates because it “does not contain even rudimentary vertebral structures. There are no well-documented cases of caudal appendages containing caudal vertebrae or an increased number of vertebrae in the medical literature, and there is no zoological precedent for a vertebral tail without caudal vertebrae.”31

  Surgical experience has shown that a coccygeal process can be amputated with little consequence. Once upon a time, highly reputable physicians and surgeons thought the same was true of the caudal appendage. In 1984, a report in the respected journal Human Pathology said that a “vestigial tail” could be “easily removed surgically, without residual effects.”32 A year later, the equally prestigious Journal of Neurosurgery reported that “the true human tail is a benign condition not associated with any underlying [spinal] cord malformation.”33

  But increasingly more precise diagnostic imaging techniques have made it abundantly clear that an infant born with a caudal appendage requires a complete physical evaluation prior to surgery. What looks like a tail may really be a spinal dysraphism, a term used to describe a group of congenital abnormalities including defects in the vertebrae, the spinal cord, and the roots of nerve attached there.34 There may also be other associated problems and defects ranging from cleft palate to clubfoot to abnormalities of the spinal cord itself. In 1998, when a team of doctors from the Department of Pediatrics at the National Taiwan University Hospital (Taipei) examined more than fifty infants born with between 1960 and 1999, each with a caudal appendage, and then toted up the list of defects most likely to be associated with the fake tail, this is what they found:

  DEFECTS ASSOCIATED WITH “HUMAN TAIL”

  Defect # Patients with Defect/# Patients

  Spinal malformation 29/59

  Meningocele (spinal cord protruding through the spinal column) 8/29

  Spina bifida only 21/29

  Lipoma (fatty tumor) 16/59

  Syndactyly (webbed fingers and/or toes) 2/59

  Hemangioma (vascular tumor) 1/59

  Cleft palate 1/59

  Clubfoot 1/59

  Tetralogy of Fallot (heart defects) 1/59

  Their conclusion, of course, was that the caudal appendage is not, as was once assumed, “a benign occurrence in otherwise healthy children.” In fact, they proposed that “[p]reoperative detailed image studies are needed to clarify the possibility of tethered spinal cord syndrome developing in the future and thus prevent it. Magnetic resonance imaging is the modality of choice if available. Long-term follow-up for possible sequelae after operation, especially in cases with spinal dysraphism, is necessary.”35, 36 True, said a similar 2013 report from the Sheri-Kashmir Institute for Medical Science (Srinagar, India). “Some authors,” the Indian doctors wrote, “have considered this rare and curious condition to be evidence of man’s descent from or relation to other animals, while others have made it the subject of superstition. Advanced imagining technology in recent decades has allowed more thorough investigation of these patients and better defined the association of such lesions with spinal dysraphism requiring a complete neurological history and examination as well as magnetic resonance imaging or computed tomography scan. After diagnosis, microsurgery should be performed if there is any intraspinal component, to avoid damage and neurological deficit.”37

  So much for the tail.

  Now for the tailbone.

  AT THE TAIL END

  The coccyx, otherwise known as your tailbone, is three to five vertebrae usually fused together. It is connected to the sacrum, a similarly fused set of bones. Both the coccyx and the sacrum are part of the ring of bones that form your pelvis, and most of the time, it just sits there, bothering no one. In fact, you are most likely to notice your coccyx only if you unfortunately fracture it by falling onto your rear end or, in the case of women, during childbirth. In extreme cases, if the fracture does not heal well, your doctor may recommend a coccygectomy, that is, surgical removal of the coccyx, sitting neatly in the pelvic girdle.

  Nonetheless, the normally shy and quiet tailbone may be one of the easiest platforms on which to stand when disputing the idea that vestigiality and rudimentary mean no-good-for-anything. It’s true that your tailbone doesn’t bear weight while you are standing, but it is a thoroughly useful part of the boney frame that keeps you upright when you are sitting. In addition, it is an attachment site for ligaments, tendons, and important muscles including the pelvic sling muscle (pubococcygeus) that helps supports your pelvic organs as well as the renowned gluteus maximus, the largest of the muscles that assist in moving you forward when you walk, run, hop, or skip. In other words, it is many things, none of them useless, and as even those who credit evolution rather than a deity for our existence will acknowledge (incorporating a bit of poetic license here):

  “The knee bone’s connected to the thigh bone,

  The thigh bone’s connected to the hip bone,

  The hip bone’s connected to the tail bone,

  Now hear the word of the Lord!”

  FLOWERS & FUNNIES & MEN WITH TAILS

  Tossing an idea out into the world is like tossing pebbles into a pond: you never know how far the ripples will go. Darwin’s musing on the missing human tail certainly rippled far and wide, from the serious to the popular, the latter a place where hucksters and promoters mined for public relations gold.

  Edward William Cole (1832–1918), an Englishman who migrated first to South Africa and then to Melbourne (Australia), dug with the best of them. After a series of menial jobs Down Under, in 1873 he decided to open a small bookshop. Having read Darwin and assimilated a central fact that he interpreted as our universal descent from monkeys, he wrote and published in the Melbourne Herald in 1873 an advertisement titled “Discovery of a Race of Human Beings with Tails.” This was the supposed report of a “Mr. Thomas Jones, the talented and observant traveller [who] informs us that he arrived by ship at the native village of Etihwretep, on the north-east coast of New Guinea, on the 24th of December, 1871” that states that he came across a whole tribe of men with, yes, tails. Not surprisingly, Cole’s ad brought him both notoriety and customers, which he multiplied with a series of popular books that include Cole’s Funny Picture Book (he offered a reward of one hundred pounds to anyone who could prove it was not the funniest book of its kind) along with gardening books such as Cole’s Penny Garden Guide, rumored to have been abridged from someone else’s larger and more complete work.

  In 1883, he opened Cole’s Book Arcade, boasting of a never-verified two million books on the shelves, permission for customers to browse and read the books on his store’s shelves for as long as they wished, plus a band playing on the second floor each afternoon. After that, it was on its way to becoming one of Australia’s major book businesses, which, with typical modest
y, Cole called “The largest bookstore in the world.” That remains a question, but his success was obvious and his shop so famous that authors like Rudyard Kipling and Mark Twain made it a point to stop by when in the neighborhood. After Coles died in 1918, the Book Arcade remained a popular meeting place for eleven more years until it closed its doors in 1929.38, 39

  4

  Ear Rings

  The Auricular Muscles

  “Malvolio: Mistress Mary, if you prized my lady’s favor at anything more than contempt, you would not give means for this uncivil rule. She shall know of it, by this hand.

  Maria: Go shake your ears.”

  —William Shakespeare, Twelfth Night, Act 2, scene 3

  “The extrinsic muscles which serve to move the external ear, and the intrinsic muscles which move the different parts, are in a rudimentary condition in man, and they all belong to the system of the panniculus; they are also variable in development, or at least in function. I have seen one man who could draw the whole ear forwards; other men can draw it upwards; another who could draw it backwards; and from what one of these persons told me, it is probable that most of us, by often touching our ears, and thus directing our attention towards them, could recover some power of movement by repeated trials. The power of erecting and directing the shell of the ears to the various points of the compass, is no doubt of the highest service to many animals, as they thus perceive the direction of danger; but I have never heard, on sufficient evidence, of a man who possessed this power, the one which might be of use to him.”

  —Charles Darwin, The Descent of Man

  BREATHING THROUGH YOUR EARS

  Artists and sculptors from Praxiteles to Picasso have celebrated the beauty of the human body with its rounded female arms and curving hips and broad male shoulders and long sinewy legs. Facial features also get their due, none more so than Mona Lisa’s eyes that follow you around the room and her mouth with its wonderful, mysterious smile.

  But who appreciates the equally beautiful and thoroughly useful shell-shaped human ear?

  Practically no one, that’s who—except, perhaps, the ancient Egyptians. Their pictures of people were rather stick-like, but their art celebrated the ear as a symbol through which to communicate with the gods, either via a sculpted model of an ear or with an ear-stele, a stone or wooden slab decorated with an image of one or two or three ears, to symbolize the human placing the call. Under the human ears, there were also images of the appropriate gods, most commonly Ptah, the god of craftsmen and artists; Amon, the father of life; Horus, war (and childbirth); Thoth (wisdom and writing); and Isis, the mother of them all.1, 2

  The most famous ear in art isn’t a statue or a picture. It’s the one Vincent Van Gogh sliced away at in December 1888 and is said to have handed to a prostitute and then memorialized the following month in two paintings, Self-portrait with bandaged ear and Self-portrait with bandaged ear, easel and Japanese print.3 Although a thoroughly nonviolent man, if pushed to choose a side, Charles Darwin would probably have gone with Van Gogh.4

  Darwin was not a fan of the human auricle a.k.a. the pinna, the pieces of skin-covered shell-shape cartilage on either side of your head. He considered this outer ear an unnecessary add-on, and he called the auriculares, the muscles inside and around the outside of the auricle, useless and therefore vestigial. He was completely wrong about the auricle and maybe half right about its muscles. To see how he got there, start with this simple question: can you breathe through your ears? The short answer is no. The longer answer is also no, but with caveats.

  As Ernst Haeckel’s drawings of the developing fetus show (Chapter 2), early in our embryonic development we humans look a lot like fish. It’s not just what looks like a tail; it’s also the slits or pouches on the side of our head that mimic gills, the openings through which fish breathe. But as we grow from embryo to fetus, these slits fold into the Eustachian tubes that connect our throat with our middle ear, open and close to stabilize pressure inside the ear, muffle sound to protect the ear from sudden loud noises, and provide a path through which secretions and foreign material drain from the middle ear.

  This seems to parallel the anatomical path of one of our very earliest ancestors, the 370-million-year-old Panderichthys. Pander, for short, is a species halfway between a fish and the first animals to come out of the water onto dry land (or back onto dry land, as University of Oregon paleontologist and geologist Greg Retallack suggests, Chapter 6). He, or she, had both gills and round tube-like ear bones that eventually evolved into the land animals’ ears.5, 6 Our vertebrate inheritance is a pair of organs that serve two purposes. The first, of course, is powering our ability to hear the world around us. The second is helping to manage our ability to stay upright while listening, a function maintained by fluid-filled tubes (the semicircular canals) in the inner ear. As for our having a pair of ears, in the words of the Greek Stoic philosopher Epictetus (55–135 CE), “We have two ears and one mouth so that we can listen twice as much as we speak.”

  HOW WE HEAR

  Like Caesar’s Gaul,7 mammalian ears, including ours, are divided into three parts: The outer ear, the middle ear, and the inner ear.

  The Three-Part Ear, Gray’s Anatomy

  Darwin considered the outer ear an annoyance. “The whole external shell,” he wrote in The Descent of Man, “may be considered a rudiment, together with the various folds and prominences (helix and anti-helix, tragus and anti-tragus, &c.) which in the lower animals strengthen and support the ear when erect, without adding much to its weight.”

  Well, not quite. In fact, the auricle is an efficiently designed trumpet that funnels sound waves into the concha, the slightly off-center opening with a bump called the tragus in front and another, the anti-tragus, in back.8 Behind the concha is the auditory canal, a tube-like structure about an inch long, lined with skin, fine hairs, and glands that secrete the stuff that makes up your earwax, known in science-speak as cerumen.

  SMELLY EARS = SMELLY ARMPITS

  Everyone’s earwax or cerumen is a blend of secretions from the glands in the external ear canal. But is your own earwax wet or dry? Yellow-brown or white? Smelly or not so much? Researchers at Philadelphia’s Monell Chemical Senses Center and the University of Pennsylvania School of Medicine in Philadelphia say the answers to these questions may predict your ethnicity. “Our previous research has shown that underarm odors can convey a great deal of information about an individual, including personal identity, gender, sexual orientation, and health status,” says Monell’s George Preti. Finding a variation of a gene known as ABCC11 linked to scent in both underarm sweat and earwax, the folks at Monell went on to test earwax from eight healthy male Caucasians and an equal number of East Asians. No, they didn’t smell the stuff themselves. They collected earwax samples, heated the samples in glass vials to warm up the organic compounds in the wax so they would release vapors, then used gas chromatography mass spectrometry (a lab test that separates the vapors) to identify the compounds in the wax. They identified twelve different ones in all the wax, but the Caucasian guys had much higher levels than did the others, thus accounting for the smellier earwax. Does this matter? Yes. “Odors in earwax,” Preti says, “may be able to tell us what a person has eaten and where they have been. Earwax is a neglected body secretion whose potential as an information source has yet to be explored.” One thing he will not have to explore is the idea that the consistency of a woman’s earwax might predict her risk of breast cancer. This suggestion emerged from a Japanese study several years ago to make the rounds of women’s magazines has never been replicated, and in 2011, an Australian study of 3,598 Caucasian women found “no evidence for an association” between the earwax gene and the risk of breast cancer. Whew!9, 10, 11

  The auditory canal ends at the membrane called the tympanum or “ear drum” because, yes, the Latin and Greek words tympanum and tympanon mean drum. As sound waves enter the concha and the auditory canal, the eardrum adjusts the pressure inside the ear, modulati
ng the waves so that their energy does not overwhelm our ability to understand the vibrations as words or music or just plain noise.

  Behind the tympanum is the middle ear, a hollow space known as the tympanic cavity that links the Eustachian tube to the nasal cavity. This link makes it possible to equalize pressure between the middle ear and throat, the thing you hope to accomplish when holding your nose and blowing as fluctuating air pressure closes your ears at a plane’s take-off or landing. The tympanic cavity holds three ossicles (small bones), the Latinate malleus, incus, and stapes, which, in deference to their shapes, are also known, respectively, as the hammer, the anvil, and the stirrup. These bones work together. The malleus pushes the incus, which pushes the stapes, sending vibrations on to the oval window, a small membrane that covers the opening to the cochlea, a spiral tube coiled like a snail’s shell (the Greek word kochlos means snail). Inside the cochlea is the organ of corti, the structure that enables us to interpret and identify sound wave energy as everything from words and music to the almost silent click of a key in a lock or the amazingly loud crash of your favorite crystal bowl hitting the kitchen floor.