The Body Rhymes

You ran on her hormones, then ran out

For the first days of your life you were not running on your own chemistry. In the last weeks of pregnancy a mother's estrogen crosses the placenta and switches on tissue all over the body of the child. Then the baby is born, the supply is cut, and the hormone drains away over a few days. The drain is the part you can see.

About 1 in 20 newborns, boys and girls alike, leak actual milk from the breast. Khan 2015 The old word for it is witch's milk, from a time when people thought a spirit was stealing it in the night. Most newborns, around 70 percent, have breast buds you can feel. And somewhere between 3 and 10 percent of newborn girls have a small vaginal bleed in the first week, the lining their mother's estrogen built up, shedding now that the estrogen is gone. Ogawa 2024 None of it means anything is wrong. It is a hormone withdrawal, the first of the millions she will run on her own later.

Now skip to the far end, where the same tide turns and runs the other way. After menopause a woman's estrogen falls while her body keeps making a little testosterone, and the ratio tips. Follicles that sat quiet for sixty years read the new signal and wake up: roughly 4 in 10 women past menopause grow new facial hair, most often on the chin. Ali 2011 Men get the mirror image of the same chemistry. The androgens that thin the hair on top of a man's head turn the fine hairs inside his ears and nose into coarse ones, a switch that can take thirty years of exposure to throw, which is why it belongs to old men and not young ones. Randall 2008

You arrive on a flood of someone else's hormones and leave on the slow reversal of your own. Both times the body grows hair and tissue it has no use for, and both times it is chemistry running with nobody at the wheel.

The light comes up slowly, and goes down the same way

A newborn can see, but barely, and only up close. Its sharpest focus falls at about 8 to 12 inches, which happens to be the distance from a feeding baby's eyes to its mother's face. AAP Color arrives over months. At first only big, saturated, mostly red things register at all, and the world comes in dim and soft and partial.

It leaves the same way. The lens of the eye yellows and stiffens over the decades, and the pupil shrinks by about 0.4 mm every ten years. Put those together and the retina of a 60-year-old takes in roughly a third of the light a 20-year-old's does in the same room. Weale 1961 The yellowing lens absorbs blue first, so blues go muddy and dark while the reds and yellows hold on. Pokorny 1987

You can watch this happen to a painter. Claude Monet's cataracts browned the lenses of his eyes in his seventies. By 1922 his water-lily canvases had gone red and muddy, and he had taken to sorting his paint tubes by the printed labels because he could no longer trust the colors to his eye. Gruener 2015 Then surgeons removed the clouded lens in 1923, and the opposite happened. With nothing left to filter it, blue and even ultraviolet light came flooding in, and he complained that everything now looked too blue. He went back and repainted some of the muddy canvases once he could see them again.

The world dims and yellows on the way out in nearly the same way it was dim and colorless on the way in. The first clear thing a baby sees is a face a foot away. The eyes meet in the middle, at a world of accurate color most people never think to be grateful for.

You come in and go out without them

A crying newborn usually makes no tears. The plumbing is there from birth, but for the first few weeks, sometimes a couple of months, it does not produce enough to spill, so the cry is loud and dry. Isenberg 1998 Tears that actually fall are a skill the body switches on a little after it first needs to cry.

It switches them off again at the other end. Tear production drops with age until dry eye is common enough that more than one in five women over 75 has it. TFOS DEWS II The eyes that could not yet cry at the start become eyes that can no longer quite manage it. In between sits a whole life of working tears the body never once mentions.

Unfinished at the start, undone at the end

A newborn skeleton is a kit that has not been fully assembled. A baby has around 270 separate bones, many still soft cartilage, that will knit over the next twenty-odd years into the roughly 206 of an adult. StatPearls (You will see 300 quoted a lot. It is a rounded guess, because the true count depends on when you decide to count the pieces that have not fused yet.) The skull is the clearest case. It ships in plates with gaps between them, the soft spots, so the head can fold to clear the birth canal and then keep pace with a fast-growing brain. You can feel a pulse through the largest gap. It does not close over until sometime after the first birthday. Fontanelles

At the far end the frame comes apart. The obvious part is height: you lose an inch or two, more in women, as the cushioning discs between the vertebrae dry out and the spine settles and curves. Sorkin 1999 The stranger part is the face. The bones themselves shrink and tilt, so the eye sockets widen by something like a sixth, the angle of the jaw opens out, and the middle of the face pulls back and down. Shaw 2011 The skull's own openings, sealed in childhood, slowly widen again. The frame that took twenty years to put together spends its last years quietly taking itself apart.

The body also stops holding its own heat at both ends, for matching reasons. A newborn has too little fat to insulate it and cannot shiver well yet. An old body has lost the fat and the muscle and the quick blood-vessel reflexes, and often does not feel the cold coming on at all. Kenney 2003 We put hats on babies for the same reason we worry about an old man in a cold house. Neither end can keep itself warm.

You are built up and taken down in the same direction. Soft, unfinished, and unable to hold your own heat at one end. Softening, unsettling, and unable to hold it again at the other.

A hole at the start, a hole at the end

You cannot remember being a baby. Almost no one's memories reach back before about age three, and the earliest ones are thin and few. Bauer 2015 The old assumption was that an infant brain simply could not record yet. Newer work points the other way: babies do form memories, but the hippocampus, the brain's filing clerk, is rewiring itself so fast in the first years that the early files get overwritten or lost track of. Akers 2014 The memories may be made and then buried. Either way, the start of your life is a room you cannot get back into.

The other hole opens at the end, and it fills from the wrong side. In ordinary aging it is recent memory that thins first, what you did this morning, while the deep past stays sharp. Ask a very old person for their most vivid memories and a strange share of them cluster in one window, roughly ages 10 to 30, the years that built who they are. Rubin 1997 The newest memories will not stick and the oldest will not leave. A life that opened behind a wall you cannot see over closes with the recent years dissolving while the early ones stay lit.

The same reflex at both ends

Stroke the sole of a newborn's foot and the big toe curls up while the others fan out. It is called the Babinski response, and in a baby it is exactly right. Around the first or second birthday it disappears, because the long nerves running from brain to spinal cord finish wrapping themselves in insulation and the matured brain takes over and quiets the reflex. From then on, stroke a healthy sole and the toes curl down. StatPearls

The up-going toe comes back exactly once more, when those same nerves are damaged. A Babinski sign in an adult is one of the oldest tells in neurology that something has broken in the wiring between brain and cord. It is the reflex you were born with, lost as a toddler, and will only ever show again if the wiring fails. The newborn grasp runs the same arc. A baby's grip is strong enough that it can briefly hang from a bar by its own hands, Futagi 2012 the reflex fades in infancy, and it reappears in some dementias, when the front of the brain wears down and stops holding it in check. Clinical Methods

This is not a metaphor, it has a clinical name. In Alzheimer's disease, abilities tend to fall away in close to the reverse of the order a child gains them. The neurologist Barry Reisberg built a standard staging scale on exactly that pattern: a person who can no longer pick out their own clothes is functioning at about the level of a five-to-seven-year-old, and by the last stage the losses run backward through the first year of life, speech down to a few words and then one and then none, the ability to walk, then to sit up, and finally, the way it came first in the baby, the ability to hold up the head. Reisberg 1988

It is easy to make this prettier and falser than it is, so here is the careful version. This is the brain failing, in a disease, not a feature of growing old. Most people reach the end without their toes ever turning back up. The order is rough, not a law, and a great deal survives it. People deep in dementia still laugh at a joke, which no neat reversal of childhood would predict. Ageing & Society 2024 What is left when you strip out the overreach is still strange enough. The body keeps a few of its very first reflexes in a back room for ninety years, and the only key that opens that room again is damage.

You are already in it

If you are in your thirties or forties with no baby and no aging parent in the house, both ends of this are easy to file as other people's news. They are not. The far end has already started in you. It just starts so quietly that it reads as nothing at all.

The first move is usually the eyes. Somewhere around 42 the lens stiffens enough that you can no longer pull focus up close, and you start holding the menu a little farther from your face. Presbyopia It is called presbyopia, it is universal, and it is the same lens that will keep yellowing and dimming for the rest of your life. The highest sounds began slipping out of range even earlier, in your twenties. Cochlear aging Your hair has been graying since your thirties. Panhard 2012 You passed peak bone around thirty and have given a little back every year since. Baxter-Jones 2011 The retina is already letting in less light than it did when you were twenty.

None of that is a countdown, and the countdown is not the point. The shape is the point. You spent the first years of your life unfinished, running on borrowed chemistry, unable to hold your own heat or your tears or your memories or the curl of your own toes. You will spend the last ones handing those same things back, roughly in reverse. The long, steady stretch between, the body you think of as simply and permanently yours, is the smallest part of the loop and the only part that holds still.

You were yellow once. You ran on someone else's hormones, and you could not yet cry. Some of that is waiting for you again at the far end, and that is less a thing to dread than a thing to notice. You are not an object slowly wearing out. You are a process the universe is briefly running, and for a few decades in the middle it runs so smoothly you can forget it is running at all.

Sources, and how to read them

Every number here is tied to a real source, cited where it appears. The research behind it was told to attack the claims rather than flatter them, which is why the awkward facts are left in: the famous "300 bones" is a rounded guess, the line that "ears never stop growing" is mostly gravity and not growth, and the reflexes that come back at the end come back as the brain fails, not as a normal part of getting old.