We all hope our lives will have meaning. But for the agents of biochemistry, our deaths are just another job number.
Nobody’s yet come up with a formula for physical immortality, so many of us construct instead a future beyond the grave through metaphysical notions of afterlife—heaven, reincarnation, cryogenics. Others seek the salve of legacy. We like the idea of writing our chapter in a never-ending story. Philanthropists donate libraries, establish trusts. Politicians alter flags in their own image. Some people name their children after themselves. The rest of us, seeking to leave behind some physical evidence of our contribution, just build patios.
But thinking about death alters our behaviour in more subtle ways, too, say researchers, who cite what they call “mortality salience manipulations”. One study found that we get funnier, others have shown that people become more tolerant of racism, more nationalistic, more antagonistic towards gays and lesbians and prostitutes. It seems we get more right-wing when death confronts. Other work hints that, in some Western cultures at least, the closer we get to death, the less we fear it. This seems only reasonable: younger people have more to lose, harbour ambitions, relish prospects, have projects in train.
So how does your body decide when it’s time to call it a day? It was once thought that cells were immortal, that they could simply replicate forever. But we now know they eventually run up against the Hayflick Limit, after between 50 and 70 divisions. Every time a human cell divides, the telomeres get shorter. Telomeres are strings of nucleotides, buffers at each end of a chromosome, which form protective caps that prevent any collision or inadvertent fusion with neighbouring chromosomes. Your chromosomes can clone themselves, but the enzymes that Xerox your DNA never quite reach each end, so those chromosomes shrink every time they divide. There’s some evidence to suggest that immune function degrades as telomeres shorten, which may be borne out by the reality that people rarely die of old age: something usually kills them first. Even if it doesn’t, your telomeres will eventually become so truncated that they’ll simply stop dividing. That’s your Hayflick Limit. Game over.
Some have suggested that the longer your telomeres, the longer you can expect to live. In 2003, researchers at Glasgow University picked a short-lived study subject—zebra finches—to test the contention. They measured the telomeres of 99 birds not long after fledging, then regularly throughout their lives. Then they waited: the most ephemeral finch lasted just over six months. But the study wasn’t complete for another nine years, when the most doughty finally fell off its perch. The longest-lived birds turned out to be the ones with the longest telomeres, and the most reliable predictor of lifespan, found the team, was telomere length at 25 days old.
So what happens to your body when your last chromosomes switch off? Well, if you aspire to death with dignity, better stop reading, because it’s not pretty. On death, all your muscles relax, including the ones you were using to hold in wee and poo. While there can be no peristalsis, you will… leak, somewhat. The good news is that it’s not your problem.
Then you will enter autolysis—your body will start to consume itself. Once your cells are denied oxygen, chemical reactions in them produce acidic enzymes, which literally begin to digest cell membranes. Typically, this starts in your liver and brain, where enzyme activity is high, before your other organs begin to break down, too. If you signed an organ donor card, your heart and lungs must be fed oxygen artificially until they can be removed, but less-energy-hungry organs—corneas, bone marrow, even heart valves—can still be extracted 12 hours after you die.
Dying blood cells will start to pool in whatever extremity is lowest, and maybe your skin will take on a purple hue there. Then your muscles will begin to stiffen. The moment you stop breathing, your cells stop making adenosine triphosphate, the chemical that tells living muscles to relax after contraction. Fibres start to tense—first in your eyelids, neck and jaw—two to four hours after death. Within 12 hours, as lactic acids dissipate in your larger muscle groups, you’re in full rigor mortis. By now, your body temperature has equalised with the ambient surroundings, which hopefully will be the chill of an undertaker’s workshop. His or her craft is to arrest these processes until the formalities of your funeral and interment or cremation are done.
This is how we all want to go—a pretty corpse—but let’s for a moment assume the worst: that you met some unfortunate fate alone and far from the saving grace of formaldehyde, in which case the gut bacteria your immune system was keeping pinned down now have access to all areas. They’ll start eating that acidic leachate from your cells, and use it to start consuming your intestines, then the surrounding tissues, before entering your digestive system and lymph nodes. Then they will head for your liver and spleen, and on into the heart and brain. So predictable is that pathway that forensic experts can estimate the time of someone’s death from where their gut bacteria have reached.
Your soft tissues are turning from molecules into gases, liquids and salts. You are, I regret to inform you, putrefying.
What was until now an aerobic process is usurped by anaerobic microbes that ferment the sugars in your tissues. As they do, they emit methane, hydrogen sulphide and ammonia, raising blisters on your skin. You’ll start to blow up like a balloon, and that extra pressure will force more body fluids from your various orifices.
Some of the compounds produced in putrefaction are well understood, and known by the temporal descriptions cadaverine and putrescine. They mark the beginning of bloating. They’re not novel—they were always inside you, and might have made their presence known if you ever suffered bad breath.
Two more are skatole (no prizes for guessing what that smells like) and indole, which sort of smells like mothballs. Now here’s an odd thing: in low concentrations, both can actually smell rather pleasant. Indole is found in jasmine oil, and skatole, believe it or not, is used—judiciously—to flavour some ice creams. But quirky facts are little comfort to you now, because you’re producing more than 400 other compounds that are colluding to make you stink to high heaven.
Those anaerobic bacteria are starting to metabolise your haemoglobin molecules using sulphur. The by-product—sulfhaemoglobin—will turn you first yellow, then greenish-black, by which time your decomposition is well advanced. Sheets of your skin will rent and peel away from your frame. Your abdomen may actually burst from the pent-up pressure within. A vast cohort of creatures, attracted by your sickly-sweet stench, have been waiting for these gates to open. They occupy you. Now, you are an ecosystem, and the metaphorical grazing herds of your visceral Serengeti will be the maggots, so many that their writhing attentions will raise your body temperature by as much as 10ºC.
After just a few hours, they will crawl replete from your corpse to moult into larger versions of themselves, before returning to fill the void they’ve created. Then they’ll repeat the cycle until, as stage-three maggots, they’ll leave you again to pupate into adult flies. But they’re not finished with you: they’ll stop to lay as many as 250 eggs each on your remains, perpetuating the cycle until there’s nothing left.
For every kilogram of dry body mass you once weighed, you will free up roughly 32 grams of nitrogen, 10 grams of phosphorus, four grams of potassium and one gram of magnesium. Your chemical legacy is actually toxic at first. It may be the excess of nitrogen, or maybe your antibiotics, consumed by the maggots but excreted unprocessed. You’ll kill off some of the vegetation around you, but ultimately your essence will be assimilated into the wild. You will dissemble into the elements from which you were once made.
Maybe you did donate a library, but your enduring legacy will be 7×1027 atoms—mostly hydrogen—the building blocks of some new organism. Whether you meant to or not, you have donated your body to science.