The Body: A Guide for Occupants

1: How to Build a Human

• “DNA exists for just one purpose – to create more DNA. Your DNA is simply an instruction manual for making you.”
• “What genes specifically do is provide instructions for building proteins. Most of the useful things in the body are proteins.”
• “Don’t forget that your genes come from ancestors who most of the time weren’t even human. Some of them were fish. Lots more were tiny and furry and lived in burrows. These are the beings from whom you have inherited your body plan. You are the product of three billion years of evolutionary tweaks. We would all be a lot better off if we could just start fresh and give ourselves bodies built for our particular Homo sapien needs – to walk upright without wrecking our knees and backs, to swallow without the heightened risk of choking, to dispense babies as if from a vending machine. But we weren’t built for that.”
• DNA can last for tens of thousands of years, longer than anything you own, any other trace of you. It copies in extreme fidelity with about one error for every billion copied - about three mutations per cell division
• enzymes, hormones and antibodies are all types of proteins
• about a hundred mutations that aren’t either of your parents
• “No one can say why those seven billion billion billion atoms have such an urgent desire to be you”
• “Unpacked, you are positively enormous.”
• “is soft and rather lovely, is accommodatingly mobile and pliant, reproduces itself with enthusiasm, makes jokes, feels affection, appreciates a red sunset and a cooling breeze”
• “Suicide by lifestyle takes ages. Even when you do nearly everything wrong, your body maintains and preserves you.”
• “We are not perfect by any means, goodness knows. We get impacted molars because we have evolved jaws too small to accommodate all the teeth we are endowed with, and have pelvises too small to pass children without excruciating pain. We are hopelessly susceptible to backache. We have organs that mostly cannot repair themselves”
• “What is perhaps most remarkable is that nothing is in charge. Each component of the cell responds to signals from other components, all of them bumping and jostling like so many dodgem cars, yet somehow all this random motion results in smooth, coordinated action, not just across the cell but across the whole body as cells communicate with other cells in different parts of your personal cosmos.”
• “Every day, it has been estimated, between one and five of your cells turns cancerous and your immune system captures and kills them.”
• “Nearly all animals produce their own vitamin C, but we can’t”

2: The Outside: Skin and Hair

• The outermost surface of the epidermis, called the stratum corneum, is made up entirely of dead cells
• Skin flakes are properly called squames (meaning scales).
• Pimples plague young people simply because their sebaceous glands – like all their glands – are highly active
• As David J. Linden points out in Touch, if you sink a spade into gravel or sand, you can feel the difference between them even though all you are touching is the spade
• Women are much better than men at tactile sensitivity with fingers, but possibly just because they have smaller hands and thus a more dense network of sensors. (not specific enough check the source: Linden, Touch, p. 73.)
• melanin. It is one of the oldest molecules in biology and is found throughout the living world. It doesn’t just colour skin. It gives birds the colour of their feathers, fish the texture and luminescence of their scales, squid the purply blackness of their ink. It is even involved in making fruit go brown.
• Its [melanin] production slows dramatically as we age, which is why older people’s hair tends to turn grey
• All of us, whatever our race, have the same number of melanocytes
• It used to be thought that depigmentation probably took perhaps ten to twenty thousand years but now thanks to genomics we know it can happen much more quickly – in probably just two or three thousand years. We also know that it has occurred repeatedly.
• light skin may be a consequence of human migration and the rise of agriculture. The argument is that hunter-gatherers got a lot of their vitamin D from fish and game, and that these inputs fell sharply when people started growing crops, especially as they moved into northern latitudes. It therefore became a great advantage to have lighter skin, to synthesize extra vitamin D.
• Pregnant women frequently undergo a darkening of the nipples and areolae, and sometimes of other parts of the body such as the abdomen and face, as a result of increased production of melanin. The process is known as melasma, but its purpose is not understood.
• When the body is poised for a fight, it mostly diverts blood flow to where it is really needed – namely the muscles – so why it would send blood to the face, where it confers no obvious physiological benefit, remains a mystery. One possibility suggested by Jablonski is that it helps in some way to mediate blood pressure. Or it could just serve as a signal to an opponent to back off because one is really angry.
• ‘Some people have de-pigmented, some have re-pigmented,’ Jablonski says. ‘Some people have altered skin tones a lot in moving to new latitudes, others hardly at all.’ Indigenous populations in South America, for instance, are lighter skinned than would be expected at the latitudes they inhabit. That is because in evolutionary terms they are recent arrivals. ‘They were able to get to the tropics quite quickly and had lots of gear, including some clothing,’ Jablonski told me. ‘So in effect they thwarted evolution’
• We are actually as hairy as our cousins the apes. It’s just that our hair is much wispier and fainter.
• Hair is unique to mammals.
• it is known from genetic studies that dark pigmentation dates from between 1.2 and 1.7 million years ago. Dark skin wasn’t necessary when we were still furry, so that would strongly suggest a time frame for hairlessness.
• Hair on the head acts as a good insulator in cold weather and a good reflector of heat in hot weather. According to Nina Jablonski, tightly curled hair is the most efficient kind ‘because it increases the thickness of the space between the surface of the hair and the scalp, allowing air to blow through’.
• A study published in 2017 in Royal Society Open Science by researchers from Australia concluded that human pheromones probably don’t exist and certainly play no detectable role in attraction.
• Every hair on your body has a growth cycle, with a growing phase and a resting phase. For facial hair a cycle is normally completed in four weeks, but a scalp hair may be with you for as much as six or seven years. A hair in your armpit is likely to last about six months, a leg hair for two months.
• “measured for eleven oddly specific attributes – height when seated, length of left little finger, cheek width – which Bertillon had chosen because they would not change with age. Bertillon’s system was developed not to convict criminals but to catch recidivists.” (there were stiffer sentences for repeat offenders)
• What evolutionary imperative led us to get whorls on the ends of our fingers? The answer is that nobody knows. […] They are assumed to aid in gripping, in the way tyre treads improve traction on roads, but no one has ever actually proved that. Others have suggested that the whorls of fingerprints may drain water better, or make the skin of the fingers more stretchy and supple, or perhaps improve sensitivity, but again these are just guesses.
• As Jablonski has written: ‘The loss of most of our body hair and the gain of the ability to dissipate excess body heat through eccrine sweating helped to make possible the dramatic enlargement of our most temperature-sensitive organ, the brain.’ That, she says, is how sweat helped to make you brainy.
• No one can say why we are so suggestible with respect to itches or even why in the absence of obvious irritants we have them at all. No single location in the brain is devoted to itching, so it is all but impossible to study neurologically.
• Itching […] is confined to the outer layer of skin and a few moist outposts – eyes, throat, nose, and anus primarily. No matter how else you suffer, you will never have an itchy spleen.
• WHY don’t we have wetness receptors?
• skin colour is a classic case of convergent evolution
• highly melanated skin by default and depigmented by evolving differently in different areas
• possible genetic connection between sweat glands and fingerprints
• “Most quadrupeds cool by panting, which is incompatible with sustained running and simultaneous heavy breathing, especially for furry creatures in hot climates.” Then why do dogs do it?
• “The one known cure for baldness is castration.” I thought some forms of hormone therapy could do that but maybe not, I’ll look it up

3: Microbial You

• The microbes that live on you depend to a surprising degree on what soaps or laundry detergents you use, whether you favour cotton clothing or wool, whether you shower before work or after. Some of your microbes are permanent residents. Others camp out on you for a week or a month
• tiny mites called Demodex folliculorum […] have lived with us for so long that, according to one study, their DNA can be used to track the migrations of our ancestors from hundreds of thousands of years ago.
• For nitrogen to be useful to us, it must be converted into more sociable forms, like ammonia, and it is bacteria that do that job for us. Without their help, we would die. Indeed, we could never have existed. It is time to say thank you to your microbes.
• the average bacterium weighs about one trillionth of the weight of a dollar bill and lives for no more than twenty minutes
• bacteria can swap genes among themselves
• Bacterial DNA is less scrupulous in its proofreading, too, so they mutate more often, giving them even greater genetic nimbleness.
• “Make no mistake. This is a planet of microbes. We are here at their pleasure. They don’t need us at all. We’d be dead in a day without them.”
• “Altogether your private load of microbes weighs roughly three pounds, about the same as your brain. People have even begun describing our microbiota as one of our organs.”
• “bacterial cells are tiny whereas human cells are comparatively gigantic, so in terms of massiveness, not to mention the complexity of what they do, human cells are unquestionably more consequential. Then again, looked at genetically, you have about twenty thousand genes of your own within you, but perhaps as many as twenty million bacterial genes, so from that perspective you are roughly 99 per cent bacterial and not quite 1 per cent you.”
• “Luckily, most microbes have nothing to do with us. Some live benignly inside us and are known as commensals. Only a tiny portion make us ill. Of the million or so microbes that have been identified, just 1,415 are known to cause disease in humans”
• “together those 1,415 tiny, mindless entities cause one-third of all the deaths on the planet.”
• “Archaea are very like bacteria in that they are quite simple and have no nucleus, but they have the great benefit to us that they cause no known diseases in humans. All they give us is a little gas, in the form of methane.”
• “A virus, in the immortal words of the British Nobel laureate Peter Medawar, is ‘a piece of bad news wrapped up in a protein’. Actually, a lot of viruses are not bad news at all, at least not to humans. Viruses are a little weird, not quite living but by no means dead. Outside living cells they are just inert things. […] ; they hitchhike. We must go out and collect them […] but put them into a living cell and they will burst into animate existence and reproduce as furiously as any living thing.”
• “most viruses infect only bacterial cells and have no effect on us at all.”
• “It wasn’t until 1959 that they [fungi] were recognized as quite separate and given their own kingdom.”
• “They [fungi] essentially divide into two groups – moulds and yeasts.”
• “By and large fungi leave us alone. Only about three hundred out of several million species affect us at all, and most of those mycoses, as they are known, don’t make you really ill, but rather cause only mild discomfort or irritation,”
• the fungus for thrush is sometimes found inside the body on organs
• “Altogether fungi are thought to be responsible for about a million deaths globally every year, so they are hardly inconsequential.”
• “A protist is anything that isn’t obviously plant, animal or fungus; it is a category reserved for all those life forms that don’t fit anywhere else. Originally, in the nineteenth century, all single-celled organisms were called protozoa. It was assumed that all were closely related, but over time it became evident that bacteria and archaea were separate kingdoms. Protists is a huge category and includes amoebas, paramecia, diatoms, slime moulds and many others that are mostly obscure”
• an odd and ancient ‘microbe mimicking’ virus that was huge and very genetically complex found only in a single ancient cooling tower, later destroyed along with it
• five groups of giant virus totally different from everything on earth and also each other - likely another domain of life we don’t yet understand
• “Before penicillin, the closest thing to a wonder drug that existed was Salvarsan, developed by the German immunologist Paul Ehrlich in 1910, but Salvarsan was effective against only a few things, principally syphilis, and had a lot of drawbacks. For a start, it was made from arsenic”
• “Every bit of penicillin made since that day is descended from that single random cantaloupe”
• “As early as 1945, in his Nobel acceptance speech, Fleming warned that microbes could easily evolve resistance to antibiotics if they were carelessly used. Seldom has a Nobel speech been more prescient.”
• “Almost three-quarters of the forty million antibiotic prescriptions written each year in the United States are for conditions that cannot be cured with antibiotics”
• “According to Jeffrey Linder, professor of medicine at Harvard, antibiotics are prescribed for 70 per cent of acute bronchitis cases even though guidelines explicitly state that they are of no use there.”
• “in the United States 80 per cent of antibiotics are fed to farm animals, mostly to fatten them. Fruit growers can also use antibiotics to combat bacterial infections in their crops. In consequence, most Americans consume second-hand antibiotics in their food […] Sweden banned the agricultural use of antibiotics in 1986. The European Union followed in 1999. In 1977, the US Food and Drug Administration ordered a halt to the use of antibiotics for purposes of fattening farm animals, but backed off”
• “On some diseases penicillin now has no effect at all. In consequence, the death rate from infectious diseases has been climbing and is back to the level of about forty years ago”
• new antibiotics aren’t being developed by many companies due to COST reasons, that is outrageous
• “At the current rate of spread, antimicrobial resistance is forecast to lead to ten million preventable deaths a year – that’s more people than die of cancer now”
• “Bacteria never mount an attack until they have assembled sufficient numbers – what is known as a quorum – to make it worthwhile to do so. The idea would be to produce quorum-sensing drugs that wouldn’t kill all bacteria, but would just keep their numbers permanently below the threshold”
• “Another possibility is to enlist a bacteriophage, a kind of virus, to hunt down and kill harmful bacteria for us”
• “each one targets a particular bacterium. That means clinicians would have to identify the offending pathogen and select the right phage to kill it, a more costly and time-consuming process, but it would make it much harder for bacteria to evolve resistance.”
• we are not far from not being able to do routine procedures just because of the risk of infection

4: The Brain

• tbc