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wider world。
some people think even greater surprises may await us。 鈥渁 leading british ethno…biologist；鈥潯rote the economist in 1995； 鈥渢hinks a megatherium； a sort of giant ground slothwhich may stand as high as a giraffe 。 。 。 may lurk in the fastnesses of the amazon basin。鈥�
perhaps significantly； the ethnobiologist wasn鈥檛 named； perhaps even more significantly；nothing more has been heard of him or his giant sloth。 no one； however； can categorically saythat no such thing is there until every jungly glade has been investigated； and we are a longway from achieving that。
but even if we groomed thousands of fieldworkers and dispatched them to the farthestcorners of the world； it would not be effort enough； for wherever life can be； it is。 life鈥檚extraordinary fecundity is amazing； even gratifying； but also problematic。 to survey it all； youwould have to turn over every rock； sift through the litter on every forest floor； sieveunimaginable quantities of sand and dirt； climb into every forest canopy； and devise muchmore efficient ways to examine the seas。 even then you would overlook whole ecosystems。 inthe 1980s； spelunkers entered a deep cave in romania that had been sealed off from theoutside world for a long but unknown period and found thirty…three species of insects andother small creatures鈥攕piders； centipedes； lice鈥攁ll blind； colorless； and new to science。
they were living off the microbes in the surface scum of pools； which in turn were feeding onhydrogen sulfide from hot springs。
our instinct may be to see the impossibility of tracking everything down as frustrating；dispiriting； perhaps even appalling； but it can just as well be viewed as almost unbearablyexciting。 we live on a planet that has a more or less infinite capacity to surprise。 whatreasoning person could possibly want it any other way？
what is nearly always most arresting in any ramble through the scattered disciplines ofmodern science is realizing how many people have been willing to devote lifetimes to the most sumptuously esoteric lines of inquiry。 in one of his essays； stephen jay gould notes howa hero of his named henry edward crampton spent fifty years； from 1906 to his death in1956； quietly studying a genus of land snails in polynesia called partula。 over and over； yearafter year； crampton measured to the tiniest degree鈥攖o eight decimal places鈥攖he whorls andarcs and gentle curves of numberless partula； piling the results into fastidiously detailedtables。 a single line of text in a crampton table could represent weeks of measurement andcalculation。
only slightly less devoted； and certainly more unexpected； was alfred c。 kinsey； whobecame famous for his studies of human sexuality in the 1940s and 1950s。 but before hismind became filled with sex； so to speak； kinsey was an entomologist； and a dogged one atthat。 in one expedition lasting two years； he hiked 2；500 miles to assemble a collection of300；000 wasps。 how many stings he collected along the way is not； alas； recorded。
something that had been puzzling me was the question of how you assured a chain ofsuccession in these arcane fields。 clearly there cannot be many institutions in the world thatrequire or are prepared to support specialists in barnacles or pacific snails。 as we parted at thenatural history museum in london； i asked richard fortey how science ensures that whenone person goes there鈥檚 someone ready to take his place。
he chuckled rather heartily at my naivet茅。 鈥渋鈥檓 afraid it鈥檚 not as if we have substitutessitting on the bench somewhere waiting to be called in to play。 when a specialist retires or；even more unfortunately； dies； that can bring a stop to things in that field； sometimes for avery long while。鈥�
鈥渁nd i suppose that鈥檚 why you value someone who spends forty…two years studying asingle species of plant； even if it doesn鈥檛 produce anything terribly new？鈥�
鈥減recisely；鈥潯e said； 鈥減recisely。鈥潯nd he really seemed to mean it。
24 CELLS
灏彙…t…xt…澶ｅ爞
it starts with a single cell。 the first cell splits to bee two and the two bee fourand so on。 after just forty…seven doublings； you have ten thousand trillion（10；000；000；000；000；000） cells in your body and are ready to spring forth as a human being。
1and every one of those cells knows exactly what to do to preserve and nurture you from themoment of conception to your last breath。
you have no secrets from your cells。 they know far more about you than you do。 each onecarries a copy of the plete genetic code鈥攖he instruction manual for your body鈥攕o itknows not only how to do its job but every other job in the body。 never in your life will youhave to remind a cell to keep an eye on its adenosine triphosphate levels or to find a place forthe extra squirt of folic acid that鈥檚 just unexpectedly turned up。 it will do that for you； andmillions more things besides。
every cell in nature is a thing of wonder。 even the simplest are far beyond the limits ofhuman ingenuity。 to build the most basic yeast cell； for example； you would have tominiaturize about the same number of ponents as are found in a boeing 777 jetliner andfit them into a sphere just five microns across； then somehow you would have to persuade thatsphere to reproduce。
but yeast cells are as nothing pared with human cells； which are not just more variedand plicated； but vastly more fascinating because of their plex interactions。
your cells are a country of ten thousand trillion citizens； each devoted in some intensivelyspecific way to your overall well…being。 there isn鈥檛 a thing they don鈥檛 do for you。 they letyou feel pleasure and form thoughts。 they enable you to stand and stretch and caper。 whenyou eat； they extract the nutrients； distribute the energy； and carry off the wastes鈥攁ll thosethings you learned about in junior high school biology鈥攂ut they also remember to make youhungry in the first place and reward you with a feeling of well…being afterward so that youwon鈥檛 forget to eat again。 they keep your hair growing； your ears waxed； your brain quietlypurring。 they manage every corner of your being。 they will jump to your defense the instantyou are threatened。 they will unhesitatingly die for you鈥攂illions of them do so daily。 andnot once in all your years have you thanked even one of them。 so let us take a moment now toregard them with the wonder and appreciation they deserve。
we understand a little of how cells do the things they do鈥攈ow they lay down fat ormanufacture insulin or engage in many of the other acts necessary to maintain a plicatedentity like yourself鈥攂ut only a little。 you have at least 200；000 different types of protein1actually； quite a lot of cells are lost in the process of development； so the number you emerge with is reallyjust a guess。 depending on which source you consult the number can vary by several orders of magnitude。 thefigure of ten thousand trillion （or quadrillion） is from margulis and sagan； 1986。
laboring away inside you； and so far we understand what no more than about 2 percent ofthem do。 （others put the figure at more like 50 percent； it depends； apparently； on what youmean by 鈥渦nderstand。鈥潱﹕urprises at the ce