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ngle set of blueprints。
further probings revealed the existence of a clutch of master control genes； each directingthe development of a section of the body； which were dubbed homeotic （from a greek wordmeaning 鈥渟imilar鈥潱r hox genes。 hox genes answered the long…bewildering question of howbillions of embryonic cells； all arising from a single fertilized egg and carrying identicaldna； know where to go and what to do鈥攖hat this one should bee a liver cell； this one astretchy neuron； this one a bubble of blood； this one part of the shimmer on a beating wing。 itis the hox genes that instruct them； and they do it for all organisms in much the same way。
interestingly； the amount of genetic material and how it is organized doesn鈥檛 necessarily； oreven generally； reflect the level of sophistication of the creature that contains it。 we haveforty…six chromosomes； but some ferns have more than six hundred。 the lungfish； one of theleast evolved of all plex animals； has forty times as much dna as we have。 even themon newt is more genetically splendorous than we are； by a factor of five。
clearly it is not the number of genes you have； but what you do with them。 this is a verygood thing because the number of genes in humans has taken a big hit lately。 until recently itwas thought that humans had at least 100；000 genes； possibly a good many more； but thatnumber was drastically reduced by the first results of the human genome project； whichsuggested a figure more like 35；000 or 40；000 genes鈥攁bout the same number as are found ingrass。 that came as both a surprise and a disappointment。
it won鈥檛 have escaped your attention that genes have been monly implicated in anynumber of human frailties。 exultant scientists have at various times declared themselves tohave found the genes responsible for obesity； schizophrenia； homosexuality； criminality；violence； alcoholism； even shoplifting and homelessness。 perhaps the apogee （or nadir） of thisfaith in biodeterminism was a study published in the journal science in 1980 contending thatwomen are genetically inferior at mathematics。 in fact； we now know； almost nothing aboutyou is so acmodatingly simple。
this is clearly a pity in one important sense； for if you had individual genes that determinedheight or propensity to diabetes or to baldness or any other distinguishing trait； then it wouldbe easy鈥攑aratively easy anyway鈥攖o isolate and tinker with them。 unfortunately； thirty…five thousand genes functioning independently is not nearly enough to produce the kind ofphysical plexity that makes a satisfactory human being。 genes clearly therefore mustcooperate。 a few disorders鈥攈emophilia； parkinson鈥檚 disease； huntington鈥檚 disease； andcystic fibrosis； for example鈥攁re caused by lone dysfunctional genes； but as a rule disruptivegenes are weeded out by natural selection long before they can bee permanentlytroublesome to a species or population。 for the most part our fate and fort鈥攁nd even oureye color鈥攁re determined not by individual genes but by plexes of genes working inalliance。 that鈥檚 why it is so hard to work out how it all fits together and why we won鈥檛 beproducing designer babies anytime soon。
in fact； the more we have learned in recent years the more plicated matters have tendedto bee。 even thinking； it turns out； affects the ways genes work。 how fast a man鈥檚 beard grows； for instance； is partly a function of how much he thinks about sex （because thinkingabout sex produces a testosterone surge）。 in the early 1990s； scientists made an even moreprofound discovery when they found they could knock out supposedly vital genes fromembryonic mice； and the mice were not only often born healthy； but sometimes were actuallyfitter than their brothers and sisters who had not been tampered with。 when certain importantgenes were destroyed； it turned out； others were stepping in to fill the breach。 this wasexcellent news for us as organisms； but not so good for our understanding of how cells worksince it introduced an extra layer of plexity to something that we had barely begun tounderstand anyway。
it is largely because of these plicating factors that cracking the human genome becameseen almost at once as only a beginning。 the genome； as eric lander of mit has put it； is likea parts list for the human body： it tells us what we are made of； but says nothing about howwe work。 what鈥檚 needed now is the operating manual鈥攊nstructions for how to make it go。
we are not close to that point yet。
so now the quest is to crack the human proteome鈥攁 concept so novel that the termproteome didn鈥檛 even exist a decade ago。 the proteome is the library of information thatcreates proteins。 鈥渦nfortunately；鈥潯bserved scientific american in the spring of 2002； 鈥渢heproteome is much more plicated than the genome。鈥�
that鈥檚 putting it mildly。 proteins； you will remember； are the workhorses of all livingsystems； as many as a hundred million of them may be busy in any cell at any moment。 that鈥檚a lot of activity to try to figure out。 worse； proteins鈥櫋ehavior and functions are based notsimply on their chemistry； as with genes； but also on their shapes。 to function； a protein mustnot only have the necessary chemical ponents； properly assembled； but then must also befolded into an extremely specific shape。 鈥渇olding鈥潯s the term that鈥檚 used； but it鈥檚 amisleading one as it suggests a geometrical tidiness that doesn鈥檛 in fact apply。 proteins loopand coil and crinkle into shapes that are at once extravagant and plex。 they are more likefuriously mangled coat hangers than folded towels。
moreover； proteins are （if i may be permitted to use a handy archaism） the swingers of thebiological world。 depending on mood and metabolic circumstance； they will allowthemselves to be phosphorylated； glycosylated； acetylated； ubiquitinated； farneysylated；sulfated； and linked to glycophosphatidylinositol anchors； among rather a lot else。 often ittakes relatively little to get them going； it appears。 drink a glass of wine； as scientificamerican notes； and you materially alter the number and types of proteins at large in yoursystem。 this is a pleasant feature for drinkers； but not nearly so helpful for geneticists who aretrying to understand what is going on。
it can all begin to seem impossibly plicated； and in some ways itis impossiblyplicated。 but there is an underlying simplicity in all this； too； owing to an equallyelemental underlying unity in the way life works。 all the tiny； deft chemical processes thatanimate cells鈥攖he cooperative efforts of nucleotides； the transcription of dna into rna鈥攅volved just once and have stayed pretty well fixed ever since across the whole of nature。 asthe late french geneticist jacques monod put it； only half in jest： 鈥渁nything that is true of e。
coli must be true of elephants； except more so。鈥�
every living thing is an elaboration on a single original plan。 as humans we are mereincrements鈥攅ach of us a musty archive of adjustments； adaptations； modifications； andprovidential tinkerings stretching back 3。8 billion years。 remarkably； we are even quite closely related to fruit and vegetables。 about half the chemical functions that take place in abanana are fundamentally the same as the chemical functions that take place in you。
it cannot be said too often： all life is one。 that is； and i suspect will forever prove to be； themost profound true statement there is。
part vithe road to usdescended from the apes！ my dear；let us hope that it is not true； but if it is；let us pray that it will not beegenerally known。
…remark attributed to the wife ofthe bishop of worcester afterdarwin鈥檚 theory of evolution was explained to her
w w w。 xiao shuotxt。 co m
27 ICE TIME
灏彙〃t：xt。。澶″爞
i had a dream； which was notall a dream。
the bright sun wasextinguish鈥檇； and the starsdid wander 。 。 。
鈥攂yron； 鈥渄arkness鈥�
in 1815 on the island of sumbawa in indonesia； a handsome and long…quiescent mountainnamed tambora exploded spectacularly； killing a hundred thousand people with its blast andassociated tsunamis。 it was the biggest volcanic explosion in ten thousand years鈥�150 timesthe size of mount st。 helens； equivalent to sixty thousand hiroshima…sized atom bombs。
news didn鈥檛 travel terribly fast in those days。 in london； the times ran a small story鈥攁ctually a letter from a merchant鈥攕even months after the event。 but by this time tambora鈥檚effects were already being felt。 thirty…six cubic miles of smoky ash； dust； and grit haddiffused through the atmosphere； obscuring the sun鈥檚 rays and causing the earth to cool。
sunsets were unusually but blearily colorful； an effect memorably captured by the artist j。 m。
w。 turner； who could not have been happier； but mostly the world existed under anoppressive； dusky pall。 it was this deathly dimness that inspired the byron lines above。
spring never came and summer never warmed： 1816 became known as the year withoutsummer。 crops everywhere failed to grow。 in ireland a famine and associated typhoidepidemic killed sixty…five thousand people。 in new england； the year became popularlyknown as eighteen hundred and froze to death。 morning frosts continued until june andalmost