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doesn鈥檛 know what he is talkingabout。
the specifics of mayr鈥檚 criticisms are too technical to need extensive airing here鈥攖heyinvolve issues of meiotic sexuality； hennigian cladification； and controversial interpretationsof the genome of methanobacterium thermoautrophicum； among rather a lot else鈥攂utessentially he argues that woese鈥檚 arrangement unbalances the tree of life。 the bacterialrealm； mayr notes； consists of no more than a few thousand species while the archaean has amere 175 named specimens； with perhaps a few thousand more to be found鈥斺�渂ut hardlymore than that。鈥潯y contrast； the eukaryotic realm鈥攖hat is； the plicated organisms withnucleated cells； like us鈥攏umbers already in the millions。 for the sake of 鈥渢he principle ofbalance；鈥潯ayr argues for bining the simple bacterial organisms in a single category；prokaryota； while placing the more plex and 鈥渉ighly evolved鈥潯emainder in the empireeukaryota； which would stand alongside as an equal。 put another way； he argues for keepingthings much as they were before。 this division between simple cells and plex cells 鈥渋swhere the great break is in the living world。鈥�
the distinction between halophilic archaeans and methanosarcina or between flavobacteriaand gram…positive bacteria clearly will never be a matter of moment for most of us； but it isworth remembering that each is as different from its neighbors as animals are from plants。 ifwoese鈥檚 new arrangement teaches us anything it is that life really is various and that most ofthat variety is small； unicellular； and unfamiliar。 it is a natural human impulse to think ofevolution as a long chain of improvements； of a never…ending advance toward largeness andplexity鈥攊n a word； toward us。 we flatter ourselves。 most of the real diversity inevolution has been small…scale。 we large things are just flukes鈥攁n interesting side branch。 ofthe twenty…three main divisions of life； only three鈥攑lants； animals； and fungi鈥攁re largeenough to be seen by the human eye； and even they contain species that are microscopic。
indeed； according to woese； if you totaled up all the biomass of the planet鈥攅very living thing； plants included鈥攎icrobes would account for at least 80 percent of all there is； perhapsmore。 the world belongs to the very small鈥攁nd it has for a very long time。
so why； you are bound to ask at some point in your life； do microbes so often want to hurtus？ what possible satisfaction could there be to a microbe in having us grow feverish orchilled； or disfigured with sores； or above all expire？ a dead host； after all； is hardly going toprovide long…term hospitality。
to begin with； it is worth remembering that most microorganisms are neutral or evenbeneficial to human well…being。 the most rampantly infectious organism on earth； abacterium called wolbachia； doesn鈥檛 hurt humans at all鈥攐r； e to that； any othervertebrates鈥攂ut if you are a shrimp or worm or fruit fly； it can make you wish you had neverbeen born。 altogether； only about one microbe in a thousand is a pathogen for humans；according to national geographic 鈥攖hough； knowing what some of them can do； we couldbe forgiven for thinking that that is quite enough。 even if mostly benign； microbes are still thenumber…three killer in the western world； and even many less lethal ones of course make usdeeply rue their existence。
making a host unwell has certain benefits for the microbe。 the symptoms of an illnessoften help to spread the disease。 vomiting； sneezing； and diarrhea are excellent methods ofgetting out of one host and into position for another。 the most effective strategy of all is toenlist the help of a mobile third party。 infectious organisms love mosquitoes because themosquito鈥檚 sting delivers them directly to a bloodstream where they can get straight to workbefore the victim鈥檚 defense mechanisms can figure out what鈥檚 hit them。 this is why so manygrade…a diseases鈥攎alaria； yellow fever； dengue fever； encephalitis； and a hundred or soother less celebrated but often rapacious maladies鈥攂egin with a mosquito bite。 it is afortunate fluke for us that hiv； the aids agent； isn鈥檛 among them鈥攁t least not yet。 any hivthe mosquito sucks up on its travels is dissolved by the mosquito鈥檚 own metabolism。 whenthe day es that the virus mutates its way around this； we may be in real trouble。
it is a mistake； however； to consider the matter too carefully from the position of logicbecause microorganisms clearly are not calculating entities。 they don鈥檛 care what they do toyou any more than you care what distress you cause when you slaughter them by the millionswith a soapy shower or a swipe of deodorant。 the only time your continuing well…being is ofconsequence to a pathogen is when it kills you too well。 if they eliminate you before they canmove on； then they may well die out themselves。 this in fact sometimes happens。 history；jared diamond notes； is full of diseases that 鈥渙nce caused terrifying epidemics and thendisappeared as mysteriously as they had e。鈥潯e cites the robust but mercifully transientenglish sweating sickness； which raged from 1485 to 1552； killing tens of thousands as itwent； before burning itself out。 too much efficiency is not a good thing for any infectiousorganism。
a great deal of sickness arises not because of what the organism has done to you but whatyour body is trying to do to the organism。 in its quest to rid the body of pathogens； theimmune system sometimes destroys cells or damages critical tissues； so often when you areunwell what you are feeling is not the pathogens but your own immune responses。 anyway；getting sick is a sensible response to infection。 sick people retire to their beds and thus areless of a threat to the wider munity。 resting also frees more of the body鈥檚 resources toattend to the infection。
because there are so many things out there with the potential to hurt you； your body holdslots of different varieties of defensive white cells鈥攕ome ten million types in all； eachdesigned to identify and destroy a particular sort of invader。 it would be impossibly inefficientto maintain ten million separate standing armies； so each variety of white cell keeps only afew scouts on active duty。 when an infectious agent鈥攚hat鈥檚 known as an antigen鈥攊nvades；relevant scouts identify the attacker and put out a call for reinforcements of the right type。
while your body is manufacturing these forces； you are likely to feel wretched。 the onset ofrecovery begins when the troops finally swing into action。
white cells are merciless and will hunt down and kill every last pathogen they can find。 toavoid extinction； attackers have evolved two elemental strategies。 either they strike quicklyand move on to a new host； as with mon infectious illnesses like flu； or they disguisethemselves so that the white cells fail to spot them； as with hiv； the virus responsible foraids； which can sit harmlessly and unnoticed in the nuclei of cells for years before springinginto action。
one of the odder aspects of infection is that microbes that normally do no harm at allsometimes get into the wrong parts of the body and 鈥済o kind of crazy；鈥潯n the words of dr。
bryan marsh； an infectiou