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into a shelf beside the table。 〃One thing I don't understand。〃
〃Only one？〃 Malcolm said。
〃All this business about evolution；〃 she said。 〃Darwin wrote his book a long time ago； right？〃
〃Darwin published the Origin of Species in 1859；〃 Malcolm said。
〃And by now； everybody believes it； isn't that right？〃
〃I think it's fair to say that every scientist in the world agrees that evolution is a feature of life on earth；〃 Malcolm said。 〃And that we are descended from animal ancestors。 Yes。〃
〃Okay；〃 Kelly said。 〃So； what's the big deal now？〃
Malcolm smiled。 〃The big deal；〃 he said； 〃is that everybody agrees evolution occurs； but nobody understands how it works。 There are big problems with the theory。 And more and more scientists are admitting it。〃
Malcolm pushed his plate away。 〃You have to track the theory；〃 he said； 〃over a couple of hundred years。 Start with Baron Georges Cuvier： the most famous anatomist in the world in his day； living in the intellectual center of the world； Paris。 Around 1800； people began digging up old bones； and Cuvier realized that they belonged to animals no longer found on earth。 That was a problem； because back in 1800； everybody believed that all the animal species ever created were still alive。 The idea seemed reasonable because the earth was thought to be only a few thousand years old。 And because God； who had created all the animals； would never let any of his creations bee extinct。 So extinction was agreed to be impossible。 Cuvier agonized over these dug…up bones； but he finally concluded that God or no God； many animals had bee extinct … as a result； he thought； of worldwide catastrophes； like Noah's flood。〃
〃Okay。。。〃
〃So Cuvier reluctantly came to believe in extinction；〃 Malcolm said； 〃but he never accepted evolution。 In Cuvier's mind； evolution didn't occur。 Some animals died and some survived； but none evolved。 In his view； animals didn't change。 Then along came Darwin； who said that animals did evolve； and that the dug…up bones were actually the extinct predecessors of living animals。 The implications of Darwin's idea upset lots of people。 They didn't like to think of God's creations changing； and they didn't like to think of monkeys in their family trees。 It was embarrassing and offensive。 The debate was fierce。 But Darwin amassed a tremendous amount of factual data … he had made an overwhelming case。 So gradually his idea of evolution was accepted by scientists； and by the world at large。 But the question remained： how does evolution happen？ For that； Darwin didn't have a good answer。〃
〃 Natural selection；〃 Arby said。
〃Yes； that was Darwin's explanation。 The environment exerts pressure which favors certain animals； and they breed more often in subsequent generations； and that's how evolution occurs。 But as many people realized； natural selection isn't really an explanation。 It's just a definition： if an animal succeeds； it must have been selected for。 But what in the animal is favored？ And how does natural selection actually operate？ Darwin had no idea。 And neither did anybody else for another fifty years。〃
〃But it's genes；〃 Kelly said。
〃Okay；〃 Malcolm said。 〃Fine。 We e to the twentieth century。 Mendel's work with plants is rediscovered。 Fischer and Wright do population studies。 Pretty soon we know genes control heredity…whatever genes are。 Remember； through the first half of the century； all during World War I and World War II； nobody had any idea what a gene was。 After Watson and Crick in 1953； we knew that genes were nucleotides arranged in a double helix。 Great。 And we knew about mutation。 So by the late twentieth century； we have a theory of natural selection which says that mutations arise spontaneously in genes； that the environment favors the mutations that are beneficial； and out of this selection process evolution occurs。 It's simple and straightforward。 God is not at work。 No higher organizing principle involved。 In the end； evolution is just the result of a bunch of mutations that either Survive or die。 Right？〃
〃Right；〃 Arby said。
〃But there are problems with that idea；〃 Malcolm said。 〃First of all； there's a time problem。 A single bacterium … the earliest form of life has two thousand enzymes。 Scientists have estimated how long it would take to randomly assemble those enzymes from a primordial soup。 Estimates run from forty billion years to one hundred billion years。 But the earth is only four billion years old。 So； chance alone seems too slow。 Particularly since we know bacteria actually appeared only four hundred million years after the earth began。 Life appeared very fast … which is why some scientists have decided life on earth must be of extraterrestrial origin。 Although I think that's just evading the issue。〃
〃Okay。。。〃
〃Second； there's the coordination problem。 If you believe the current theory； then all the wonderful plexity of life is nothing but the accumulation of chance events … a bunch of genetic accidents strung together。 Yet when we look closely at animals； it appears as if many elements must have evolved simultaneously。 Take bats； which have echolocation…they navigate by sound。 To do that； many things must evolve。 Bats need a specialized apparatus to make sounds； they need specialized ears to hear echoes； they need specialized brains to interpret the sounds； and they need specialized bodies to dive and swoop and catch insects。 If all these things don't evolve simultaneously； there's no advantage。 And to imagine all these things happen purely by chance is like imagining that a tornado can hit a junkyard and assemble the Parts into a working 747 airplane。 It's very hard to believe。〃
〃Okay；〃 Thorne said。 〃I agree。〃
〃Next problem。 Evolution doesn't always act like a blind force should。 Certain environmental niches don't get filled。 Certain plants don't get eaten。 And certain animals don't evolve much。 Sharks haven't changed for a hundred and sixty million years。 Opossums haven't changed since dinosaurs became extinct； sixty…five million years ago。 The environments for these animals have changed dramatically； but the animals have remained almost the same。 Not exactly the same； but almost。 In other words； it appears they haven't responded to their environment。〃
〃Maybe they're still well adapted；〃 Arby said。
〃Maybe。 Or maybe there's something else going on that we don't understand。〃
〃 Like what？〃
〃Like other rules that influence the oute。〃
Thorne said； 〃Are you saying evolution is directed？〃
〃No；〃 Malcolm said。 〃That's Creationism and it's wrong。 Just plain wrong。 But I am saying that natural selection acting on genes is probably not the whole story。 It's too simple。 Other forces are also at work。 The hemoglobin molecule is a protein that is folded like a sandwich around a central iron atom that binds oxygen。 Hemoglobin expands and contracts when it takes on and gives up oxygen…like a tiny molecular lung。 Now； we know the sequence of amino acids that make up hemoglobin。 But we don't know how to fold it。 Fortunately； we don't need to know that； because if you make the molecule； it folds all by itself。 It organizes itself。 And it turns out； again and again； that living things seem to have a self…organizing quality。 Proteins fold。 Enzymes interact。 Cells arrange themselves to form organs and the organs arrange themselves to form a coherent individual。 Individuals organize themselves to make a population。 And populations organize themselves to make a coherent biosphere。 From plexity theory； we're starting to have a sense of how this self…organization may happen； and what it means。 And it implies a major change in how we view evolution。〃
〃But；〃 Arby said； 〃in the end； evolution still must be the result of the environment acting on genes。〃
〃I don't think it's enough； Arb；〃 Malcolm said。 〃I think more is involved … I think there has to be more； even to explain how our own species arose。〃
〃About three million years ago；〃 Malcolm said； 〃some African apes that had been living in trees came down to the ground。 There was nothing special about these apes。 Their brains were small and they weren't especially smart。 They didn't have claws or sharp teeth for weapons。 They weren't particularly strong； or fast。 They were certainly no match for a leopard。 But because they were short； they started standing upright on their hind legs； to see over the tall African grass。 That's how it began。 just some ordinary apes； looking out over the grass。
〃As time went on； the apes stood upright more and more of the time。 That left their hands free to do things。 Like all apes； they were tool…users。 Chimps； for example； use twigs to fish for termites。 That sort of thing。 As time went on； our ape ancestors developed more plex tools。 That stimulated their brains to grow in size and plexity。 It began a spiral： more plex tools provoked more plex brains which provoked more plex tools。 And our brains literally exploded； in evolutionary terms。 Our brains more than doubled in size in about a million years。 And that caused problems for us。〃
〃Like what？〃
〃Like getting born； for one thing。 Big brains can't pass through the birth canal … which means that both mother and child die in childbirth。 That's no good。 What's the evolutionary response？ To make human infants born very early in development； when their brains are still small enough to pass through the pelvis。 It's the marsupial solution … most of the growth occurs outside the mother's body。 A human child's brain doubles during the first year of life。 That's a good solution to the problem of birth； but it creates other problems。 It means that human children will be helpless long after birth。 The infants of many mammals can walk minutes after they're born。 Others walk in a few days； or weeks。 But human infants can't walk for a full year。 They can't feed themselves for even longer。 So one price of big brains was that our ancestors had to evolve new； stable social organizations to permit long…term child care； lasting many years； These big…brained； totally helpless children changed society。 But that's not the most important consequence。〃
〃No？〃
〃No。 Being born in an immature state means that human infants have unformed brains。 They don't arrive with a lot of built…in； instinctive behavior。 Instinctively； a newborn infant can suck and grasp； but that's about all。 plex human behavior is not instinctive at all。 So human societies had to develop education to train the brains of their children。 To teach them how to act。 Every human society expends tremendous time and energy teaching its children the right way to behave。 You look at a simpler society； in the rain forest somewhere； and you find that every child is born into a network of adults responsible for helping to raise the child。 Not only parents； but aunts and uncles and grandparents and tribal elders。 Some teach the child to hunt or gather food or weave； some teach them about sex or war。 But the responsibilities are clearly defined； and if a child does not have； say； a mother's brother's sister to do a specific teaching job； the people get together and appoint a substitute。 Because raising children is； in a sense； the reason the society exists in the first place。 It's the most important thing that happens； and it's the culmination of all the tools and language and social structure that has evolved。 And eventually； a few million years later； we have kids using puters。
〃Now； if this picture makes sense； where does natural selection act？ Does it act on the body； enlarging the brain？ Does it act on the developmental sequence； pushing the kids out early？ Does it act on social behavior； provoking cooperation and child…caring？ Or does it act everywhere all at once … on bodies； on development； and on social behavior？〃
〃Everywhere at once；〃 Arby said。
〃I think so；〃 Malcolm said。 〃But there may also be parts of this story that happen automatically； the result of self…organization。 For example； infants of all species have a characteristic appearance。 Big eyes； big heads； small faces； uncoordinated movements。 That's true of kids and puppies and baby birds。 And it seems to provoke adults of all species to act tenderly toward them。 In a sense； you might say infant appearance seem