of chad （an area that had never beforeyielded ancient bones） found a hominid almost 7 million years old； which they labeledsahelanthropus tchadensis。 （some critics believe that it was not human； but an early ape andtherefore should be called sahelpithecus。） all these were early creatures and quite primitivebut they walked upright； and they were doing so far earlier than previously thought。
bipedalism is a demanding and risky strategy。 it means refashioning the pelvis into a fullload…bearing instrument。 to preserve the required strength； the birth canal must beparatively narrow。 this has two very significant immediate consequences and one longer…term one。 first； it means a lot of pain for any birthing mother and a greatly increased dangerof fatality to mother and baby both。 moreover to get the baby’s head through such a tightspace it must be born while its brain is still small—and while the baby； therefore； is stillhelpless。 this means long…term infant care； which in turn implies solid male–female bonding。
all this is problematic enough when you are the intellectual master of the planet； but whenyou are a small； vulnerable australopithecine； with a brain about the size of an orange；3therisk must have been enormous。
3absolute brain size does not tell you everything…or possibly sometimes even much。 elephants and whales bothhave brains larger than ours； but you wouldnt have much trouble outwitting them in contract negotiations。 it isrelative size that matters； a point that is often overlooked。 as gould notes； a。 africanus had a brain of only 450cubic centimeters； smaller than that of a gorilla。 but a typical africanus male weighed less than a hundredpounds； and a female much less still； whereas gorillas can easily top out at 600 pounds （gould pp。 181…83）。
so why did lucy and her kind e down from the trees and out of the forests？ probablythey had no choice。 the slow rise of the isthmus of panama had cut the flow of waters fromthe pacific into the atlantic； diverting warming currents away from the arctic and leading tothe onset of an exceedingly sharp ice age in northern latitudes。 in africa； this would haveproduced seasonal drying and cooling； gradually turning jungle into savanna。 “it was not somuch that lucy and her like left the forests；” john gribbin has written； “but that the forestsleft them。”
but stepping out onto the open savanna also clearly left the early hominids much moreexposed。 an upright hominid could see better； but could also be seen better。 even now as aspecies； we are almost preposterously vulnerable in the wild。 nearly every large animal youcan care to name is stronger； faster； and toothier than us。 faced with attack； modern humanshave only two advantages。 we have a good brain； with which we can devise strategies； andwe have hands with which we can fling or brandish hurtful objects。 we are the only creaturethat can harm at a distance。 we can thus afford to be physically vulnerable。
all the elements would appear to have been in place for the rapid evolution of a potentbrain； and yet that seems not to have happened。 for over three million years； lucy and herfellow australopithecines scarcely changed at all。 their brain didn’t grow and there is no signthat they used even the simplest tools。 what is stranger still is that we now know that forabout a million years they lived alongside other early hominids who did use tools； yet theaustralopithecines never took advantage of this useful technology that was all around them。
at one point between three and two million years ago； it appears there may have been asmany as six hominid types coexisting in africa。 only one； however； was fated to last： homo；which emerged from the mists beginning about two million years ago。 no one knows quitewhat the relationship was between australopithecines and homo； but what is known is thatthey coexisted for something over a million years before all the australopithecines； robust andgracile alike； vanished mysteriously； and possibly abruptly； over a million years ago。 no oneknows why they disappeared。 “perhaps；” suggests matt ridley； “we ate them。”
conventionally； the homo line begins with homo habilis； a creature about whom we knowalmost nothing； and concludes with us； homo sapiens （literally “man the thinker”）。 inbetween； and depending on which opinions you value； there have been half a dozen otherhomo species： homo ergaster； homo neanderthalensis； homo rudolfensis； homoheidelbergensis； homo erectus； and homo antecessor。
homo habilis （“handy man”） was named by louis leakey and colleagues in 1964 and wasso called because it was the first hominid to use tools； albeit very simple ones。 it was a fairlyprimitive creature； much more chimpanzee than human； but its brain was about 50 percentlarger than that of lucy in gross terms and not much less large proportionally； so it was theeinstein of its day。 no persuasive reason has ever been adduced for why hominid brainssuddenly began to grow two million years ago。 for a long time it was assumed that big brainsand upright walking were directly related—that the movement out of the forests necessitatedcunning new strategies that fed off of or promoted braininess—so it was something of asurprise； after the repeated discoveries of so many bipedal dullards； to realize that there wasno apparent connection between them at all。
“there is simply no pelling reason we know of to explain why human brains gotlarge；” says tattersall。 huge brains are demanding organs： they make up only 2 percent of thebody’s mass； but devour 20 percent of its energy。 they are also paratively picky in what they use as fuel。 if you never ate another morsel of fat； your brain would not plainbecause it won’t touch the stuff。 it wants glucose instead； and lots of it； even if it means short…changing other organs。 as guy brown notes： “the body is in constant danger of beingdepleted by a greedy brain； but cannot afford to let the brain go hungry as that would rapidlylead to death。” a big brain needs more food and more food means increased risk。
tattersall thinks the rise of a big brain may simply have been an evolutionary accident。 hebelieves with stephen jay gould that if you replayed the tape of life—even if you ran it backonly a relatively short way to the dawn of hominids—the chances are “quite unlikely” thatmodern humans or anything like them would be here now。
“one of the hardest ideas for humans to accept；” he says； “is that we are not theculmination of anything。 there is nothing inevitable about our being here。 it is part of ourvanity as humans that we tend to think of evolution as a process that； in effect； wasprogrammed to produce us。 even anthropologists tended to think this way right up until the1970s。” indeed； as recently as 1991； in the popular textbook the stages of evolution； c。
loring brace stuck doggedly to the linear concept； acknowledging just one evolutionary deadend； the robust australopithecines。 everything else represented a straightforwardprogression—each species of hominid carrying the baton of development so far； then handingit on to a younger； fresher runner。 now； however； it seems certain that many of these earlyforms followed side trails that didn’t e to anything。
luckily for us； one did—a group of tool users； which seemed to arise from out of nowhereand overlapped with the shadowy and much disputed homo habilis。 this is homo erectus； thespecies discovered by eugène dubois in java in 1891。 depending on which sources youconsult； it existed from about 1。8 million years ago to possibly as recently as twenty thousandor so years ago。
according to the java man authors； homo erectus is the dividing line： everything thatcame before him was apelike in character； everything that came after was humanlike。 homoerectus was the first to hunt； the first to use fire； the first to fashion plex tools； the first toleave evidence of campsites； the first to look after the weak and frail。 pared with all thathad gone before； homo erectus was extremely human in form as well as behavior； itsmembers long…limbed and lean； very strong （much stronger than modern humans）； and withthe drive and intelligence to spread successfully over huge areas。 to other hominids； homoerectus must have seemed terrifyingly powerful； fleet； and gifted。
erectus was “the velociraptor of its day；” according to alan walker of penn stateuniversity and one of the world’s leading authorities。 if you were to look one in the eyes； itmight appear superficially to be human； but “you wouldn’t connect。 you’d be prey。”
according to walker； it had the body of an adult human but the brain of a baby。
although erectus had been known about for almost a century it was known only fromscattered fragments—not enough to e even close to making one full skeleton。 so it wasn’tuntil an extraordinary discovery in africa in the 1980s that its importance—or； at the veryleast； possible importance—as a precursor species for modern humans was fully appreciated。
the remote valley of lake turkana （formerly lake rudolf） in kenya is now one of theworld’s most productive sites for early human remains； but for a very long time no one hadthought to look there。 it was only because richard leakey was on a fl