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40 percent。 johanson breezily replied that he had discounted the106 bones of the hands and feet—more than half the body’s total； and a fairly important half；too； one would have thought； since lucy’s principal defining attribute was the use of thosehands and feet to deal with a changing world。 at all events； rather less is known about lucythan is generally supposed。 it isn’t even actually known that she was a female。 her sex ismerely presumed from her diminutive size。
two years after lucy’s discovery； at laetoli in tanzania mary leakey found footprints leftby two individuals from—it is thought—the same family of hominids。 the prints had beenmade when two australopithecines had walked through muddy ash following a volcaniceruption。 the ash had later hardened； preserving the impressions of their feet for a distance ofover twenty…three meters。
the american museum of natural history in new york has an absorbing diorama thatrecords the moment of their passing。 it depicts life…sized re…creations of a male and a femalewalking side by side across the ancient african plain。 they are hairy and chimplike indimensions； but have a bearing and gait that suggest humanness。 the most striking feature ofthe display is that the male holds his left arm protectively around the female’s shoulder。 it is atender and affecting gesture； suggestive of close bonding。
the tableau is done with such conviction that it is easy to overlook the consideration thatvirtually everything above the footprints is imaginary。 almost every external aspect of thetwo figures—degree of hairiness； facial appendages （whether they had human noses or chimpnoses）； expressions； skin color； size and shape of the female’s breasts—is necessarilysuppositional。 we can’t even say that they were a couple。 the female figure may in fact havebeen a child。 nor can we be certain that they were australopithecines。 they are assumed to beaustralopithecines because there are no other known candidates。
i had been told that they were posed like that because during the building of the dioramathe female figure kept toppling over； but ian tattersall insists with a laugh that the story isuntrue。 “obviously we don’t know whether the male had his arm around the female or not；but we do know from the stride measurements that they were walking side by side and closetogether—close enough to be touching。 it was quite an exposed area； so they were probablyfeeling vulnerable。 that’s why we tried to give them slightly worried expressions。”
i asked him if he was troubled about the amount of license that was taken in reconstructingthe figures。 “it’s always a problem in making re…creations；” he agreed readily enough。 “youwouldn’t believe how much discussion can go into deciding details like whether neandertalshad eyebrows or not。 it was just the same for the laetoli figures。 we simply can’t know thedetails of what they looked like； but we can convey their size and posture and make somereasonable assumptions about their probable appearance。 if i had it to do again； i think i might have made them just slightly more apelike and less human。 these creatures weren’t humans。
they were bipedal apes。”
until very recently it was assumed that we were descended from lucy and the laetolicreatures； but now many authorities aren’t so sure。 although certain physical features （theteeth； for instance） suggest a possible link between us； other parts of the australopithecineanatomy are more troubling。 in their book extinct humans； tattersall and schwartz point outthat the upper portion of the human femur is very like that of the apes but not of theaustralopithecines； so if lucy is in a direct line between apes and modern humans； it meanswe must have adopted an australopithecine femur for a million years or so； then gone back toan ape femur when we moved on to the next phase of our development。 they believe； in fact；that not only was lucy not our ancestor； she wasn’t even much of a walker。
“lucy and her kind did not loote in anything like the modern human fashion；” insiststattersall。 “only when these hominids had to travel between arboreal habitats would they findthemselves walking bipedally； ‘forced’ to do so by their own anatomies。” johanson doesn’taccept this。 “lucy’s hips and the muscular arrangement of her pelvis；” he has written； “wouldhave made it as hard for her to climb trees as it is for modern humans。”
matters grew murkier still in 2001 and 2002 when four exceptional new specimens werefound。 one； discovered by meave leakey of the famous fossil…hunting family at laketurkana in kenya and called kenyanthropus platyops （“kenyan flat…face”）； is from about thesame time as lucy and raises the possibility that it was our ancestor and lucy was anunsuccessful side branch。 also found in 2001 were ardipithecus ramidus kadabba； dated atbetween 5。2 million and 5。8 million years old； and orrorin tugenensis； thought to be 6 millionyears old； making it the oldest hominid yet found—but only for a brief while。 in the summerof 2002 a french team working in the djurab desert 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 wou