White Intel Thought

White Intel Thought - HUIt‘I'IL'lH-l' \‘(ll Lll lEI'II...

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Unformatted text preview: HUIt‘I'IL'lH-l' \‘(ll Lll lEI'II iLll'l'L'lIl .\l\l-illi'\ volutionai‘yr science lies at the heart of a modern under— standing of the natural world. Darwin's theory has withstood 150 years of scientific scrutiny. and today it not only explains the origin and design of living things. but high- lights the importance of a scientific understanding in our culture and in our lives. Recently the movement known as Intelligent Design has attracted the attention ofjournalists. educators, and legislators. The scientific community is puzzled and saddened by this trend— not only because it distorts modern biology. but also because it diverts people from the truly fascinating ideas emerging from the real science of evolution. Here, join sixteen of our preeminent thinkers whose clear. accessible, and passionate essays reveal the fact and power of Darwin's theory. and the beauty of the scientific quest to understand our world. "Evolutionary biology certainly hasn't explained everything that Perplexes biologists. but Intelligent Design hasn't yet tried to explain anything at all." -—-Daniel C. Dennett, Philosopher "Natural selection is not some desperate last resort ol’a Lheory. It is an idea whose plausibility and power hits you between the eyes with a stunning force, once you understand it in all its elegant sim» plicity." *Richard Dawkins, Evolutionary Biologist "An evolutionary understanding of the human condition. far from being incompatible with a moral sense. can explain why we have one." —Steven Pinker. Psychologist US. $14.00 Can. $1895 issN 0-30?-2??22--’+ Cover deung i. J 5 ll 4 D D CorerEJht'flfigl _ | l 9 ?80307 277220 .Lti'ls'JIlui‘tJ. .LI-l—‘iix—la I 1.1.4.1.. 3H1. SI‘ISHEIA 33N312|S INTELLIGENT THOUGHT SCIENCE VERSUS THE INTELLIGENT DESIGN MOVEMENT Contributors include.- Psychologist Steven Pinker. Evolutionary Biologist Richard Dawltins, Philosopher Daniel C. Dennett, Physicist Lisa Randall. Evolutionary Psychologist Marc D. Hauser. and Paleontologist Tim D. W'hite TIM D. WHITE Human Evolution: The Evidence The question of questions for mankind—the probiem which underiies ail others, and is more deeply interesting than any other—is the ascertainment of the piace which M'an occupies in nature and of his relations to the uni— verse of things. —T. H. Huxley, On the Reianons of Man to the Lower/inimals [1861] SUNK BETWEEN TWO imposing escarpments of broken lava rock, the triangle-shaped floor ofAfrica’s Afar depres- sion is a vast, barren, sparsely inhabited corner of the continent. The Awash River winds through this desolate region, fed by seasonal rains in the adjacent Ethiopian highlands. Thin ribbons oi‘riverine forest mark the winding course of the muddy Awash. In its middle portion, the river sweeps southeast and then bends sharply north around a peninsular projection of low hills on its left bank, called Bouri by the nomadic Afar pastoralists who live there. In their language, bout-i means dust. 65 66 TIM D. WHITE In January of 1997, instruments on buoys in the Pacific off the coast of Peru began to record abnormally high sea- water temperatures. The El Nifio that these temperatures heralded became the strongest in more than fifty years. Its effects were global. Rains inundated the Afar, where our international research team converges every autumn to conduct investigations into the deep human past. After the deluge, the 1997 field season would yield a bumper crop of newly exposed evidence for our geologists, archaeologists, and paleontologists. The road to Bouri’s Herto village snakes along a drainage divide in the Ethiopian highlands. Rainwater draining to the east flows into the Blue Nile and ends up in the Mediter- ranean. West of the road, rainwater flows down the steep rift escarpment into the swamps and lakes dotting the Afar floor. The Afar is a gigantic basin, a trap where the water- transported sands and silts have accumulated to form a mile-deep layer-cake succession of ancient sediments. When we finally managed to get the vehicles across swollen streams and deep mud, we found Herto aban- doned. No herdsmen, no goats, cats, children, sheep, cows, camels, or life. Houses once covered with grass mats were now silent skeletons of curved sticks. The plain stretching away to the southeast was covered with a bright stubble of newly sprouted grass. The usual swarms of curious naked children did not materialize—it was a once-in-a-lifetime chance for a peaceful lunch at Herto. Most of the crew dis- persed to look around, while the rest of us stretched a tarp from a roof rack for shelter against the harsh sun. One investigator found a small fragment of brown and white bone. Measuring less than a centimeter thick, it fit comfortably into his palm. "Hominid," he announced. It was a piece of human skull. After lunch, I sent him back with INTELLIGENT THOUGHT 67 yellow plastic pin flags to mark the location of additional fragments, and we collected evidence in the eerie silence. The skull had been damaged postmortem. Its left side had emerged first from the sands, and the broken, fos- silized pieces of its vault had been scattered by passing livestock and the whirlwinds that regularly sweep this landscape. A pattern emerged as the yellow pin flags were placed. The spread of flags narrowed and concentrated on a spot about the size of a football. In a forensic case, investigators tiptoe through the crime scene so as not to disturb the smallest clue. Blood-spatter, fibers, fingerprints, DNA, and many other traces provide the clues needed to probe the past and solve the crime. The past probed by forensic scientists is usually not very old. In paleontological science, the past can be millions of years deep. But in both sciences, every detail is docu- mented photographically and trace evidence is sealed in special containers. At Herto, the outline of a human cra» niurn arose from the indurated sands of an ancient riverbed, as a fine paintbrush swept away the loose sand. The profile above the right eye socket was prominent; there was no accompanying lower jaw nor a trace of the other approximately 200 bones that would have com- prised this individual's body in life. For fossils and forensics alike, establishing a timeline of events is crucial. Whose cranium was this? How had it come to rest in this sand- stone layer at Herto? What had happened here? And when? The detective work to solve this case would not be easy; the clues were few, the case cold. Here was a brittle, fossilized human cranium from a past that nobody could remember, exposed to the light of day by El Nifio rains. To remove it, I excavated the sands around it and solidified them with superglue. We applied a 65 TIM D. WHITE separating layer of wet tissue paper, and then plaster, which would protect the fossil from further damage on the long trip back to the laboratory; we lifted it from its resting place that night, safe in its plaster jacket. The investigative team returned to the scene the next morning, hoping to collect more evidence. A grid was established around the site and all surface objects were plotted. Excavation of the immediate scene produced no further remains, so we moved outward. Geologists traced the sandstone layer south to where it was covered by sev- eral feet of consolidated volcanic glass, which had formed when a nearby volcano erupted. Since the skull-bearing sands were below this layer, they would be older than the eruption. Archaeologists scoured the neighborhood for more outcrops of these sands, collecting thousands of stone tools and fossilized animal bones contemporary with the human cranium. Many bones were embedded nearby in the same sandstone layer, including those of a large buffalo- lilte animal with horns as long as your arm, an animal that had vanished from Africa long before domestic cattle ar- rived thousands of years ago. Other stones within the sandstone also pointed to a great antiquity; they were finely shaped implements of obsidian and basalt, yet the nearest natural outcrops of these volcanic rocks are miles away. The Herto villagers of today do not make such stone tools, so this was obviously not the grave of a local inhabitant. And there was no disturbance of the sandstone layers encasing the cranium. Within weeks the fieldwork ended. The evidence, includ- ing the human cranium in its plaster jacket, was carefully packed and transported to the National Museum of Ethiopia, in Addis Ababa. Five years of laboratory investigation would ensue before our team was ready to present its conclusions INTELLIGENT THOUGHT 69 based on the evidence recovered. Removing the hardened sandstone one grain at a time from the fragile cranium alone took months. Working with a needle under a micro. scope, we hardened the fossil with preservative as its fragile face emerged. It was a massive, deep face, but one with a depression beneath the eye sockets matching that of modem peeple. The missing brain's volume was measured at 1,450 Cubic centimeters—some 100 cc more capacious than that of the average modern human. The frontal bone was verti— cal, as were the bones forming the sides of the cranial dome. The rear of the vault showed scars indicating the attach— ment of heavy muscles. This was a large individual but clearly a male of our species, Homo sapiens. Meanwhile, the volcanic rock samples were being fingerprinted at the Los Alamos National Laboratory in New Mexico. Each volcanic eruption has its own unique chemical composition; ours matched a layer from southern Ethiopia. FractiOns of this correlative rock were melted with a laser and the released argon gas measured in a mass spectrometer. The amount of gas trapped in the rock since it cooled would correspond to the decay rate of the radioactive element potassium—hence we could calibrate the timeline: The Herto individual died at least 155,000 years ago. Earth has been home to life for billions of years. Compared with dinosaurs, which arose approximately 225 million years ago and went extinct some 160 million years later, the Herto individual was a relative youngster, but in human generations he was old enough to be someone's great-great-great- (insert about 8,000 “ greats") grandfather. In a forensic investigation, genealogical relationships are often established through DNA analysis. Unfortunately, the Herto man’s DNA had decomposed. Our identifica— tion would have to rely on comparative anatomy. We com- 3‘0 TIM D. WHITE pared Herto to more than 5,000 recent human crania in institutions ranging from the Smithsonian to the Univer— sity of Tokyo. Even though he came from Africa, the Herto man was like no recent African. His face was too tall, the bony ridges atop his eye sockets too prominent, his neck» muscle attachments too robust. Of all modern human populations, he most closely resembled Australian aborigi- nals. Analysis showed his anatomy to lie at the outer limits of the large envelope of skull form among modern humans. From a paleontological perspective, this individual's skull was evidence for evolutiOn, linking living people with their hominid ancestors. What had his world been like? The archaeologists had most of the evidence for that. Their studies of cutrnarks left by stone tools on hippopotamus and bovine bones feund in the sandstone showed that these people were butchers, with a taste for mammalian flesh. Studies of the associated artifacts showed them to be adept at manufac- turing the tools needed for a life of foraging in the tropical African PleistOCene. The Herto man died of unknown causes about 8,000 human generations ago, near a freshwater river. He lived at a time when the Northern Hemisphere was locked in an ice age and a refrigerated Europe was inhabited by cave dwellers with skull shapes very different from the Herto people. Where did the Herto people come from? And what became of their descendants? Anthropologists have long known that every culture has a traditional story about how people were created. There are Babylonian, Hindu, Cherokee, Yoruba, Maori, Norse, Mayan, and dozens of other myths. Our Western biblical origin sto- ries are rooted in the pastoral societies of the Middle East and have been retold for centuries. Literal interpretation of INTELLIGENT THOUGHT 3'1 the biblical account holds that humans remained basically unchanged after they were created. This interpretation was tested by the discovery of the Herto man. Here was some— one whose anatomy linked hirn to earlier fossils that Were not human. When he appeared 0n the cover of Nature in 2003, he represented new evidence for an old debate. Who was this man and what did he represent? Answers to these questions came quickly from people wishing to accommodate the new evidence to their partic- ular views. The Herto man, dead for some 155,000 years, ignited a controversy that pitted leading creationist min- istries against each other. One group, Answers in Genesis, an Australian-based ministry whose stated aim is "to develop a biblical worldview [and] expose the bankruptcy of evolu~ tionary ideas," contested the radiometric dating and saw the I-Ierto man as a descendant of Adam. The other, the Progressive Creationists—whose chief spokesman is the televangelist Dr. Hugh Ross, author of Creation and Time— accepted the dating but called Herto a nonhuman bipedal primate. In the ensuing set-to, these parties accused each other of special pleading, sinning, distortion, and the com- mission of factual errors. The Progressives, noted Answers in Genesis, represented "a greater danger to the church than attacks by atheistic evolutionists from 'without the camp.’ " The debate proved sterile, but itself constitutes evidence of the degree to which human fossils can upset strongly held religious beliefs. Atop the mile-thick Afar sediment stack, the processes of deposition and fossilization continue today. Dead cows and crocodiles settle to the bottom of swamps, where they are covered with sediment. Slowly their bones turn to Stone- Below them are the remains of their ever-older ancestors; a menagerie including many animals now extinct. 3'2 TIM D. WHITE These fossils would remain suspended in the sediment deep below the surface of the Afar were it not for the fact that the Arabian peninsula is slowly rotating away from the African continent. The continental separation is geologi- cally fast but too slow for humans to observe without instruments; the rift valleys created by the movement of the Arabian plate widen by only a few centimeters a year. Since the time of the Pharoahs, the Afar rift has widened about the length of a football field. Because it is one of the most tectonically and volcanically active places on Earth, we don't need a drill or a mining operation to reach the sediment layers beneath the Herto sandstone. Over the last 6 million years, bits of the thick Afar sediment pack have been thrust back to the earth's surface. The resulting patchwork of re-exposed sediments provides investigators with a variety of windows on deep time. Annually eroded by seasonal rains, they regularly yield the voluminous bony and trace evidence through which we come to know the distant past. In chapter 6 of his Descent ofMan (1371], Darwin wrote that "those regions which are the most likely to afford remains connecting man with some extinct ape-like crea- ture, have not as yet been searched by geologists." But not even Darwin could have imagined that a single ge010gical depression in the Horn of Africa would by 2005 have yielded a record of human evolution stretching across the last 6 million years. A stone’s throw from the Herto discovery site, a promi- nent volcanic ash dated to 250,000l years ago underlies the Herto sandstone. Below it We have found the remains of thousands of extinct animals, including some fossilized hippopotamus bones bearing cutmarks made by ancient butchers who left hundreds of their finely made handaxes INTELLIGENT THOUGHT 3'3 to record their presence. Our surveys have failed to recover any bones of the people who made these tools, but several miles downstream, on the opposite bank of the modern Awash River at Bodo, another package of sediments has yielded handaxes even more primitive and the cranium of a man more than twice as old as the fellow who so dis- turbed the dueling creationists. Dated to 500,000 years before the present, this cranium from Bodo is different from that of any living human, but it is hardly the cranium of an ape. The braincase measures 1,250 cc, smaller than Herto’s but much larger than any modern ape’s. Deeper in time, we have found cruder stOne handaxes at Bouri, several hundred meters east of the Herto find. Here we unearthed a more heavily browed but smaller [995 cc) Skullcap of yet another hominid, this time eroding from sediments including a volcanic ash a million years old. This individual is so unmistakably not human that it bears a sep- arate species name, Homo crews. The animal fossils found in these so-called Daka strata contain animals that, unlike the Herto fauna, no longer exist. Some disappeared with- Out descendants; others persisted but changed through time. And so it goes, as you proceed into deeper and deeper sediment layers in the Middle Awash sediment trap. Moving east of the Daka, toward the Awash River, you cross a large time gap in sedimentation, reflecting local non- deposition. Because of this sedimentation hiatus, the Mid- dle Awash lacks a good record of what happened here between 1.0 million and 2.5 million years ago. But farther south in the African rift, sedimentation preserves abundant evidence dating from this interval. At Bouri, there are even older sediments, dated to about 2.5 million years ago. Fos- sils feund in these sediments are removed from us by 125,000 generations. If just one genealogical lineage with ?4 TIM D. WHITE all the intervening mothers and fathers were buried in pairs in foot-deep coffins, the coffin stack would be twenty-three miles deep. And this is only halfway down the time range sampled by the deep Middle Awash sediment stack! For deep geneaology, the terrestrial geological record is unfortunately incomplete. The bodies of most mothers and fathers decay and leave no traces. It is only under special conditions, like those in the Afar, that a small fraction of mortal remains can be preserved and then recovered after such a colossal stretch of time. A creature known as Aus- tralopithecus garhi lived in the Afar 2.5 milliOn years ago. Its brain was only abOut the size ofa large orange. Its muz- zle jutted out below its eye sockets. It was superficially ape-like, but its canines were much smaller and blunter than any ape'S, and its molars were much larger. Nearby we found evidence that large mammals had been butchered with stone tools, the earliest evidence of this kind of activ- ity on Earth. The earliest stone tools, dated to 2.6 million years ago, also come from the Afar, about a day's drive along the camel tracks that stretch north fi'om Bouri. North of the Middle Awash, a female's partial skeleton was trapped in sands at Hadar about 3.2 million years ago. She was found in 1974 by the Chicago paleoanthropologist Don- ald Johanson and nicknamed Lucy. Her species, Australa- pirhecus afarensis, is well known from skeletal evidence at Hadar and from footprints in volcanic ash uncovered at Laetoli, in northern Tanzania. In the Middle Awash, we have found teeth, limb bones, and the most complete lower jaw of this species ever rec0vered. The deeper you go into the paleoanthropological record, the more difficult it is to recover evidence. For years fol- lowing the discovery and analysis of Lucy and her con- specifics, little was known about her ancestors. Only a few dental scraps of earlier hominids were found. But during INTELLIGENT THOUGHT 75 the last decade, discoveries in several new fossil fields have allowed us to break through the 4-million~year barrier to find out about earlier hominids. The Central Awash Complex is a block of sediments and interbedded lavas that dominates the landscape north of Bouri. Here in 1992, at a place called Aramis, our team probed a 4.4-million-year—old sediment package that yielded a primate called Ardipithecus ramidus, a creature like the younger Australopithecus but even more primitive. Five years later, Yohannes Haile-Selassie (the head of physical anthropology at the Cleveland Natural History Museum and no relation to the former emperor) began to recover pri- mate teeth and bones from 5.7-milljon-year-old sediments in the foothills of the Middle Awash rift margin. This was an even more ape-like bipedal species, which he named Arcti- pirhecus kadabba. At this writing, we have recovered 227 hominid indi- viduals, now under study at Ethiopia’s National Museum, many of them already published in top science journals. So here, in one place in the Horn of Africa, we have an ordered set of snapshots through geological time. These glimpses, made available only during the past twenty-five years, are vital to understanding human origins and evolu- tion, yet there are still many questions about our origins that we cannot answer, simply because we don’t yet have enough fossils. The Middle Awash sediment stack, with Herto man near the top, is but one set of windows on the past. Its unique record has allowed us to test those models that predict modern people all the way back to an allegedly abrupt origin in the oldest sediments. We have not found any evidence for that scenario. Rather, all the evidence is consistent with the hypothesis that the Herto man and his modern human descendants evolved. Each fossil our team 76 TIM 0. WHITE collects from Middle Awash sediments tests hypotheses about evolution. We have now collected thousands of arti— facts and 15,619 vertebrate individuals, from bats and shrews to crocodiles and gigantic elephants. We never find anatomically modern humans—or modern bats, or modern shrevvs, or modern hippos, or modern elephants—in the oldest sediments. We find modem species, like our own, in sediments at the top of the geological succession and extinct or ancestral ones at the bottom. We have hundreds of fossils that anatomically and chronologically are intermediate between modem animals and older ancestors. Among the hominids, Herto is inter- mediate between living humans and the underlying Bodo man, and Bodo is intermediate between Herto and Daka. Given the 25,000 generations separating the Daka, Bodo, and Herto individuals, it is all the more amazing that Bodo is so anatomically and chronologically intermediate. Will modern humans ever be found alongside Australa- pithecus in the older sediments at Afar or elsewhere? As sci- entists, we must leave that possibility open, but realistically it becomes more remote each time we find another fossil. We can think of biological evolution as a singular exper— iment on a vast scale. The experiment recorded itself in the form of fossils and artifacts and their contexts—and also in the form of the modern biological world, a world rich in physical evidence of biological evolution. How do we go about reconstructing the experiment? The good news is that the experiment only happened once—there is only one past to reconstruct. The bad news is that our records of the experiment are so poor. But today’s biological world is rich in readily available information. Let’s start there. Comparative biology shows a narrow genetic divide but broad behavioral and anatomical gulfs between modem INTELLIGENT THOUGHT y; humans and modern chimpanzeesThe fossil record can illu_ minate from what sort of common ancestor th05e differences arose, and how. In the mid-18005, the human fossil record was virtually nonexistent and even living African apes were little known; it would be over 100 years before the molecu- lar anatomy of chimpanzees and humans could be com- pared. But the muscular and skeletal anatomy of humans and modern apes was available to early anatomists, like Thomas Henry Huxley. They performed careful comparative studies of bones, muscles, and organs of these primates and con- cluded that these apes were not our ancestors [after all, they were still alive] but rather our closest living relatives. A century later, this conclusion would be amply con- firmed by molecular studies. Today we know that the genomes of modern humans and modern chimpanzees dif- fer by only a few percent. But compared to the living great apes—and all the hundreds of other primates [and thou- sands of other mammals, like rats and rabbits]-we humans are very odd. At first glance, we seem to stand apart. Why are we so bizarre, and how did we get this way? These are central issues in the study of human evolution. Of the thousands of modern mammalian species pro- duced by the grand experiment of evolution, there are only around 190 primate species. Of these, we humans are the most unusual. For this reason, people place themselves in their own zoological family, the Hominidae. Living humans are hominids with the following characteristics: We are the only primate (indeed, the only mammal] that walks habit- ually on two legs. Our brains are large relative to our body size. Our small canine teeth are set in tiny faces. Our tech- nology is overwhelming, Our communication system extra- ordinary. We tend to eat much meat, share Our food, and display unique sexual anatomy and physiology. And we ?3 TIM D. WHITE have traditionally interpreted ourselves as the pinnacle of the evolutionary process, the top of the tree. This view of the past is a narrow and misleading rendering of evolution- ary history. The preSent has too often been imposed upon the past, the data of the past too quickly accommodated to preconceptions derived from the present. Our ancient human ancestors were neither humans nor chimpanzees— they were creatures busy being themselves. Some went extinct. Others became us. We now understand that human ancestors were confined to Africa from the time when they split, sometime before 7 million years ago, from the line leading to living chim- panzees. The earliest hominids are found in wooded set- tings. Beginning about 4.2 million years ago, new hominids appeared in Africa, intermediate between the earlier ones and later ones, such as Lucy, but sharing with the latter the basic biology of a fundamentally bipedal locomotor pat- tern, ape-sized brains, and teeth and jaws much larger than ours. Lucy herself was neither chimp nor human. [Nor was she halfway between, because chimpanzees are still alive today.) Rather, Lucy was a member of a unique, widespread species well adapted to Pliocene Africa. By 2.5 million years ago, a basic division among hominids had occurred, and specialized Species of Australopirhems lived in southern and eastern Africa alongside subsequently smaller-toothed and larger—brained human ancestors who would expand from Afi'ica. The earliest expansion hap— pened some 1.8 million years ago, based on evidence from Georgia and Indonesia. These colonizers had spread across the Old World by the time the cycle of ice ages began, about a million years ago. By then, the specialized forms of Australopirhecus had vanished from the African record. European populations of the hominid colonizers would evolve into Neanderthals, an ice-adapted set of popula— INTELLIGENT THOUGHT F9 tions that evolved in accordance with the same evolution- ary principles as other mammals, diverging from ancestral Species and adapting to special conditions. Neanderthals, sophisticated bipeds who were much closer relatives of ours than any of the living apes are, went extinct long after the Herto people arose and spread from Africa. [The recently discovered remains of a dwarf hominid found in cave sediment on Flores Island in Indonesia may be evi- dence of yet another close-relative-recently-gone-extinct.) We're all familiar with the iconography misleading us into imagining that the evolutionary experiment resulting in the modern world Was an orderly, gradual, progressive affair, a ladder-like ascent to the preSent. But ever since Darwin, we have known this to be a narrow, self—serving view of the past. As Mark Twain observed in his essay "Was the World Made for Man?": "If the Eiffel tower were now representing the world's age, the skin of paint on the pinnacle-knob at its summit would represent man's share of that age; 8: anybody would perceive that that skin was what the tower was built for. I reckon they would. I dunno." Of course he knew. Darwin's predictions about human evolution have been tested by the recovery of evidence showing that the living world was articulated by evolution. Humans were part of that process. There is a lot more to learn about how that hap— pened. The ultimate cause[s) are currently intractable, but there's already plenty of evidence to show that evolution did happen and that we humans are among its products There are now tens of thousands of hominid fossils in museums around the world supporting our current knowl- edge of human evolution. The pattern that emerges from this vast body of hard evidence is consistent across thou- sands of investigations. All models, all myths involving the singular, instantaneous creation of modern humans fail in BO TIM D.WHITE the face of this evidence. The origin stories developed a few thousand years ago by prehistoric pastoralists in the Middle East, hunter-gatherers in Australia, and farmers in Mesoamerica are all interesting and important, but these anthropological perspectives belong in the context of reli- gious studies, not in science classrooms. And none of these myths have predicted what we have so far learned from the recovery and analysis of fossil evidence as well as from the biochemical and anatomical similarities and differences that characterize living things. A denial of evolution— however motivated—As a denial of evidence, a retreat from reason to ignorance. Today, evolution is the bedrock of biology, from medi- cine to molecules, from AIDS to zebras. Biologists can't afford to ignore the interconnectedness of living things, much as politicians can’t understand people, institutions, or countries without understanding their histories. As organisms, and as products of evolution, humans live and die in a biological world that has evolved and continues to evolve. The genes that determine much about how we live our lives—and how we die-—are the products of evolution. Our lives depend on foods genetically modified by Neo- lithic ancestors. Our sufferings and deaths are often caused by microbes that have evolved resistance to our drugs. The implications of human evolution for law, medicine, agri- culture, and biotechnology are vast. Our very futures are tied to emergent diseases and changing climates. We ignore these realities only at our peril. The past is not a half-empty version of the present. An evolutionary perspective, based on the evidence, reveals past worlds as very different, complex, and fascinating places—places we still know very little about. Rather than characterizing evolution as a process designed to create the INTELLIGENT THOUGHT 81 world for ourselves, our studies of evidence lead to under- standing evolution as a vast ongoing experiment whose results happen to include us. Nor is Homo sapiens the end product of evolution, the top rung on the ladder, the tip of the tree. We hominids were never a particularly bushy branch of that tree. As a species, we would never have gotten to where we are with- out our technology. Moreover, the evidence shows that our species is a peculiar creature whose cultural adaptation is currently perturbing the planet's ecosystems in drastic ways. Ironically, the world’s lone remaining species of bipedal primate is poised to go down in evolutionary his- tory as the greatest biological eliminator of species diverw sity that the planet has ever witnessed. In this, the broader perspective, we are a fairly recent product of a still unfolding process. Human evolutionary history has important lessons for our species. The fossil record demonstrates that our closest relatives, bipedal pri- mates far more like us than any modern ape, have repeat- edly gone extinct during the last 6 million years. We can now recognize the outlines of our parentage in consider- able detail: It is knowledge that should prove uSeful to a primate whose future is increasingly in its own hands. TIM D. WHITE, a paleontologist at the University of Cali- fornia at Berkeley, is co-director of the Middle Awash pro- ject in the Afar Basin of Ethiopia, the largest and to date most successful multidisciplinary investigation into human origins and evolution. He is the author of The Human Bone Manual. ...
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This note was uploaded on 01/19/2011 for the course IB 35AC taught by Professor Hlusko during the Spring '08 term at Berkeley.

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White Intel Thought - HUIt‘I'IL'lH-l' \‘(ll Lll lEI'II...

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