Human evolution is the biological and cultural development of humans. A human isany member of the species Homo sapiens, meaning wise man.
Since at leastthe Upper Paleolithic era, some 40,000 years ago, every human society hasdevised a creation myth to explain how humans came to be. Creation myths arebased on cultural beliefs that have been adopted as a legitimate explanation bya society as to where we came from. The science of paleoanthropology, which alsotries to create a narrative about how humans came to be, is deeply technical. Paleoantropology is the science of the evolution of humans, and it is the baseof all research in that field. Humans have undergone many different changesduring the last hundred million years, and it is the paleoanthropologists jobto identify and explain these changes.
In this research paper I will examine:human physical traits that define their species, human origins from pre-humansto modern humans, major discoveries and the history of human evolution, and whatthe future may hold as far as evolution for the human species. Homo sapiens arethe only living representative of the family Hominidae. The Hominidae, orhominids are a group of upright walking primates with relatively large brains. So all humans are hominids, but not all hominids could be called human.
Next allhumans are primates. The mammalian order of primates include about 180 speciesof prosimians (lemur like animals), monkeys, apes, and ourselves. Primates areunusual mammals for they have evolved such distinctive traits as highlydeveloped binocular vision, mobile fingers and toes with flat nails instead ofclaws, a shortened snout with a reduced sense of smell, and large brainsrelative to body size. If primates are unusual for mammals, humans are even moreunusual for primates. We are essentially elaborated African apes. We sharealmost 99 percent of our genetic material with chimpanzees.
Yet we have severaltraits that are very different. Two legged walking, or bipedalism seems to beone of the earliest of the major hominine characteristics to have evolved. Toaccommodate this strange position, we have developed a specialized pelvis, hipand leg muscles, and an S-shaped vertebral column. Because these changes can bedocumented in fossil bone, bipedalism is seen as the defining trait of the subfamily Homininae. Much of the human ability to make and use tools and otherobjects stem from the large size and complexity of the human brain.
Most modernhumans have a braincase volume of between 79. 3 and 91. 5 cubic inches. In thecourse of human evolution the size of the brain has more than tripled.
Theincrease in brain size may be related to changes in hominine behavior. Over timestone tools, and other artifacts became increasingly numerous and sophisticated. It is likely that the increase in human brain size took place as part of acomplex interrelationship that included the elaboration of tool use and toolmaking, as well as other learned skills which permitted our ancestors to beincreasingly able to live in a variety of environments. The earliest homininefossils show evidence of marked differences in body size, which may reflect apattern of the different sexes in our early ancestors. The bones suggest thatfemales may have been 3 to 4 ft in height and about 60 to 70 lb.
in weight,while males may have been somewhat more than about 5 ft tall, weighing about 150lb. The reasons for this body size difference are disputed, but may be relatedto specialized patterns of behavior in early hominine social groups. Thisextreme difference between sexes appears to disappear gradually sometime after amillion years ago. The third major trend in hominine development is the gradualdecrease in the size of the face and teeth. All the great apes are equipped withlarge, tusklike canine teeth that project well beyond the level of the otherteeth.
The earliest hominine remains possess canines that project slightly, butthose of all later hominines show a marked reduction in size. Also, the chewingteeth, the premolars and molars, have decreased in size over time. Associatedwith these changes is a gradual reduction in the size of the face and jaws. Inearly hominines, the face was large and positioned in front of the braincase. Asthe teeth became smaller and the brain expanded, the face became smaller and itsposition changed. Thus, the relatively small face of modern humans is locatedbelow, rather than in front of, the large, expanded braincase.
Evidence ofimmediate relatives of the human species begins about five million years agowith the Australopithecus genus and leads in to the primitive Homo genus tomodern humans. The nature of the humans evolution before that is uncertain,but scientists have hypothesized some ideas. What they do know is that between 7and 20 million years ago, primitive apelike animals were widely distributed onthe African and later on the Eurasian continents. Although many fossil bones andteeth have been found, the way of life of these creatures, and theirevolutionary relationships to the living apes and humans, remain matters ofstrong disagreement among scientists. One of these fossil apes, known asSivapithecus, appears to share many features with the living Asian great ape andthe orangutan, whose direct ancestor it may well be. None of these fossils,however, offers convincing evidence of being on the evolutionary line leading tothe hominid family generally.
But they do help paint a picture of what earlyhuman relatives could have been like. The convincing fossil evidence for humanevolution begins with Australopithecus. Fossils of this genus have beendiscovered in a number of sites in eastern and southern Africa, and were firstidentified in South Africa in 1924. Earliest fossils show them existing about3. 9 million years ago, and the genus flourished until it seemed to have becomeextinct about 1. 5 million years ago.
All the australopithecines were efficientlybipedal and thus indisputable hominines. In details of their teeth, jaws, andbrain size, however, they differ enough among themselves to warrant divisioninto four species: A. afarensis, A. africanus, A. robustus, and A.
boisei. Theearliest australopithecine is A. afarensis, which lived in eastern Africabetween 3 and 3. 9 million years ago. Found in the Afar region of what is nowEthiopia and in Tanzania, A.
afarensis had a brain size a little larger thanthose of chimpanzees. Some of the species possessed canine teeth somewhat moreprojecting than those of later hominines. No tools of any kind have been foundwith A. afarensis fossils. Between about 2. 5 and 3 million years ago, A.
afarensis apparently evolved into a later australopithecine, A. africanus. Knownprimarily from sites in southern Africa, A. africanus possessed a brain similarto that of its predecessor. However, although the size of the chewing teethremained large, the canines, instead of projecting, grew only to the level ofthe other teeth. As with A.
afarensis, no stone tools have been found inassociation with A. africanus fossils. By about 2. 6 million years ago, thefossil evidence reveals the presence of at least two, and perhaps as many asfour, separate species of hominines. An evolutionary split seems to haveoccurred in the hominine line, with one group evolving toward the genus Homo,and finally to modern humans, and the others developing into australopithecinespecies that eventually became extinct. The australopithecine species thateventually became extinct includes the robust australopithecines, A.
robustus,that lived in southern Africa, and A. boisei, found only in eastern Africa. Therobust australopithecines represent an unusual adaptation because theirprincipal difference from other australopithecines lies in the large size oftheir chewing teeth, jaws, and jaw muscles. The robust australopithecines becameextinct about 1. 5 million years ago.
Although scientists do not agree, manybelieve that after the evolutionary split that led to robust australopithecines,A. africanus evolved into the genus Homo. This was a species called Homo habilis,or “handy man. ” Appearing about 2.
5 million years ago, the new hominidprobably didn’t look terribly different from its predecessors, but it had asomewhat larger brain. And, perhaps as a result of some mental connection otherhominids were unable to make, Homo habilis figured out for the first time how tomake tools. Earlier species had used tools like bits of bone for digging, orsticks for fishing termites out of their mounds (something modern chimps stilldo). But Homo habilis deliberately hammered on rocks to crack and flake theminto useful shapes.
The tools were probably not used for hunting, as scientistsonce thought. Homo habilis, on average, was less than 5 ft. tall and weighedunder 100 lbs. , and it could hardly have competed with the lions and leopardsthat stalked the African landscape. The hominids were probably scavengersinstead, supplementing a mostly vegetarian diet with meat left over frompredators’ kills.
Even other scavengers like hyenas, jackals and the such werestronger and tougher than early humans. But Homo habilis presumably had theintelligence to anticipate the habits of predators and scavengers, and probablyused tools to butcher leftovers quickly and get back to safety. Theiradaptations to the rigors of prehistoric African life enabled members of theHomo habilis species to survive for 500,000 years or more, and at least onegroup of them apparently evolved, around 2 million years ago. Around this time,East African mammals adapted to drier more open grassland conditions. It wasabout this time that the new form of human emerged in Africa, a hominid with amuch larger brain, excellent vision, and limbs and hips fully adapted to anupright posture. Paleoanthropologists call this hominid Homo Erectus, a humanmuch taller than its diminutive predecessors, standing on average five feet sixinches tall, with hands capable of precision gripping and many kinds oftool-making.
The skull is more rounded than those of earlier hominids, but stillhad a sloping forehead and retreating brow ridges. Homo Erectus was morenumerous and more adaptable than Homo habilis, and, on present evidence, was amuch longer lived species. Archaeological sites for this species appear athigher, cooler elevations in southern, eastern, and northern Africa. Homoerectus may have been a skilled big game hunter, capable of organizing quiteelaborate hunting and foraging expeditions, and using multipurpose axes andcleaving tools. Like all hunters and foragers, Homo Erectus had probably learnedto live with natural fires and was not afraid of them. In time, the new hominidmay have made a habit of conserving fire, taking advantage of smoldering treestumps ignited by lightning strikes and other natural causes to light dry bush.
Then came the biggest step of all, the making of fire. Perhaps as early as 1. 5million years ago, Homo erectus may have learned to create fire in East Africa,but scientists still debate the issue. Fire offers not only warmth, butprotection against predators and an easy way of hunting game, even insects androdents. The toxins from many common vegetable foods can be roasted or parchedout in hot ashes, allowing people to use a wider range of foods in their diet.
Homo erectus was a much larger species than its predecessors meaning that thenewcomers needed larger quantities of food to satisfy higher metabolic rates. This meant they had to range over much larger hunting territories perhaps movinginto more open country, where trees were rarer. Perhaps, the bands now carriedfire brands with them as a weapon that would enable them to operate safely awayfrom trees, and to occupy dark caves where predators often lurked. It alsoenabled Homo erectus to settle and live in far cooler environments. It may be nocoincidence that the earliest human settlement of Europe and Asia occurred afterHomo Erectus could make as well as tame, fire. Somewhere between 200,000 and300,000 years ago, Homo erectus evolved into Homo sapiens.
There is noparticular reason to identify why evolution happened during this period andexactly when it happened. In fact, certain fossils from this period areclassified as late Homo erectus by some scientists and as early Homo sapiens byothers, depending on the scientists belief in what happened. Even though theyare in the same genus and species as modern humans, these early Homo sapiens donot have identical physical traits to modern humans. New fossil evidencesuggests that modern man, sometimes called Homo sapiens sapiens (a sub-speciesof Homo sapiens), first appeared more than 90,000 years ago. There is somedisagreement among scientists on whether the hominine fossil record shows acontinuous evolutionary development from the first appearance of Homo sapiens tomodern humans.
This disagreement has especially focused on the place ofNeandertals (or Neanderthals), often classified as H. sapiens neanderthalis, inthe chain of human evolution. The Neanderthals (named for the Neander Valley inGermany, where one of the earliest skulls was found) occupied parts of Europeand the Middle East from 100,000 years ago until about 35,000 to 40,000 yearsago, when they disappeared from the fossil record. Fossils of additionalvarieties of early Homo sapiens have been discovered in other parts of theEurasia.
The dispute over the Neanderthals also involves the question of theevolutionary origins of modern human populations, or races. Although a precisedefinition of the term race is not possible (because modern humans showcontinuous variation from one geographic area to another), widely separate humanpopulations are marked by a number of physical differences. Most of thesedifferences represent adaptations to local environmental conditions, a processthat some scientists believe began with the spread of Homo erectus sometimeafter a million years ago. In their view, human development since Homo erectushas been one continuous, in-position evolution, meaning, local populations haveremained, changing in appearance over time. What they are trying to say is thatthe peopling of the world, the spreading of humans, has not changed since HomoErectus. The Neanderthals and other early Homo sapiens are seen as descendingfrom Homo erectus and are ancestral to modern humans.
Other scientists viewracial differentiation as a relatively recent phenomenon. In their opinion, thefeatures of the Neanderthals which are a low, sloping forehead, large browridge, and a large face without a chin are too primitive for them to beconsidered the ancestors of modern humans. They place the Neanderthals on a sidebranch of the human evolutionary tree that became extinct. According to thistheory, the origins of modern humans can be found in southern Africa or theMiddle East. Evolving perhaps 90,000 to 200,000 years ago, these humans thenspread to all parts of the world, supplanting the local, earlier Homo sapienspopulations.
In addition to some fragmentary fossil finds from southern Africa,support for this theory comes from comparisons of mitochondrial DNA, a DNA forminherited only from the mother, taken from women representing a worldwidedistribution of ancestors. These studies suggest that humans derived from asingle generation in southern Africa or southeastern Asia. Because of thetracing through the material line, this work has come to be called the Evehypothesis. Its results are not accepted by most scientists, who consider thehuman race to be much older.
Whatever the outcome of this scientificdisagreement, the evidence shows that early Homo sapiens groups were highlyefficient at exploiting the sometimes harsh climates of Ice Age Europe. Further,for the first time in human evolution, hominines began to bury their deaddeliberately, the bodies sometimes being accompanied by stone tools, by animalbones, and even by flowers. Although the evolutionary appearance of modernpeoples did not dramatically change the basic pattern of adaptation that hadcharacterized the earlier stages of human history, some innovations did takeplace. In addition to the first appearance of the great cave art of France andSpain some anthropologists have argued that it was during this time that humanlanguage originated, a development that would have had profound implications forall aspects of human activity. About 10,000 years ago, one of the most importantevents in human history took place, plants were domesticated, and soon after,animals as well. This agricultural revolution set the stage for the events inhuman history that eventually led to civilization.
The next evolutionary stage,is modern humans as we know them. Early Homo sapiens developed the traits thatwere discussed earlier, and man as we know it, came to exist. But how do we knowall these things occurred, and why? It all comes from several very importantsteps in paleoanthropology. The earliest human skeleton ever found wasdiscovered in 1974 in a remote region of Ethiopia, a very well preserved A. afarensis fossil. Nicknamed Lucy, paleoanthropologists have found out periods ofmillions of years through her, and have used that knowledge to speculate onother discoveries.
Footprints, bones, teeth, etc. are all used to help piecetogether the puzzle. Human evolution may have reached a dead end, foreseeablefor a while at least. Despite the enormous changes that we have wreaked on ourenvironment, major evolutionary changes in humans will not occur in the distantfuture.
Scientists dismiss the idea that the species is going somewhereunder natural selection and then describe how most successful species are stablethrough their geological lifetimes. Furthermore, given the relative pace ofcultural change and lack of isolation of human populations, there is littlechance for a new different human species. Modern understanding of humanevolution rests on known fossils, but the picture is far from complete. Onlyfuture fossil discoveries will enable scientists to fill many of the blanks inthe present picture of human evolution. Employing sophisticated technologicaldevices as well as the accumulated knowledge of the patterns of geologicaldeposition, anthropologists are now able to pinpoint the most promisinglocations for fossil hunting more accurately.
In the years ahead this willresult in an enormous increase in the understanding of human biological history. BibliographyEdgar, Blake, and Johanson, Donald. From Lucy to Language. New York: Simonand Schuster, 1996. Fagan, Brian.
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