Evolution from apes to humans, s. mubasher


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Evolution from apes to humans, s. mubasher

  1. 1. Dr. Mubasher’s Blog DEPARTMENT OF BIOLOGY OXFORD HIGH SCHOOL T. M. KHANNovember 20, 2012The EvolutionFrom Apes to Humans Posted byDr. Solangi Mubasher, D.V.MInside the story  What is human evolution?  If apes turned into humans, then apes should no longer exist?  Is there any role of tools in evolution?  Is there any role of environment in evolution?  Scientific disciplines involved in evolution, including, Taxonomical, physical, anatomical, anthropological, archaeological and genetical aspects. IntroductionThe humans and apes evolved from a common ancestor. That makes humansand apes related species. The molecular evidence showed very clearly thatchimpanzees are our closest living relatives, and so, logically, we must share anancestor in common at some point in the past. This common ancestor, wasn’tnecessarily identical to modern chimpanzees- remember, all populations are ina state of evolutionary flux, it’s just that some are required by theirenvironments to evolve faster than others. Either way, we need to understandthat the phrase “Humans evolved from apes” has two distinct meanings forpeople who hear it. One emphasizes the word “apes” and the other emphasizesthe word “from.” By one way of thinking, the phrase means “Homo sapiens isone of several species of ape.” By the other way of thinking, the phrase means“Homo sapiens evolved from apes into something different.” Either way, somepeople will be annoyed. Either way, the statement may be correct. Afterdiverging with the other great apes, bipedalism evolved in theAustralopithecines, but they weren’t human quite yet. Once a large enoughbrain evolved, rudimentary tools began to be used, as seen in Homo habilis, theHandyman. These then became migratory hunter/gatherers, as seen in Homoerectus. Modern humans evolved the use of language, and migrated out ofAfrica and all over the world, to where we are today.
  2. 2. Evolution from apes to humans by Dr. S. Mubasher, D.V.MEvolution from apes to humansGeology teaches that the earth was lifeless in the beginning, when where andwhy was life started, no one knows about that. Many people have been willingto admit that evolution may occur in plants and animals, but they refuse toconcede that it occurs in man. Indeed, some have been unwilling to considerman an animal. As far as mans evolution is concerned, there is abundantevidence from embryology, comparative anatomy, and other fields to illustrate 2his emergence from other forms (a common ancestor of apes and humans). Noevolutionist maintains that man sprang from any of our present day apes andmonkeys. On the contrary, it is thought that millions of years ago there was anapelike group of animals which gave rise to two branches. The first branchincluded the arboreal apes, and the second was a terrestrial group, the mananimals. By the process of evolution man emerged from this apelike stock as a"new creation." According to the evolutionists the first ape like group of animalsserved as ancestors to humans and apes, this statement is based upon thefindings, fossils of present day humans with slight variations or related ones.Eventually it is not clear that first group of animals were alike to presenthumans or apes. However, it is hard to trace early human history, for therehave been comparatively few finds. Asia, often called the "cradle of the race,"and Africa have been little explored. As we consider this very brief outline ofthe story of early man, we must remember that the conclusions are based onobservations not of complete specimens, but rather of fragmentary, fossil,skeletal remains. Knowledge of present day savages, comparison of theskeletons of man with those of the present-day great apes, as well as a studyof the life of these living animals and the biology of modern man all affordevidence of the origin and evolution of modern man. According to the earliertaxonomists that have a better look on evolutionary aspects of classificationthere are three major groups of organisms that share a single ancestor.  The New World monkeys, living on the American continents  The Old World primates, including monkeys and apes throughout Africa and Europe  The various species of monkeys that lived in Asia, but those are all extinct for various reasonsNote that all humans belong to that second group, only because primatesinclude old age animals, and those may be considered as ancestor to humanand apes, wherever they might have migrated since. Later, the ape lineageitself split into two groups  The "lesser ape", the current descendants of which are called gibbons  The "great ape", which includes all other apes like gorillas, chimps and humans.The closest living relatives to humans living today are the chimps, of whichthere are two species: Pan Troglodytes (the common chimp) and Pan Paniscus(the bonobo chimp). Human evolution is characterized by a number ofmorphological, developmental, physiological, and behavioral changes that havetaken place since the split between the last common ancestor of humans andchimpanzees. The most significant of these adaptations are1. Bimetallism2. Increased brain size3. Lengthened ontogeny (gestation and infancy)4. Decreased sexual dimorphism
  3. 3. Evolution from apes to humans by Dr. S. Mubasher, D.V.MOther physiological changes that have also characterized the process ofevolution are increased importance on vision rather than smell; a smaller gut;loss of body hair; evolution of sweat glands; a change in the shape of thedental arcade from being u-shaped to being parabolic; development of a chin(only found in Homo sapiens), development of styled; development ofa descended larynx. Natural selection and environment also played animportant role in evolution. Natural selection is variations in genetic variety thatchanges a species within itself. For instance, say a tribe of fair skinned people 3traveled to a very hot climate, those people with darker skin would be morelikely to survive thereby passing on their dark skinned genes and eventuallyweeding out the fair skinned people. Evolution only occurs when it is necessary.Some apes evolved into man because either they moved to a new environmentor their existing environment changed, making evolution necessary for survival.So, the apes who needed to adapt to their new environment through evolutionto survive either did so or were wiped out (apparently, they changed, creatingthe human race), or stayed in a friendly environment, making evolutionunnecessary and therefore, nonexistent (the apes in these conditions remainedapes). As Lamarck (1744-1820) pointed out that “animals and plants varywith changing environmental conditions and that, as they adjustthemselves to new conditions, they apparently change their form….Organs used tend to develop and those not used tend to atrophy (PerryD. Straus bough, General Biology, 2nd ed. 1947, p.623)”.HomoHomo sapiens are the only extant species of Homo genus. While some other,extinct Homo species might have been ancestors of Homo sapiens, many werelikely our "cousins", having speculated away from our ancestral line.Zoological classification showingExtant hominoids: humans (genus Homo), chimpanzees and bonobos (genus Pan), gorillas(genus Gorilla), orangutans (genus Pongo), and gibbons (four genera of the family Hylobatidae:Hylobates, Hoolock,Nomascus, and Symphalangus). All except gibbons are hominids.The topic of evolution from apes to Humans usually only covers theevolutionary history of primates, in particular the genus Homo, and theemergence of Homo sapiens as a distinct species of hominids (or "greatapes"), and according to it The humans and apes evolved from a commonancestor (which may either alike to humans or apes). Species close to the lastcommon ancestor of gorillas, chimpanzees and humans may be representedby Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece.
  4. 4. Evolution from apes to humans by Dr. S. Mubasher, D.V.MMolecular evidence suggests that between 8 and 4 million years ago, firstthe gorillas, and then the chimpanzees (genus Pan) split off from the lineleading to the humans; According to the human evolutionary genetics humanDNA is approximately 98.4% identical to that of chimpanzees when comparingsingle nucleotide polymorphisms. But the fossil record of gorillas andchimpanzees is limited due to both poor preservation and sampling bias. Theearliest documented members of the genus Homo are Homo habilis whichevolved around 2.3 million years ago. Homo habilis is the first species for which 4we have positive evidence of use of stone tools. The diagram below shows thegreat apes.The brains of these early hominines were about the same size as that of achimpanzee. During the next million years a process of encephalization began,and with the arrival of Homo erectus in the fossil record, cranial capacity haddoubled to 850cc. Homo erectus and Homo ergaster were the first of thehominine to leave Africa, and these species spread through Africa, Asia, andEurope (1.3 to 1.8 million years ago)In the eye of HistoryAlthough the work upon evolution was started first by the Greek philosophersby giving a concept of derivation of higher organisms from lower ones (ArthurW. Haupt, Fundamentals of Biology, 3rd ed. 1940, p.389). There are threemajor theories concern to the evolution. No one theory is entirely adequateeach has its strong and weak points. Thus the method by which evolutionarychanges have come about is still imperfectly understood. 1. French naturalist, Jean Baptiste de Lamarck (1477-1829), the theory was based upon inheritance and acquired characters, 1801. 2. English naturalist, Charles Darwin (1809-1882), the theory was based upon natural selection 3. Dutch botanist Hugo de Vries, The theory mutation, 1901Some other experts also talked about the topic.
  5. 5. Evolution from apes to humans by Dr. S. Mubasher, D.V.M 5 Linnaeus assigned the humans and apes to asingle taxonomic order. He stated nothing about ape to human evolution,but his categorization of humans with the apes certainly encouraged laternaturalists to think of the two as related by descent.” (Order Primates,10th ed.,1758). The voyages of discovery had revealed the existence of chimpanzees,orangutans, and gibbons (the gorilla remained unknown to European scienceuntil the 1840s, and the bonobo, until the 1920s). For the most part, taxonomicclassifications prepared by Linnaeus successors kept Homo separate from theapes. By 1800 this was the norm. But even those classifiers who failed to followLinnaeus classification and placed humans and non-human primates inseparate orders (Order Bimanes and Order Quadrumanes, respectively)generally recognized an affinity between apes and human beings.For example, Comte de Buffon stated that an ape "is only an animal, but avery singular animal, which a man cannot view without returning tohimself." (Histoire naturelle, vol.14, p.4, 1766). Philosophe Delisle de Salescommented that “the apes seem to form an intermediate line betweenanimals and human beings." (Histoire philosophique du monde primitive,1794). The French naturalist Constant Duméril speaks about thegenus Pithecus as containing "the species of apes that most closelyapproach man (Zoologie analytique, 1806, p. 8)." Similarly, in his systematicarrangement of the animal kingdom Cuvier follows the separate arrangement,but describes Quadrumanes as "the order closest to man (Règne Animale, p.79).” Jean Baptiste de Lamarck (1744-1829)The idea of ape to human evolution found its original spark in the 18th centurywhen Jean-Baptiste Lamarck the first naturalist with the nerve to proposepublicly and explicitly that; human beings had evolved from apes. He said“Certainly, if some race of apes, especially the most perfect amongthem, lost, by necessity of circumstances, or some other cause, thehabit of climbing trees and grasping branches with the feet, and if theindividuals of that race, over generations, were forced to use their feetonly for walking and ceased to use their hands as feet, doubtless theseapes would be transformed into two-handed beings and their feetwould no longer serve any purpose other than to walk (Philosophiezoologique, 1809).”Robert Chambers stated that “the primates are distinguished by greaterrelative magnitude of brain, by agility, and by the use of the hand. The
  6. 6. Evolution from apes to humans by Dr. S. Mubasher, D.V.Msignal superiority of the human species is thus prepared for andbetokened in the immediately preceding portions of the line: it mighthave been seen, ere man existed, that a remarkable creature wascoming upon the earth (Vestiges of the Natural History of Creation (1844).”Darwin and evolutionCharles Darwin is considered to be the presenter of the modern theory of 6organic evolution. He has a scientific background for environment as well asheredity as his father and grandfather were physicians and maternalgrandfather was a pot maker. The possibility of linking humans with earlierapes by descent only became clear after 1859 with the publication of CharlesDarwins book the “Origin of Species”. However some other scientists andresearchers also commented on same topic but no one clearly declaredanything about human evolution as much clear as the Darwin. AlthoughDarwins book did not address the question of human evolution, saying onlythat "Light will be thrown on the origin of man and his history", but 25years research on evolution published in this book has had a more profoundinfluence on human thought than any other scientific work ever written. It wasthis book that resulted in the establishment of the principle of evolution as afundamental scientific generalization. The first debates about the nature ofhuman evolution arose between Thomas Huxley and Richard Owen. HuxleyDarwins friend and advocate Thomas Henry Huxley was far bolder on this topicthan was Darwin himself, he argued for human evolution from apes byillustrating many of the similarities and differences between humans and apes,and did so particularly in his book Huxley, Evidence as to Mans Place in Nature,1863. Huxley summarized the many anatomical traits shared by humans andapes and asserted that such evidence supported the hypothesis that humansand apes had evolved from a recent common ancestor. It was the first bookdevoted expressly to the topic of human evolution. However, many of Darwinsearly supporters (such as Alfred Russell Wallace and Charles Lyell) did notagree that the origin of the mental capacities and the moral sensibilities ofhumans could be explained by natural selection. Darwin published nothing onthe topic until 1871, when his own book “The Descent of Man, 1871” appeared.Darwin applied the theory of evolution and sexual selection to humans. He notonly discuss the topic but give firm bases of evolution and suggest that how theevolution takes place, his theory is based upon variation, heredity and naturalselection or survival to the fittest. It has been suggested that the factor ofisolation must be added to that of natural selection for the effective creation ofnew species. As everyone knows that if dog is compared to wolf and cat than itis more alike to the wolf than cat, but dog is more alike to cat if it is comparedto the horse. Eventually dog, cat and wolf are canines where as horse isherbivore. Thus more is the resemblance of two organisms shows their closerrelationship.First fossilA major problem of the entire process of evolution was the lack of fossilintermediaries, despite the 1891 discovery by Eugène Dubois of what is nowcalled Homo erectus. It was only in the 1920s when such fossils werediscovered in Africa, that intermediate species began to accumulate. In1925 Raymond Dart described Australopithecus africanus. The type specimenwas the Taung child, an Australopithecine infant which was discovered in a
  7. 7. Evolution from apes to humans by Dr. S. Mubasher, D.V.Mcave. The childs remains were a remarkably well-preserved tiny skull andan endo cranial cast of the brain. Although the brain was small (410 cm³), itsshape was rounded, unlike that of chimpanzees and gorillas, and more like amodern human brain. Also, the specimen showed short canine teeth, and theposition of the foramen magnum was evidence of bipedal locomotion. All ofthese traits convinced Dart that the Taung baby was a bipedal human ancestor,a transitional form between apes and humans. 7Steps of evolutionA bipedal step, to be precise- the first thing to distinguish our ancestors fromchimpanzee ancestors is the ability to walk upright. But being able to walkupright doesn’t earn the scientific, phylogenetic designation of human. Australopithecus, (~3 to 2 m. years), South AfricaWe designate all human species by the genus “Homo” as in our binomial,“Homo sapiens.” But these first human ancestors weren’t human enough to beconsidered part of our genus, and instead are called, “Australopithecus.” Onespecies of this genus in particular is thought to have been ancestral to humans-Australopithecus afarensis, one specimen of which has been nicknamed, “Lucy.”Like most of the Australopithecines, Lucy lived in Africa. Lucy, and the rest ofher species, resembled chimpanzees in a lot of ways, but one difference isobvious- she walked upright, like a human. And not just sometimes, the bonestructure of her pelvis indicates that she was upright most of the time.The expansion of the brain was the next big change in human evolution. Thiswas different than a lot of scientists had expected- they had assumed that alarger brain would have been the first change in the human-chimpanzeedivergence, followed by other human traits such as bipedalism and tool use.
  8. 8. Evolution from apes to humans by Dr. S. Mubasher, D.V.M Homo habilis, (~2.5 to 1.5 m. years), AfricaThe first human, or at least the first recognizable human species to whichwe’re willing to give the designation, is the Handyman, Homo habilis. TheHandyman lived between 1.5 and 2.5 million years ago, and he gets his name 8because rudimentary tools have been found with fossils of this species. Thesetools weren’t anything spectacular- just flakes of stone used as rudimentaryknives, for the cutting of meat off dead animals. It’s unlikely that theHandyman was a hunter- more likely, he would have taken meat from alreadydead animals like a scavenger. Homo erectus, (~2 to 0.4 m. years), Africa, ChinaHomo erectus just next to the Homo habilis; is the major step in humanevolution. Homo erectus or the Upright Man arose in Africa about 1.5 to 1.8million years ago. Homo erectus had a larger brain than Homo habilis, and itsanatomy was more similar to modern humans. But the most interesting thingabout Homo erectus was its incredible success- it was the first human speciesto engage in actual hunting, and this had the effect of expanding its territory.There is also evidence that Homo erectus was able to control fire. Homo sapiens (0.2 m. years, present)Homo erectus is the last major evolutionary transition before we get to modernhumans, Homo sapiens. Homo floresiensis (~0.09 to 0.013 m. years), IndonesiaIn 2003 a skeleton was found, believed to be a woman of about 30 years ofage. It has been dated to approximately 18,000 years old, one meter in height,with a brain volume of just 380 cm3 (considered small for a chimpanzee andless than a third of the H. sapiens average of 1400 cm3). Homo floresiensis(hobbit) has been named for its small size, possibly shared a common ancestorwith modern humans, but split from the modern human lineage and followed adistinct evolutionary path. However, there is an ongoing debate overwhether H. floresiensis is indeed a separate species. Some scientists holdthat H. floresiensis was a modern H. sapiens with pathological dwarfism, analso it was found with tools only associated with H. sapiens. The hypothesis ofpathological dwarfism, however, fails to explain additional anatomicalfeatures like form of bones in the wrist, forearm, shoulder, knees, and feet thatare unlike those of modern humans (diseased or not) but much like those ofancient members of our genus. Additionally, this hypothesis fails to explain the
  9. 9. Evolution from apes to humans by Dr. S. Mubasher, D.V.Mfind of multiple examples of individuals with these same characteristics,indicating they were common to a large population, and not limited to oneindividual.Geographic distribution of evolutionIn 2007, Japanese scientists believe they found the jawbone and teeth of justsuch an animal. By studying the size and shape of the teeth, they determined 9that the ape was gorilla-sized and had an appetite for hard nuts and seeds.They named it Nakalipithecus nakayamai and calculated its age to be 10 millionyears old. That puts the ape in the right place on the time line. More important,the scientists found the ancient bones in the Samburu Hills of northern Kenya.That puts N. nakayamai in the right geographic place, along a trajectory ofhominid evolution that stretches for several hundred miles in eastern Africa.The Middle Awash region of Ethiopia lies to the north, where the Africancontinent dead-ends into the Red Sea. In this theory, there was a coastaldispersal of modern humans from the Horn of Africa around 70,000 years ago.This group helped to populate Southeast Asia and Oceania, explaining thediscovery of early human sites in these areas much earlier than those inthe Levant. A second wave of humans dispersed across the Sinai Peninsula intoAsia, resulting in the bulk of human population for Eurasia. This second grouppossessed a more sophisticated tool technology and was less dependent oncoastal food sources than the original group. Much of the evidence for the firstgroups expansion would have been destroyed by the rising sea levels at theend of each glacial maximum.Richard Dawkins has come out in support of an “Out of Africa again and again”hypothesis, which suggests that Homo sapiens migrated out of and back intoAfrica several times before finally spreading out over all the continents. Thishypothesis is backed up by genetic evidence tracing the genetic similarity ofvarious genes among different human populations, and it looks the mostpromising. One of the major differences setting Homo sapiens aside from theother hominids is our use of language. This development is likely what allowedmodern human society to expand and become as complex as it is now. Becausediet of Homo erectus became more reliant on animals than plants, it began tomigrate, and thus spread out of Africa, and colonized south East Asia, evengoing up farther north into Eurasia.Anatomic evidences of evolutionWe classify human species- that is, species that belong to the genus “Homo”not only on the basis of walking upright and pelvis but also to the vertebralcolumn, feet and ankles, and skull the expanding brain followed soon after.Perhaps the most significant changes are in the pelvic region, where the longdownwards facing iliac blade was shortened and became wide as a requirementfor keeping the center of gravity stable while walking. The shortening andnarrowing of the pelvis evolved as a requirement for bipedalism and hadsignificant effects on the process of human birth which is much more difficult inmodern humans than in other primates. The femur evolved into a slightly moreangular position to move the center of gravity towards the geometric center ofthe body. The knee and ankle joints became increasingly robust to bettersupport increased weight. Also in order to support the increased weight on eachvertebra in the upright position the human vertebral column became S-shaped
  10. 10. Evolution from apes to humans by Dr. S. Mubasher, D.V.Mand the lumbar vertebrae became shorter and wider. In the feet the big toemoved into alignment with the other toes to help in forward locomotion. Thearms and forearms shortened relative to the legs making it easier to runbipedal.Genetic evidences of evolutionAnthropologists in the 1980s were divided regarding some details of 10reproductive barriers and migratory dispersals of the Homo genus.Subsequently, genetics has been used to investigate and resolve these issues.Progress in DNA sequencing, specifically mitochondrial DNA (mtDNA) andthen Y-chromosome DNA advanced the understanding of human origins.Sequencing mtDNA and Y-DNA sampled from a wide range of indigenouspopulations revealed ancestral information relating to both male and femalegenetic heritage. Aligned in genetic tree differences were interpreted assupportive of a recent single origin. Analyses have shown a greater diversity ofDNA patterns throughout Africa. The research also located the origin of modernhuman migration in south-western Africa, near the coastal borderof Namibia and Angola. The fossil evidence was insufficient for Richard Leakeyto resolve this debate. Studies of in Y-chromosomal DNA and mitochondrialDNA have largely supported a recent African origin. Evidence from autosomalDNA also predominantly supports a Recent African origin. However, newevidence has just been made available that shows by examining the human andchimpanzee genomes that human and chimpanzee ancestors diverged and thenconverged, before diverging for a final time less than 5 million years ago.Genetic analysis suggests that humans and chimpanzees evolved into separatespecies which then interbred, forming a hybrid species which then bred backinto one of the parent populations. It’s not clear whether this human-chimpanzee hybrid returned to the human or the chimpanzee population, butthe molecular evidence is clear that the hybridization did happen- the Xchromosome has a particularly recent connection to the chimpanzee genome.This means that human-chimpanzee hybrid males would have been infertile,but the females were not. Thus the characters returned back to the parentalpopulation, mixing chimpanzee and human genes each time. But regardless ofthe human-chimpanzee hybrids, eventually the two lines did split for good. Andgradually, our ancestors changed from being something that was willing tomate with a chimpanzee, into something that would rather hunt them for food,train them for entertainment, or sequence their DNA. What was the first step?The first step, as it seems, is literally a step. A bipedal step, to be precise- thefirst thing to distinguish our ancestors from chimpanzee ancestors is the abilityto walk upright.Some common questionsIf apes turned into humans, then apes should no longer exist?Although there are several ways to attack this assertion, the bottom linerebuttal is simple; the humans didnt descend from apes. Thats not to sayhumans and apes arent related, but the relationship cant be traced backwardalong a direct line of descent, one form morphing into another. It must betraced along two independent lines, far back into time until the two linesmerge. The intersection of the two lines represents something special, whatbiologists refer to as a common ancestor. This apelike ancestor, which probably
  11. 11. Evolution from apes to humans by Dr. S. Mubasher, D.V.Mlived 5 to 11 million years ago in Africa, gave rise to two distinct lineages, oneresulting in hominids (humanlike species) and the other resulting in the greatape species living today. Or, to use a family tree analogy, the common ancestoroccupied a trunk, which then divided into two branches. Hominids developedalong one branch, while the great ape species developed along another branch.Is there any role of tools in evolution?The brain of a modern human consumes about 20 watts (400 kilocalories per 11day), a fifth of bodys total energy consumption. Increased tool use would allowhunting for energy-rich meat products, and would enable processing moreenergy-rich plant products. Researchers have suggested that early hominidswere thus under evolutionary pressure to increase their capacity to create anduse tools.Is there any role of environment in evolution?Evolution only occurs when it is necessary. Some apes evolved into manbecause either they moved to a new environment or their existing environmentchanged, making evolution necessary for survival. So, the apes who needed toadapt to their new environment through evolution to survive either did so orwere wiped out (apparently, they changed, creating the human race), or stayedin a friendly environment, making evolution unnecessary and therefore,nonexistent (the apes in these conditions remained apes).Study suggested: th 1. Charles Darwin, The origin of Species by means of natural Selection, 6 ed. st 2. Joseph II, Homo Sapience, 1 ed. 2009 nd 3. Perry D. Straus bough and Bernal R. Weimer, General Biology, 2 ed. 1947 rd 4. Arthur W. Haupt, Fundamentals of Biology, 3 ed. 1940 5. Are humans really descended from apes? by William Harris 6. Falsehood: Humans evolved from apes by Greg Laden, June 25, 2010 7. If people evolved from apes why are there still apes? Land Mammals Questions, Answers.com 8. Out of Africa again and again by Richard Dawkins 9. Microevolution.net 10. Sinobiological.com 11. Wikipedia.com For queries and kind suggestions drmubasher.webnode.com mubasher.solangi@facebook.com