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Darwinian Theory Of Evolution Essay

Theories explaining biological evolution have been bandiedabout since the ancient Greeks, but it was not until theEnlightment of the 18th century that widespread acceptance anddevelopment of this theory emerged. In the mid 19th centuryenglish naturalist Charles Darwin – who has been called the”father of evolution” – conceived of the most comprehensivefindings about organic evolution ever1. Today many of hisprinciples still entail modern interpretation of evolution. I’ve assessed and interpreted the basis of Darwin’s theorieson evolution, incorporating a number of other factors concerningevolutionary theory in the process.

Criticism of Darwin’sconclusions abounds somewhat more than has been paid tribute to,however Darwin’s findings marked a revolution of thought andsocial upheaval unprecedented in Western consciousnesschallenging not only the scientific community, but the prominentreligious institution as well. Another revolution in science ofa lesser nature was also spawned by Darwin, namely the remarkablesimplicity with which his major work The Origin of the Specieswas written – straightforward English, anyone capable of alogical argument could follow it – also unprecedented in thescientific community (compare this to Isaac Newton’s horriblycomplex work taking the scientific community years tointerpret2). Evolutionary and revolutionary in more than one sense ofeach word. Every theory mentioned in the following reading, infact falls back to Darwinism. DARWINIAN THEORY OF BIOLOGICAL EVOLUTIONModern conception of species and the idea of organicevolution had been part of Western consciousness since the mid-17th century (a la John Ray)3, but wide-range acceptance of thisidea, beyond the bounds of the scientific community, did notarise until Darwin published his findings in 19584. Darwin firstdeveloped his theory of biological evolution in 1938, followinghis five-year circumglobal voyage in the southern tropics (as anaturalist) on the H.

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M. S. Beagle, and perusal of one ThomasMalthus’ An Essay on the Principle of Population which proposedthat environmental factors, such as famine and disease limitedhuman population growth5. This had direct bearing on Darwin’stheory of natural selection, furnishing him with an enhancedconceptualization of the “survival of the fittest” – thecompetition among individuals of the same species for limitedresources – the “missing piece” to his puzzle6. For fear ofcontradicting his father’s beliefs, Darwin did not publish hisfindings until he was virtually forced after Alfred Wallace senthim a short paper almost identical to his own extensive works onthe theory of evolution. The two men presented a joint paper tothe Linnaean Society in 1958 – Darwin published a much largerwork (“a mere abstract of my material”) Origin of the Species ayear later, a source of undue controversy and opposition (frompious Christians)7, but remarkable development for evolutionarytheory.

Their findings basically stated that populations oforganisms and individuals of a species were varied: someindividuals were more capable of obtaining mates, food and othermeans of sustenance, consequently producing more offspring thanless capable individuals. Their offspring would retain some ofthese characteristics, hence a disproportionate representation ofsuccessive individuals in future generations. Therefore futuregenerations would tend have those characteristics of moreaccommodating individuals8. This is the basis of Darwin’s theoryof natural selection: those individuals incapable of adapting tochange are eliminated in future generations, “selected against”. Darwin observed that animals tended to produce more offspringthan were necessary to replace themselves, leading to the logicalconclusion that eventually the earth would no longer be able tosupport an expanding population. As a result of increasingpopulation however, war, famine and pestilence also increaseproportionately, generally maintaining comparatively stablepopulation9.

Twelve years later, Darwin published a two-volume workentitled The Descent of Man, applying his basic theory to likecomparison between the evolutionary nature of man and animals andhow this related to socio-political development man and hisperception of life. “It is through the blind and aimlessprogress of natural selection that man has advance to his presentlevel in love, memory, attention, curiosity, imitation, reason,etc. as well as progress in “knowledge morals and religion”10. Here is where originated the classic idea of the evolution of manfrom ape, specifically where he contended that Africa was thecradle of civilization. This work also met with opposition butbecause of the impact of his “revolutionary” initial work thisopposition was comparatively muted11.

A summary of the critical issues of Darwin’s theory might beabridged into six concise point as follows:1Variation among individuals of a species does not indicatedeficient copies of an ideal prototype as suggested by theplatonic notion of Eidos. The reverse is true: variationis integral to the evolutionary process. 2The fundamental struggle in nature occurs within singlespecies population to obtain food, interbreed, and resistpredation. The struggle between different species (ie. foxvs.

hare) is less consequential. 3The only variations pertinent to evolution are those whichare inherited. 4Evolution is an ongoing process which must span many moonsto become detectably apparent. 5Complexity of a species may not necessarily increase withthe evolutionary process – it may not change at all, evendecrease. 6Predator and prey have no underlying purpose for maintenanceof any type of balance – natural selection is opportunisticand irregular12. THE THEORY OF BIOLOGICAL EVOLUTION: CONTRIBUTING ELEMENTSThe scientific range of biological evolution is remarkablyvast and can be used to explain numerous observations within thefield of biology.

Generally, observation of any physical,behaviourial, or chemical change (adaptation) over time owingdirectly to considerable diversity of organisms can be attributedto biological evolution of species. It might also explain thelocation (distribution) of species throughout the planet. Naturalists can hypothesize that if organisms are evolvingthrough time, then current species will differ considerably fromtheir extinct ancestors. The theory of biological evolutionbrought about the idea for a record of the progressive changes anearly, extinct species underwent.

Through use of this fossilrecord paleontologists are able to classify species according totheir similarity to ancestral predecessors, and thereby determinewhich species might be related to one another. Determination ofthe age of each fossil will concurrently indicate the rate ofevolution, as well as precisely which ancestors preceded oneanother and consequently which characteristics are retained orselected against. Generally this holds true: probable ancestorsdo occur earlier in the fossil record, prokaryotes precedeeukaryotes in the fossil record. There are however, significant”missing links” throughout the fossil record resulting fromspecies that were, perhaps, never fossilized – nevertheless it isrelatively compatible with the theory of evolution13. It can be postulated that organisms evolving from the sameancestor will tend to have similar structural characteristics. New species will have modified versions of preexisting structuresas per their respective habitats (environmental situations).

Certainly these varying species will demonstrate cleardifferentiation in important structural functions, however anunderlying similarity will be noted in all. In this case thesimilarity is said to be homologous, that is, structure origin isidentical for all descended species, but very different inappearance. This can be exemplified in the pectoral appendagesof terrestrial vertebrates: Initial impression would be that ofdisparate structure, however in all such vertebrates fourdistinct structural regions have been defined: the regionnearest the body (humerus connecting to the pectoral girdle, themiddle region (two bones, radius and ulna are present), a thirdregion – the “hand” – of several bones (carpal and metacarpal,and region of digits or “fingers”. Current species might alsoexhibit similar organ functions, but are not descended from thesame ancestor and therefore different in structure. Suchorganisms are said to be analogous and can be exemplified intetrapods, many containing similar muscles but not necessarilyoriginating from the same ancestor.

These two anatomicallikenesses cannot be explained without considerable understandingof the theory of organic evolution14. The embryology, or early development of species evolved fromthe same ancestor would also be expected to be congruent. Related species all share embryonic features. This has helped indetermining reasons why development takes place indirectly,structures appearing in embryonic stage serve no purpose, and whythey are absent in adults. All vertebrates develop a notchord,gill slits (greatly modified during the embryonic cycle) and atail during early embryology, subsequently passing through stagesin which they resemble larval amphioxus, then larval fishes. The notchord will only be retained as discs, while only the earcanal will remain of the gills in adults.

Toothless Baleenwhales will temporarily develop teeth and hair during earlyembryology leading to the conclusion that their ancestors hadthese anatomical intricacies. A similar pattern, exists inalmost all animal organisms during the embryonic stage fornumerous formations of common organs including the lungs andliver. Yet there is a virtually unlimited variation ofanatomical properties among adult organisms. This variation canonly be attributed to evolutionary theory15. Biological evolution theory insists that in the case of acommon ancestor, all species should be similar on a molecularlevel. Despite the tremendous diversity in structure, behaviourand physiology of organisms, there is among them a considerableamount of molecular consistency.

Many statements have alreadybeen made to ascertain this: All cells are comprised of the sameelemental organic compounds, namely proteins, lipid andcarbohydrates. All organic reactions involve the action ofenzymes. Proteins are synthesized in all cells from 20 knownamino acids. In all cells, carbohydrate molecules arederivatives of six-carbon sugars (and their polymers). Glycolysis is used by all cells to obtain energy through thebreakdown of compounds.

Metabolism for all cells as well asdetermination of definitude of proteins through intermediatecompounds is governed by DNA. The structure for all vitallipids, proteins, some important co-enzymes and specializedmolecules such as DNA, RNA and ATP are common to all organisms. All organisms are anatomically constructed through function ofthe genetic code. All of these biochemical similarities can bepredicted by the theory of biological evolution but, of coursesome molecular differentiation can occur. What might appear asminor differentiation (perhaps the occurrence-frequency of asingle enzyme) might throw species into entirely different ordersof mammals (ie. cite the chimpanzee and horse, thedifferentiation resulting from the presence of an extra 11cytochrome c respiratory enzymes).

Experts have thereforetheorized that all life evolve from a single organism, thechanges having occurred in each lineage, derived in concert froma common ancestor16. Breeders had long known the value of protective resemblancelong before Darwin or any other biological evolution theoristsmade their mark. Nevertheless, evolutionary theory can predictand explain the process by which offspring of two somewhatdifferent parents of the same species will inherit the traits ofboth – or rather how to insure that the offspring retains thebeneficial traits by merging two of the same species with likephysical characteristics. It was the work of Mendel thatactually led to more educated explanations for the value inprotective resemblance17. The Hardy-Weinburg theory specifically,employs Mendel’s theory to a degree to predict the frequency ofoccurrence of dominantly or recessively expressing offspring. Population genetics is almost sufficient in explaining the basisfor protective resemblance.

Here biological evolutionary theorymight obtain its first application to genetic engineering18. Finally, one could suggest that species residing in aspecific area might be placed into two ancestral groups: thosespecies with origins outside of the area and those speciesevolving from ancestors already present in the area. Because theevolutionary process is so slow, spanning over considerablelengths of time, it can be predicted that similar species wouldbe found within comparatively short distances of each other, dueto the difficulty for most organisms to disperse across an ocean. These patterns of dispersion are rather complex, but it isgenerally maintained by biologists that closely related speciesoccur in the same indefinite region.

Species may also beisolated by geographic dispersion: they might colonize anisland, and over the course of time evolve differently from theirrelatives on the mainland. Madagascar is one such example – infact approximately 90 percent of the birds living there areendemic to that region. Thus as predicted, it follows thatspeciation is concurrent with the theory of biologicalevolution19. WALLACE’S CONTRIBUTIONSThere is rarely a sentence written regarding Wallace thatdoes not contain some allusion to Darwin.

Indeed, perhaps thesingle most significant feat he preformed was to compel Darwin toenter the public scene20. Wallace, another English naturalist haddone extensive work in South America and southeast Asia(particularly the Amazon and the Malay Archipelago) and, likeDarwin, he had not conceived of the mechanism of evolution untilhe read (recalled, actually) the work of Thomas Malthus – thenotion that “in every generation the inferior would be killed offand the superior would remain – that is the fittest wouldsurvive”. When the environment changed therefore, he determined”that all the changes necessary for the adaptation of the species. . .

would be brought about; and as the great changes are alwaysslow there would be ample time for the change to be effected bythe survival of the best fitted in every generation”. He sawthat his theory supplanted the views of Lamarck and the Vistagesand annulled every important difficulty with these theories21. Two days later he sent Darwin (leading naturalist of thetime) a four-thousand word outline of his ideas entitled “On theLaw Which has Regulated the Introduction”. This was more thanmerely cause for Darwin’s distress, for his work was so similarto Darwin’s own that in some cases it parallelled Darwin’s ownphrasing, drawing on many of the same examples Darwin hit upon. Darwin was in despair over this, years of his own work seemed togo down the tube – but he felt he must publish Wallace’s work. Darwin was persuaded by friends to include extracts of his ownfindings when he submitted Wallace’s work On the Law Which HasRegulated the Introduction of New Species to the Linnaean Societyin 1858, feeling doubly horrible because he felt this would betaking advantage of Wallace’s position.

Wallace never once gavethe slightest impression of resentment or disagreement, even tothe point of publishing a work of his own entitled Darwinism. This itself was his single greatest contribution to the field:encouraging Darwin to publish his extensive research on theissues they’d both developed22. He later published Contributions to the Theory of NaturalSelection, comprising the fundamental explanation andunderstanding of the theory of evolution through naturalselection. He also greatly developed the notion of naturalbarriers which served as isolation mechanisms, keeping apart notonly species but also whole families of animals – he drew up aline (“Wallace’s line”) where the fauna and flora of southeastAsia were very distinct from those of Australasia23. HARDY-WEINBERG PRINCIPLEPrior to full recognition of Mendel’s work in the early1900’s, development of quantitative models describing the changesof gene frequencies in population were not realized.

Followingthis “rediscovery” of Mendel, four scientists independently,almost simultaneously contrived the Hardy-Weinberg principal(named after two of the four scientists) which initiated thescience of population genetics: exploration of the statisticalrepercussions of the principle of inheritance as devised byMendel. Read concisely the Hardy-Weinberg principle might bestated as follows:Alternate paradigms of genes in ample populations will not bemodified proportionately as per successive generation, unlessstimulated by mutation, selection, emigration, or immigration ofindividuals. The relative proportion of genotypes in thepopulation will also be maintained after one generation, shouldthese conditions be negated or mating is random24. Through application of the Hardy-Weinberg principle theprecise conditions under which change does not occur in thefrequencies of alleles at a locus in a given population (group ofindividuals able to interbreed and produce fertile offspring) canbe formulated: the alleles of a locus will be at equilibrium.

Aspecies may occur in congruous correspondence with its populationcounterpart, or may consist of several diverse populations,physically isolated from one another25. In accordance with Mendelian principle, given twoheterozygous alleles A and B, probability of the offspringretaining prominent traits of either parent (AA or BB) is 25percent, probability of retaining half the traits of each parent(AB) is 50 percent. Thus allele frequencies in the offspringparallel those of the parents. Likewise, given one parent AB andanother AA, allele frequencies would be 75 percent A and 25percent B, while genotype frequencies would be 50 percent AA and50 percent AB – the gametes generated by these offspring wouldalso maintain the same ratio their parents initiated (given, ofcourse a maximum of two alleles at each locus).

In true-to-life application however, where numerous allelesmay occur at any given locus numerous possible combinations ofgene frequencies are generated. Assuming a population of 100individuals = 1, 30 at genotype AA, 70 at genotype BB. Applyingthe proportionate theory, only 30% (0. 30) of the gametes producedwill retain the A allele, while 70% (0. 70) the B allele.

Assuming there is no preference for AA or BB individuals formates, the probability of the (30% of total population) AA malesmating with AA females is but 9% (0. 3 x 0. 3 = 0. 09). Likewisethe probability of an BB to BB match is 49%, the remainderbetween (30%) AA and (70%) BB individuals, totalling a 21%frequency.

Frequency of alleles in a population in are commonlydenoted p and q respectively, while the AB genotype is denoted2pq. Using the relevant equation p + pq + q = 1, the sameproportions would be obtained. It can therefore be noted thatthe frequencies of the alleles in the population are unchanged. If one were to apply this equation to the next generation,similarly the genotype frequencies will remain unchanged per eachsuccessive generation. Generally speaking, the Hardy-Weinbergprinciple will not favour one genotype over another producingfrequencies expected through application of this law.

The integral relevance for employment of the Hardy-Weinbergprinciple is its illustration of expected frequencies wherepopulations are evolving. Deviation from these projectedfrequencies indicates evolution of the species may be occurring. Allele and genotype frequencies are typically modified per eachsuccessive generation and never in ideal Hardy-Weinbergequilibrium. These modifications may be the result of naturalselection, but (particularly among small populations) may simplyresult from random circumstance.

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They might also arise formimmigration of individuals form other populations where genefrequencies will be unique, or form individuals who do notrandomly choose mates from their wide-ranged species26. COMPARISON: LAMARCK vs. DARWINDespite the lack of respect lamarckian theory was dealt atthe hands of the early evolution-revolutionaries, the enormousinfluence it had on numerous scientists, including Lyell, Darwinand the developers of the Hardy-Weinberg theory cannot be denied. Jean Lamarck, a French biologist postulated the theory of aninherent faculty of self-improvement by his teaching that neworgans arise form new needs, that they develop in proportion tohow often they are used and that these acquisitions are handeddown from one generation to the next (conversely disuse ofexisting organs leads to their gradual disappearance). He alsosuggested that non-living matter was spontaneously created intothe less complex organisms who would evolve over time intoorganisms of greater and greater complexity.

He published hisconclusions in 1802, then later (1909) released an expanded formentitled Philosophie zoologique. The English public was firstexposed to his findings when Lyell popularized them with hisusual flair for writing, but because the influential Lyell alsoopenly criticized these findings they were never fully accepted27. Darwin’s own theories were based on those of olderevolutionists and the principle of descent with modification,the principle of direct or indirect action of the environment onan individual organism, and a wavering belief in Lamarck’sdoctrine that new characteristics acquired by the individualthrough use or disuse are transferred to its descendants. Darwinbasically built around this theory, adding that variation occursin the passage each progressive generation. Lamarck’s findingscould be summarized by stating that it is the surroundingenvironment that has direct bearing on the evolution of species.

Darwin instead contested that it was inter-species strife “thewill to power” or the “survival of the fittest”28. CertainlyLamarck was looking to the condition of the sexes: thesignificantly evolved difference of musculature between male andfemales can probably be more easily explained by Lamarckiantheory than Darwinian. There was actually quite a remarkablesimilarity between the conclusions of Darwin’s grandfather,Erasmus Darwin and Lamarck – Lamarck himself only mentionedErasmus in a footnote, and with virtual contempt. The fact isneither Lamarck nor Darwin ever proposed a means by which speciestraits were passed on, although Lamarck is usually recalled asone of those hopelessly erroneous scientists of past it wasmerely the basis for his conclusions that were hopelessly out ofdepth – the conclusions were remarkably accurate29.

DARWIN’S INFLUENCESIn 1831 a young Charles Darwin received the scientificopportunity of lifetime, when he was invited to take charge f thenatural history side of a five year voyage on the H. M. S. Beagle,which was to sail around the world, particularly to survey thecoast of South America.

Darwin’s reference material consisted ofworks of Sir Charles Lyell, a British geologist (he developed aconcept termed uniformitarianism which suggested that geologicalphenomena could be explained by prevailing observations ofnatural processes operating over a great spans of time – he hasbeen accused synthesizing the works of others30) who was theauthor of geologic texts that were required reading throughoutthe 19th century including Principals of Geology, which alongwith his own findings (observing the a large land shift resultingfrom an earthquake), convinced him of geologicaluniformitarianism, hypothesizing for example, that earthquakeswere responsible for the formation of mountains. Darwinfaithfully maintained this method of interpreting facts – byseeking explanations of past events by observing occurrences inpresent time – throughout his life31. The lucid writing style ofLyell and straightforward conclusions influence all of his work. When unearthing remains of extinct animals in Argentina he notedthat their remains more closely resembled those of contemporarySouth American mammals than any other animals in the world. Henoted “that existing animals have a close relation in form withextinct species”, and deduced that this would be expected “if thecontemporary species had evolved form South American ancestors”not however, if thereexisted an ideal biota for each environment.

When he arrived on the Galapagos islands (islands having beenformed at about the same time and characteristically similar), hewas surprised to observe unique species to each respectiveisland, particularly tortoises which possessed sufficientlydifferentiated shells to tell them apart. From theseobservations he concluded that the tortoises could only haveevolved on the islands32. Thomas Robert Malthus was an English economist and clergymanwhose work An Essay on the Principal of Population led Darwin toa more complete understanding of density dependent factors andthe “struggle in nature”. Malthus noted that there waspotential for rapid increase in population through reproduction -but that food cannot increase as fast as population can, andtherefore eventuality will allow less food per person, the lessable dying out from starvation or sickness.

Thus did Malthusidentify population growth as an obstacle to human progress andpedalled abstinence and late marriage in his wake. For theseconclusions he came under fire from the Enlightment movementwhich interpreted his works as opposing social reform33. Erasmus Darwin, grandfather of Darwin, was anunconventional, freethinking physician and poet who expressed hisardent preoccupation for the sciences through poetry. In thepoem Zoonomia he initiated the idea that evolution of an organismresults from environmental implementation.

This coupled with astrong influence from the similar conclusions of Lamarck shapedDarwin’s perception on the environment’s inherent nature to mouldand shape evolutionary form34. METHODS OF SCIENTIFIC DEDUCTIONEarly scientists, particularly those in the naturalist fieldderived most of their conclusions from observed, unprovenempirical facts. Without the means of logically explainingscientific theory, the hypothesis was incurred – an educatedguess to be proven through experimentation. Darwin developed histheory of natural selection with a viable hypothesis, butpredicted his results merely by observing that which wasavailable. Following Lyell’s teaching, using modern observationsto determine what occurred in the past, Darwin developed theoriesthat “only made sense” – logical from the point of view of thehuman mind (meaning it was based on immediate human perception)but decidedly illogical from a purely scientific angle.

Byperusing the works of Malthus did Darwin finally hit upon histheory of natural selection – not actually questioning theseconclusions because they fit so neatly into his own puzzle. Earlydevelopment of logical, analytic scientific theory did not occuruntil the advent of philosopher Rene Descartes in the mid-17thcentury (“I think therefore I am”35). Natural selection was shownto be sadly lacking where it could not account for howcharacteristics were passed down to new generations36. However,it did present enough evidence for rational thought to be appliedto his theory. Thus scientists were able to develop fairlyaccurate conclusions with very limited means of divination.

Opposition from oppressive Judeo-Christian church allowed littleroom science. Regardless, natural selection became the basis forall present forms of evolutionary theory. 37LIMITS TO DARWIN’S THEORYDarwinism, while comparatively rational and well documentednevertheless upheld the usual problem that can be found in manylogical scientific conclusions – namely deliberate ignorance offacts which might modify or completely alter years theconclusions of years of research. Many biologists were less thanconvinced with an evolutionary hypothesis that could not explainthe mechanism of inheritance. It was postulated by others thatoffspring will tend to have a blend of their two parentscharacteristics, the parents having a blend of characteristicsfrom their ancestors, the ancestors having a blend ofcharacteristics from their predecessors – allotting the finaloffspring impure, diminished desirable characteristics38.

Thusdid they believe a dilution of desirable traits evolved even morediluted desirable traits – these traits now decidedly muted. Itwas more than two decades after Darwin’s death that Mendeliantheory of the gene finally came to light at the turn of thecentury39. Because of this initial scepticism with Darwin’snatural selection, when Mendel’s work became widely availablebiologists emphasized the importance of mutation over selectionin evolution. Early Mendelian geneticists believe thatcontinuous variation (such features as body size) hardly factoredin the formation of new species – perhaps nothing to do withgenetic control.

Inferences on the gradual divergence ofpopulations diminished in wake of notions of significantmutations40. This gave rise to neo-Darwinian theory in the 1930’s, whatis called “modern synthesis” which encompasses paleontology,biogeography, systematics and, of course, genetics. Geneticistshave noted that acquired characteristics cannot, indeed beinherited, while observing that continuous variation is inheritedthrough the effects of many genes and have therefore concludedthat continuously distributed characteristics are also influencedby natural selection and evolve through time. Modern synthesis,in other words, differs little form Darwinian theory, but alsoincorporates current understanding of inheritance. Modernsynthesis maintains that random mutations introduce variationinto population, natural selection inaugurating new genes ingreater proportions. Despite revolutionary progress thediscovery of the gene has made, neo-Darwinian theory is stillbased on the arbitrary assumption that the primary factor causingadaptive change in populations is natural selection41.

MORPHOLOGICAL & BIOLOGICAL CONCEPTSSpecies have been traditionally described based on theirmorphological characteristics. This has proven to be somewhatpremature to say the least: some organisms in extremelydifferent forms are quite similar in their genetic make-up. Maleand females in many species develop more than a few manycharacteristic physical differences, yet are indeed the samespecies (imagine that!). Likewise some organisms appear to bequite morophologically similar but are completely incompatible. There are many species of budworm moths, all of which are highlyindistinguishable – most of which do not interbreed42. The idea of species is usually called the biological speciesconcept, stressing the importance of interbreeding amongindividuals in a population as a general description.

An entirepopulation might be thought of as a single unit of evolution. However similar difficulties arise in attempting a universalapplication of this theory. Because morphologically similarspecies occur in widely separated regions, it is virtuallyimpossible to exact whether they could or could not interbreed. One might ask whether cactus finches from the Galapagosinterbreed – the answer may invariably be yes. . .

but due rather tothe morphological similarities between them. Consider furtherasexually producing species, which can be defined by appearancealone: each individual would have to be defined as differentbiological species – a fact which would remain irrelevant. Thereare also cases for which no real standard can be applied – thedonkey and horse, for example can mate and produce healthyoffspring, mules which are almost always sterile and thereforesomething completely undefinable. Therefore, despite seemingideal in its delimitation, the biological species concept cannotbe employed in describing many natural species43. It isnonetheless a popular concept for theoretical discussions sinceit can distinguish which populations might evolve through timecompletely independent of other similar populations.

Species classification is therefore not defined by fixedprinciples surrounding biological and morphologicalclassifications both. The random nature of evolution itself ispredictable perhaps only in that one respect: that it remainvirtually unpredictable. In accordance with the Hardy-Weinbergtheory the proportion of irregularity should not necessarilyincrease, but because, by its own admission this theory cannot beemployed as a standard but merely to predict results, even it islimited random un-law of nature44. BIO-EVOLUTION: POPULATION vs.

INDIVIDUALSAccording to the theory of evolution, all life or most ofit, originated from the evolution of a single gene. Allrelatives – species descended from a common ancestor – bydefinition share a certain percentage of their genes. If naughtelse than these genes are of a very similar nature. A speciesdepends on the remainder of its population in developingcharacteristics which allow easier adaptability to the changingenvironment. These modified genes will ultimately expressthemselves as new species or may be passed on to otherpopulations within a given species. For these traits to beexpressed individually is certainly not going to benefit thespecies (ie.

the mule retains remarkable traits but cannotreproduce – they’re also a literal pain in the ass to generate). Nevertheless should but one individual in a million retain abeneficial characteristic, opportunity for this to be passed onis significantly increased. In short order, as per naturalselection highly adapted species can develop where they weredying out (over centuries to be sure, but dying out nonetheless)only a (‘n evolutionarily) short span of time ago. Plantbreeders especially know the value of the gene pool.

They dependon the gene pool of the wild relatives of these plants to developstrains that are well adapted to local conditions (here we referto comparatively exotic plants). The gene pool is there for allcompatible species (and that could be a large amount down theline) to partake of – given the right random conditions and thefuture for plant breeders brightens45. MECHANISMS FOR GENETIC VARIATIONThere are a number of known factors are capable of changingthe genetic structure of a population, each inconsistent with theHardy-Weinberg principle. Three primary contributing factors aremigration, mutation and selection and are referred to assystematic processes – the change in gene frequency iscomparatively predictable in direction and quantity. Thedispersive process of genetic is predictable only in quantitativenature. When species are sectioned into diverse, geographicallyisolated populations, the populations will tend to evolvedifferently on account of the following accepted standards:1Geographically isolated populations will mutateexclusively to their population.

2The adaptive value for these mutations and gene combinationswill differentiate per each population. 3Different gene frequencies existed before the population wasisolated and are therefore not representative of theirancestors. 4During intervals of small population size gene frequencieswill be fluctuating and unpredictable forming a genetic”bottleneck” from which all successive organisms will arise46. Gene frequencies can be altered when a given population isexposed to external populations, the change in frequency modifiedas per the proportion of foreigners to the mainstream population. Migration may be eliminated between two populations in regions ofgeographic isolation, which will isolate in turn, the gene poolswithin the population. If this isolation within populationdevelops over a sufficient span of time the physical differencesbetween two given gene pools may render them incompatible.

Thushave the respective gene pools become reproductively isolated andare now defined as biologically different species. However,speciation (division into new species) does not arise exclusivelyfrom division into new subgroups inside a population, otheraspects might be equally effective47. The primary source for genetic variability is mutation,usually the cause of depletion of species’ fitness but sometimesmore beneficial. The ability of a species to survive isdependent on its store of genetic diversity, allowing generationof new genotypes with greater tolerance for changing environment. However, some of the best adapted genotypes may still be unableto survive if environmental conditions are too severe. Unlessnew genetic material is obtained outside the gene pool, evolutionwill have a limited range of tolerance for change.

Generallyspeaking, spontaneous mutations whether they are required or not. This means many mutations are useless, even harmful under currentenvironmental conditions. These crippling mutations are usuallyweeded out or kept at low frequencies in the population throughnatural selection. The mutation rate for most gene loci isbetween one in 100 thousand to one in a million. Therefore,although mutations are the source of genetic variability, evenwithout natural selection changes in the population would beunnoticeable and very slow.

Eventually, if the only pressureaffecting the locus is from mutation, gene frequencies willchange and fall back to comparative equilibrium48. The fundamental restriction on the validity of the Hardy-Weinberg equilibrium law occurs where population size inimmeasurably large. Thus the disseminating process of geneticdrift is applicable for gene frequency alteration in situationsof small populations. In such a situation inbreeding isunavoidable, hence the primary contributing factor for change ofgene frequencies through inbreeding (by natural causes) isgenetic drift.

The larger the sample size, the smaller thedeviation will be from predicted values. The action of samplinggametes from a small gene pool has direct bearing on geneticdrift. Evidence is observed via the random fluctuation of genefrequencies per each successive generation in small populationsif systematic processes are not observed as contributing factors. From this four basic assumptions have been made for idealizedpopulations as follows:1Mating and self-fertilization in respective subgroups ofgiven populations are completely random. 2Overlap of one generation to its successor does not occurallotting distinct characteristics for each new generation.

3In all generations and lines of descent the number ofpossible breeding individuals is the same. 4Systematic factors such as migration, mutation and naturalselection are defunct49. In small populations certain alleles, perhaps held as commonto a species may not be present. The alleles will have becomerandomly lost somewhere in the population in the process ofgenetic drift.

The result is much less variability among smallpopulations that among larger populations. If every locus isfixed in these small populations they will have no geneticvariability, and therefore be unable to generate new adaptiveoffspring through genetic recombination. The ultimate fate ofsuch a population if it remains isolated is extinction50. GENETIC VARIATION ; SPECIATIONThrough genetic variation new species will arise, in aprocess termed speciation.

It is generally held that speciationoccurs as two given species evolve their differences over largespans of time – these differences are defined as their geneticvariation. The most popular model use to explain how speciesformed is the geographic speciation model, which suggests thatspeciation occurs only when an initial population is divided intotwo or more smaller populations – via genetic variation throughsystematic means of mutation, natural selection or genetic drift- geographically isolated (physically separated) from oneanother. Because they are isolated, gene flow (migration) cannotoccur between the respective new populations51. These “daughter”populations will eventually adapt to their new environmentsthrough genetic variation (process of evolution). If theenvironments of each isolated population are different then theywould be expected to adapt to different conditions and thereforeevolve differently. According to the model of geographicspeciation, the daughter populations will eventually evolvesufficiently to become incompatible with one another (thereforeunable to interbreed or produce viable offspring).

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As a resultof this incompatibility, gene flow could not effectively occureven if the populations were no longer geographically isolated. The differentiated, but closely related species are now termedspecies pair, or species group. Eventually differentiation willprogress far enough for them to be defined as different species. While divergence is a continuing process, it does notnecessarily occur at a constant rate – fluctuating betweenextremely rapid rates and very slow rates of evolution. Twostandard methods have been postulated for the occurrence ofgeographic speciation: i) Individuals from a species mightpopulate a new, isolated region of a give area (such as anisland).

Their offspring would evolve geographically isolatedfrom the original species. Eventually, geographical isolationfrom the population on the mainland would evolved distinguishablecharacteristics. ii) Individuals might, alternately begeographically isolated as physical barriers arise or the rangeof the species or individuals of a population diminishes52. However, neither of these forms of speciation through geographicisolation and consequent individual genetic variation have beenobserved or studied direct because of the time span and generaldifficulty of unearthing desired fossils.

Evidence for this formof speciation is therefore indirect and based on postulatedtheory53. DARWIN’S FINCHESThe finches of the Galapagos islands provided Darwin withan important lead towards his development of his theory ofevolution. They were (are) a perfect example of how isolatedpopulations could evolve. Here Darwin recognized that lifebranched out from a common prototype in what is now calledadaptive radiation. There were no indigenous finches to theislands when they arrived – some adapted to tree-living, othersto cactus habitat, others to the ground. The differentiation wascomparatively small, and yet there evolved fourteen species ofbird classified under six separate genera, each visibly differentonly in the characteristics of its beak54.

Joint selection pressure equations have been used tocalculate the change in gene frequency and consequent rate ofmutation resulting from action the of natural selection. Populations of Galapagos finches arrived at their islands fromSouth America and were provided with varying methods ofobtainment of sustenance. Only those individuals that evolvedcharacteristics allowing them to more easily obtain food fromvarying sources were not selected against. Populations wereisolated on certain islands and had to adapt to different foodsources. The result was an adaptation to food (seeds) fromtrees, ground or cactus-dominated ares.

However, the migratorynature of these finches prompted them to emigrate to alternateislands, therefore interbreeding with otherwise isolatedpopulations of finches. The result has been a variation onsingle specific characteristics which retain certain propertiesdue to the singular islands they predominantly occupied. Whenthe population of immigrants was high enough, the gene pools ofdiverse populations of finches presently occupying the island wasmodified enough such that offspring would inherit some of thetraits of otherwise isolated finch populations55. Nevertheless,these finches developed characteristics endemic to theirparticular habitat, and because finches tend to remain in groupsrather than individual families, these particular characteristicsbecame dominant enough to evolve morphologically and later evenbiologically different characteristics. These discrepanciescould only lead to greater genetic variation down the line. Eventually immigrants from the mainland and even other Galapagosislands were completely incompatible with specific finchpopulations endemic to their respective islands56.

Generally,selection pressure decreased as mutations resulting fromsystematic processes of genetic variation could no longer occur. This produced a significantly less versatile gene pool, however,via genetic drift from individuals of alternate populations whohad, at some point evolved from ancestors the population inquestion. Thus the gene pool could be modified without reallyaffecting the gene frequencies57 – joint pressures were thereforestabilized, along with the newly developed population. SPECIATION vs. CONVERGENT EVOLUTIONSpeciation is substantially more relevant to the evolutionof species than convergent evolution.

Through natural selectionsimilar characteristics and ways of life may be evolved bydiverse species inhabiting the same region, in what is calledconvergent evolution – reflecting the similar selective pressureof similar environments. While separate populations of the samespecies occupying similar habitats may also evidence similarphysical characteristics – due primarily to the environmentrather than their species origin – it should noted that theyprogressed form the same ancestor. A defining principle for thealternate natures of speciation and convergent evolution putsimply: speciation results form a common ancestor, convergentevolution results from any number of ancestors58. Morphologically similar populations resulting from the sameancestor may be compatible and able to produce viable offspring(if in some occasions not fertile offspring).

Morphologicallysimilar species resulting form different ancestors are nevercompatible with one another – even if they are virtualmorphological twins. In fact, morphologically disparatepopulations of the same species may be compatible with oneanother – whereas those disparate through convergent evolutionwould be more than merely incompatible, they may be predator andprey. Convergent evolution may only account for single specificphysical characteristics of very disparate, unrelated species -such as the development of flipper-like appendages for the seaturtle (reptile), penguin (bird) and walrus (mammal)59. CONCEPT OF ADAPTATIONIf individuals were unable to adapt to changes in theenvironment they would be extinct in short order. Adaptabilityis often based on nuclear inheritance down the generations. Should an organism develop a resistance to certain environmentalconditions, this characteristic may be passed down through thegene pool, and then through natural selection be dominant for allorganisms of a given population.

Bacteria are able to accomplish this feat at a remarkablyfast rate. Most, if not all forms of bacteria are compatiblewith one another, that is able to exchange genetic information. The speed at which bacteria reproduces is immeasurably fasterthan that of more complex, eukaryote organisms. Bacteria have amuch shorter lifespan as well – but because they can develop veryquickly into large colonies given ideal conditions, it is easierto understand bacteria in clusters. Should a single bacterialorganism develop a trait that slightly aids its resistance todestructive environmental conditions, it can pass its modifiedgenetic structure on to half of a colony in a matter of hours.

In the meantime the colony is quickly expanding, fully adapted tothe environment – soon however, it has developed more than it canbe accommodated. The population will drop quickly in the face ofinadaptability. But that (previosly mentioned) exteriorbacterial organism with the modified trait releases informationyielding new growth, allowing the colony to expand further. Itis generally accepted that bacterial colonies will achieve amaximum capability – however, through adaptation the bacterialpopulation will quickly excel once again60. Antibiotics are nowsent to destroy the bacteria. Soon they will be obliterated -and now all that remains of the colony are a few choice bacterialorganisms.

However, an otherwise isolated bacteria enters thesystem to exchange genetic information with the much smallerbacterial colony, conditions are favourable, the bacteriaexpands again. Antibiotics are sent again to destroy this colony- but the exterior bacteria, originating in another organism andhaving developed a resistance to this type of antibody hasprovided much of the colony with the means for resistance tothese antibodies as well. Once again the bacterial culture hasexpanded having resisted malignant exterior interlopers61. Thisis how bacteria develops, constantly exchanging nuclearinformation, constantly able to adapt to innumerable harmfulsources. As bacteria are exposed to more destructive forces, themore they decelop resistace to, as surely many of the billions ofbacteria could develop an invulnerability to any threateningexterior sources given ideal environmental conditions. PUNCTUATED EQUILIBRIUMRecently the concept of punctuated equilibrium, as proposedby American paleontologist Stephen Jay Gould has be the subjectof much controversy in the scientific world.

Gould advanced theidea that evolutionary changes take place in sudden bursts, andare not modified for long periods time when they are reasonablyadapted to altered environment62. This almost directly contradicts the older, establishedDarwinian notions that species evolve through phyleticgradualism, that evolution occurs at a fairly constant rate. Itis not suggested by adherents of the punctuated equilibrium modelthat pivotal fluctuations in morphology occur spontaneously or inonly a few generations changes are established in populations -they argue instead that the changes may occur in but 100 to 1000generations. It is difficult to determine which model could moreadequately describe what transpires over the course of speciationand evolution due to gaps in fossil-record, 50 to 100 thousandyears of strata often covering deposits bearing fossils. Geneticmake-up need not change much for rapid, discernable morphologicalalterations to detected63.

Impartial analysts on the two theories conclude that theyare both synonymous with evolutionary theory. Their primarydifferences entail their emphasis on the importance of speciationin long-term evolutionary patterns in lineage. While phyleticgradualism emphases the significance of changes in a singlelineage and the revision of species through slight deviation,punctuated equilibrium emphases the significance of alterationoccurring during speciation, maintaining that local (usuallysmall) populations adapt rapidly to local circumstance inproduction of diverse species – some of which acquire the meansfor supplantation of their ancestors and rampant settlement inmany important adaptive breakthroughs64. One must consider thatDarwin was not aided by Mendelian theory.

Under suchcircumstances Darwin would have surely produced an entirelydifferent theory for the inheritance of beneficial traits. Consider that mutations can presumably occur spontaneously, giventhe properly modified parent. It can therefore be stated thatpunctuated equilibrium is probably a more likely explanation asit does take into account modern cell, and genetic theory. Phyletic gradualism, while certainly extremely logical is atheory which simply cannot encompass those circumstance in whichsignificant change is recorded over comparatively short periodsof time. Both are complementary to be sure, but perhaps one ofthe two distorts this complementary nature formulating inaccurateassumption. VALUE/LIMITATIONS: THE THEORY BIOLOGICAL EVOLUTIONWhether or not the theory of evolution is useful depends onwhether or one values progress above development of personalnotions of existence.

Certainly under the blanket of asuperficial American Dream one would be expected to subscribe toideals that society, that the state erects. Of course, theseideals focus on betterment of society as a whole – which nowunfortunately, means power to the state. Everybody is thuscaught up in progress, supposedly to “improve the quality oflife”, and have been somewhat enslaved by the notion of work. Work has become something of an idol, nothing can be obtainedwithout work – for the state. Whether one agrees with thethoughtless actions of the elite or not, people are oppressed byconforming to ideals that insist upon human suffering.

Someirresponsible, early religious institutions did just that,erecting a symbol of the people’s suffering and forcing them tobow before it. Development of aeronautic, or even cancerresearch contributes primarily to this ideal of progress. Development of such theories as biological evolution, contributenothing toward progress. It instills in the people newprinciples, to dream and develop an understanding of themselvesand that which surrounds them ones, freeing their will from thatshuffling mass, stumbling as they are herded towards that whichwill reap for them suffering and pain. The state provides thissoulless mass with small pretty trinkets along the way, wheedlingand cajoling them with media images of how they should lead theirlives – the people respond with regrets.

Modern theory of biological evolution is actually sadlylacking in explanation for exactly how characteristics are passeddown to future generations. It is understood how nitrogen basesinteract to form a genetic code for an organism – but how themodification that the organism develops, occurs is unknown. Somehow the organism mutates to adapt to environmentalconditions, and then presumably the offspring of this organismwill retain these adaptations65. Of course, biological evolutioncannot also explain precisely how first organisms developed:Generally, the theory accounts for energy and chemicalinteractions at a level consistent enough to establish a constantflow of said interactions – but even here it falls short. Andwhat of phyletic gradualism? It is completely unable to explainthe more sudden mutations that occur. .

. for obvious reasons itcannot explain this (Darwin had no knowledge of genetics), buteven punctuated gradualism doesn’t balance this problem. I’msure there are numerous other problems which can be addressed butthese can be dealt with where opinion can be more educated. ALTERNATE EXPLANATIONS OF BEINGMan it would appear, has always sought meaning for hisexistence. Development of many theories of existence have beenconceived and passed down through the ages. Institutionsconferring single metaphysical and elemental viewpoints have beenestablished, some of which have been particularly irresponsibleand oppressive towards the people they were supposed to”enlighten”.

Most religious institutions have been used aspolitical tools for means of manipulation of the masses, goingback to early Roman days when empower Augustus absorbedChristianity into the Roman worship of the sun, Sol Invectus, asa means of subjugating the commoners to Roman doctrine. Generally religious institutions have exploited the people andhave been used as excuses for torture, war, mass exterminationsand general persecution and oppression of the people it pretendsto serve, telling the people they must suffer to reach ultimatetranscendent fulfilment. Unfortunately this oppression continuesin today’s modern – even Western – world. There have actuallybeen almost innumerable explanations for the physical presence ofman – these explanations merely been suppressed by the prevailingreligious institutions for fear that they will be deprivedabsolute power over the people. .

. they’re right. CONCLUSIONSWithout Darwin it can be concluded, reasonableinterpretation of biological evolution simply would not be. Natural selection, the process determining the ultimate survivalof a new organism, remains the major contributing factor to eventhe most modern evolutionary theory.

The evolutionary processspans over the course of hundreds of thousands of generations,organisms evolving through systematic and dispersive mechanismsof speciation. Recently, heated debate surrounding whethercharacteristics are passed on in bursts of activity throughpunctuated equilibrium or at a constant rate through the moretraditional phyletic gradualism66. The release of Mendeliantheory into the scientific community filled the primary linkmissing in Darwin’s theory – how biological characteristics werepassed on to future generations. Applications of genetic theoryto evolutionary theory however, are somewhat limited. It isdifficult to classify all species even through modern means ofpaleontology and application to the theory of organic evolution. BIBLIOGRAPHY1Brent, Peter.

Charles Darwin, A Man of Enlarged Curiosity. Toronto: George J. McLeod Ltd. , 1981.

2Dawkins, Richard. The Selfish Gene. New York: Paladin,1978. 3Farrington, Benjamin. What Darwin Really Said.

New York:Shoken Books, 1966. 4Gailbraith, Don. Biology: Principals, Patterns andProcesses. Toronto: John Wiley and Sons Canada Ltd.

1989, Un. 6: Evolution. 5Glass, Bently. Forerunners of Darwin 1745-1859. New York:Johns Hopkins Press, 1968.

6Gould, S. J. Ever Since Darwin. New York: Burnett Books,1978.

7Grolier Encyclopedia, New. New York:Grolier Publishing, Inc. , 1991. 8Haldane, J. B.

S. The Causes of Evolution. London:Green and Co. , 1982.

9Leakey, Richard E. . Mankind and Its Beginnings. New York:Anchor Press/Doubleday, 1978. 10Miller, Johnathan. Darwin For Beginners.

New York:Pantheon Books, 1982. 11Moore, Johh A. Heredity and the Environment. New York:Oxford University Press, 1973.

12Patterson, Colin. Evolution. London: British Museum ofNatural History Press, 1976. 13Random House Encyclopedia, The.

New York:Random House Inc. , 1987, p. 406-25. 14Ridley, Mark. The Essential Darwin. London, Eng:Allen & Unwin, 1987.

15Smith, J. M. On Evolution. London: Doubleday, 1972.

16Stansfield, William D. . Genetics 2/ed. New York:McGraw-Hill Book Company, 1983, p.

266-287. 17Thomas, K. S. .

H. M. S. Beagle, 1820-1870.

Washington:Oxford University Press, 1975. ENDNOTES_______________________________1. Johnathan Miller, Darwin for Beginners,New York, Pantheon Books, 1982, p. 8.

2. Mark Ridley, The Essential Darwin, London Eng:Allen & Unwin, 1987, p. 23. 3. J. M.

Smith, On Evolution, London, Eng. :London/Doubleday, 1972, 48. 4. Peter Brent, Charles Darwin, A Man of EnlargedCuriosity, Toronto: George J. McLeod Ltd.

, 1981, p. 313. 5. Don Gailbraith, Biology, Principals, Patterns andProcesses, Toronto: John Wiley and Sons Canada Ltd. 1989, Un. 6: Evolution, p.

403. 6. opsit. , p. 92.

7. opsit. , p. 96.

8. J. B. S.

Heldane, The Causes of Evolution, London:Green and Co. , 1982, p. 237. 9.

ibid. , p. 444. 10. Benjamin Farrington, What Darwin Really Said,New York: Shocken Books, 1966, p. 52.

11. ibid. , p. 61.

12. opsit. , p. 405-06.

13. opsit. , p. 383. 14.

ibid. , p. 390. 15.

ibid. , p. 388. 16. ibid.

, p. 381. 17. John A. Moore, Heredity and the Environment,New york: Pantheon Books, 1980, p. 141.

18. opsit. , p. 417.

19. opsit. , p. 385. 20. K.

S. Thomas, H. M. S. Beagle, 1820-1870,Washington: Oxford University Press, p.

229. 21. opsit. p. 8022. opsit.

, p. 262. 23. ibid.

, p. 536. 24. opsit. , p. 417.

25. opsit. , p. 183.

26. opsit. , p. 419. 27. The Random House Encyclopedia, New York:Random House Inc.

, 1987, p. 432. 28. ibid.

, p. 437. 29. opsit. , p.

348. 30. The New Grolier Electronic Encyclopedia,Grolier Electronic Publishing, Inc. , 1991,MALTHUS. 31.

opcit. , p. 403. 32. ibid.

, p. 404. 33. opsit.

, MALTHUS. 34. opsit. , p. 309.

35. opsit. , p. 841.

36. Bently Glass, Forerunners of Darwin 1745-1859,New York: Johns Hopkins Press, 1968. 37. opsit.

, p. 351. 38. Richard E. Leakey, Mankind and Its Beginnings,New York: Anchor Press/Doubleday, p. 177.

39. ibid., p. 156.40. opsit., p. 218.41. opsit., p. 408.42. opcit., p.431.43. ibid., p. 432/44. opsit., p. 253.45. ibid., p. 554.46. William D. Stansfield, Genetics 2/ed,New York: McGraw-Hill Book Company, 1983, p. 266.47. ibid. p. 269.48. opsit., p. 272.49. ibid., p. 274.50. ibid., p. 275.51. opsit., p. 434.52. ibid., p. 432.53. ibid., p. 435.54. opsit, p. 420.55. opsit., p.374.56. ibid. p. 421.57. opsit., p. 299.58. opsit., p. 160.59. opsit., p. 412.60. opsit. p. 138.61. ibid. p. 95.62. opsit., p. 441.63. ibid., p. 441-264. ibid., p. 443.65. opsit., p. 572.66. opsit., p. 441.

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Darwinian Theory Of Evolution Essay
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Theories explaining biological evolution have been bandiedabout since the ancient Greeks, but it was not until theEnlightment of the 18th century that widespread acceptance anddevelopment of this theory emerged. In the mid 19th centuryenglish naturalist Charles Darwin - who has been called the"father of evolution" - conceived of the most comprehensivefindings about organic evolution ever1. Today many of hisprinciples still entail modern interpretation of evolution. I've assessed and interpr
2021-03-01 07:20:33
Darwinian Theory Of Evolution Essay
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