Theories explaining biological evolution have been bandied about since the ancient Greeks, but it was notuntil the Enlightment of the 18th century that widespread acceptance and development of this theoryemerged. In the mid 19th century english naturalist Charles Darwin – who has been called the father ofevolution – conceived of the most comprehensive findings about organic evolution ever1. Today many ofhis principles still entail modern interpretation of evolution. I’ve assessed and interpreted the basis ofDarwin’s theories on evolution, incorporating a number of other factors concerning evolutionary theory inthe process.
Criticism of Darwin’s conclusions abounds somewhat more than has been paid tribute to,however Darwin’s findings marked a revolution of thought and social upheaval unprecedented in Westernconsciousness challenging not only the scientific community, but the prominent religious institution aswell. Another revolution in science of a lesser nature was !also spawned by Darwin, namely the remarkable simplicity with which his major work The Origin of theSpecies was written – straightforward English, anyone capable of a logical argument could follow it – alsounprecedented in the scientific community (compare this to Isaac Newton’s horribly complex work takingthe scientific community years to interpret2). Evolutionary and revolutionary in more than one sense ofeach word. Every theory mentioned in the following reading, in fact falls back to Darwinism.
DARWINIAN THEORY OF BIOLOGICAL EVOLUTION
Modern conception of species and the idea of organic evolution had been part of Western consciousnesssince the mid-17th century (a la John Ray)3, but wide-range acceptance of this idea, beyond the bounds ofthe scientific community, did not arise until Darwin published his findings in 19584. Darwin firstdeveloped his theory of biological evolution in 1938, following his five-year circumglobal voyage in thesouthern tropics (as a naturalist) on the H.M.S. Beagle, and perusal of one Thomas Malthus’ An Essay onthe Principle of Population which proposed that environmental factors, such as famine and disease limitedhuman population growth5.
This had direct bearing on Darwin’s theory of natural selection, furnishing himwith an enhanced conceptualization of the survival of the fittest – the competition among individuals ofthe same species for limited resources – the missing piece to his puzzle6. For fear of contradicting hisfather’s beliefs, Darwin did not publish his find!ings until he was virtually forced after Alfred Wallace sent him a short paper almos t identical to his ownextensive works on the theory of evolution.
The two men presented a joint paper to the Linnaean Society in1958 – Darwin published a much larger work (a mere abstract of my material) Origin of the Species ayear later, a source of undue controversy and opposition (from pious Christians)7, but remarkabledevelopment for evolutionary theory. Their findings basically stated that populations of organisms andindividuals of a species were varied: some individuals were more capable of obtaining mates, food andother means of sustenance, consequently producing more offspring than less capable individuals. Theiroffspring would retain some of these characteristics, hence a disproportionate representation of successiveindividuals in future generations.
Therefore future generations would tend have those characteristics ofmore accommodating individuals8. This is the basis of Da!rwin’s theory of natural selection: those individuals incapable of adapting to change are eliminated in futuregenerations, selected against. Darwin observed that animals tended to produce more offspring than werenecessary to replace themselves, leading to the logical conclusion that eventually the earth would no longerbe able to support an expanding population. As a result of increasing population however, war, famine andpestilence also increase proportionately, gener ally maintaining comparatively stable population9.
Twelveyears later, Darwin published a two-volume work entitled The Descent of Man, applying his basic theory tolike comparison between the evolutionary nature of man and animals and how this related to socio-politicaldevelopment man and his perception of life. It is through the blind and aimless progress of naturalselection that man has advance to his present level in love, memory, attention, curiosity, imitation, reason,etc. as well as progress in k!nowledge morals and religion10. Here is where originated the classic idea of the evolution of man fromape, specifically where he contended that Africa was the cradle of civilization.
This work also met withopposition but because of the impact of his revolutionary initial work this opposition was comparativelymuted11.A summary of the critical issues of Darwin’s theory might be abridged into six concise point as follows:
- Variation among individuals of a species does not indicate deficient copies of an ideal prototype assuggested by the platonic notion of Eidos. The reverse is true: variation is integral to the evolutionaryprocess.
- The fundamental struggle in nature occurs within single species population to obtain food, interbreed, andresist predation. The struggle between different species (ie. fox vs. hare) is less consequential.
- The only variations pertinent to evolution are those which are inherited.
- Evolution is an ongoing process which must span many moons to become detectably apparent.
- Complexity of a species may not necessarily increase with the evolutionary process – it may not change atall, even decrease.
- Predator and prey have no underlying purpose for maintenance of any type of balance – natural selectionis opportunistic and irregular.
THE THEORY OF BIOLOGICAL EVOLUTION: CONTRIBUTING ELEMENTS
The scientific range of biological evolution is remarkably vast and can be used to explain numerousobservations within the field of biology. Generally, observation of any physical, behaviourial, or chemicalchange (adaptation) over time owing directly to considerable diversity of organisms can be attributed tobiological evolution of species. It might also explain the location (distribution) of species throughout theplanet.Naturalists can hypothesize that if organisms are evolving through time, then current species will differconsiderably from their extinct ancestors.
The theory of biological evolution brought about the idea for arecord of the progressive changes an early, extinct species underwent. Through use of this fossil recordpaleontologists are able to classify species according to their similarity to ancestral predecessors, andthereby determine which species might be related to one another. Determination of the age of each fossilwill concurrently indicate the rate of evolution, as well as precisely which ancestors preceded one anotherand consequently which characteristics are retained or selected against. Generally this holds true: probableancestors do occur earlier in the fossil record, prokaryotes precede eukaryotes in the fossil record. There arehowever, significant missing links throughout the fossil record resulting from species that were, perhaps,never fossilized – never!theless it is relatively co mpatible with the theory of evolution13.It can be postulated that organisms evolving from the same ancestor will tend to have similar structuralcharacteristics.
New species will have modified versions of preexisting structures as per their respectivehabitats (environmental situations). Certainly these varying species will demonstrate clear differentiation inimportant structural functions, however an underlying similarity will be noted in all. In this case thesimilarity is said to be homologous, that is, structure origin is identical for all descended species, but verydifferent in appearance. This can be exemplified in the pectoral appendages of terrestrial vertebrates: Initialimpression would be that of disparate structure, however in all such vertebrates four distinct structuralregions have been defined: the region nearest the body (humerus connecting to the pectoral girdle, themiddle region (two bones, radius and ulna are present), a third region – the hand – of several bones (carpaland metacarpal, and !region of digits or finger s. Current species might also exhibit similar organ functions, but are notdescended from the same ancestor and therefore different in structure.
Such organisms are said to beanalogous and can be exemplified in tetrapods, many containing similar muscles but not necessarilyoriginating from the same ancestor. These two anatomical likenesses cannot be explained withoutconsiderable understanding of the theory of organic evolution14.The embryology, or early development of species evolved from the same ancestor would also be expectedto be congruent. Related species all share embryonic features. This has helped in determining reasons whydevelopment 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 theembryonic cycle) and a tail during early embryology, subsequently passing through stages in which theyresemble larval amphioxus, then larval fishes.
The notchord will only be retained as discs, while only theear canal will remain of the gills in adults. Toothless Baleen whales will temporarily develop teeth and hairduring early embryology leading to the conclusion that their ancestors had these anatomical intricacies. Asimilar pattern, exists in almost all animal organisms during the embryonic stage for numerous formationsof common organs including the lungs and live!r. Yet there is a virtual ly unlimited variation of anatomical properties among adult organisms. Thisvariation can only be attributed to evolutionary theory15.Biological evolution theory insists that in the case of a common ancestor, all species should be similar on amolecular level. Despite the tremendous diversity in structure, behaviour and physiology of organisms,there is among them a considerable amount of molecular consistency.
Many statements have already beenmade to ascertain this: All cells are comprised of the same elemental organic compounds, namely proteins,lipid and carbohydrates. All organic reactions involve the action of enzymes. Proteins are synthesized in allcells from 20 known amino acids. In all cells, carbohydrate molecules are derivatives of six-carbon sugars(and their polymers). Glycolysis is used by all cells to obtain energy through the breakdown of compounds.Metabolism for all cells as well as determination of definitude of proteins through intermediate compoundsis governed by DNA.
The structure for all vital lipids, proteins, some important co-enzymes and specializedmolecules such as DNA, RNA and !ATP are common to all or ganisms.All organisms are anatomically constructed through function of the genetic code. All of these biochemicalsimilarities can be predicted by the theory of biological evolution but, of course some moleculardifferentiation can occur. What might appear as minor differentiation (perhaps the occurrence-frequency ofa single enzyme) might throw species into entirely different orders of mammals (ie. cite the chimpanzeeand horse, the differentiation resulting from the presence of an extra 11 cytochrome c respiratory enzymes).
Experts have therefore theorized that all life evolve from a single organism, the changes having occurred ineach lineage, derived in concert from a common ancestor16.Breeders had long known the value of protective resemblance long before Darwin or any other biologicalevolution theorists made their mark. Nevertheless, evolutionary theory can predict and explain the processby which offspring of two somewhat different parents of the same species will inherit the traits of both – orrather how to insure that the offspring retains the beneficial traits by merging two of the same species withlike physical characteristics. It was the work of Mendel that actually led to more educated explanations forthe value in protective resemblanc.
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 inexplaining the basis for protective resemblance. Here biological evolutionary theory might obtain its firstapplication to genetic engineering.Finally, one could suggest that species residing in a specific area might be placed into two ancestral groups:those species with origins outside of the area and those species evolving from ancestors already present inthe area.
Because the evolutionary process is so slow, spanning over considerable lengths of time, it can bepredicted that similar species would be found within comparatively short distances of each other, due to thedifficulty for most organisms to disperse across an ocean. These patterns of dispersion are rather complex,but it is generally maintained by biologists that closely related species occur in the same indefinite region.Species may also be isolated by geographic dispersion: they might colonize an island, and over the courseof time evolve differently from their relatives on the mainland. Madagascar is one such example – in factapproximately 90 percent of the birds living there are endemic to that region. Thus as predicted, it followsthat speciatio!n is concurrent with the theory of biological evolution.
There is rarely a sentence written regarding Wallace that does not contain some allusion to Darwin. Indeed,perhaps the single most significant feat he preformed was to compel Darwin to enter the public scene20.Wallace, another English naturalist had done extensive work in South America and southeast Asia(particularly the Amazon and the Malay Archipelago) and, like Darwin, he had not conceived of themechanism of evolution until he read (recalled, actually) the work of Thomas Malthus – the notion that inevery generation the inferior would be killed off and the superior would remain – that is the fittest wouldsurvive.
When the environment changed therefore, he determined that all the changes necessary for theadaptation of the species … would be brought about; and as the great changes are always slow there wouldbe ample time for the change to be effected by the survival of the best fitted in every generation. He sawthat his theory supplanted the views of Lamarck and!the Vistages and annulled ev ery important difficulty with these theories.
Two days later he sent Darwin (leading naturalist of the time) a four-thousand word outline of his ideasentitled On the Law Which has Regulated the Introduction. This was more than merely cause forDarwin’s distress, for his work was so similar to Darwin’s own that in some cases it parallelled Darwin’sown phrasing, drawing on many of the same examples Darwin hit upon. Darwin was in despair over this,years of his own work seemed to go down the tube – but he felt he must publish Wallace’s work. Darwinwas persuaded by friends to include extracts of his own findings when he submitted Wallace’s work On theLaw Which Has Regulated the Introduction of New Species to the Linnaean Society in 1858, feelingdoubly horrible because he felt this would be taking advantage of Wallace’s position.
Wallace never oncegave the slightest impression of resentment or disagreement, even to the point of publishing a work of hisown entitled Darwinism. This itself was his single greatest contrib!ution to the field: encoura ging Darwin to publish his extensive research on the issues they’d bothdeveloped22.He later published Contributions to the Theory of Natural Selection, comprising the fundamentalexplanation and understanding of the theory of evolution through natural selection. He also greatlydeveloped the notion of natural barriers which served as isolation mechanisms, keeping apart not onlyspecies but also whole families of animals – he drew up a line (Wallace’s line) where the fauna and floraof southeast Asia were very distinct from those of Australasia.
Prior to full recognition of Mendel’s work in the early 1900’s, development of quantitative modelsdescribing the changes of gene frequencies in population were not realized. Following this rediscovery ofMendel, four scientists independently, almost simultaneously contrived the Hardy-Weinberg principal(named after two of the four scientists) which initiated the science of population genetics: exploration ofthe statistical repercussions of the principle of inheritance as devised by Mendel. Read concisely the Hardy-Weinberg principle might be stated as follows:Alternate paradigms of genes in ample populations will not be modified proportionately as per successivegeneration, unless stimulated by mutation, selection, emigration, or immigration of individuals.
The relativeproportion of genotypes in the population will also be maintained after one generation, should theseconditions be negated or mating is random.Through application of the Hardy-Weinberg principle the precise conditions under which change does notoccur in the frequencies of alleles at a locus in a given population (group of individuals able to interbreedand produce fertile offspring) can be formulated: the alleles of a locus will be at equilibrium.
A species mayoccur in congruous correspondence with its population counterpart, or may consist of several diversepopulations, physically isolated from one another25.In accordance with Mendelian principle, given two heterozygous alleles A and B, probability of theoffspring retaining prominent traits of either parent (AA or BB) is 25 percent, probability of retaining halfthe traits of each parent (AB) is 50 percent. Thus allele frequencies in the offspring parallel those of theparents.
Likewise, given one parent AB and another AA, allele frequencies would be 75 percent A and 25percent B, while genotype frequencies would be 50 percent AA and 50 percent AB – the gametes generatedby these offspring would also maintain the same ratio their parents initiated (given, of course a maximumof two alleles at each locus).In true-to-life application however, where numerous alleles may occur at any given locus numerouspossible combinations of gene frequencies are generated.
Assuming a population of 100 individuals = 1, 30at genotype AA, 70 at genotype BB. Applying the proportionate theory, only 30% (0.30) of the gametesproduced will retain the A allele, while 70% (0.70) the B allele. Assuming there is no preference for AA orBB individuals for mates, the probability of the (30% of total population) AA males mating with AAfemales is but 9% (0.3 x 0.3 = 0.09). Likewise the 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 apopulation in are commonly denoted p and q respectively, while the AB genotype is denoted 2pq. Using therelevant equation p + pq + q = 1, the same proportions would be obtained. It can therefore be noted that thefrequencies of the alleles in the population are unchanged. If !one were to apply thi s equation to the next generation, similarly the genotype frequencies will remainunchanged per each successive generation.
Generally speaking, the Hardy-Weinberg principle will notfavour one genotype over another producing frequencies expected through application of this law.The integral relevance for employment of the Hardy-Weinberg principle is its illustration of expectedfrequencies where populations are evolving. Deviation from these projected frequencies indicates evolutionof the species may be occurring.Allele and genotype frequencies are typically modified per each successive generation and never in idealHardy-Weinberg equilibrium. These modifications may be the result of natural selection, but (particularlyamong small populations) may simply result from random circumstance. They might also arise formimmigration of individuals form other populations where gene frequencies will be unique, or formindividuals who do not randomly choose mates from their wide-ranged species.
COMPARISON: LAMARCK vs. DARWIN
Despite the lack of respect lamarckian theory was dealt at the hands of the early evolution-revolutionaries,the enormous influence it had on numerous scientists, including Lyell, Darwin and the developers of theHardy-Weinberg theory cannot be denied. Jean Lamarck, a French biologist postulated the theory of aninherent faculty of self-improvement by his teaching that new organs arise form new needs, that theydevelop in proportion to how often they are used and that these acquisitions are handed down from onegeneration to the next (conversely disuse of existing organs leads to their gradual disappearance).
He alsosuggested that non-living matter was spontaneously created into the less complex organisms who wouldevolve over time into organisms of greater and greater complexity. He published his conclusions in 1802,then later (1909) released an expanded form entitled Philosophie zoologique. The English public was firstexposed to his findings when Lyell popularized them wi!th his usual flair for writ ing, but because the influential Lyell also openly criticized these findings theywere never fully accepted27.Darwin’s own theories were based on those of older evolutionists and the principle of descent withmodification, the principle of direct or indirect action of the environment on an individual organism, and awavering belief in Lamarck’s doctrine that new characteristics acquired by the individual through use ordisuse are transferred to its descendants.
Darwin basically built around this theory, adding that variationoccurs in the passage each progressive generation. Lamarck’s findings could be summarized by stating thatit is the surrounding environment that has direct bearing on the evolution of species. Darwin insteadcontested that it was inter-species strife the will to power or the survival of the fittest28.Certainly Lamarck was looking to the condition of the sexes: the significantly evolved difference ofmusculature between male and females can probably be more easily explained by Lamarckian theory thanDarwinian. There was actually quite a remarkable similarity between the conclusions of D arwin’sgrandfather, Erasmus Darwin and Lamarck – Lamarck himself only mentioned Erasmus in a footnote, andwith virtual contempt.
The fact is neither Lamarck nor Darwin ever proposed a means by which speciestraits were passed on, although Lamarck is usually recalled as one of those hopelessly erroneous scientistsof past it was merely the basis for his conclusions that were hopelessly out of depth – the conclusions wereremarkably accurate.
In 1831 a young Charles Darwin received the scientific opportunity of lifetime, when he was invited to takecharge f the natural history side of a five year voyage on the H.M.S. Beagle, which was to sail around theworld, particularly to survey the coast of South America. Darwin’s reference material consisted of works ofSir Charles Lyell, a British geologist (he developed a concept termed uniformitarianism which suggestedthat geological phenomena could be explained by prevailing observations of natural processes operatingover a great spans of time – he has been accused synthesizing the works of others30) who was the author ofgeologic texts that were required reading throughout the 19th century including Principals of Geology,which along with his own findings (observing the a large land shift resulting from an earthquake),convinced him of geological uniformitarianism, hypothesizing for example, that earthquakes wereresponsible for the formation of mountains.
Darwin faith!fully maintained this method of interpreting facts – by seeking explanations of past events by observingoccurrences in present time – throughout his life31. The lucid writing style of Lyell and straightforwardconclusions influence all of his work. When unearthing remains of extinct animals in Argentina he notedthat their remains more closely resembled those of contemporary South American mammals than any otheranimals in the world. He noted that existing animals have a close relation in form with extinct species,and deduced that this would be expected if the contemporary species had evolved form South Americanancestors not however, if thereexisted an ideal biota for each environment.
When he arrived on theGalapagos islands (islands having been formed at about the same time and characteristically similar), hewas surprised to observe unique species to each respective island, particularly tortoises which possessedsufficiently differentiated shells to tell them apart. !From these observations he concluded that the tortoises cou ld only have evolved on the islands32.Thomas Robert Malthus was an English economist and clergyman whose work An Essay on the Principalof Population led Darwin to a more complete understanding of density dependent factors and the strugglein nature.
Malthus noted that there was potential for rapid increase in population through reproduction -but that food cannot increase as fast as population can, and therefore eventuality will allow less food perperson, the less able dying out from starvation or sickness. Thus did Malthus identify population growth asan obstacle to human progress and pedalled abstinence and late marriage in his wake.
For these conclusionshe came under fire from the Enlightment movement which interpreted his works as opposing socialreform.Erasmus Darwin, grandfather of Darwin, was an unconventional, freethinking physician and poet whoexpressed his ardent preoccupation for the sciences through poetry. In the poem Zoonomia he initiated theidea that evolution of an organism results from environmental implementation. This coupled with a stronginfluence from the similar conclusions of Lamarck shaped Darwin’s perception on the environment’sinherent nature to mould and shape evolutionary form.
METHODS OF SCIENTIFIC DEDUCTION
Early scientists, particularly those in the naturalist field derived most of their conclusions from observed,unproven empirical facts. Without the means of logically explaining scientific theory, the hypothesis wasincurred – an educated guess to be proven through experimentation. Darwin developed his theory of naturalselection with a viable hypothesis, but predicted his results merely by observing that which was available.Following Lyell’s teaching, using modern observations to determine what occurred in the past, Darwindeveloped theories that only made sense – logical from the point of view of the human mind (meaning itwas based on immediate human perception) but decidedly illogical from a purely scientific angle.
Byperusing the works of Malthus did Darwin finally hit upon his theory of natural selection – not actuallyquestioning these conclusions because they fit so neatly into his own puzzle. Early development of logical,analytic scientific theory did not occur u!ntil the advent of philosophe r Rene Descartes in the mid-17th century (I think therefore I am35).Natural selection was shown to be sadly lacking where it could not account for how characteristics werepassed down to new generations36.Philosophy Essays