Evolution : Explanatory Theories
TABLE OF CONTENTS
DARWINIAN THEORY OF EVOLUTION
THE THEORY OF BIOLOGICAL EVOLUTION:
COMPARISON: LAMARCK vs. DARWIN
METHODS OF SCIENTIFIC DEDUCTION
LIMITS TO DARWIN’S THEORY
MORPHOLOGICAL ; BIOLOGICAL CONCEPTS
BIO-EVOLUTION: POPULATION vs. INDIVIDUALS
MECHANISMS FOR GENETIC VARIATION
GENETIC VARIATION AND SPECIATION
SPECIATION vs. CONVERGENT EVOLUTION
CONCEPT OF ADAPTATION
VALUE/LIMITATIONS: THE THEORY OF BIOLOGICAL EVOLUTION
ALTERNATE EXPLANATIONS OF BEING
Theories explaining biological evolution have been bandied about since the ancient Greeks, but it was not until the Enlightment of the 18th century that widespread acceptance and development of this theory emerged. In the mid 19th century english naturalist Charles Darwin – who has been called the father of evolution – conceived of the most comprehensive findings about organic evolution ever. Today many of his principles still entail modern interpretation of evolution.
I’ve assessed and interpreted the basis of Darwin’s theories on evolution, incorporating a number of other factors concerning evolutionary theory in the 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 Western consciousness challenging not only the scientific community, but the prominent religious institution as well. 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 the Species was written – straightforward English, anyone capable of a logical argument could follow it – also unprecedented in the scientific community (compare this to Isaac Newton’s horribly complex work taking the scientific community years to interpret).
Evolutionary and revolutionary in more than one sense of each 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 consciousness since the mid-17th century (a la John Ray), but wide-range acceptance of this idea, beyond the bounds of the scientific community, did not arise until Darwin published his findings in 1958. Darwin first developed his theory of biological evolution in 1938, following his five-year circumglobal voyage in the southern tropics (as a naturalist) on the H.M.S. Beagle, and perusal of one Thomas Malthus’ An Essay on the Principle of Population which proposed that environmental factors, such as famine and disease limited human population growth. This had direct bearing on Darwin’s theory of natural selection, furnishing him with an enhanced conceptualization of the survival of the fittest – the competition among individuals of the same species for limited resources – the missing piece to his puzzle. For fear of contradicting his father’s beliefs, Darwin did not publish his findings until he was virtually forced after Alfred Wallace sent him a short paper almost identical to his own extensive works on the theory of evolution. The two men presented a joint paper to the Linnaean Society in 1958 – Darwin published a much larger work (a mere abstract of my material) Origin of the Species a year later, a source of undue controversy and opposition (from pious Christians), but remarkable development for evolutionary theory.
Their findings basically stated that populations of organisms and individuals of a species were varied: some individuals were more capable of obtaining mates, food and other means of sustenance, consequently producing more offspring than less capable individuals. Their offspring would retain some of these characteristics, hence a disproportionate representation of successive individuals in future generations. Therefore future generations would tend have those characteristics of more accommodating individuals. This is the basis of Darwin’s theory of natural selection: those individuals incapable of adapting to change are eliminated in future generations, selected against. Darwin observed that animals tended to produce more offspring than were necessary to replace themselves, leading to the logical conclusion that eventually the earth would no longer be able to support an expanding population. As a result of increasing population however, war, famine and pestilence also increase proportionately, generally maintaining comparatively stable population.
Twelve years later, Darwin published a two-volume work entitled The Descent of Man, applying his basic theory to like comparison between the evolutionary nature of man and animals and how this related to socio-political development man and his perception of life. It is through the blind and aimless progress of natural selection that man has advance to his present level in love, memory, attention, curiosity, imitation, reason, etc. as well as progress in knowledge morals and religion. Here is where originated the classic idea of the evolution of man from ape, specifically where he contended that Africa was the cradle of civilization. This work also met with opposition but because of the impact of his revolutionary initial work this opposition was comparatively muted.
A summary of the critical issues of Darwin’s theory might be abridged into six concise point as follows:
1 Variation among individuals of a species does not indicate deficient copies of an ideal prototype as suggested by the
platonic notion of Eidos. The reverse is true: variation is integral to the evolutionary process.
2 The fundamental struggle in nature occurs within single species population to obtain food, interbreed, and resist predation. The struggle between different species (ie. fox vs. hare) is less consequential.
3 The only variations pertinent to evolution are those which are inherited.
4 Evolution is an ongoing process which must span many moons to become detectably apparent.
5 Complexity of a species may not necessarily increase with the evolutionary process – it may not change at all, even
6 Predator and prey have no underlying purpose for maintenance of any type of balance – natural selection is 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 numerous observations within the field of biology. Generally, observation of any physical, behaviourial, or chemical change (adaptation) over time owing directly to considerable diversity of organisms can be attributed to biological evolution of species. It might also explain the location (distribution) of species throughout the planet.
Naturalists can hypothesize that if organisms are evolving through time, then current species will differ considerably from their extinct ancestors. The theory of biological evolution brought about the idea for a record of the progressive changes an early, extinct species underwent. Through use of this fossil record paleontologists are able to classify species according to their similarity to ancestral predecessors, and thereby determine which species might be related to one another. Determination of the age of each fossil will concurrently indicate the rate of evolution, as well as precisely which ancestors preceded one another and consequently which characteristics are retained or selected against. Generally this holds true: probable ancestors do occur earlier in the fossil record, prokaryotes precede eukaryotes in the fossil record. There are however, significant missing links throughout the fossil record resulting from species that were, perhaps, never fossilized – nevertheless it is relatively compatible with the theory of evolution.
It can be postulated that organisms evolving from the same ancestor will tend to have similar structural characteristics. New species will have modified versions of preexisting structures as per their respective habitats (environmental situations). Certainly these varying species will demonstrate clear differentiation in important structural functions, however an underlying similarity will be noted in all. In this case the similarity is said to be homologous, that is, structure origin is identical for all descended species, but very different in appearance. This can be exemplified in the pectoral appendages of terrestrial vertebrates: Initial impression would be that of disparate structure, however in all such vertebrates four distinct structural regions have been defined: the region nearest the body (humerus connecting to the pectoral girdle, the middle region (two bones, radius and ulna are present), a third region – the hand – of several bones (carpal and metacarpal, and region of digits or fingers. Current species might also exhibit similar organ functions, but are not descended from the same ancestor and therefore different in structure. Such organisms are said to be analogous and can be exemplified in tetrapods, many containing similar muscles but not necessarily originating from the same ancestor. These two anatomical likenesses cannot be explained without considerable understanding of the theory of organic evolution.
The embryology, or early development of species evolved from the same ancestor would also be expected to be congruent. Related species all share embryonic features. This has helped in determining reasons why development takes place indirectly, structures appearing in embryonic stage serve no purpose, and why they are absent in adults. All vertebrates develop a notchord, gill slits (greatly modified during the embryonic cycle) and a tail during early embryology, subsequently passing through stages in which they resemble larval amphioxus, then larval fishes. The notchord will only be retained as discs, while only the ear canal will remain of the gills in adults. Toothless Baleen whales will temporarily develop teeth and hair during early embryology leading to the conclusion that their ancestors had these anatomical intricacies. A similar pattern, exists in almost all animal organisms during the embryonic stage for numerous formations of common organs including the lungs and liver. Yet there is a virtually unlimited variation of anatomical properties among adult organisms. This variation can only be attributed to evolutionary theory.
Biological evolution theory insists that in the case of a common ancestor, all species should be similar on a molecular 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 been made 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 all cells 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 compounds is governed by DNA. The structure for all vital lipids, proteins, some important co-enzymes and specialized molecules such as DNA, RNA and ATP are common to all organisms.
All organisms are anatomically constructed through function of the genetic code. All of these biochemical similarities can be predicted by the theory of biological evolution but, of course some molecular differentiation can occur. What might appear as minor differentiation (perhaps the occurrence-frequency of a single enzyme) might throw species into entirely different orders of mammals (ie. cite the chimpanzee and 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 in each lineage, derived in concert from a common ancestor.
Breeders had long known the value of protective resemblance long before Darwin or any other biological evolution theorists made their mark. Nevertheless, evolutionary theory can predict and explain the process by which offspring of two somewhat different parents of the same species will inherit the traits of both – or rather how to insure that the offspring retains the beneficial traits by merging two of the same species with like physical characteristics. It was the work of Mendel that actually led to more educated explanations for the value in protective resemblance. The Hardy-Weinburg theory specifically, employs Mendel’s theory to a degree to predict the frequency of occurrence of dominantly or recessively expressing offspring. Population genetics is almost sufficient in explaining the basis for protective resemblance. Here biological evolutionary theory might obtain its first application 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 in the area. Because the evolutionary process is so slow, spanning over considerable lengths of time, it can be predicted that similar species would be found within comparatively short distances of each other, due to the difficulty 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 course of time evolve differently from their relatives on the mainland. Madagascar is one such example – in fact approximately 90 percent of the birds living there are endemic to that region. Thus as predicted, it follows that speciation 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 scene. 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 the mechanism of evolution until he read (recalled, actually) the work of Thomas Malthus – the notion that in every generation the inferior would be killed off and the superior would remain – that is the fittest would survive. 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 always slow there would be ample time for the change to be effected by the survival of the best fitted in every generation. He saw that his theory supplanted the views of Lamarck and the Vistages and annulled every important difficulty with these theories.
Two days later he sent Darwin (leading naturalist of the time) a four-thousand word outline of his ideas entitled On the Law Which has Regulated the Introduction. This was more than merely cause for Darwin’s distress, for his work was so similar to Darwin’s own that in some cases it parallelled Darwin’s own 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. Darwin was persuaded by friends to include extracts of his own findings when he submitted Wallace’s work On the Law Which Has Regulated the Introduction of New Species to the Linnaean Society in 1858, feeling doubly horrible because he felt this would be taking advantage of Wallace’s position. Wallace never once gave the slightest impression of resentment or disagreement, even to the 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 the issues they’d both developed.
He later published Contributions to the Theory of Natural Selection, comprising the fundamental explanation and understanding of the theory of evolution through natural selection. He also greatly developed the notion of natural barriers which served as isolation mechanisms, keeping apart not only species but also whole families of animals – he drew up a line (Wallace’s line) where the fauna and flora of 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 models describing the changes of gene frequencies in population were not realized. Following this rediscovery of Mendel, 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 of the 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 successive generation, unless stimulated by mutation, selection, emigration, or immigration of individuals. The relative proportion of genotypes in the population will also be maintained after one generation, should these conditions be negated or mating is random.
Through application of the Hardy-Weinberg principle the precise conditions under which change does not occur in the frequencies of alleles at a locus in a given population (group of individuals able to interbreed and produce fertile offspring) can be formulated: the alleles of a locus will be at equilibrium. A species may occur in congruous correspondence with its population counterpart, or may consist of several diverse populations, physically isolated from one another.
In accordance with Mendelian principle, given two heterozygous alleles A and B, probability of the offspring retaining prominent traits of either parent (AA or BB) is 25 percent, probability of retaining half the traits of each parent (AB) is 50 percent. Thus allele frequencies in the offspring parallel those of the parents. Likewise, given one parent AB and another AA, allele frequencies would be 75 percent A and 25 percent B, while genotype frequencies would be 50 percent AA and 50 percent AB – the gametes generated by these offspring would also maintain the same ratio their parents initiated (given, of course a maximum of two alleles at each locus).
In true-to-life application however, where numerous alleles may occur at any given locus numerous possible combinations of gene frequencies are generated. Assuming a population of 100 individuals = 1, 30 at genotype AA, 70 at genotype BB. Applying the proportionate theory, only 30% (0.30) of the gametes produced will retain the A allele, while 70% (0.70) the B allele. Assuming there is no preference for AA or BB individuals for mates, the probability of the (30% of total population) AA males mating with AA females is but 9% (0.3 x 0.3 = 0.09). Likewise the probability of an BB to BB match is 49%, the remainder between (30%) AA and (70%) BB individuals, totalling a 21% frequency. Frequency of alleles in a population in are commonly denoted p and q respectively, while the AB genotype is denoted 2pq. Using the relevant equation p + pq + q = 1, the same proportions would be obtained. It can therefore be noted that the 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 each successive generation. Generally speaking, the Hardy-Weinberg principle will not favour 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 expected frequencies where populations are evolving. Deviation from these projected frequencies indicates evolution of the species may be occurring.
Allele and genotype frequencies are typically modified per each successive generation and never in ideal Hardy-Weinberg equilibrium. These modifications may be the result of natural selection, but (particularly among small populations) may simply result from random circumstance. They might also arise form immigration of individuals form other populations where gene frequencies will be unique, or form individuals 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 the Hardy-Weinberg theory cannot be denied. Jean Lamarck, a French biologist postulated the theory of an inherent faculty of self-improvement by his teaching that new organs arise form new needs, that they develop in proportion to how often they are used and that these acquisitions are handed down from one generation to the next (conversely disuse of existing organs leads to their gradual disappearance). He also suggested that non-living matter was spontaneously created into the less complex organisms who would evolve 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 first exposed to his findings when Lyell popularized them with his usual flair for writing, but because the influential Lyell also openly criticized these findings they were never fully accepted.
Darwin’s own theories were based on those of older evolutionists and the principle of descent with modification, the principle of direct or indirect action of the environment on an individual organism, and a wavering belief in Lamarck’s doctrine that new characteristics acquired by the individual through use or disuse are transferred to its descendants. Darwin basically built around this theory, adding that variation occurs in the passage each progressive generation. Lamarck’s findings could be summarized by stating that it is the surrounding environment that has direct bearing on the evolution of species. Darwin instead contested that it was inter-species strife the will to power or the survival of the fittest. Certainly Lamarck was looking to the condition of the sexes: the significantly evolved difference of musculature between male and females can probably be more easily explained by Lamarckian theory than Darwinian. There was actually quite a remarkable similarity between the conclusions of Darwin’s grandfather, Erasmus Darwin and Lamarck – Lamarck himself only mentioned Erasmus in a footnote, and with virtual contempt. The fact is neither Lamarck nor Darwin ever proposed a means by which species traits were passed on, although Lamarck is usually recalled as one of those hopelessly erroneous scientists of past it was merely the basis for his conclusions that were hopelessly out of depth – the conclusions were remarkably accurate.
In 1831 a young Charles Darwin received the scientific opportunity of lifetime, when he was invited to take charge f the natural history side of a five year voyage on the H.M.S. Beagle, which was to sail around the world, particularly to survey the coast of South America. Darwin’s reference material consisted of works of Sir Charles Lyell, a British geologist (he developed a concept termed uniformitarianism which suggested that geological phenomena could be explained by prevailing observations of natural processes operating over a great spans of time – he has been accused synthesizing the works of others) who was the author of geologic 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 were responsible for the formation of mountains. Darwin faithfully maintained this method of interpreting facts – by seeking explanations of past events by observing occurrences in present time – throughout his life. The lucid writing style of Lyell and straightforward conclusions influence all of his work. When unearthing remains of extinct animals in Argentina he noted that their remains more closely resembled those of contemporary South American mammals than any other animals 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 American ancestors not however, if thereexisted an ideal biota for each environment. When he arrived on the Galapagos islands (islands having been formed at about the same time and characteristically similar), he was surprised to observe unique species to each respective island, particularly tortoises which possessed sufficiently differentiated shells to tell them apart. From these observations he concluded that the tortoises could only have evolved on the islands.
Thomas Robert Malthus was an English economist and clergyman whose work An Essay on the Principal of Population led Darwin to a more complete understanding of density dependent factors and the struggle in 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 per person, the less able dying out from starvation or sickness. Thus did Malthus identify population growth as an obstacle to human progress and pedalled abstinence and late marriage in his wake. For these conclusions he came under fire from the Enlightment movement which interpreted his works as opposing social reform.
Erasmus Darwin, grandfather of Darwin, was an unconventional, freethinking physician and poet who expressed his ardent preoccupation for the sciences through poetry. In the poem Zoonomia he initiated the idea that evolution of an organism results from environmental implementation. This coupled with a strong influence from the similar conclusions of Lamarck shaped Darwin’s perception on the environment’s inherent 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 was incurred – an educated guess to be proven through experimentation. Darwin developed his theory of natural selection 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, Darwin developed theories that only made sense – logical from the point of view of the human mind (meaning it was based on immediate human perception) but decidedly illogical from a purely scientific angle. By perusing the works of Malthus did Darwin finally hit upon his theory of natural selection – not actually questioning these conclusions because they fit so neatly into his own puzzle. Early development of logical, analytic scientific theory did not occur until the advent of philosopher Rene Descartes in the mid-17th century (I think therefore I am). Natural selection was shown to be sadly lacking where it could not account for how characteristics were passed down to new generations. However, it did present enough evidence for rational thought to be applied to his theory. Thus scientists were able to develop fairly accurate conclusions with very limited means of divination. Opposition from oppressive Judeo-Christian church allowed little room science. Regardless, natural selection became the basis for all present forms of evolutionary theory.
LIMITS TO DARWIN’S THEORY
Darwinism, while comparatively rational and well documented nevertheless upheld the usual problem that can be found in many logical scientific conclusions – namely deliberate ignorance of facts which might modify or completely alter years the conclusions of years of research. Many biologists were less than convinced with an evolutionary hypothesis that could not explain the mechanism of inheritance. It was postulated by others that offspring will tend to have a blend of their two parents characteristics, the parents having a blend of characteristics from their ancestors, the ancestors having a blend of characteristics from their predecessors – allotting the final offspring impure, diminished desirable characteristics. Thus did they believe a dilution of desirable traits evolved even more diluted desirable traits – these traits now decidedly muted. It was more than two decades after Darwin’s death that Mendelian theory of the gene finally came to light at the turn of the century. Because of this initial scepticism with Darwin’s natural selection, when Mendel’s work became widely available biologists emphasized the importance of mutation over selection in evolution. Early Mendelian geneticists believe that continuous variation (such features as body size) hardly factored in the formation of new species – perhaps nothing to do with genetic control. Inferences on the gradual divergence of populations diminished in wake of notions of significant mutations.
This gave rise to neo-Darwinian theory in the 1930’s, what is called modern synthesis which encompasses paleontology, biogeography, systematics and, of course, genetics. Geneticists have noted that acquired characteristics cannot, indeed be inherited, while observing that continuous variation is inherited through the effects of many genes and have therefore concluded that continuously distributed characteristics are also influenced by natural selection and evolve through time. Modern synthesis, in other words, differs little form Darwinian theory, but also incorporates current understanding of inheritance. Modern synthesis maintains that random mutations introduce variation into population, natural selection inaugurating new genes in greater proportions. Despite revolutionary progress the discovery of the gene has made, neo-Darwinian theory is still based on the arbitrary assumption that the primary factor causing adaptive change in populations is natural selection.
MORPHOLOGICAL & BIOLOGICAL CONCEPTS
Species have been traditionally described based on their
morphological characteristics. This has proven to be somewhat premature to say the least: some organisms in extremely different forms are quite similar in their genetic make-up. Male and females in many species develop more than a few many characteristic physical differences, yet are indeed the same species (imagine that!). Likewise some organisms appear to be quite morophologically similar but are completely incompatible. There are many species of budworm moths, all of which are highly indistinguishable – most of which do not interbreed.
The idea of species is usually called the biological species concept, stressing the importance of interbreeding among individuals in a population as a general description. An entire population might be thought of as a single unit of evolution. However similar difficulties arise in attempting a universal application of this theory. Because morphologically similar species occur in widely separated regions, it is virtually impossible to exact whether they could or could not interbreed.
One might ask whether cactus finches from the Galapagos interbreed – the answer may invariably be yes…but due rather to the morphological similarities between them. Consider further asexually producing species, which can be defined by appearance alone: each individual would have to be defined as different biological species – a fact which would remain irrelevant. There are also cases for which no real standard can be applied – the donkey and horse, for example can mate and produce healthy offspring, mules which are almost always sterile and therefore something completely undefinable. Therefore, despite seeming ideal in its delimitation, the biological species concept cannot be employed in describing many natural species. It is nonetheless a popular concept for theoretical discussions since it can distinguish which populations might evolve through time completely independent of other similar populations.
Species classification is therefore not defined by fixed principles surrounding biological and morphological classifications both. The random nature of evolution itself is predictable perhaps only in that one respect: that it remain virtually unpredictable. In accordance with the Hardy-Weinberg theory the proportion of irregularity should not necessarily increase, but because, by its own admission this theory cannot be employed as a standard but merely to predict results, even it is limited random un-law of nature.
BIO-EVOLUTION: POPULATION vs. INDIVIDUALS
According to the theory of evolution, all life or most of it, originated from the evolution of a single gene. All relatives – species descended from a common ancestor – by definition share a certain percentage of their genes. If naught else than these genes are of a very similar nature. A species depends on the remainder of its population in developing characteristics which allow easier adaptability to the changing environment. These modified genes will ultimately express themselves as new species or may be passed on to other populations within a given species. For these traits to be expressed individually is certainly not going to benefit the species (ie. the mule retains remarkable traits but cannot reproduce – they’re also a literal pain in the ass to generate). Nevertheless should but one individual in a million retain a beneficial characteristic, opportunity for this to be passed on is significantly increased. In short order, as per natural selection highly adapted species can develop where they were dying out (over centuries to be sure, but dying out nonetheless) only a (‘n evolutionarily) short span of time ago. Plant breeders especially know the value of the gene pool. They depend on the gene pool of the wild relatives of these plants to develop strains that are well adapted to local conditions (here we refer to comparatively exotic plants). The gene pool is there for all compatible species (and that could be a large amount down the line) to partake of – given the right random conditions and the future for plant breeders brightens.
MECHANISMS FOR GENETIC VARIATION
There are a number of known factors are capable of changing the genetic structure of a population, each inconsistent with the Hardy-Weinberg principle. Three primary contributing factors are migration, mutation and selection and are referred to as systematic processes – the change in gene frequency is comparatively predictable in direction and quantity. The dispersive process of genetic is predictable only in quantitative nature. When species are sectioned into diverse, geographically isolated populations, the populations will tend to evolve differently on account of the following accepted standards:
1 Geographically isolated populations will mutate exclusively to their population.
2 The adaptive value for these mutations and gene combinations will differentiate per each population.
3 Different gene frequencies existed before the population was isolated and are therefore not representative of their ancestors.
4 During intervals of small population size gene frequencies will be fluctuating and unpredictable forming a genetic bottleneck from which all successive organisms will arise.
Gene frequencies can be altered when a given population is exposed to external populations, the change in frequency modified as per the proportion of foreigners to the mainstream population. Migration may be eliminated between two populations in regions of geographic isolation, which will isolate in turn, the gene pools within the population. If this isolation within population develops over a sufficient span of time the physical differences between two given gene pools may render them incompatible. Thus have the respective gene pools become reproductively isolated and are now defined as biologically different species. However, speciation (division into new species) does not arise exclusively from division into new subgroups inside a population, other aspects might be equally effective.
The primary source for genetic variability is mutation, usually the cause of depletion of species’ fitness but sometimes more beneficial. The ability of a species to survive is dependent on its store of genetic diversity, allowing generation of new genotypes with greater tolerance for changing environment. However, some of the best adapted genotypes may still be unable to survive if environmental conditions are too severe. Unless new genetic material is obtained outside the gene pool, evolution will have a limited range of tolerance for change. Generally speaking, spontaneous mutations whether they are required or not. This means many mutations are useless, even harmful under current environmental conditions. These crippling mutations are usually weeded out or kept at low frequencies in the population through natural selection. The mutation rate for most gene loci is between one in 100 thousand to one in a million. Therefore, although mutations are the source of genetic variability, even without natural selection changes in the population would be unnoticeable and very slow. Eventually, if the only pressure affecting the locus is from mutation, gene frequencies will change and fall back to comparative equilibrium.
The fundamental restriction on the validity of the Hardy-Weinberg equilibrium law occurs where population size in immeasurably large. Thus the disseminating process of genetic drift is applicable for gene frequency alteration in situations of small populations. In such a situation inbreeding is unavoidable, hence the primary contributing factor for change of gene frequencies through inbreeding (by natural causes) is genetic drift. The larger the sample size, the smaller the deviation will be from predicted values. The action of sampling gametes from a small gene pool has direct bearing on genetic drift. Evidence is observed via the random fluctuation of gene frequencies per each successive generation in small populations if systematic processes are not observed as contributing factors. From this four basic assumptions have been made for idealized populations as follows:
1 Mating and self-fertilization in respective subgroups of given populations are completely random.
2 Overlap of one generation to its successor does not occur allotting distinct characteristics for each new generation.
3 In all generations and lines of descent the number of possible breeding individuals is the same.
4 Systematic factors such as migration, mutation and natural selection are defunct.
In small populations certain alleles, perhaps held as common to a species may not be present. The alleles will have become randomly lost somewhere in the population in the process of genetic drift. The result is much less variability among small populations that among larger populations. If every locus is fixed in these small populations they will have no genetic variability, and therefore be unable to generate new adaptive offspring through genetic recombination. The ultimate fate of such a population if it remains isolated is extinction.
GENETIC VARIATION ; SPECIATION
Through genetic variation new species will arise, in a process termed speciation. It is generally held that speciation occurs as two given species evolve their differences over large spans of time – these differences are defined as their genetic variation. The most popular model use to explain how species formed is the geographic speciation model, which suggests that speciation occurs only when an initial population is divided into two or more smaller populations – via genetic variation through systematic means of mutation, natural selection or genetic drift – geographically isolated (physically separated) from one another. Because they are isolated, gene flow (migration) cannot occur between the respective new populations. These daughter populations will eventually adapt to their new environments through genetic variation (process of evolution). If the environments of each isolated population are different then they would be expected to adapt to different conditions and therefore evolve differently. According to the model of geographic speciation, the daughter populations will eventually evolve sufficiently to become incompatible with one another (therefore unable to interbreed or produce viable offspring). As a result of this incompatibility, gene flow could not effectively occur even if the populations were no longer geographically isolated. The differentiated, but closely related species are now termed species pair, or species group. Eventually differentiation will progress far enough for them to be defined as different species.
While divergence is a continuing process, it does not necessarily occur at a constant rate – fluctuating between extremely rapid rates and very slow rates of evolution. Two standard methods have been postulated for the occurrence of geographic speciation: i) Individuals from a species might populate a new, isolated region of a give area (such as an island). Their offspring would evolve geographically isolated from the original species. Eventually, geographical isolation from the population on the mainland would evolved distinguishable characteristics. ii) Individuals might, alternately be geographically isolated as physical barriers arise or the range of the species or individuals of a population diminishes. However, neither of these forms of speciation through geographic isolation and consequent individual genetic variation have been observed or studied direct because of the time span and general difficulty of unearthing desired fossils. Evidence for this form of speciation is therefore indirect and based on postulated theory.
The finches of the Galapagos islands provided Darwin with an important lead towards his development of his theory of evolution. They were (are) a perfect example of how isolated populations could evolve. Here Darwin recognized that life branched out from a common prototype in what is now called adaptive radiation. There were no indigenous finches to the islands when they arrived – some adapted to tree-living, others to cactus habitat, others to the ground. The differentiation was comparatively small, and yet there evolved fourteen species of bird classified under six separate genera, each visibly different only in the characteristics of its beak.
Joint selection pressure equations have been used to calculate the change in gene frequency and consequent rate of mutation resulting from action the of natural selection. Populations of Galapagos finches arrived at their islands from South America and were provided with varying methods of obtainment of sustenance. Only those individuals that evolved characteristics allowing them to more easily obtain food from varying sources were not selected against. Populations were isolated on certain islands and had to adapt to different food sources. The result was an adaptation to food (seeds) from trees, ground or cactus-dominated ares. However, the migratory nature of these finches prompted them to emigrate to alternate islands, therefore interbreeding with otherwise isolated populations of finches. The result has been a variation on single specific characteristics which retain certain properties due to the singular islands they predominantly occupied. When the population of immigrants was high enough, the gene pools of diverse populations of finches presently occupying the island was modified enough such that offspring would inherit some of the traits of otherwise isolated finch populations. Nevertheless, these finches developed characteristics endemic to their particular habitat, and because finches tend to remain in groups rather than individual families, these particular characteristics became dominant enough to evolve morphologically and later even biologically different characteristics. These discrepancies could only lead to greater genetic variation down the line. Eventually immigrants from the mainland and even other Galapagos islands were completely incompatible with specific finch populations endemic to their respective islands. Generally, selection pressure decreased as mutations resulting from systematic 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 who had, at some point evolved from ancestors the population in question. Thus the gene pool could be modified without really affecting the gene frequencies – joint pressures were therefore stabilized, along with the newly developed population.
SPECIATION vs. CONVERGENT EVOLUTION
Speciation is substantially more relevant to the evolution of species than convergent evolution. Through natural selection similar characteristics and ways of life may be evolved by diverse species inhabiting the same region, in what is called convergent evolution – reflecting the similar selective pressure of similar environments. While separate populations of the same species occupying similar habitats may also evidence similar physical characteristics – due primarily to the environment rather than their species origin – it should noted that they progressed form the same ancestor. A defining principle for the alternate natures of speciation and convergent evolution put simply: speciation results form a common ancestor, convergent evolution results from any number of ancestors.
Morphologically similar populations resulting from the same ancestor may be compatible and able to produce viable offspring (if in some occasions not fertile offspring). Morphologically similar species resulting form different ancestors are never compatible with one another – even if they are virtual morphological twins. In fact, morphologically disparate populations of the same species may be compatible with one another – whereas those disparate through convergent evolution would be more than merely incompatible, they may be predator and prey. Convergent evolution may only account for single specific physical characteristics of very disparate, unrelated species – such as the development of flipper-like appendages for the sea turtle (reptile), penguin (bird) and walrus (mammal).
CONCEPT OF ADAPTATION
If individuals were unable to adapt to changes in the environment they would be extinct in short order. Adaptability is often based on nuclear inheritance down the generations. Should an organism develop a resistance to certain environmental conditions, this characteristic may be passed down through the gene pool, and then through natural selection be dominant for all organisms of a given population.
Bacteria are able to accomplish this feat at a remarkably fast rate. Most, if not all forms of bacteria are compatible with one another, that is able to exchange genetic information. The speed at which bacteria reproduces is immeasurably faster than that of more complex, eukaryote organisms. Bacteria have a much shorter lifespan as well – but because they can develop very quickly into large colonies given ideal conditions, it is easier to understand bacteria in clusters. Should a single bacterial organism develop a trait that slightly aids its resistance to destructive environmental conditions, it can pass its modified genetic structure on to half of a colony in a matter of hours. In the meantime the colony is quickly expanding, fully adapted to the environment – soon however, it has developed more than it can be accommodated. The population will drop quickly in the face of inadaptability. But that (previosly mentioned) exterior bacterial organism with the modified trait releases information yielding new growth, allowing the colony to expand further. It is generally accepted that bacterial colonies will achieve a maximum capability – however, through adaptation the bacterial population will quickly excel once again. Antibiotics are now sent to destroy the bacteria. Soon they will be obliterated – and now all that remains of the colony are a few choice bacterial organisms. However, an otherwise isolated bacteria enters the system to exchange genetic information with the much smaller bacterial colony, conditions are favourable, the bacteria expands again. Antibiotics are sent again to destroy this colony – but the exterior bacteria, originating in another organism and having developed a resistance to this type of antibody has provided much of the colony with the means for resistance to these antibodies as well. Once again the bacterial culture has expanded having resisted malignant exterior interlopers. This is how bacteria develops, constantly exchanging nuclear information, constantly able to adapt to innumerable harmful sources. As bacteria are exposed to more destructive forces, the more they decelop resistace to, as surely many of the billions of bacteria could develop an invulnerability to any threatening exterior sources given ideal environmental conditions.
Recently the concept of punctuated equilibrium, as proposed by American paleontologist Stephen Jay Gould has be the subject of much controversy in the scientific world. Gould advanced the idea that evolutionary changes take place in sudden bursts, and are not modified for long periods time when they are reasonably adapted to altered environment.
This almost directly contradicts the older, established Darwinian notions that species evolve through phyletic gradualism, that evolution occurs at a fairly constant rate. It is not suggested by adherents of the punctuated equilibrium model that pivotal fluctuations in morphology occur spontaneously or in only a few generations changes are established in populations – they argue instead that the changes may occur in but 100 to 1000 generations. It is difficult to determine which model could more adequately describe what transpires over the course of speciation and evolution due to gaps in fossil-record, 50 to 100 thousand years of strata often covering deposits bearing fossils. Genetic make-up need not change much for rapid, discernable morphological alterations to detected.
Impartial analysts on the two theories conclude that they are both synonymous with evolutionary theory. Their primary differences entail their emphasis on the importance of speciation in long-term evolutionary patterns in lineage. While phyletic gradualism emphases the significance of changes in a single lineage and the revision of species through slight deviation, punctuated equilibrium emphases the significance of alteration occurring during speciation, maintaining that local (usually small) populations adapt rapidly to local circumstance in production of diverse species – some of which acquire the means for supplantation of their ancestors and rampant settlement in many important adaptive breakthroughs. One must consider that Darwin was not aided by Mendelian theory. Under such circumstances Darwin would have surely produced an entirely different theory for the inheritance of beneficial traits. Consider that mutations can presumably occur spontaneously, given the properly modified parent. It can therefore be stated that punctuated equilibrium is probably a more likely explanation as it does take into account modern cell, and genetic theory. Phyletic gradualism, while certainly extremely logical is a theory which simply cannot encompass those circumstance in which significant change is recorded over comparatively short periods of time. Both are complementary to be sure, but perhaps one of the two distorts this complementary nature formulating inaccurate assumption.
VALUE/LIMITATIONS: THE THEORY BIOLOGICAL EVOLUTION
Whether or not the theory of evolution is useful depends on whether or one values progress above development of personal notions of existence. Certainly under the blanket of a superficial American Dream one would be expected to subscribe to ideals that society, that the state erects. Of course, these ideals focus on betterment of society as a whole – which now unfortunately, means power to the state. Everybody is thus caught up in progress, supposedly to improve the quality of life, and have been somewhat enslaved by the notion of work. Work has become something of an idol, nothing can be obtained without work – for the state. Whether one agrees with the thoughtless actions of the elite or not, people are oppressed by conforming to ideals that insist upon human suffering. Some irresponsible, early religious institutions did just that, erecting a symbol of the people’s suffering and forcing them to bow before it. Development of aeronautic, or even cancer research contributes primarily to this ideal of progress. Development of such theories as biological evolution, contribute nothing toward progress. It instills in the people new principles, to dream and develop an understanding of themselves and that which surrounds them ones, freeing their will from that shuffling mass, stumbling as they are herded towards that which will reap for them suffering and pain. The state provides this soulless mass with small pretty trinkets along the way, wheedling and cajoling them with media images of how they should lead their lives – the people respond with regrets. Modern theory of biological evolution is actually sadly lacking in explanation for exactly how characteristics are passed down to future generations. It is understood how nitrogen bases interact to form a genetic code for an organism – but how the modification that the organism develops, occurs is unknown. Somehow the organism mutates to adapt to environmental conditions, and then presumably the offspring of this organism will retain these adaptations. Of course, biological evolution cannot also explain precisely how first organisms developed: Generally, the theory accounts for energy and chemical interactions at a level consistent enough to establish a constant flow of said interactions – but even here it falls short. And what of phyletic gradualism? It is completely unable to explain the more sudden mutations that occur…for obvious reasons it cannot explain this (Darwin had no knowledge of genetics), but even punctuated gradualism doesn’t balance this problem. I’m sure there are numerous other problems which can be addressed but these can be dealt with where opinion can be more educated.
ALTERNATE EXPLANATIONS OF BEING
Man it would appear, has always sought meaning for his existence. Development of many theories of existence have been conceived and passed down through the ages. Institutions conferring single metaphysical and elemental viewpoints have been established, some of which have been particularly irresponsible and oppressive towards the people they were supposed to enlighten. Most religious institutions have been used as political tools for means of manipulation of the masses, going back to early Roman days when empower Augustus absorbed Christianity into the Roman worship of the sun, Sol Invectus, as a means of subjugating the commoners to Roman doctrine. Generally religious institutions have exploited the people and have been used as excuses for torture, war, mass exterminations and general persecution and oppression of the people it pretends to serve, telling the people they must suffer to reach ultimate transcendent fulfilment. Unfortunately this oppression continues in today’s modern – even Western – world. There have actually been almost innumerable explanations for the physical presence of man – these explanations merely been suppressed by the prevailing religious institutions for fear that they will be deprived absolute power over the people…they’re right.
Without Darwin it can be concluded, reasonable interpretation of biological evolution simply would not be. Natural selection, the process determining the ultimate survival of a new organism, remains the major contributing factor to even the most modern evolutionary theory. The evolutionary process spans over the course of hundreds of thousands of generations, organisms evolving through systematic and dispersive mechanisms of speciation. Recently, heated debate surrounding whether characteristics are passed on in bursts of activity through punctuated equilibrium or at a constant rate through the more traditional phyletic gradualism. The release of Mendelian theory into the scientific community filled the primary link missing in Darwin’s theory – how biological characteristics were passed on to future generations. Applications of genetic theory to evolutionary theory however, are somewhat limited. It is difficult to classify all species even through modern means of paleontology and application to the theory of organic evolution.
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