Реферат: Evolution Charles Darwin Essay Research Paper EVOLUTION
Evolution Charles Darwin Essay, Research Paper
EVOLUTION
TABLE OF CONTENTS Page
INTRODUCTION ………………………………………… 2
DARWINIAN THEORY OF EVOLUTION ………………………… 4
THE THEORY OF BIOLOGICAL EVOLUTION:
CONTRIBUTING ELEMENTS …………………… 7
WALLACE’S CONTRIBUTIONS ……………………………… 13
HARDY-WEINBERG PRINCIPLE ……………………………. 15
COMPARISON: LAMARCK vs. DARWIN ……………………… 16
DARWIN’S INFLUENCES ………………………………… 20
METHODS OF SCIENTIFIC DEDUCTION ……………………… 23
LIMITS TO DARWIN’S THEORY …………………………… 25
MORPHOLOGICAL & BIOLOGICAL CONCEPTS …………………… 27
BIO-EVOLUTION: POPULATION vs. INDIVIDUALS ……………. 29
MECHANISMS FOR GENETIC VARIATION ……………………… 31
GENETIC VARIATION AND SPECIATION ……………………… 35
DARWIN’S FINCHES …………………………………… 37
SPECIATION vs. CONVERGENT EVOLUTION …………………… 39
CONCEPT OF ADAPTATION ………………………………. 41
PUNCTUATED EQUILIBRIUM ………………………………43
VALUE/LIMITATIONS: THE THEORY OF BIOLOGICAL EVOLUTION …. 45
ALTERNATE EXPLANATIONS OF BEING ……………………… 47
CONCLUSIONS ………………………………………… 48
INTRODUCTION
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 ever1. 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 interpret2). 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)3, but wide-range acceptance of this idea, beyond the bounds of
the scientific community, did not arise until Darwin published his findings in 19584. 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 growth5. 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 puzzle6. For fear of contradicting his
father’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 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)7, 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 individuals8. This is the basis of Da!
rwin’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, gener ally maintaining comparatively stable population9. 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 “k!
nowledge morals and religion”10. 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
muted11.
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 decrease.
6 Predator and prey have no underlying purpose for maintenance of any type of balance – natural selection
is opportunistic and irregular12.
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 – 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 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 “finger s”. 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 evolution14.
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 live!
r. Yet there is a virtual ly unlimited variation of anatomical properties among adult organisms. This
variation 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 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 or ganisms.
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 ancestor16.
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 resemblance17.
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 engineering18.
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 speciatio!
n is concurrent with the theory of biological evolution19.
WALLACE’S CONTRIBUTIONS
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 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 ev ery important difficulty with these theories21.
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 contrib!
ution to the field: encoura ging Darwin to publish his extensive research on the issues they’d both
developed22.
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 Australasia23.
HARDY-WEINBERG PRINCIPLE
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 random24.
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 another25.
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 thi s 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 species26.
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 wi!
th his usual flair for writ ing, but because the influential Lyell also openly criticized these findings they
were never fully accepted27.
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”28.
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 D arwin’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 accurate29.
DARWIN’S INFLUENCES
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 others30) 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 faith!
fully maintained this method of interpreting facts – by seeking explanations of past events by observing
occurrences in present time – throughout his life31. 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 cou ld only have evolved on the islands32.
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
reform33.
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 form34.
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 u!
ntil the advent of philosophe r Rene Descartes in the mid-17th century (”I think therefore I am”35).
Natural selection was shown to be sadly lacking where it could not account for how characteristics were
passed down to new generations36.