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Title of Paper : Theory of Evolution
Grade Received on Report : 87
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 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 Wa!
llace 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 al!
so 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
decrease.
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 metacarpa!
l, 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 .
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 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 c!
ontribution 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 .
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 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 un!
changed. 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 simila!
rity 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 .
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 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 fai!
thfully 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 a!
part. 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 oc!
cur 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.
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