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Theories Explaining Biological Evolution

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.

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 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)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 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 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. well as progress in “knowledge 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: 1Variation 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. 2The 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. 3The only variations pertinent to evolution are those which are inherited. 4Evolution is an ongoing process which must span many moons to become detectably apparent. 5Complexity of a species may not necessarily increase with the evolutionary process – it may not change at all, even decrease.

Predator and prey have no underlying purpose for maintenance of any type of balance – natural selection is opportunistic and irregular12. 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 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 “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 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 liver. Yet there is a virtually 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 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 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 speciation is concurrent with the theory of biological evolution19.

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