Evolution
1. Introduction
In an 1802 paper written by Erasmus Darwin, the theory was mentioned but it had not been explained thoroughly. It was not until the inception of the Origin of Species in 1858 that Charles Darwin and Alfred Russell Wallace presented the details behind the theory of evolution and the process of natural selection. This has become the building block of modern evolutionary theory, speciation and the overall understanding of the living world and what has passed into oblivion.
Life on Earth began more than 3 billion years ago, evolving from the most basic of microbes into a dazzling array of complexity over time. At the heart of this development is genetic change, the change in an organism’s gene frequency over time. Genetic change comes about primarily through the process of natural selection, the process by which the environment plays a role in the survival and reproductive success of an individual. Natural selection generally acts to eliminate changes in gene frequency which are deleterious, however under certain circumstances it can lead to the spread of a particular genetic variant, and if this process occurs over a long enough period of time, natural selection can result in an alteration of the overall characteristics of a species. Through this mechanism of natural selection, genetic change and reproductive isolation can result in the formation of a new species from an existing population of a species. This has been the driving force behind the changes in the living world from its most primitive of forms through to what we are familiar with today. This concept that a new species comes from an old species was foreign to many when first proposed.
2. Theories of Evolution
We do, in fact, find writers who seem to confuse the survival of the fittest with evolution despite the clarity of the statement which Huxley (1858) made in anticipation of the modern synthesis, that the argument of the Origin is not that all things are as they are because they have been evolved, but that they have been evolved because the alternatives were worse. The survival of the fittest is consistent with pure stasis if no new variations turn up. And in the paleontological record, as interpreted in the light of neo-Darwinian theory, its most dramatic effects should be found among successful invaders or colonists exterminating the less fit autochthonous forms. But even in the case of competitive displacement, it is not always the fittest in the precise current environment who survives. If we reflect on the history of Europe for the past two millennia, it would be hard to argue in every case that the modern descendants of the ancient world’s barbarian invaders have proved to be superior genetic stock to the peoples whom they conquered. For this reason, biologists have sought, and found, a more general and less controversial model of selection in the concept of the ecological theatre. Pattern thinking has also made it clear that recognition of pattern among currently living forms often requires knowledge of historical sequences.
Three distinct aspects of the competition view can be discerned. Darwin (1859) discussed two principles that apply to man: “the struggle for existence” and natural selection. “The struggle for existence” carries no implication of agonistic behaviour because he intended it to be taken in a Malthusian sense as due to an increase in numbers of a species beyond the food supply, which leads necessarily to a higher death rate at all ages. But when he then says “natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working at the improvement of each organic being”, it seems undeniable that Darwin had in mind an eliminative process by means of contests in which the loser is pushed aside or destroyed, making survival in the absence of further testing a mere metaphor.
Two Theories
3. Mechanisms of Evolution
In the example provided by Dr. Piertney of the European population of red deer, two genetically different clines of red deer meet on the European continent. Scottish red deer are smaller in size than Hungarian red deer. The introduction of sika deer into both regions gave an advantage to smaller deer, as sika deer are smaller in size. Over time, the Scottish red deer and Hungarian red deer became smaller than the original size due to higher reproductive success in smaller deer, an example of natural selection.
The ideas of genetics and evolution, proposed by Gregor Mendel and Charles Darwin, are tied together in the modern synthesis, the updated theory of evolution. Natural selection is the best studied of the evolutionary mechanisms, but there are several others, including genetic drift, gene flow, and mutation. Natural selection is the process by which individuals with certain heritable traits tend to produce more surviving offspring than individuals without the trait. When a significant majority of individuals in a population have the same trait, this can result in a differing characteristic of the species at a later point in its evolution.
A. Natural selection
4. Evidence of Evolution
These include specific expectations of the genetic and molecular evidence which would exist if two species share a common ancestor or if they do not. The genetics of the simple traits should have very little change between the species, and the molecular evidence for the complex traits should show a pattern of a divergent nature. Predictions from the same concept are also derived on a basic level of the fossils which could be discovered. If the traits were lost after the species had branched off from a common ancestor, fossils would be discovered of a transitional nature then the currently existing species. This would be a pattern consistent with the evolution of the West Indian manatee, in which its move to a completely aquatic life is associated with the loss of hind limbs.
The main evidence of common descent is based on the concept that the simple traits exhibited in organisms, along with complex traits, are best explained by an overlapping pattern of resemblances between species. Atavisms are the simple traits which are remnants of ancestors; they are retained through a pattern of descending from a complex to a simple state of a trait. An example of this is the atavism in cetaceans hindlimbs, as cetaceans descended from a four-legged land mammal. The complex traits, in comparison, are explained through the idea of traits having multiple components which can be modified and adapt different functions. An example of this is the forelimb of all vertebrates. This concept of complex and simple traits formulates a prediction which is highly consistent and is directly supported by empirical data from many areas of science.
Evidence of evolution and common descent of living organisms has been discovered by scientists since Darwin’s On the Origin of Species was published in 1859. Evidence of common descent is the process of making and detailing the evidence in order to construct and support the idea that all living organisms have a common ancestor. Evolutionary theory predicts and explains common descent by a combination of the following.
5. Implications of Evolution
Micro evolution, or change beneath the species level, is basic to the evolutionary process. One of the clearest implications of this was noted by Theodosius Dobzhansky, a leading evolutionary theorist. He suggested that nothing in biology makes sense except in the light of evolution. This is basic to the success of genetic research in curing diseases. On a more negative note, the eugenics movement of the late 19th and early 20th centuries stated that human intelligence and other attributes are determined by genetics, and the marker of a defective gene pool is the causation of social ills. This movement culminated in Nazi Germany, who led a program of natural selection – selecting the genes that they believed to be beneficial to future generations by the extermination of individuals who possess certain traits. This is the negative side of micro evolution.
The theory of evolution by natural selection was first proposed by Charles Darwin. This theory, though supported by so much evidence, suggests that man is merely just another succession from the primordial slime in terms of evolutionary superiority. This thought is interesting to a number of different fields, and even the common person. The implications of the evolutionary theory at the various levels, from micro evolution through to macro evolution, are far-reaching.
