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Biological Evolution

Biological Evolution

Wikipedia defines biological evolution as “the change over time in one or more inherited traits found in populations of organisms. Inherited traits are particular distinguishing characteristics, including anatomical, biochemical or behavioral characteristics, that are passed on from one generation to the next. Evolution may occur when there is variation of inherited traits within a population. The major sources of such variation are mutation, genetic recombination and gene flow. Evolution has led to the diversification of all living organisms, from a common ancestor, which are described by Charles Darwin as ‘endless forms most beautiful and most wonderful’.”

“There are four common mechanisms of evolution. The first mechanism is natural selection, a process in which there is differential survival and/or reproduction of organisms that differ in one or more inherited traits. A second mechanism is genetic drift, a process in which there are random changes to the proportions of two or more inherited traits within a population. A third mechanism is mutation, which is a permanent change in a DNA sequence. Finally, the fourth mechanism is gene flow, which is the incorporation of genes from one population into another.”

“Evolution may in the long term lead to speciation, whereby a single ancestral species splits into two or more different species.”

In 1859, Charles Darwin wrote his book, The Origin of Species, and turned the scientific world upside down. In his argument, he maintained that all forms of life evolved from a lower form of life in a process of mutations and natural selection. Up until this time, most scientists had made their assumptions based upon the record of creation as recorded in the first eleven chapters of Genesis with special emphasis on the results of the world wide flood during the days of Noah. For those who would like to read this book, go the the Web site: Origin of Species.

Much of the book addresses the issues of microevolution which we have already discussed extensively and shown that this does exist within the various species (or kinds as Genesis calls them. There is not a problem with cross breeding as they all have the same DNA structure. But Darwin goes further. He strongly argues that life forms have crossed the limitations and bounders of specie structure and that there has been a migration, across the species, as lower forms of life evolve into higher forms of life. In his concluding chapter, he expresses great concern that the fossil records did not support his conclusions. However, he had little doubt the future finds would validate his conclusions.

Darwin based his theory on two processes – natural selection and mutations. Now let us examine these claims.

Natural Selection

Wikipedia has this to say, “Natural selection is a natural process by which genetically, heritable traits, become more or less common in a population over successive generations. This selection in interaction with the production of variation, the possible genetic fixation process and possibly, in several cases, with little epigenetic process determine the evolution of the species.”

“The natural genetic variation within a population of organisms means that some individuals will survive and reproduce more successfully than others in their current environment. For example, the peppered moth exists in both light and dark colors in the United Kingdom, but during the industrial revolution many of the trees on which the moths rested became blackened by soot, giving the dark-colored moths an advantage in hiding from predators. This gave dark-colored moths a better chance of surviving to produce dark-colored offspring, and in just a few generations the majority of the moths were dark. Factors which affect reproductive success are also important; an issue which Charles Darwin developed in his ideas on sexual selection.”

“Natural selection acts on the phenotype, or the observable characteristics of an organism, but the genetic (heritable) basis of any phenotype which gives a reproductive advantage will become more common in a population (see allele frequency). Over time, this process can result in adaptations that specialize populations for particular ecological niches (a term describing the relational position of a species or population in its ecosystem to each other) and may eventually result in the emergence of new species. In other words, natural selection is an important process (though not the only process) by which evolution takes place within a population of organisms. As opposed to artificial selection, in which humans favor specific traits, in natural selection the environment acts as a sieve through which only certain variations can pass.”

The above statement is true within species, however, as we have previously argued; it is not true across the species. Now let us look at mutation. The argument is made that by mutations the animals can transition from one specie to another.

Mutations

The web site, Genetics Home Reference, defines mutation as follows. “A gene mutation is a permanent change in the DNA sequence that makes up a gene. Mutations range in size from a single DNA building block (DNA base) to a large segment of a chromosome.”

“Gene mutations occur in two ways: they can be inherited from a parent or acquired during a person’s lifetime. Mutations that are passed from parent to child are called hereditary mutations or germ line mutations (because they are present in the egg and sperm cells, which are also called germ cells). This type of mutation is present throughout a person’s life in virtually every cell in the body.”

“Mutations that occur only in an egg or sperm cell, or those that occur just after fertilization, are called new (de novo) mutations. De novo mutations may explain genetic disorders in which an affected child has a mutation in every cell, but has no family history of the disorder.”

“Acquired (or somatic) mutations occur in the DNA of individual cells at some time during a person’s life. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot be passed on to the next generation.”

“Mutations may also occur in a single cell within an early embryo. As all the cells divide during growth and development, the individual will have some cells with the mutation and some cells without the genetic change. This situation is called mosaicism.”

“Some genetic changes are very rare; while others are common in the population. Genetic changes which occur in more than 1 percent of the population are called polymorphisms. They are common enough to be considered a normal variation in the DNA. Polymorphisms are responsible for many of the normal differences between people such as eye color, hair color, and blood type. Although many polymorphisms have no negative effects on a person’s health, some of these variations may influence the risk of developing certain disorders.”

Some mutations can be healthy but the most are harmful. About 70% of these mutations have damaging effects, and the remainder being either neutral or weakly beneficial. Due to the damaging effects that mutations can have on cells, organisms have evolved mechanisms such as DNA repair to remove mutations.”

If we extrapolate the trend of the large number of bad mutations over a long period of time, we would see that life would deteriorate—not evolve into a more complex superior form of life. “Mutation is generally accepted by biologists as the mechanism by which natural selection acts, generating advantageous new traits that survive and multiply in offspring as well as disadvantageous traits, in less fit offspring, that tend to die out.”