Evolutionary Theory
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BibArch Home Up Processes Species

The Darwinian paradigm for biological evolution has its basis in natural selection wherein some genetic variations increase and others cease. Darwin's original theories became inadequate explanations since he did not understand the role of genetics in inheritance. Today the synthetic theory of evolution, or the scientific theory of evolution, based upon genetics serves as the standard scientific explanation of how life evolves. Genetic variation arises from the interaction of four natural phenomena: mutation, natural selection, gene flow, and genetic drift.

The chemical basis of inheritance lies in DNA (deoxyribonucleic acid). Reproduction of DNA in reproductive or "sex" cells, known as gametes, permits transfer of genetic material, called genes, from parent to offspring. An offspring’s genetic endowment consists of the genes acquired from the offspring’s parents. Genes may have alternative forms known as alleles. Some genes have only a single allele and others have more. A population’s gene pool consists of the total aggregate of genes in that population at any one time.

  • Mutations. A change in genetic code known as a mutation consists of changes in the hereditary instructions contained within a gene. A mutation, the ultimate source of all genetic variation, must occur in reproductive cells to cause genetic change in offspring. The process of mutation involves random genetic change primarily due to chemical factors and ionizing radiation. 

  • Gene Flow. The movement of genes from one population to another, describes the process of the loss or gain of genes in a population due to the emigration or immigration of fertile individuals, or the transfer of gametes, between populations. This process introduces new genes into a population resulting in populations becoming more similar to one another. 

  • Genetic Drift. The process of genetic drift, dealing with chance preservation or extinction of particular genes, may be defined as a variation in the gene pool, a change in allele frequency, in a small population due to chance. 

  • Natural Selection. The process of natural selection refers to the differential survival and reproduction of organisms as a result of their biological characteristics.

Biological evolution consists of genetic change over deep time wherein long-term patterns of genetic change occur (such as the development of the fetus inside of the mother’s body, the development of upright posture in hominids, and the like). The study of biological evolution includes analysis of both microevolution and macroevolution.

Microevolution, which may be may be defined as a change in allele frequencies in a population over successive generations, consists of the study of evolution in terms of the phenomena bringing about genetic variation in populations including mutation, natural selection, gene flow, and genetic drift. Microevolution involves short-term evolutionary change and the phenomena which bring it about.

Macroevolution, defined as evolutionary change in relatively large and complex changes over many generations and on taxonomic groups higher than the species level, deals with long-term evolutionary change. Macroevolution deals with changes of sufficient magnitude to bring about new taxonomic groups, e.g., new phyla, genera, families.

Biologists have come to challenge some of the assumptions and inferences of the synthetic theory of evolution. Over the last three decades certain empirical conditions have given rise to at least four factors of sufficient complexity and significance to challenge the established theoretical model. These consist of the following: 

  1. a rapid increase in fossil discoveries,

  2. technological advances in instrumentation and associated methodologies,

  3. massive amounts of data from the archaeological record, and

  4. the state of contemporary knowledge in molecular biology. 

While many discoveries have fine-tuned the scientific theory of evolution, a fair number of the revisions remain incompatible with the underlying model. At this time no coherent alternative model from which a body of theory may be deduced has been produced.

Many religious people reject biological evolution. Creationists argue that the scientific method has a flaw in that it brings with it cultural assumptions and biases and that it cannot by its own definition ever arrive at absolute truth. Moreover, they argue, there exists a "species barrier" that cannot be abridged. They claim accounts of "new species" break down under analysis since the argument has its foundation on what factors characterizes a species or differentiates one species from another. A Genesis "kind" may or may not be exactly the same as what biologists now call a species. Moreover, the argument reduces to a debate largely over taxons and taxonomy. 

Creations argue further that evolution also has its basis in faith. They reason that if evolution exists then there must be a mechanism that produces evolution. They argue that belief in such a mechanism requires faith. A scientist simply states that the scientific method assumes a knowable universe as a starting point and that this "faith" can be no more than a non-issue since "a knowable universe" does not require a creator per se.

Page last edited: 01/25/06 06:56 PM

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