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Evolution and Genetics

In the 18th century Carolus Linnaeus developed biological taxonomy. He viewed differences and similarities among organisms as part of God’s plan rather than as evidence for evolution. Charles Darwin and Alfred Russel Wallace proposed that natural selection could explain the origin of species, biological diversity, and similarities among related life forms. Natural selection requires variety in the population undergoing selection. Though breeding experiments with peas in 1856 Gregor Mendel discovered that genetic traits pass on as units. These are now known to be chromosomes which occur in homologous pairs. Mendel also formulated the law of independent assortment. Each of the seven traits he studied in peas were inherited independently of all the others. Independent assortment of chromosomes and their recombination provide some of the variety needed for natural selection. But the major source of such variety is mutation, an alteration in the DNA molecules of which genes are made. Biochemical or molecular, genetic studies structure, function, and changes in genetic material- DNA. Genetic changes that provide variety within a population include base substitution mutations, chromosomal rearrangements, and genetic recombination. Population genetics studies gene frequencies in stable and changing populations. Natural selection is the most important mechanism of evolutionary change. Natural selection works with traits already present in the population. If variety is insufficient to permit adaptation to environmental change, extinction is likely. Other mechanisms of genetic evolution complement natural selection. Gene flow and interbreeding keep subgroups of the same species genetically connected and thus impede speciation. The modern synthetic theory of evolution blends the Darwin and Wallace theory of evolution through natural selection with Mendel’s discovery of gene. Microevolution and macroevolution are two ends ( short terms and long terms)  of a continuum of evolutionary change in which gradually changing allele frequencies in a population lead to the formation of new species. Punctuated equilibrium theory states that long periods of stasis (stability ) during which species change little are interrupted by evolutionary leaps.