Question

1.Why is the theory of evolution a scientific theory and not a scientific hypothesis? Explain an example relevant to zoology.

2. Describe the inter-relationship between random genetic mutation, selection (natural, sexual or kin) and reproductive barriers (allopatric, parapatric or sympatric speciation) and how they result in the evolution of species

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Answer 1

The scientific definition of the word "theory" is different from the definition of the word in colloquial use. In the vernacular, "theory" can refer to guesswork, a simple conjecture, an opinion, or a speculation that does not have to be based on facts and need not be framed for making testable predictions.

In science, however, the meaning of theory is more rigorous. A scientific theory is "a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses." Theories are formed from hypotheses that have been subjected repeatedly to tests of evidence which attempt to disprove or falsify them. In the case of evolution through natural selection, Darwin conceived the hypothesis around 1839, and made a first draft of the concept three years later in 1842. He discussed this widely with many of his intellectual companions, and conducted further research in the background to his other writings and work. After years of development, he finally published his evidence and theory in On the Origin of Species in 1859.

The "theory of evolution" is actually a network of theories that created the research program of biology. Darwin, for example, proposed five separate theories in his original formulation, which included mechanistic explanations for:

1. populations changing over generations
2. gradual change
3. speciation
4. natural selection
5. common descent^[24]

Since Darwin, evolution has become a well-supported body of interconnected statements that explains numerous empirical observations in the natural world. Evolutionary theories continue to generate testable predictions and explanations about living and fossilized organisms.

Phylogenetic theory is an example of evolutionary theory. It is based on the evolutionary premise of an ancestral descendant sequence of genes, populations, or species. Individuals that evolve are linked together through historical and genealogical ties. Evolutionary trees are hypotheses that are inferred through the practice of phylogenetic theory. They depict relations among individuals that can speciate and diverge from one another. The evolutionary process of speciation creates groups that are linked by a common ancestor and all its descendants. Species inherit traits, which are then passed on to descendants. Evolutionary biologists use systematic methods and test phylogenetic theory to observe and explain changes in and among species over time. These methods include the collection, measurement, observation, and mapping of traits onto evolutionary trees. Phylogenetic theory is used to test the independent distributions of traits and their various forms to provide explanations of observed patterns in relation to their evolutionary history and biology. The neutral theory of molecular evolution is used to study evolution as a null model against which tests for natural selection can be applied.