Evolution • Means “change.” • In a narrower sense referring to organisms, means a permanent change occurring in a species over generations. • Can evolution be a fact?
Forms that evolution may take • Extinction. • Artificial selection. • Natural Selection – Darwin/Wallace 1859.
Natural Selection Natural Selection works with Variation. Variation refers to: • A very specific aspect of a physical trait, e.g. hair texture. • occurring within a species. Must be capable of being passed between generations. • It is assumed to be pre-existing and immutable (in contrast to the theory of Acquired Characteristics and much sci-fi literature. • Is either distributed continuously or discontinuously in a population.
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Variation is subjected to Natural and Sexual selection In the case of natural selection, the force of selection stems from the environment: The environment is all-encompassing, amounting to anything that can potentially kill an individual from the moment it is conceived, e.g. mom’s drug or alcohol use, diet, etc. while pregnant. • It is also specific to the variation under consideration.
In the case of sexual selection the force of selection is the mating choice of the opposite sex. Sexual selection acts upon (and explains) secondary sexual characteristics. Secondary sexual characteristics are those physical traits which differentiate males from females, excluding the sexual organs (the primary sexual characteristics).
Examples of secondary sexual characteristics • Feathers on peacocks/peahens. • Manes on lions. Humans?
Outcomes of selection: • Individual lives or dies. • Individual mates or doesn’t Natural selection cannot work without failure!!!!! What would happen to a population if all organisms lived and mated?
Inheritance One of the most important concepts in the theory of natural selection is Fitness. Definition of fitness: differential reproductive success. Reproduction must result in viable offspring for an individual to be deemed fit. Famous people with 0 fitness: W.A. Mozart., L. van Beethoven, Johannes Brahms, George Washington, Abraham Lincoln, Oprah Winfrey.
People with dubious fitness prospects: The Clintons, Anna Nicole Smith Nadya Suleman? Bottom line: for an individual to have an evolutionary impact, genes must be passed to the next generation and beyond. Was Darwin fit?
Adaptation • Adaptation – permanent change in a population brought about by natural selection. • Not to be confused with adaptability. • It is the net result of hundreds or thousands of instances of selection.
Implications of Natural Selection for Evolution • No goals to evolution. • No progress in evolution. • It is an amoral process. • Traits that are favored are entirely contingent upon a given environment, hence strength or aggression are not necessarily favorable characteristics.