Natural Selection

***The following notes are taken directly from Population, Genetics and Natural Selection– Chapter 4 of  Ecology:  Concepts and Applications, 5th edition, by Manuel C. Molles Jr.**

CHAPTER 4:  POPULATION GENETICS AND NATURAL SELECTION

In 1835, Charles Darwin visited the Galapagos Islands and became convinced various populations had evolved from ancestral form.

–He theorized that some individuals would have a competitive advantage conferred by favorable characteristics; this is known as The Theory of Evolution by Natural Selection.

Natural Selection can be summarized as follows:

1. Organisms beget like organisms. (Offspring appear, behave, function, and so forth like their parents.)

2.There are chance variations between individuals in a species.  Some variations (differences among parents) are heritable (passed on to offspring).

3.  More offspring are produced each generation than can be supported by the environment.4.  Some individuals, because of their physical or behavioral traits, have a higher chance of surviving and reproducing than other individuals in the same population.——-

*Darwin proposed that differential survival and reproduction of individuals would produce changes in species populations over time.*The evolutionary process that changes anatomy, physiology, or behavior, resulting in an improved ability of the members of a poplulation to live in a particular environment is known as adaptation.


*Gregor Mendel discovered characteristics pass from parents to offspring in form of discrete packages called genes.  He also discovered alleles–alternative forms of genes (some of which are “dominant” and others “recessive.”)VARIATION WITHIN POPULATIONS


*Phenotypic variation among individuals in a populatoin results fr
om the combined effects of genes and environment.*Phenotypic plasticity is the variation a mong individuals in form and function as a result of environmental influences.*In order to understand how populatoins can evolve, we need to first understand some aspects of the genetics of populations, or population genetics.HARDY WEINBERG

*The Hardy-Weinberg Equilibrium Model helps identify evolutionary forces that can change gene frequencies in populations.

*The Hardy-Weinberg Principle states that in a population mating at random in the absence of evolutionary forces, allele frequencies will remain constant.

*Change in allele frequencies due to chance or random events is called genetic drift.

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