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Natural Selection
Population can change over generations if individuals that posses certain heritable traits leave more offspring than other individuals.
Result is evolutionary adaptation.
If enviornment changes over time, or if individuals of a particular species move to a new enviornment, natural selection may result in adaptation to these new conditions, sometimes giving rise to new species in the process.
Evolutionary Adaptation
An accumulation of inherited characteristics that enahnce organisms' ability to survive and reproduce in specific enviornments.
A change over time in the genetic composition of a population.
Scala nature: arranged on increasing complexity
Coincided with the Old Testament: all species are individually designed by God and therefore are perfect.
Founder of taxonomy (branch of biology concerned with baming and classifying organisms)
Adopted nesting classification system, grouping similiar species into increasinly general categories
Georges Cuvier
Largely developed paleontolgy, the study of fossils.
The deeper/older the strata, the more dissimilar the fossils are from current life.
Advocated catastrophism, speculating that each boundary between strata represents a catastrophe, such as a flood/drought, that destroyed many of the species at that time.
James Hutton
Advocated gradualism, the idea that profound change can take place through the cumulative effect of slow but continuous processes.
Charles Lyell
Incorporated Hutton's theory into uniformatitarianism, the same geologic processes re operating today as in the past, and at the same rate.
Jean-Baptiste de Lamarck
Two principles:
Use and disuse, parts of the body that are used extensively become larger and stronger, while those that are not used deteriorate.
Inheritance of acquired characteristics, an organism could pass these these modifications to its offspring.
Alfred Russel Wallace
Developed a theory of natural selection similar to Darwin's.
The Origin of Species
Evolution expalins life's unity and diversity and that natural selection is a cause of adaptive evolution.
Descent with Modification
Unity in life, all organisms related through descent from an ancestor that lived in the remote past.
Ernst Mayr
Observations and inferences from Darwin.
Artificial selection
Selecting and breeding individuals that possess desired traits.
A group of interbreeding individuals belonging to a particular species and sharing a common geographic area.
Homologous structures
EX: Arms, forelegs, flippes, and wings of different mammals.
Represent variations on a structural theme that was present in their common ancestor.
Vestigal organs
Structures of marginal, if any, importantce to the organism. Remnants of structures that served important functions in the organism's ancestors.
A change in the genetic makeup of a population from generation to generation.
Gene pool
The aggregate of genes in a population at any one time. Consists of all alleles at all gene loci in all individuals of the population. If only one allele exists at a particular locus in a population, that allele is said to be FIXED in the genepool, and all individuals are homozygous for that allele.
Conditions for Hardy-Weinberg Equilibrium
1. Extremely large population size.
2. No gene flow.
3. No mutations.
4. Random mating.
5. No natural selection.
Sexual recombination
Far more important than mutation on a generation-to-generation time scale in rpoducing the variations that make adaptation possible. Nealry all phenotypic variations based on genetic differences result from recombinational shuffling of the existing alleles in the gene pool.
Genetic drift
Similar deviations from the expected result, which occur, because real populations are finite in size rather than infinite, explain how allele frequencies can flucuate unpredictably from one generation to the next.
Bottleneck effect
A sudden change in the enviornment, such as a fire or flood, may drastically reduce the size of a population. In effect, the survivors have passed through a restrictive "bottleneck" and their gene pool may no longer be reflective of the original population's gene pool.
Founder effect
When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool is not reflective of the source population.
Gene flow
Genetic additions to and/or subtractions from a population resulting from the movement of fertile individuals or gametes. Reduces differences between populations.
Phenotypic polymorphism
If two or more distinct morphs are each represented in high enough frequencies to be readily noticeable.
The contribution an individuals makes to the genepool of the next generation, relative to the contributions of other individuals.
Relative fitness
The contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus.
Directional selection
Most common when a population's enviornemnt changes or when members of a population migrate to a new habitat with differenct enviornmental conditions than their former one.
Disruptive selection
When conditions favor individuals on both extremes of a phenotypic range over individuals with intermediate phenotypes.
Stablizing selection
Act against extreme phenotypes and favors intermediate variants. This mode of selection reduces variation and maintains the status quo for a particular phenotypic character.
Balancing selection
Occurs when natural selection maintains stable frquencies of two or more phenotypics forms in a populations, a state called balanced polymorphism. This type of selection includes heterzygote advantage and frequency dependent selection.
Heterozygous advantage
If individuals who are heterozygous at a particular gene locus ahve greater fitness than the homozygotes, natural selection will tend to maintain two or more alleles at the locus.
Frequency-dependent selection
The fitness of any one morph declines if it becomes too common in the population.
Genes that have become inactivated by mutations, genetic noise is free to accumulate in all parts of the gene.

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