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The hypothesis by Georges Cuvier that each boundary between strata corresponded in time to a catastrophe, such as a flood or drought, that had destroyed many of the species living there at that time.

Natural Selection

Differential success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment. Evolution occurs when natural selection causes changes in relative frequencies of alleles in the gene pool.


All the changes that have transformed life on Earth from its earliest beginnings to the diversity that characterizes it today.


the study of the past and present distribution of species

Vestigial Organ(s)

A structure of marginal, if any, importance to an organism. Vestigial organs are historical remnants of structures that had important functions in ancestors.

Homologous Structure(s)

Structures in different species that are similar because of common ancestry.


A view of Earth's history that attributes profound change to the cumulative product of slow but continuous processes.


Referring to a species that is confined to a specific, relatively small geographic area

Artificial Selection

The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.


Ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences, leading to a classification scheme; the branch of biology concerned with naming and classifying the diverse forms of life.

Hardy-Wemberg Equilibrium

The condition describing population (one that is in genetic equilibrium)


A change in the DNA of a gene, ultimately creating genetic diversity

Directional Selection

Natural selection that favors individuals at one end of the phenotypic range.

Gene Pool

The total aggregate of genes in a population at any one time


an aberration in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated.


The contribution that an individual makes to the gene pool of the next generation compared to the contributions of other individuals

Genetic Drift

Unpredictable fluctuations in allele frequencies from one generation to the next because of a population's finite size

Phenotypic Polymorphism

The existence of two or more distinct morphs (discrete forms), each represented in a population in high enough frequencies to be readily noticeable

Bottleneck Effect

Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.

Intersexual Selection

Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.

Intrasexual Selection

A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.

Gene Flow

Genetic additions to or substractions from a population resulting from the movement of fertile individuals or gametes.


A DNA segment very similar to a real gene but which does not yield a functional product; a gene that has become inactivated in a particular species because of mutation.

Stabilizing Selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

Founder Effect

Genetic drift that occurs when a few individuals become isolated from a larger population, with the result that the new population's gene pool is not reflective of the original population.

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