Key Terms And Concepts

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mutation

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a sudden departure from the parent type in one or more heritable characteristics, caused by a change in a gene or a chromosome.

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selection

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any natural or artificial process that results in differential reproduction among the members of a population so that the inheritable traits of only certain individuals are passed on, or are passed on in greater proportion, to succeeding generations.

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Fossil

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A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded and preserved in the earth's crust.

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population

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all the individuals of one species in a given area.

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sediments

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Solid fragmented material, such as silt, sand, gravel, chemical precipitates, and fossil fragments, that is transported and deposited by water, ice, or wind or that accumulates through chemical precipitation or secretion by organisms, and that forms layers on the Earth's surface. Sedimentary rocks consist of consolidated sediment.

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convergent evolution

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The adaptive evolution of superficially similar structures, such as the wings of birds and insects, in unrelated species subjected to similar environments.

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divergent evolution

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the process by which a species evolves into two or more descendant or different forms; also, the process of tracing two or more species back to a common ancestor

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adaptation

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the ability of a species to survive in a particular ecological niche, esp. because of alterations of form or behavior brought about through natural selection.

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extinct

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no longer in existence; that has ended or died out

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gradualism

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a tenet in evolutionary theory maintaining that species evolve slowly and continuously over long periods of geological time.

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divergence

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The evolutionary tendency or process by which animals or plants that are descended from a common ancestor evolve into different forms when living under different conditions.

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speciation

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the formation of new species as a result of geographic, physiological, anatomical, or behavioral factors that prevent previously interbreeding populations from breeding with each other.

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absolute dating

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the determination of the age of an object with reference to a specific time scale, such as a fixed calendar or in years before present (BP), based on measurable physical or chemical qualities or associations with written records

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relative dating

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in archaeology, the arrangement of artifacts or events in a sequence relative to one another but without ties calendrically measured time; the arrangement of artifacts in a typological sequence or seriation

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vestigial structures

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remnants of once useful structures

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homologous structures

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are characteristics which are shared by related species because they have been inherited in some way from a common ancestor.

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behavioral isolation

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An isolating mechanism in which two allopatric species do not mate because of differences in courtship behavior.

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temporal isolation

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is a category of mechanisms that prevent two or more populations from exchanging genes.

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reproductive isolation

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is a category of mechanisms that prevent two or more populations from exchanging genes.

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punctuated equilibrium

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In the fossil record, long periods of little change in lineages interspersed with brief periods of relatively rapid change.

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variation

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Marked difference or deviation from the normal or recognized form, function, or structure.

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Hardy-weinberg principle

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shows that in bigger populations of a species, inheritance can't change the frequencies of the different alleles.

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descent with modification

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the unity underlying homology and homoplasy as seen through an analysis of development and evolution.

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common ancestor

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any person to whom two or more persons claim descent; also, the most recent ancestral form or species from which two different species evolved

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survival of the fittest

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The idea that species adapt and change by natural selection with the best suited mutations becoming dominant.

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genes

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a region of DNA that controls a hereditary characteristic

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common descent

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the idea that we can take these diagrams all the way back, until there is one single ancestral species.

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directional selection

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when natural selection favors a single phenotype and therefore allele frequency continuously shifts in one direction.

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stabilizing selection

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favors the norm, the common, average traits in a population.

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disruptive selection

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favors the extremes traits in a population.

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genetic drift

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the statistical effect that results from the influence that chance has on the survival of alleles

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founder effect

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when a new colony is started by a few members of the original population.

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genetic equilibrium

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a hypothetical state in which a population is not evolving because the allele frequencies remain constant over time.

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relative frequency

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is another term for proportion; it is the value calculated by dividing the number of times an event occurs by the total number of times an experiment is carried out.

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single-gene trait

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expressions of two alleles at one gene.

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polygenic trait

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traits are determined by the combined effect of more than one pair of genes.

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co-evolution

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is the mutual evolutionary influence between two species.

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adaptive radiation

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A look at natural selection in the long term

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era

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a period of time marked by distinctive character, events, etc.

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geographical isolation

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a form of reproductive isolation in which members of a population become separated from another population by geographical barriers that prevent the interchange of genes between the separated populations.