Biology‎ > ‎

Unit 9

Chapter Overview
Students analyze evidence for evolution and scientific explanations of that evidence.  They also analyze and evaluate the mechanism of natural selection and its results.  Students analyze and evaluate the unity and diversity of life as explained by evolutionary theory.  More specifically, students analyze and evaluate various aspects of this scientific theory including evolutionary mechanisms, common ancestry, fossil record, natural selection, adaptation and the development of diversity.

Main Ideas
***Natural selection produces change in populations, not individuals.
***Natural selection and other evolutionary mechanisms lead to the unity and diversity of life.
***Several lines of evidence support the theory of evolution.

***Students may think the theory of evolution explains the origin of life, rather than understanding that the central focus of the theory is on how life changed and diversified after it began and the processes that led to diversification.
***Students may think an individual organism can evolve new characteristics in response to environmental change, rather than understanding that evolution occurs at the population level over the course of generations.
***Students may think evolution implies that organisms are evolving or progressing toward perfection, rather than understanding that evolution refers to changes in population based on environmental pressures and “fitness”.  This fitness, a result of successful genetic combinations or diversity coupled with selection pressure caused by the ever changing environment, leads to changes in populations and not necessarily changes toward “perfection”.


Evolution – A change in the gene pool of a population that results in a successive change over time. 

Charles Darwin – Scientist who identified the process of natural selection; Darwin studied finches on the Galapagos Islands.

Ancestry – An organism’s lineage of descendants.

Population – All of the organisms of one species within a particular ecosystem.

Speciation – An evolutionary event that results in the formation of a new species.

Natural Selection – A mechanism of evolution; the process that results in the survival or reproductive fitness of an individual or group that is best adapted to its environment.

Genetic Variation – The variety of gene combinations that exist within a population.

Fossil Record – The total number of fossils and their locations in rock formations and sedimentary layers which provide information about those organisms.

Homology – Two characteristics that are similar because they originated from a common ancestor.

Molecular Homologies – DNA and RNA similarities between organisms.

Developmental Homologies – Embryonic similarities between organisms of different species.

Vestigial Structure – An organ so reduced in size that it is a nonfunctioning remnant of a similar organ in another species

Biological Fitness – An organism’s ability to survive and produce viable, fertile offspring.

Adaptation – An alteration in an organism’s characteristics that better enables it to survive in its environment.

Reproductive Success – An organism’s ability to pass on its genes.

Overpopulation – More organisms in an area than an ecosystem can support.

Limiting Factor – A biotic or abiotic environmental factor that restricts the growth of a population.

Biodiversity – The total variation of species within a given ecosystem.

Species – A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.

Subspecies – A subdivision of the taxonomic group known as species; these organisms can interbreed.

Punctuated Equilibrium – The theory that species evolve rapidly over short periods of time, followed by long periods of stability where little genetic variation occurs.

Gradualism – The theory that species evolve slowly and gradually over extended periods of time.

Other Valuable Resources

Evidence of Evolution

Evidence of Evolution: Crash Course

Natural Selection: Crash Course

Speciation: Crash Course

Mechanisms of Evolution: Beetles