• [Mechanisms of evolution: Grades 13-16] Evolution occurs through multiple mechanisms.
• [Mechanisms of evolution: Grades 13-16] Evolution results from natural selection acting upon genetic variation within a population.
• [Mechanisms of evolution: Grades 13-16] Evolution results from genetic drift acting upon genetic variation within a population.
• [Mechanisms of evolution: Grades 13-16] Natural selection acts on phenotype as an expression of genotype.
• [Mechanisms of evolution: Grades 13-16] Inherited characteristics affect the likelihood of an organism's survival and reproduction.
• [Mechanisms of evolution: Grades 13-16] Over time, the proportion of individuals with advantageous traits may increase (and the proportion with disadvantageous traits may decrease) due to their chances of surviving and reproducing.
• [Mechanisms of evolution: Grades 13-16] Natural selection can act on the variation in a population in different ways.
• [Mechanisms of evolution: Grades 13-16] Natural selection may favor individuals with one extreme value for a trait, shifting the average value of that trait in one direction over the course of many generations.
• [Mechanisms of evolution: Grades 13-16] Selection favoring an extreme trait value reduces genetic variation in a population.
• [Mechanisms of evolution: Grades 13-16] Natural selection may favor individuals with traits at each extreme of the range for that trait.
• [Mechanisms of evolution: Grades 13-16] Selection favoring individuals with traits at each extreme of a range maintains genetic variation in a population.
• [Mechanisms of evolution: Grades 13-16] Natural selection may favor individuals with an intermediate value for a trait.
• [Mechanisms of evolution: Grades 13-16] Selection favoring an intermediate value for a trait reduces genetic variation in a population.
• [Mechanisms of evolution: Grades 13-16] Smaller populations are more strongly affected by genetic drift than are larger populations.
• [Mechanisms of evolution: Grades 13-16] Genetic drift can cause loss of genetic variation in a population.
• [Mechanisms of evolution: Grades 13-16] Founder effects occur when a population is founded from a small number of individuals.
• [Mechanisms of evolution: Grades 13-16] Founder effects can affect the genetic makeup of a newly started population (and reduce its genetic variation) through sampling error.
• [Mechanisms of evolution: Grades 13-16] Bottlenecks occur when a population's size is greatly reduced.
• [Mechanisms of evolution: Grades 13-16] Bottlenecks can affect the genetic makeup of a population (and reduce its genetic variation) through sampling error.

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Demonstrating and measuring evolution in a laboratory environment with animal species is typically very challenging. However, insects are among the most amenable species for such studies and the bean beetle, Callosobruchus maculatus, is the easiest species in which such studies may be conducted. Bean beetles are agricultural pest insects of Africa and Asia. Females lay their eggs on the surface of beans (Family Fabaceae) and the entire pre-adult parts of the life cycle occur inside the host bean.

CAUTION:
Instructors should caution students to prevent the accidental release of bean beetles from the laboratory environment. Callosobruchus maculatus is a potential agricultural pest insect that is not distributed throughout the United States and Canada. It is essential that you keep your cultures secured in a laboratory environment to ensure that they are not released to the natural environment. Disposal of cultures (and beans (seeds) exposed to live beetles of any life cycle stage) requires freezing (0°C) for a minimum of 72 hours prior to disposal as food waste. If you have any questions about the handling or disposal of bean beetles, please contact Larry Blumer at lblumer@morehouse.edu or 404 658-1142 (voice or FAX). Information also is available at: www.beanbeetles.org in the Handbook section.

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