Essential knowledge 1.A.2:

Natural selection acts on phenotypic variations in

populations.

Environments change and act as selective mechanism on populations.

http://concord.org/stem-resources/natural-selection

Example 1: Flowering time in relation to global climate change

Ecology. 2008 Feb;89(2):332-41. Global warming and flowering times in Thoreau's Concord: a community perspective. Miller-Rushing AJ, Primack RB. As a result of climate change, many plants are now flowering

measurably earlier than they did in the past. Concord, Massachusetts - Records began with six years of

observations by the famous naturalist Henry David Thoreau from 1852 to 1858, continued with 16 years of observations by the botanist Alfred Hosmer in 1878 and 1888-1902, and concluded with our own observations in 2004, 2005, and 2006.

From 1852 through 2006, Concord warmed by 2.4 degrees C due to global climate change and urbanization.

Using a subset of 43 common species, we determined that plants are now flowering seven days earlier on average than they did in Thoreau's times.

Example 2: Peppered moth

Misconceptions

Changes in phenotype are directed by changes in the environment.

False Phenotypic variations are not directed

by the environment but occur through random changes in the DNA and through new gene combinations.

Some phenotypic variations significantly increase or decrease fitness of the organism and the population.

Example 1: Sickle cell anemia

Example 2: DDT resistance in insects

Humans impact variation in other species.

Example 1: Artificial Selection

Example 2: Loss of genetic diversity within a crop species

Monoculture – Planting only one crop How is this affecting the gene pool?

Example 3: Overuse of antibiotics

Essential knowledge 1.A.2:

Natural selection acts on phenotypic variations in

populations.

Genetic Drift

Genetic drift is a nonselective process that can lead to large changes occurring in small populations.

Random drift is caused by recurring small population sizes, severe reductions in population size called "bottlenecks" and founder effect where a new population starts from a small number of individuals.

Bottleneck Effect

Founder Effect

Reducing Genes can increasing differences

Reduction of genetic variation within a given population

can increase the differences between populations of the same species.

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