Natural selection acts on phenotypic variations in populations Enduring Understanding 1A Change in genetic makeup of a population over time is evolution Essential knowledge 1.a.2 Natural selection acts on phenotypic variations in populations

Environments change and act as selective mechanisms on populations. Flowering time in relation to global climate change. Many plants are flowering earlier now than at any time in the last 250 years. A change in timing of plant flowering can disrupt the creatures that pollinate them. Similarly, changes in timing of plant or insect behavior can affect the birds that use them as food supplies.

The Peppered Moth Moth color changed after pollution from factories changed the color of tree trunks.

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 and the population.

Sickle cell anemia A mutation in the gene for the protein hemoglobin causes misshapen blood cells and decreased ability to carry oxygen. People that have sickle cell anemia, and those that carry the mutation are immune to the malarial parasite.

DDT Resistance in Insects Insect populations can develop resistance to pesticides like DDT. Some may have the genes that give them immunity and then pass those genes on to their offspring so that future generations are no longer impacted by the pesticide.

Humans impact variation in other species. Artificial selection Humans select traits in plants and animals by breeding individuals with features they feel are desirable.

Loss of genetic diversity in crop plants. Since the 1900s, some 75 percent of plant genetic diversity has been lost as farmers worldwide have left their multiple local varieties and landraces for genetically uniform, high-yielding varieties. Less genetic diversity leads to more vulnerability to pests and disease.

Overuse of antibiotics More resistant strains of bacteria are evolving in response to widespread use of antibiotics.