15-1 Notes: Adaptations and Natural Selection Evolution Unit 15-1 Notes: Adaptations and Natural Selection

Adaptations A hereditary characteristic that helps an organism survive and reproduce in its environment.

Fitness Measure of ability to survive and produce more offspring relative to other members of a population

Animal Observation

So how did these organisms become so well adapted to their environment?

Darwin proposed that animals evolved to fit their environments. Darwin’s Explanation Darwin proposed that animals evolved to fit their environments.

Evolution The change in a population of organisms over time

Darwin’s Explanation Darwin realized that animals have many offspring and some don’t survive. The survivors are better suited to their environment.

He called this process…. Natural Selection

Natural Selection Mechanism by which the environment is the selective agent Mechanism by which evolution occurs Darwin said that in nature, environment creates selective pressure

Steps of Natural Selection Overproduction -organisms have many offspring, but not all will survive.

Steps of Natural Selection 2. Genetic Variation --Individuals vary within a population --New traits appear due to genetic mutations

Steps of Natural Selection 3. Struggle to Survive --Organisms compete for resources (food, water, shelter, and mates) --Organisms have to get away from predators

Steps of Natural Selection 3. Struggle to Survive --Some adaptations allow organism to survive at higher rate and individuals are “naturally selected” to survive and produce offspring

Steps of Natural Selection 4. Descent with Modification --Organisms with the best adaptations will survive and reproduce passing these good traits down to their offspring

Natural Selection acts on phenotypes not genotypes As environment changes, different traits will become beneficial.

Examples of Natural Selection

Insects become resistant to insecticides. Insecticide kills off most insects.

Those insects that survive have a gene that makes them resistant.

Resistant insects reproduce with other resistant insects.

Their offspring have the resistant gene Their offspring have the resistant gene. Insecticides don’t work very well over time!

Other examples of evolution: Bacteria become resistant to antibiotics Don’t take antibiotics unless you have a bacteria infection!

Other Examples of Natural Selection: Peppered Moths in England There were more light moths (on light trees) before 1850. There were more dark moths (on light trees) after 1850.