Evolution and Natural Selection

Population – group of organisms of the same species living together in a given region Natural Selection – process whereby organisms with favorable variations survive and produce more offspring than less well-adapted organisms Proposed by Darwin Key mechanism of evolution Natural Selection in Populations

Lamarck’s theory of evolution Inheritance of acquired characteristics – the characteristics an organism develops over time can be passed on to offspring – Mouse gets its tail cut off, offspring should have no tails – Giraffe stretches its neck out to reach tall leaves, offspring should have longer necks Incorrect, not supported by scientific evidence Stimulated thought about evolution Scientists who came before Darwin

No individual is capable of evolving Natural selection produces changes in populations, not individual organisms Organism may be born with a favorable mutation – Example: dark-fur for pocket mouse living on lava rock Acquired traits are not passed on to offspring Natural Selection in Populations

Random mutations - color variations in moth population – Allows the moths to blend into tree trunks – Harder for birds to locate “camouflaged” moths Natural selection occurs – Moths with mutation survive and reproduce – Favorable coloring is passed on to offspring Natural Selection in Moth Population Image by Gilles San Martin (Own work) [CC-BY-SA-3.0]

Natural selection leads to development of Adaptations Genetic diversity Natural Selection

Adaptation – trait that helps an organism to survive and/or reproduce in its unique environment Natural selection favors variations of traits that increase organism’s ability to survive and reproduce What are Adaptations? Images by L. Shyamal (Own work) [CC-BY-SA-2.5]

Example: – Darwin’s Finches – Rock Pocket mouse Development of Adaptations

Genetic diversity – differences in genetic characteristics among organisms within the same species or among different species Natural selection can increase or decrease genetic diversity What is Genetic Diversity? Image by Graphodatsky et al. [CC-BY-2.0]

Monday in Biology Rock Pocket Mouse QUIZ – You will have 15 minutes to complete the quiz over the Rock Pocket mouse – Two grades One lab and one quiz grade (both major grades) Take notes over Evolution Vimeo Video: Selection, Gene Flow, Genetic Drift – Handouts and questions

Types of Natural Selection and other mechanisms of evolution

Phenotypes Frequency Phenotypes Frequency Phenotypes Frequency Phenotypes Frequency Directional Diversifying Stabilizing Three major types of natural selection can affect the diversity within a species 1.Directional 2.Diversifying 3.Stabilizing Genetic Diversity Within a Species

Phenotypes Frequency Phenotypes Frequency Directional selection – a single variation of a trait that was not previously favored is now favored in a species – Result of migration or environmental changes Directional Selection May increase or decrease diversity within a species

Phenotypes Frequency Phenotypes Frequency Diversifying selection – multiple variations of a trait are favored in a single species – Increases diversity Diversifying Selection (Disruptive)

Phenotypes Frequency Phenotypes Frequency Stabilizing selection – a single variation of a trait is favored in a species – Decreases diversity Stabilizing Selection

Mechanisms of Evolution 1.Natural Selection “survival of the fittest” 2.Mutations create new alleles 3.Migration moves alleles into and out of a population 4.Genetic drift happens when random events change the allele frequencies of small populations 5.Sexual Selection non-random mating

Giraffe video

Tuesday/Thursday

Species A group of organisms that can interbreed in nature and produce fertile offspring

Speciation How Do New Species Form? Must be isolated from other populations for a long period of time. Different selection pressures cause different traits to be selected for or against.

Geographic Isolation Species are separated from each other by a physical barrier

Geographic Isolation The Kaibab and Albert squirrels are separated by the Grand Canyon

Behavioral Isolation Species cannot interbreed because they have different mating rituals or behavior

Temporal Isolation Species mate at different times of the day or the year

Adaptive Radiation A single species evolves into many species Occurs as new opportunities for survival arise

Co-evolution When two species evolve together in response to changes in each other Example: Bees and Flowers

Evidences of Evolution

Homologous Structures Similar body structures that are adapted in different ways for different organisms Provide evidence that related organisms descended, with modifications, from a common ancestor

Vestigial Structures The structures of organisms that remain from a common ancestor, but may no longer affect its ability to survive and reproduce Example: Appendix, Tail Bone

Analogous Structures Unrelated organisms in similar environments develop similar adaptations. Example: Flight of Insects vs. Birds vs. Bats

Fossil Record The fossilized remains of organisms found in the layers of rock and soil Shows that the diversity of organisms has changed over time

Fossil Record

Embryology Organisms with a common ancestor share similar stages of development.

DNA Analysis All organisms use the same four bases for their DNA (genetic code). The more similar two sequences of DNA are, the more recent their common ancestor, or the more closely related the organisms are.

DNA Analysis Modern biologists compare DNA sequences to determine which organisms are most-closely related to each other