Evolution and Natural Selection

Evolution and Natural Selection

What Evolution is NOT

Change in a gene pool over time What Evolution IS

Evolution unites all fields of biology! Cell biology Genetics/DNA Ecology Biodiversity/Taxonomy

Carolus Linnaeus Developed the naming system that we use to classify organisms today He grouped organisms with similar characteristics together because their characteristic implied they were more closely related

Jean-Baptiste Lamarck Developed the leading theory of evolution before Darwin Said that organisms acquired new characteristics over their lifetime through use/disuse, and could pass those new characteristics on to their offspring

Geologic Change In the 1700 s scientists started to develop theories about how the Earth had changed over time These theories made Charles Darwin think about how life had also changed over time

Catastrophism Things like volcanoes and earthquakes caused mass extinctions and developed new landforms George Cuvier

Gradualism Changes on Earth occur in small steps over long periods of time James Hutton

Uniformitarianism Geologic processes add up over long periods of time to cause great change Charles Lyell

Charles Darwin Set sail on the HMS Beagle in 1831 Recorded information about the organisms encountered across the world Made most of his key observations in the Galapagos Islands

What did Darwin observe? Variations among similar species Variations are differences in the physical traits between individuals Species on each island had differences He thought that maybe the differences were a result of different ecosystems and conditions on each island

Because the variations between island species often corresponded to their environment, Darwin hypothesized that the species had adapted to their conditions An adaptation is a feature that allows an organism to survive better in its environment Adaptation

Artificial Selection Artificial Selection means that humans choose the traits they see as beneficial in other organisms and breed those organisms to make those traits more prominent People have been doing artificial selection for thousands of years! Artificial selections leads to evolution

Individuals that have inherited beneficial adaptations produce more offspring on average than other individuals Natural Selection acts on the phenotype of populations The environment acts as a selective agent-it puts pressure on populations to change Natural Selection

Natural Selection is not always at work! Certain conditions have to be met for natural selection to occur in a population The trait must be heritable Overproduction of offspring-more babies born than what the environment can support Variation-some individuals have the trait, some don t Differential reproduction-individuals with the trait produce more offspring than individuals without it

Survival of the Fittest Fitness is a measure of how well an individual can survive and reproduce relative to other individuals The fittest individual is not necessarily the biggest, smartest, or strongest! Fitness depends on the environment! If the environment changes, what trait are fit for the environment also change!

Evidence for Evolution

Darwin found evidence from a wide range of sources to support his argument for natural selection.

Older fossils are in lower layers of rock than newer fossils Fossils were found of many organisms that had similar characteristics, but were different species than living organisms Types of fossils also changed over time Fossils

Geography Closely related species are usually found in areas geographically close to each other Species that live in similar conditions across the world have similar adaptations

Embryology There are structural similarities between the embryos of many different species

Homologous Structures Similar structure, different function-result of common ancestor (Divergent evolution)

Analogous Structures Different structure, same function-no common ancestor (convergent evolution)

Vestigial Structures Evolutionary leftovers-were useful in ancestors, but no longer serve any purpose

DNA Sequence Analysis The more closely related two organisms are, the more DNA sequences they have in common

How Populations Evolve

Genetic Variation is a good thing! More versions genes means that the population is more resilient-if the environment changes, the population is better equipped to survive it

Gene Pool The number of different traits in a population

Sources of Variation There is only one way for completely new traits to enter into a population: Mutation When new individuals enter a population through migration, they also can bring new traits/variations

5 Mechanisms of Evolution 1. Population shrinks (genetic drift) 2. Sexual Selection 3. Mutation 4. Gene Flow 5. Natural Selection

Microevolution vs. Macroevolution Microevolution-changes in the gene pool Macroevolution-new species

Types of Natural Selection Directional Stabilizing Disruptive

Directional Selection One extreme phenotype becomes more common

Stabilizing Selection The intermediate phenotype becomes more common, extremes are selected against

Intermediate trait is selected against, extreme phenotypes become more common

Speciation The process where reproductively isolated populations evolve to become two different species.

Reproductive Isolation is Key to Speciation Reproductive isolation is some kind of barrier that prevents two members of different populations from mating or producing offspring

What causes reproductive isolation? Behavioral isolationdifferences in courtship or mating behaviors Geographic isolationphysical barriers that divide a population into two or more groups Temporal isolationbarriers involving timing of reproduction

Divergent Evolution One common ancestor evolves into multiple species

Convergent Unrelated species develop similar adaptations

Coevolution Two species evolve in response to each other

Extinct vs. Extant Extinct-no longer exists Extant-still exists

Punctuated Equilibrium Populations evolve very quickly, followed by periods of stasis

Adaptive Radiation Process where ancestral species diversifies rapidly (hundreds to thousands of years) into many new species after a change in the environment.