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The Theory of Natural Selection

Biology I

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I. Early Biology

• Scientists knew that organisms had changed

• Fossil evidence

• Age of the Earth

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Lamarck

• Changes from simple to complex

• Organisms want to adapt or change

• Acquired characteristics were inherited (passed on)

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Lamarck

• Later disproved

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II. Darwin• At 21, took a job as

a naturalist on the HMS Beagle

• Collected specimens, took notes of different organisms

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His voyage:

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II. Darwin

• Sailed to Galapagos Islands

• All new species, but similar to those found elsewhere

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• Finches most famous• Had slightly different beaks from island to island• Differed by their diet

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II. Darwin

• Darwin 22 years developing theory of natural selection

• Pressured into publishing by Wallace

• Published On the Origin of Species by Natural Selection

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III. Natural Selection 4 Requirements

•1. Variation exist

• 2. Differential Reproduction

• 3. Heredity Best suited survive and reproduce

• 4. Lots of Time

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1. Variation

• Variations exist– Color, size, speed, etc.

• Variations are genetically linked

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2. Differential Reproduction

• Organisms produce more offspring than can survive– creates competition and

Survival of the Fittest = Only the best are going to survive

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Heredity

• Beneficial variations survive, pass traits to offspring

• Passed through DNA

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Natural Selection

• Over time variations become more frequent in population

• Results in population being different than ancestors

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EvolutionEvolution is the change in a population over time

Natural Selection - Remember the Giraffe?How did it get the long neck?

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Evidence of Change

• Fossil Record• Anatomy & Physiology• Embryology• Biochemistry

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Fossils

• Remains or traces of living organisms

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Physiology Mimicry-An adaptation

• Enables one species to resemble another species.

• Ex.-harmless species looks like a harmful one, good tasting vs. bad tasting.

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Camouflage-An adaptation

• A species blends in with its environment to avoid predators.

• Ex.- peppered moth,

leaf frog

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Anatomy- Homologous Structures

• Common evolutionary origin. Similar in arrangement or function or both.

• Example: forelimbs of a whale, a crocodile and a bird wing.

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Anatomy- Analogous Structures

• No common evolutionary origin, but similar in function.

• Wings of a bat and wings of a butterfly.

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Anatomy- Vestigial Structures

• No function now but was probably useful to an ancestor.

• Ex. A whale has leg bones, a snake has leg bones

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Embryology

• Earliest stage of growth and development • Embryos of a fish, a chicken, a pig, a cow,

a rabbit, and a human are almost identical.• They all have gill slits and a tail.

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Biochemistry

• Comparisons of DNA and RNA • Now monera (prokaryotes) is divided into

two separate kingdoms based on their biochemistry.

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V. Mechanisms of Evolution

• Genetic Drift• Gene Flow • Artificial Selection • Natural Selection

Sexual Selection

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Genetic Drift

• Change in allele frequency by CHANCE

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GENE FLOW

• Bottleneck effect

• Founders effect

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Gene Flow

• Change in allele frequency as a result of MIGRATION

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Sources of Variation• GENE FLOW moves genes among

populations• SEXUAL REPRODUCTION

introduces new gene combinations • Random MUTATIONS in DNA

lead to the formation of new alleles (sound familiar?)

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Mutations

• Can be beneficial, neutral, or harmful for the organism

• Only mutations in gametes are inherited by offspring

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Bell:

• What is the difference between Analagous structures, Homologous Structures, and Vestigial Structures?

• What are the 4 requirements of Natural Selection?

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AGENDA•Intro to Classification•Natural Selection Today

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