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• Chapter 22~ Descent with Modification: A Darwinian View of Life

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I. Early Biology

• Scientists knew that organisms had changed

• Fossil evidence

• Age of the Earth

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Evolutionary history

• Linnaeus: taxonomy

• Hutton: gradualism

• Lamarck: evolution

• Malthus: populations

• Cuvier: paleontology

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• Lyell: uniformitarianism

• Darwin: evolution• Mendel: inheritance• Wallace: evolution

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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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Descent with Modification, I• 5 observations: • 1- Exponential fertility

• 2- But Stable population size

• 3- Limited resources • 4- Individuals vary

• 5- Heritable variation

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Descent with Modification, II• 3 Inferences:

• 1- Struggle for existence

• 2- Non-random survival

• 3- Natural selection (differential success in reproduction)

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Evolution• Evolution:

the change over time of the genetic composition of populations

• Natural selection:populations of

organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success)

• Evolutionary adaptation: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction

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November 24, 1859

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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

• Biogeography• Fossil Record• Anatomy & Physiology• Embryology• Biochemistry

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Evolution evidence: Biogeography

• Geographical distribution of species

• Examples: • Islands vs. Mainland

– Australia vs. Continents

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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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Anatomy- Homologous Structures

• Common evolutionary origin. • Similar in arrangement or

arrangement and function.• 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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Evolution evidence: Molecular

Biology

• Similarities in DNA, proteins, genes, and gene products

• Common genetic code

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Final words…...

• “Absence of evidence is not evidence of absence.”