This is a comprehensive and detailed note on chapter 22;Evolution, Natural Selection, Mass Extinctions for Biol 141.
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Chapter 22
Introduction:
1. populations—individuals of the same species that live in the same area at the same time
a. Populations of organisms evolve
2. Darwin published his theory in 1859 in a book called On the Origin of Species by Means
of Natural Selection
a. protest throughout Europe because the leading explanation for the diversity of
organisms was an idea called special creation.
i. Special creation held that:
1. all species are independent, in the sense of being unrelated to
each other
2. life on Earth is young—perhaps just 6000 years old
3. species are incapable of change
3. What is a theory? → Has a pattern and process component
a. The pattern component is a statement that summarizes a series of observations
about the natural world. The pattern component is about facts—about how things
are in nature. (evolution)
b. The process component is a mechanism that produces that pattern or set of
observations. (natural selection)
22.1:
1. Evolution by natural selection was a revolutionary idea
2. Views of species
a. Plato: typological thinking- every organism was an example of a perfect essence
created by God and unchanging. Species were fixed and did not change
b. Aristotle: used typological thinking on a scale- species were fixed typed
organized into a sequence based on increased size and complexity
(minerals/plants at the bottom and work way up to humans then Gods)
i. Remained a popular belief for over 20 centuries→ we still look at “lower”
and “higher” species today and seperate humans from others
c. Lamark: broke down typological thinking and introduced evolution- the idea that
species are not static but change through time
i. His theory was still based on the scale of nature
ii. Proposed that simple organisms originate at the base of the scale by
spontaneous generation and then evolve by moving up the scale over
time (progressive because always producing larger and more complex
species)
iii. Claimed that species change through time via the inheritance of acquired
characters
1. as an individual develops, its phenotype changes in response to
challenges posed by the environment, and it passes on these
phenotypic changes to offspring
, a. Example: giraffes develop long necks as they stretch to
reach leaves high in treetops, and they then produce
offspring with elongated necks.
d. Darwin and Wallace: evolution by natural selection
i. Evolution occurs because there is variation among species and
individuals with certain traits leave more offspring than others do
ii. Used population thinking: individuals in a population were the key to
understanding evolution
iii. Why is was revolutionary?
1. Suggests that species change (are not static)
2. Replaced typological thinking with population thinking
3. It was scientific- mechanism, can make observations, predictions,
and create experiments
22.2:
1. Darwin described evolution as descent with modification
2. Natural selection makes 2 key predictions:
a. Species change throughout time
b. Species are related by common ancestry
3. Evidence that species change throughout time:
a. Key terms:
i. Fossil: any trace of an organism that lived in the past
ii. Fossil record: all fossils that have been found on Earth and described
iii. Extant species: species living today
b. Evidence 1: Vastness of geologic time
i. James Hutton proposed uniformitarianism- geological processes
occurring today are similar to what occurred in the past
ii. Studied rock formation
1. Sedimentary rocks form from sand or other materials and are
deposited in layers
a. The rocks form at quite a slow rate
2. Charles Lyell used this information to place fossils in an age
sequence based on what layer of rock they were in (older layers at
the bottom)
3. A geological time scale was created: eons, eras, periods that
represent major events in the planet's history
iii. Marie Curie discovered radioactivity in the late 1800’s
1. Radioactive decay acts as a “natural clock” in which the decays of
natural elements can be used to measure different time scales
a. Earth is about 4.6 billion years old
c. Evidence 2: Extinction changes the species present over time
i. Scientist found fossils of never before seen species
1. First proposed that these species would be found in parts of the
globe yet to be explored
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