Download Evolution - Cerritos College

Biology 120 Lab
Cerritos College
DARWINIAN EVOLUTION
(revised 11.17.03)
Darwin Proposed “The Origin Of Species By Natural Selection":
OBSERVATION 1:
"Organisms tend to increase in a geometric ratio."
OBSERVATION 2:
"However, in spite of this, population numbers tend to remain
more or less constant over a long period of time."
DEDUCTION 1:
"Since not all of the individualists produced can survive, there
must be a struggle for existence."
OBSERVATION 3:
"There is variation in every species."
DEDUCTION 2:
"In the struggle for existence, those individuals that are better
adapted to the environment leave behind more offspring than
the less adapted individuals."
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Theory of Natural Selection Made Simple
A. The reproductive potential is great, but
a. Rabbits should cover the Earth, but
B. population tends to remain constant in
size, because
b. they don't, because
C. populations suffer a high mortality.
c. many are caught by predators.
D. Populations exhibit variation which
leads to
d. Some rabbits run faster than others
E. differential survival of individuals.
e. and escape from predators;
F. Individual traits are inherited by their
offspring.
f. so do their young.
G. The composition of the population
changes by the selective elimination
of unfit individuals.
g. Populations of rabbits, as a whole,
tend to run faster than their
predecessors.
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Summary of Main Points:
1.
2.
3.
4.
Variation – Differences exist within a population.
Overproduction – More offspring are produced than can possibly survive.
Struggle – Competition for survival.
Survival of the "Fitter" – Nature selects the best variations
Vocabulary:
evolution – ________________________________________________
natural selection – __________________________________________
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adaptation – ______________________________________________
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differential reproduction – _____________________________________
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genetic polymorphisms – _____________________________________
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gene pool – _______________________________________________
fossil – ___________________________________________________
homologous feature – _______________________________________
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analogous feature – ________________________________________
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genotype – ________________________________________________
phenotype – _______________________________________________
allele – ___________________________________________________