Download Biology Chapter 13: The Theory of Evolution

Biology Chapter 13: The Theory of Evolution
Section 1: The Theory of Evolution by Natural Selection
Darwin Proposed a Mechanism for Evolution
1. Science Before Darwin’s Voyage
a. Most scientists thought that each species was a divine creation that
didn’t change
b. Scientist started looking for explanations of fossils
c. Scientists offered different theories
i. Lamarck (1809) proposed that organisms change over time
because of use/disuse of their physical attributes – changes are
then passed on to offspring – he said that these changes were
connected to the conditions of life (environmental conditions)
2. Darwin’s Observations
a. During Beagle voyage, Darwin found evidence showing that species
change
b. Darwin found fossils of armadillos in S. America that resembled
armadillos living then
c. Some of the species Darwin found on the Galapagos Islands
resembled those found on S. American coast – might have migrated
and then changed
d. After returning from the voyage, Darwin studied his data and became
convinced of evolution
3. Growth of Populations
a. 1798 Thomas Malthus wrote that human populations are able to
increase faster than the food supply can
Evolution by Natural Selection
*Darwin decided that Malthus’s hypothesis applied to all species
*Darwin’s association:
Individuals that have physical or behavioral traits that better suit their
environment are more likely to survive and will reproduce more successfully
than those that do not have such traits. OTHERWISE KNOWN AS: Natural
Selection
1. Publication of Darwin’s Work
a. 1844 Darwin wrote down his ideas about evolution and natural
selection – didn’t publish until later due to public ridicule
2. Darwin’s Theory
a. Gained acceptance slowly from biologists
b. Theory is supported by these 4 major points:
i. Variation exists within the genes of every population or species
ii. In a particular environment, some individuals of a population or
species are better suited to survive
iii. Over time, the traits that make certain individuals of a
population able to survive and reproduce tend to spread in that
population
iv. There is overwhelming evidence from fossils and many other
sources that living species evolved from organisms that are
extinct
Darwin’s Ideas Updated – updated from new discoveries by biologists in genetics
1. Change Within Populations
a. Natural selection causes the frequency of certain alleles in a
population to increase/decrease over time
b. Mutations and the recombination of alleles that occurs during sexual
reproduction provide endless sources of new variations for natural
selection to act on
2. Species Formation
a. Environments are different  species evolve differently in different
places
3. The Tempo of Evolution
a. Gradualism – evolution occurs gradually over time
b. Punctuated equilibrium – when rapid change is separated with times
of little/no change
Section 2: Evidence of Evolution
The Fossil Record
Most scientists agree on the following points that support Darwin’s theories of
Evolution:
A. Earth is about 4.5 billion years old
B. Organisms have inhabited the Earth for most of its history
C. All organisms living today share common ancestry with earlier,
simpler life-forms
1.Formation of Fossils
a. Fossils can form when organisms are rapidly buried in fine sediments
deposited by water, wind, or volcanic eruptions
Anatomy and Development
*Some animals develop differently over time, but have the same original structures.
Biological Molecules
1. Proteins
a. Species that shared a common ancestor more recently have few amino
acid sequence differences
2. Nucleic Acids
a. Nucleotide changes cause changes in the amino acid sequence of a
protein
b. Scientists compare nucleotide sequences of genes from different
organisms to determine relationships
Section 3: Examples of Evolution
Natural Selection at Work
1. Factors in Natural Selection
a. All populations have genetic variation
b. The environment presents challenges to successful reproduction
c. Individuals tend to produce more offspring than the environment can
support
d. Individuals that are better able to cope with the challenges presented
by their environment tend to leave more offspring than those
individuals less suited to the environment do
2. Example of Natural Selection
a. TB strain mutated
3. Evolution of Antibiotic Resistance
a. Mutant antibiotic resistant bacteria survived the treatment
b. Reproduction of mutant bacteria created a larger population of
antibiotic-resistant bacteria
c. Technology is constantly trying to keep up with mutating bacteria
4. Evolution in Darwin’s Finches
a. Darwin collected 9 different species of finches from the Galapagos
Islands
b. Darwin suggested that the changes in finches occurred due to food
supply
c. Theory was tested by Lack in 1938 and found little evidence
supporting Darwin
d. Another test done in 1973 supported Darwin
Formation of New Species
1. Forming Subspecies
a. Populations of species that differ genetically because of adaptations
to different living conditions become subspecies
b. Eventually subspecies become so different they can no longer
interbreed
2. Maintaining New Species
a. Interbreeding is restricted due to genetic differences
b. Geographic isolation keeps species apart
c. Hybrid offspring may not be viable
d. Natural selection leads to the formation of new species