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Darwin’s Evolution
Section 1
The Theory of Evolution by Natural Selection
Darwin Proposed a Mechanism for Evolution
•Science Before Darwin’s Voyage Lamarck
proposed an incorrect mechanism for how organisms
evolve, but he correctly pointed out that change in
species is linked to an organism’s environment.
•Darwin’s Observations Charles Darwin (1859)
concluded that animals on the coast of South America
that resembled those on the nearby islands evolved
differences or descended with modification after
separating from a common ancestor.
Section 1
The Theory of Evolution by Natural Selection
Darwin Proposed a Mechanism
for Evolution continued
•Growth of Populations Darwin was influenced by
Thomas Malthus, who wrote that populations tend to
grow as much as the environment allows.
•Population consists of all the individuals of a
species that live in a particular area.
Section 1
The Theory of Evolution by Natural Selection
Darwin’s Theory
• 1. Inherited variation exists within the genes of
every population or species.
• 2. In a particular environment, some
individuals of a species are better suited to
survive.
• 3. Over time, the traits that make certain
individuals more apt to survive are spread
throughout the population.
• 4. There is evidence from fossils that living
species evolved from organisms that are extinct.
Section 1
The Theory of Evolution by Natural Selection
Evolution by Natural Selection
•Natural Selection Natural selection is differential
reproductive success and natural selection leads to
adaptations in a population.
•Darwin’s Theory Darwin proposed that natural
selection favors individuals that are best able to
survive and reproduce and this causes populations to
evolve.
Section 1
The Theory of Evolution by Natural Selection
Darwin’s Ideas Updated
•Change Within Populations Natural selection
causes the frequency of certain alleles in a population
to change over time.
•Species Formation Under certain conditions,
change within a species due to reproductive isolation
can lead to new species.
•The Tempo of Evolution Gradualism is a process of
evolution in which speciation occurs gradually, and
punctuated equilibrium is a process in which
speciation occurs rapidly between periods of little or
no change.
Section 2
Evidence of Evolution
The Fossil Record
•Formation of Fossils Evidence of orderly change
can be seen when fossils are arranged according to
their age.
Section 2
Evidence of Evolution
Anatomy and Development
•Vestigial Structures Reduced or
nonfunctional vestigial structures,
such as hind limbs in whales, provide
evidence of an organism’s
evolutionary history.
Section 2
Evidence of Evolution
•Homologous StructuresHomologous structures, structures in
different organism that indicate a
shared ancestry, include the vertebrate
forelimb.
Section 2
Evidence of Evolution
Section 2
Evidence of Evolution
Section 2
Evidence of Evolution
Biological Molecules
•Proteins Differences in amino acid sequences are
greater between species that are more distantly
related than between species that are more closely
related.
•Nucleic Acids Differences in DNA sequences are
greater between species that are more distantly
related than between species that are more closely
related.
Section 3
Examples of Evolution
Natural Selection at Work
•Factors in Natural Selection Individuals that
have traits that enable them to survive in a
given environment can reproduce and pass
those traits to their offspring.
•Evolution of Antibiotic Resistance
Experiments show that evolution through
natural selection has occurred within
populations of antibiotic-resistant bacteria,
such as the bacteria that cause tuberculosis.
Section 3
Examples of Evolution
Evolution in Darwin’s Finches
Experiments show that evolution through
natural selection has occurred in beak
size in Darwin’s Finches.
Section 3
Examples of Evolution
Formation of New Species
•Speciation Speciation begins as a population adapts to
its environment.
•Forming Subspecies Populations of the same species
that differ genetically because of adaptations to
different living conditions are called subspecies. Newly
formed subspecies are on the road towards speciation.
•Maintaining New Species Reproductive isolation
through reproductive barriers keeps species from
breeding with one another.