1. Mechanisms of Evolution
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2. Mechanisms of Evolution
Key Concepts
• Evolution Is Both Factual and the Basis of
Broader Theory
• Mutation, Selection, Gene Flow, Genetic
Drift, and Nonrandom Mating Result in
Evolution
• Evolution Can Be Measured by Changes
in Allele Frequencies
• Selection Can Be Stabilizing, Directional,
or Disruptive

3. Mechanisms of Evolution
Key Concepts
• Genomes Reveal Both Neutral and
Selective Processes of Evolution
• Recombination, Lateral Gene Transfer,
and Gene Duplication Can Result in New
Features
• Evolutionary Theory Has Practical
Applications

4. Opening Question
How do biologists use evolutionary
theory to develop better flu vaccines?
- Biologists use evolutionary theory to develop
better flu vaccines by studying the evolution of
the influenza virus and identifying which
strains are most likely to cause the next
outbreak. By tracking the genetic changes in
the virus over time, scientists can predict
which strains are likely to emerge and design
vaccines that target those specific strains.
In addition, evolutionary theory helps
biologists understand the mechanism of
action of the flu vaccine. The flu vaccine
works by introducing a small piece of the
virus (usually a protein) into the body,
which triggers an immune response. The
immune system then creates antibodies
that can recognize and destroy the virus
if it is encountered again.

5. Evolution Is Both Factual and the Basis of Broader
Theory
Biological populations change over time, or
evolve.
Evolutionary changes is observed in laboratory
experiments, in natural populations, and in the
fossil record.
This fact is widely accepted by the
scientific community and is supported by a
vast array of evidence from various fields of
study, including genetics, paleontology,
comparative anatomy, and molecular biology.

6. Evolution Is Both Factual and the Basis of Broader
Theory
Evolutionary theory—understanding the
mechanisms of evolutionary change.
It has many applications: study the treatment of
diseases, development of crops and industrial
processes, understanding the diversification of
life, and how species interact.
It also allows us to make predictions about the
biological world.

7. Evolution Is Both Factual and the Basis of Broader
Theory
Theory—In everyday speech, an untested
hypothesis or a guess.
Evolutionary theory is not a single hypothesis,
but refers to our understanding of the
mechanisms that result in genetic changes in
populations over time and to our use of that
understanding to interpret changes in and
interactions among living organisms.

8. Evolution Is Both Factual and the Basis of Broader
Theory
Even before Darwin, biologists had suggested
that species had changed over time, but no one
had proposed a convincing mechanism for
evolution.
These mechanisms work together to
produce the patterns of evolutionary change
that we observe in the natural world, such as
the development of new species, the extinction
of others, and the diversification of life.

9. Evolution Is Both Factual and the Basis of Broader
Theory
Charles Darwin was interested in
geology and natural history.
By studying the natural
history of animals and plants,
Darwin was able to gather evidence
in support of his theory of evolution
and to develop a more nuanced
understanding of the processes that
drive biological change.
Overall, Darwin's interest in
geology and natural history was
instrumental in shaping his views
on evolution and in providing the
evidence and insights needed to
develop one of the most important
scientific theories of all time.

10. Evolution Is Both Factual and the Basis of Broader
Theory
In 1831, Darwin
began a 5-year
voyage around the
world on a Navy
survey vessel, the
HMS Beagle.

11. The Voyage of the Beagle

12. Evolution Is Both Factual and the Basis of Broader
Theory
From the observations and insights made on the
voyage, and new ideas from geologists on the
age of the Earth, Darwin developed an
explanatory theory for evolutionary change:
• Species change over time.
• Divergent species share a common ancestor.
• The mechanism that produces change is
natural selection.

13. Evolution Is Both Factual and the Basis of Broader
Theory
In 1858, Darwin received a paper from Alfred
Russel Wallace with an explanation of natural
selection nearly identical to Darwin’s.
Both men are credited for the idea of natural
selection.
Darwin’s book, The Origin of Species, was
published in 1859.

14. Evolution Is Both Factual and the Basis of Broader
Theory
By 1900, the fact of evolution was established,
but the genetic basis of evolution was not yet
understood.
Then the work of Gregor Mendel was
rediscovered, and during the 20th
century, work
continued on the genetic basis of evolution.
A “modern synthesis” of genetics and evolution
took place 1936–1947.

15. Milestones in the Development of Evolutionary Theory

16. Evolution Is Both Factual and the Basis of Broader
Theory
The structure of DNA was established by 1953
by Watson and Crick.
In the 1970s, technology developed for
sequencing long stretches of DNA and amino
acid sequences in proteins.
Evolutionary biologists now study gene structure
and evolutionary change using molecular
techniques.

17. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Biological evolution refers to changes in the
genetic makeup of populations over time.
Population—a group of individuals of a single
species that live and interbreed in a particular
geographic area at the same time.
Individuals do not evolve; populations do.

18. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
The origin of genetic variation is mutation.
Mutation—any change in nucleotide sequences
(DNA).
Mutations occur randomly with respect to an
organism’s needs; natural selection acts on this
random variation and results in adaptation.

19. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Mutations can be deleterious, beneficial, or have
no effect (neutral).
Mutation both creates and helps maintain
genetic variation in populations.
Mutation rates vary, but even low rates create
considerable variation.

20. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Because of mutation, different forms of a gene,
or alleles, may exist at a locus.
Gene pool—sum of all copies of all alleles at all
loci in a population.
Allele frequency—proportion of each allele in
the gene pool.
Genotype frequency—proportion of each
genotype among individuals in the population.

21. A Gene Pool

22. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Many of Darwin’s observations came from
artificial selection of domesticated plants
and animals.
Selection on different characters in a single
species of wild mustard produced many crop
plants.

23. Many Vegetables from One Species

24. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Darwin bred pigeons and recognized similarities
between selection by breeders and selection in
nature.

25. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Laboratory experiments also show genetic
variation in populations.
Selection for certain traits in the fruit fly
Drosophila melanogaster resulted in new
combinations of genes that were not
present in the original population.

26. Figure 15.6 Artificial Selection Reveals Genetic Variation

27. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Natural selection:
• Far more individuals are born than survive to
reproduce.
• Offspring tend to resemble their parents, but
are not identical to their parents or to one
another.
• Differences among individuals affect their
chances to survive and reproduce, which will
increase frequency of favored traits in the next
generation.

28. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Adaptation—a favored trait that evolves through
natural selection.
Adaptation also describes the process that
produces the trait.
Individuals with deleterious mutations are less
likely to survive and reproduce and to pass
their alleles on to the next generation.

29. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Migration of individuals between populations
results in gene flow, which can change
allele frequencies.

30. Figure 15.24 Evolutionary Analysis of Surface Proteins Leads to Improved Flu Vaccines

31. Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
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