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Ch.10: Principles of Evolution
People Who Influenced
Before Darwin
• Most people believed that the Earth
was only a few thousand years old,
and that it was unchanging
• Around the 1700s, these ideas
began to change
Hutton & Lyell
• Believed that geologic features of Earth
must have taken a long time to form,
therefore Earth must be much older than a
few thousand years
• Also believed that Earth is and has always
been changing
• Darwin figured that since the Earth is
changing maybe living things change as
• 1st to come up with a hypothesis about how
organisms evolve
• Believed that body structures would become
larger or smaller due to use or disuse during
an organism’s lifetime, & that those acquired
traits could be passed to offspring
• His hypothesis was wrong, but he was
correct in that organisms do adapt to their
• Malthus was an economist who said
that the human population was growing
faster than the food supply, so
eventually resources would run out
• Darwin believed that this applied even
more strongly to plant and animal
populations, since they reproduce so
much faster than humans
Section 2: Darwin’s
• Variation is the difference in the physical
traits of an individual from those of others
• Examples:
– Tortoises who live on islands where vegetation
is high have high shell edges and long necks to
reach food & those who live on islands with low
vegetation have short necks & legs
– Finches have beaks that matched the food that
they eat
• An adaptation is a feature that
allows an organism to better
survive in its environment
• Adaptations can lead to genetic
change in a population over time
Darwin’s Evidence
• Fossils Darwin found looked similar to
living species, suggesting that they
could be the ancestors of modern
• Darwin also found fossils of marine
organisms in the mountains,
suggesting that geologic change was
occurring on Earth
Section 3: Theory of Natural
Artificial Selection
• Natural variation exists in all populations &
some variation is heritable, meaning it can be
passed from one generation to the next
• For 100s of years, humans have been using
artificial selection - the process by which
humans change a species by breeding it for
certain traits
• Darwin believed that a process similar to
artificial selection could happen in nature
Darwin Publishes his Theory
• Over 20 years after Darwin’s voyage on the
Beagle, he received a short essay from
Alfred Russel Wallace that summarized all
of Darwin’s thoughts about evolution.
• This prompted Darwin to publish his own
book called On the Origin of Species by
Means of Natural Selection.
• Natural Selection is the mechanism by
which individuals that have inherited
beneficial adaptations produce more
offspring on average than do other
4 Main Principles of Natural
1.Variation - natural genetic variation
exists in all populations
2.Overproduction - populations tend to
produce more offspring than the
environment can sustain, leading to
competition for resources
3.Adaptation - some variations allow an
individual to better survive & reproduce
– Fitness is a measure of the ability to
survive and produce more offspring
relative to other members of the
4.Descent with modification - Over time,
natural selection results in changes in
a population, as only those with the
highest fitness will pass on their genes
Natural Selection acts on
• Natural selection doesn’t create new
alleles, genetic mutations do
• Natural selection can only act on
traits that already exist in a
• As an environment changes,
different traits become beneficial
Section 4: Evidence of
Darwin’s Evidence
• The most important & convincing
evidence of evolution comes from
fossils, geography, embryology, &
• Fossils - fossil organisms in lower,
older layers of rock are more
primitive than those in upper, newer
layers; this supports descent with
• Geography - Darwin observed that
certain plants & animals in the
Galapagos Islands were similar but
not identical to mainland species
– He hypothesized that some individuals
from the mainland migrated to the
islands & then adapted to each
particular island
• Embryology - similar features of
embryos in very different organisms
suggests evolution from a distant
common ancestor
– Ex. vertebrate embryos all have gill
slits as embryos, but not as adults
• Anatomy - comparing body parts of
different species provides evidence of
– Homologous structures are features that
are similar in structure but appear in
different organisms & have different
functions (suggest a common ancestor)
– Analogous structures are structures that
perform a similar function but are not
similar in origin; they arise due to similar
environmental challenges, not common
Structural Patterns &
Evolutionary History
• Structural patterns are clues to the
history of a species
• Vestigial structures are remnants of
organs or structures that had a
function in an early ancestor, but
serve little or no function in the
– Ex. pelvic bones & hind limb bones in
– Ex. appendix & tail bone in humans
Section 5: Evolutionary
Biology Today
Fossil Record
• Paleontology was a new science in
Darwin’s time
• Our fossil record is incomplete, but it
does support the theory of evolution
• Many transitional fossils have been
found that show the change in
organisms over time
Molecular & Genetic Evidence
• DNA Sequence Analysis - The more
related two organisms are, the more
similar their DNA will be.
• Protein Comparisons - Molecular
fingerprinting compares similarities
among proteins of organisms.
Species that have the same proteins
most likely come from a common
Evolution Unites all Fields of
• All biological fields contribute to
evolutionary theory
• The theory of natural selection along with
genetics is sometimes called the modern
synthesis of evolutionary theory
• The basic principles of evolution are used
in many scientific fields such as medicine,
geology, geography, chemistry