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Chapter 10
Principles of Evolution
Early scientists proposed ideas about
evolution.
• Evolution is the biological change process by which
descendants come to differ from their ancestors.
• A species is a group of organisms that can reproduce
and have fertile offspring.
• There were many important naturalists in the 18th century.
– Linnaeus: classification system from kingdom to species
– Buffon: species shared ancestors rather than arising
separately
– E. Darwin: more-complex forms developed from lesscomplex forms
– Lamarck: environmental change leads to use or disuse
of a structure
Theories of geologic change set the stage for
Darwin’s theory.
• The age of the Earth was a key issue in the early
debates over evolution
• Common view was that Earth was created about 6000 years
ago and the Earth nor its species have changed
• There were three theories of geologic change.
– catastrophism
– gradualism
– uniformitarianism
• The theory of catastrophism states that natural
disasters such as floods and volcanic eruptions have
happened often during Earth’s history.
• Shaped landforms and caused species to become extinct
• James Hutton proposed that changes in landforms
were the result of slow changes over a long period of
time – principal of gradualism
• Uniformitarianism is the prevailing theory of
geologic change.(Lyell)
• The geologic processes that shape Erath are uniform
through time
Darwin’s observations
Charles Darwin the
Naturalist
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Charles Darwin and his Voyage on
the Beagle
• Born Feb. 12, 1809
• Joined Crew of HMS
Beagle, 1831
• Naturalist
• 5 Year Voyage around
world
• Avid Collector of Flora &
Fauna
• Astounded By Variety of
Life
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A reconstruction of the HMS Beagle sailing off Patagonia.
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Darwin Left England in 1831
Darwin returned 5 years later in 1836
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HMS Beagle’s Voyage
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The Galapagos Islands
• Volcanic islands off the
coast of South America
• Very different climates
• Island species varied
from mainland species &
from island-to-island
species
• Animals On Islands
Unique
• Tortoises
• Iguanas
• Finches
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Darwin observed differences among island
species.
• Variation is a difference in a physical trait.
• Galápagos tortoises that live in areas with tall plants have long
necks and legs.
• Galápagos finches that live in areas with hard-shelled nuts
have strong beaks.
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The Finches
• Finches on the islands resembled a mainland finch
• More types of finches appeared on the islands where the available
food was different (seeds, nuts, berries, insects…)
• Finches had different types of beaks adapted to their type of food
gathering
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• An adaptation is a feature that allow an organism to
better survive in its environment.
– Species are able to adapt to their
environment.
– Adaptations can lead to genetic
change in a population.
Darwin observed fossil and geologic
evidence supporting an ancient Earth.
• Darwin found fossils of extinct animals that resemble
modern animals.
• Darwin found fossil shells high up in the Andes mountains.
• He saw land move
from underwater
to above sea level
due to an
earthquake.
• Darwin extended
his observations to
the evolution of
organisms.
Theory of Natural Selection
KEY CONCEPT
Darwin proposed natural selection as a mechanism for
evolution.
Several key insights led to Darwin’s idea
for natural selection.
• Darwin noticed a lot of variation in domesticated
plants and animals.
• Artificial selection is the process by which humans
select traits through breeding.
neck feathers
crop
tail feathers
• Natural selection is a mechanism by which individuals
that have inherited beneficial adaptations produce
more offspring on average than do other individuals.
• Heritability is the ability of a trait to be passed down.
• There is a struggle for survival due to overpopulation
and limited resources.
• Darwin proposed that adaptations arose over many
generations.
Natural selection explains how evolution
can
occur.
• There are four main principles to the theory of natural
selection.
– variation
– overproduction
– adaptation
– descent with modification
• Fitness is the measure of survival ability and ability to
produce more offspring.
ADAPTATION
VARIATION
OVERPRODUCTION
DESCENT with
MODIFICATION
Natural selection acts on existing variation.
• Natural selection can act only on traits that already exist.
• Structures take on new functions in addition to their
original function.
five digits
wrist bone
Evidence for Evolution
KEY CONCEPT
Evidence of common ancestry among species comes
from many sources.
Evidence for evolution in Darwin’s time
came from several sources.
• Fossils provide evidence of evolution.
• Fossils in older layers are more primitive than
those in the upper layers.
• The study of geography provides evidence of evolution.
– island species most closely resemble nearest mainland
species
– populations can show variation from one island to
another
• Embryology provides evidence of evolution.
– identical larvae, different adult body forms
– similar embryos, diverse organisms
Larva
Adult crab
Adult barnacle
• The study of anatomy provides evidence of evolution.
– Homologous structures are similar in structure but
different in function.
– Homologous structures are evidence of a common
ancestor.
Human hand
Mole foot
Bat wing
• The study of anatomy provides evidence of evolution.
– Analogous structures have a similar function.
Human hand
foot
• Analogous structures are notMole
evidence
of a common ancestor.
Fly wing
Bat wing
Structural patterns are clues to the history
of• aVestigial
species.
structures are remnants of organs or structures
that had a function in an early ancestor.
• Ostrich wings are examples of vestigial structures.
Evolutionary Biology Today
Fossils provide a record of evolution.
• Paleontology is the study of fossils or extinct organisms.
• Paleontology provides evidence to support evolution.
Molecular and genetic evidence support
fossil and anatomical evidence.
• Two closely-related organisms will have similar DNA
sequences.
• Pseudogenes are sequences providing evidence of
evolution.
– no longer function
– carried along with functional DNA
– can be clues to a common ancestor
• Hox genes indicate a very distant common ancestor.
– control the development of specific structures
– found in many organisms
• Protein comparisons, or molecular fingerprinting reveals
similarities among cell types of different organisms.
Evolution unites all fields of biology.
• Scientist from any fields contribute to the understanding
of evolution.
• The basic principles of evolution are used in many
scientific fields.