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Evolution: Evidence
and Theory
Chapter 15
Section 15-1: The Fossil Record
Fossils, Paleontology, &
Geology
• The study of fossils helped to lay the groundwork for
Darwin’s ideas
• Paleontology, the study of fossils, was largely developed by
French scientist Georges Cuvier
• Cuvier advocated catastrophism, speculating that each boundary
between strata represents a catastrophe
• Geologists James Hutton and Charles Lyell perceived that
changes in Earth’s surface can result from slow continuous
actions still operating today
• Lyell’s principle of uniformitarianism states that the
mechanisms of change are constant over time
• This view strongly influenced Darwin’s thinking
Nature of Fossils
•
Fossil: trace of long-dead
organism; often found in layers of
sedimentary rock which forms
when sediment (dust, sand, mud)
is deposited by wind or water
• Minerals that form sedimentary rock
slowly replace hard body parts or
organism (shell, bones, teeth)
• Over time, hard minerals replace
tissue, leaving rocklike structure
•
Mold: type of fossil- imprint in
rock of shape of organism; some
eventually filled with hard
minerals, forming cast: rocklike
model of organism
•
1668, Robert Hooke concluded
that fossils are remains of plants &
animals; one of first to study fossils
• hypothesized that living organisms
had somehow turned to rock
Distribution of Fossils
•
Law of superposition: states that
successive layers of rock or soil
were deposited on top of one
another by wind or water
– Lowest stratum (layer) is oldest
– Top stratum is most recent
– Fossils in same stratum are
approximately same age
– Using law of superposition,
observers could establish relative
age of fossil: could say a fossil was
younger or older than another
fossil
– Absolute age: could be estimated
from amount of sediment
deposited above the fossil
Succession of Forms and
Biogeography
• Extinct: species that disappeared
• Fossil record indicates there were several mass
extinctions: brief periods during which large numbers of
species disappeared
– Resulted from drastic changes in environment, perhaps
periods following volcanic activity
• Biogeography: study of geographical distribution of
fossils and living organisms
• Comparison of recently formed fossil types and types of
living organisms in same geographic area shows that new
organisms arise in areas where similar forms already lived
Section 15.2: Theories of Evolution
Fig. 22-2
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1800
1900
1750
1850
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his hypothesis of evolution.
1830 Lyell publishes Principles of Geology.
1831–1836 Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks.
1844 Darwin writes essay on descent with modification.
1858 Wallace sends his hypothesis to Darwin.
1859 The Origin of Species is published.
A Historical Perspective
• The Greek philosopher Aristotle viewed species as
fixed and arranged them on a scala naturae
• The Old Testament holds that species were
individually designed by God and therefore perfect
• Carolus Linnaeus interpreted organismal
adaptations as evidence that the Creator had
designed each species for a specific purpose
• Linnaeus was the founder of taxonomy, the branch of
biology concerned with classifying organisms
Not the First Theory
• Jean-Baptiste Lamarck (late 1700s) hypothesized that species
evolve
• Purposed that similar species descended from a common ancestor
• Hypothesized that acquired traits were passed on to offspring
• Acquired trait: one that is not determined by genes but develops during an
organism’s lifetime as result of organism’s behavior or experience
• Ex: Giraffes stretch necks
• First to state that types of organisms change over time and that types
of organisms are modified descendants of older types
• The mechanisms he proposed are NOT SUPPORTED by
evidence
*BE VERY CAREFUL NOT TO USE LAMARCKIAN
LANGUAGE.
Darwin
• As a boy and into adulthood,
Charles Darwin had a consuming
interest in nature
• Darwin first studied medicine
(unsuccessfully), and then theology
at Cambridge University
• After graduating, he took an unpaid
position as naturalist and companion
to Captain Robert FitzRoy for a 5year around the world voyage on the
Beagle.
Voyage of the Beagle
•
Collected specimens of South American plants and animals
•
Observed adaptations of plants and animals that inhabited many diverse
environments
•
Influenced by Lyell’s Principles of Geology
• Emphasized Earth was 6000 years old
• Principles of uniformitarianism: geological structure of Earth resulted from
cycles of observable processes and that these same processes operate
continuously through time
• Ex. Silt deposited by modern day rivers was deposited same way by ancient
rivers
• Began to believe that geologic changes require many years
• Reasoned that formation of mountain ranges would slowly change habitats,
requiring organisms to adapt to these changes which would be very slow
and difficult to detect
• Interest in geographic distribution of species was kindled by a stop at the
Galápagos Islands near the equator west of South America
Voyage of the Beagle
Focus on Adaptation
•
Darwin perceived adaptation to the environment and the
origin of new species as closely related processes
•
•
1844: Darwin wrote an essay on the origin of species and
natural selection
•
•
Did not introduce his theory publicly, anticipating an
uproar
June 1858: Darwin received a manuscript from Alfred
Russell Wallace
•
•
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From studies made years after Darwin’s voyage, biologists
have concluded that this is indeed what happened to the
Galápagos finches
Developed a theory of natural selection similar to Darwin’s
Darwin’s and Wallace’s hypotheses were presented side by
side to Linnaean Society of London in 1858
The Origin of Species was published the next year
•
•
In the Darwinian view, the history of life is like a tree with
branches representing life’s diversity
Darwin’s theory meshed well with the hierarchy of
Linnaeus
Artifical Selection, Natural
Selection, and Adapation
• Darwin noted that humans have modified other
species by selecting and breeding individuals with
desired traits
• artificial selection
• Darwin then described four observations of nature
and from these drew two inferences
Observation #1:
Members of a population often
vary greatly in their traits
Observation #2:
• Traits are inherited from parents to offspring
Observation #3:
All species are capable of
producing more offspring than
the environment can support
Observation #4:
• Owing to lack of food or other resources, many of
these offspring do not survive
Two Inferences
• 1: Individuals whose inherited traits give them a
higher probability of surviving and reproducing in a
given environment tend to leave more offspring than
other individuals
• 2: This unequal ability of individuals to survive and
reproduce will lead to the accumulation of favorable
traits in the population over generations
Natural Selection: A
Summary
•
Individuals with certain heritable characteristics survive
and reproduce at a higher rate than other individuals
•
Natural selection increases the adaptation of organisms to
their environment over time
•
•
•
BUT: This is not an ACTIVE process by the organism.
Nature selects!
If an environment changes over time, natural selection
may result in adaptation to these new conditions and may
give rise to new species
•
•
•
•
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Note that individuals do not evolve; populations evolve
over time
Natural selection can only increase or decrease heritable
traits in a population
Adaptations vary with different environments
• Favorable traits have an adaptive advantage
Natural selection does not create new traits, but edits or
selects for traits already present in the population
The local environment determines which traits will be
selected for or selected against in any specific population