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Lecture #19
Date ________
• Chapter 22~
Descent with
A Darwinian View
of Life
Overview: Darwin Introduces a
Revolutionary Theory
• A new era of biology began on November 24, 1859,
the day Charles Darwin published On the Origin of
Species by Means of Natural Selection
– Focused biologists’ attention on the great diversity of
– He presented evidence that the many species of
organisms presently inhabiting the Earth are
descendants of ancestral species
– He proposed a mechanism for the evolutionary
process, natural selection as the cause of adaptive
Evolution: the change over time of the
genetic composition of populations
Natural selection: populations of
organisms can change over the
generations if individuals having
certain heritable traits leave more
offspring than others (differential
reproductive success)
Evolutionary adaptations: a prevalence
of inherited characteristics that
enhance organisms’ survival and
November 24, 1859
Influences on Darwin
Carolus Linnaeus: founder of taxonomy, classifying life’s diversity
“for the greater glory of God”
Georges Cuvier: opposed the idea of gradual evolutionary change,
instead advocated catastrophism, speculating that each boundary
between fossil strata represented a catastrophe
Geologists Hutton and Lyell: perceived that changes in Earth’s
surface can result from slow continuous actions still operating today
Lamarck: hypothesized that species evolve through use and disuse
and the inheritance of acquired trait (But the mechanisms he
proposed are unsupported by evidence)
Evolutionary history
Linnaeus: taxonomy
Hutton: gradualism
Lamarck: evolution
Malthus: populations
Cuvier: paleontology
Lyell: uniformitarianism
Darwin: evolution
Mendel: inheritance
Wallace: evolution
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, nutural selection)
Mendel (inheritance)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his theory of evolution.
1830 Lyell publishes Principles of Geology.
1831–1836 Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks on the origin of species.
1844 Darwin writes his essay on the origin of species.
1858 Wallace sends his theory to Darwin.
1859 The Origin of Species is published.
1865 Mendel publishes inheritance papers.
Descent with Modification, I
• 5 observations:
1- Exponential fertility
2- Stable population size
3- Limited resources
4- Individuals vary
5- Heritable variation
Galapagos Islands
Darwin’s Finches
Descent with Modification, II
• The phrase descent with
– Summarized Darwin’s perception
of the unity of life
– States that all organisms are
related through descent from an
ancestor that lived in the remote
3 Inferences:
1- Struggle for existence
2- Non-random survival
3- Natural selection (differential
success in reproduction)
Evolution evidence:
• Geographical
distribution of
• Examples:
Islands vs. Mainland
Evolution evidence:
The Fossil Record
• Succession of forms
over time
• Transitional links
• Vertebrate descent
Evolution evidence:
Comparative Anatomy
• Homologous
structures (homology)
• Descent from a
common ancestor
• Vestigial organs
Ex: whale/snake
hindlimbs; wings on
flightless birds
Evolution evidence:
Comparative Embryology
• Pharyngeal pouches,
‘tails’ as embryos
• Ontogeny Recapitulates
– Ernst Haeckel proposed that
the embryonal development of
an individual organism (its
ontogeny) followed the same
path as the evolutionary
history of its species (its
– Refuted, but new things can be
learned from his insights
Natural Selection and Adaptation
• Evolutionary biologist Ernst Mayr
has dissected the logic of Darwin’s
theory into three inferences based
on five observations (a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
• Observation #1: For any species, population
sizes would increase exponentially (if all
individuals that are born reproduced
• Observation #2: Nonetheless, populations
tend to be stable in size (except for
seasonal fluctuations)
• Observation #3: Resources are limited
– Inference #1: Production of more individuals
than the environment can support leads to a
struggle for existence among individuals of a
population, with only a fraction of their
offspring surviving
• Observation #4: Members of a population vary
extensively in their characteristics…no two
individuals are exactly alike
• Observation #5: Much of this variation is heritable
– Inference #2: Survival depends in part on inherited
traits…individuals whose inherited traits give them a
high probability of surviving and reproducing are likely
to leave more offspring than other individuals
– Inference #3: This unequal ability of individuals to
survive and reproduce will lead to a gradual change in
a population, with favorable characteristics
accumulating over generations
Evolution evidence:
Molecular Biology
• Similarities in DNA,
proteins, genes, and
gene products
• Common genetic code
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Rhesus monkey
Final words…...
• “Absence of evidence
is not evidence of