Download Chapter 4_Evolution

Chapter 4: Evolution
History & Evidence
Early Theories
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Many groups have considered the idea
that organisms change over time
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Empedocles (495-435 BC)
Aristotle (384-322 BC)
George Louis Buffon (1707-1788)
Erasmus Darwin (1731-1802)
Jean Baptiste Lamarck (1744-1829)
Georges-Louis Buffon

suggested that organisms change in
response to the environment
◦ he viewed the change as a degeneration of
specially created features
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He developed this theory after years of
studying anatomy, especially vestigial
structures.
Vestigial Structures

vestige= A
rudimentary organ
or part of the body
that may have been
well developed in
some ancestor or in
the embryo.
Leg bones in whales
 Wings on flightless
birds
 Wisdom teeth

Jean Baptiste Lamarck
French Zoologist
 was the first to describe a coherent,
scientific theory of evolution. (albeit an
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incorrect theory)
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His theory of inheritance of acquired
characteristics assumed that the
development, or loss of structures, was
due to use, or disuse, of these structures.
Jean Baptiste Lamarck
So what was the problem with his
theory??
 There was no mechanism by which the
newly developed, or recently lost,
characteristics could be passed to the
next generation.
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Jean Baptiste Lamarck
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In other words, a change in phenotype of
one generation would not produce to a
change a genotype in the next generation.
◦ He provided no evidence to support the idea
that changes in the environment would lead
to changes in the process of gamete
formation
How do adaptations occur?
Random changes in DNA (i.e.
independent assortment and crossing
over) creates variation in offspring.
 THEN the environment can play a role in
determining the survival of these
variations in subsequent generations.

Charles Darwin
Darwin was a well-educated member of
the English aristocracy before he took the
position of ship’s naturalist on the HMS
Beagle.
 During a 5-year voyage to map the
coastlines of South America, Darwin
observed a wide variety of living animals,
and found many fossils as well.

Darwin’s Voyage
Darwin’s Discoveries
The fossils clearly represented animals
that were no longer living, so something
must have changed between the time
where these animals flourished and the
present day.
 During his visit to the Galàpagos Islands,
he observed the terrestrial giant tortoises
and the various species of finches found
within the archipelago.

What did Darwin noticed about
these species??
Darwin noticed that the island species
exhibited some morphological similarities,
as might be the case if they had come
from the same starting population
 He also noticed they exhibited some
morphological differences from each
other, as might be the case if they had
adapted to the different environmental
conditions on each island.

Darwin’s Discoveries
Darwin continued to observe animal
populations and variations in body form
throughout his life.
 He also studied the ideas of different
scientists, economists, etc.

Darwin’s Influences-Lyell
Lyell, a geologist who put forward the
theory of uniformitarianism
 His works led Darwin to think that the
earth might be much older than the 6000
years assumed from a literal reading of
part of the Bible, and that the earth had
changed gradually over time.

Darwin’s Influences-Malthus
Darwin read an essay by Malthus, an
economist
 Darwin came to believe that populations
of organisms could grow very large if all
the organisms born had access to
unlimited resources.

◦ In reality, resource limitation controls
population size. ..for the most part.
Darwin’s Theory of Evolution

Three main parts:
◦ Species can produce more offspring than will survive
to reproduce.
◦ Individuals within a population differ due to random
mating, recombination, and mutation, among other
sources
 Darwin did not know the genetic basis of inheritance, but he
could see that offspring resembled parents strongly enough
that it was possible to breed for particular types of offspring.
◦ Variation among individuals results in some individuals
that are more suited to survive in a particular
environment than are other individuals.
Darwin’s Theory of Evolution
When resources are limited, the
individuals with advantageous traits for
that time and place are more likely to
survive and pass on their genes than the
individuals with less advantageous traits.
 Overtime, the traits that are beneficial
will begin to predominate and less
beneficial traits should become rare in the
population.
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Darwin’s Theory of Evolution
Adaptation is the process whereby the
surviving members of a population
become well suited to the particular
conditions in which they live.
 An adaptation is a feature of an organism
that increases the likelihood of survival
and reproduction in those organisms that
possess it.
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Darwin’s Theory of Evolution
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Darwin formulated his theory of natural
selection, but did not submit it for
publication until he was sent a manuscript
with many similar ideas written by Alfred
Russell Wallace.
Alfred Russell Wallace
Alfred Russell Wallace was a contemporary of
Darwin’s who had explored the Amazon Basin
and the Malay Archipelago, noting the variations
in types of animals.
 He, too, had read the works of Malthus, and he,
too, began to think that aspects of the
environment were important in determining the
survivorship of some organisms within a
population.
 Wallace and Darwin ended up presenting their
ideas together.
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Micro vs. Macroevolution
Microevolution encompasses the changes in allele
frequencies from generation to generation that
may accumulate over long time periods to
produce new types of organisms.
 Macroevolution encompasses the larger scale
changes that result in extinction and formation
of new species. Evidence for macroevolutionary
change comes from studies of: biogeography,
paleontology, comparative anatomy, molecular
biology, & develop mental patterns
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Biogeography
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How do we account for the distribution
of similar animals around the world?
Paleontology
How do fossil forms differ from modern forms,
and is there evidence of successive change
across strata of different ages?
 How have the strata changed?
 What organisms are extinct?
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Comparative Anatomy
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Are two similar structures analogous, perhaps due to
convergent evolution, or are they homologous?
Did modern vestigial structures have necessary
functions in ancestral forms?
Molecular Biology
Are sequences of
DNA inherited from
a common ancestor
and therefore
homologous?
 Can we determine
patterns of
relatedness from
comparisons of
molecules across
taxa?
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Developmental Patterns
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Are shared embryological stages
indicative of a shared evolutionary
ancestry?
Phylogeny
Using all the evidence, one can draw a
phylogeny, which is a diagrammatic
representation of the ancestor and
descendant relationships within a
particular lineage.
 A phylogenetic tree depicts the branching
pattern of ancestral forms that produced
all the modern forms.
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Phylogenetic Tree
Phylogenetic Tree