Transcript Evidence of Evolution (cont`d)

Evolution
Theories and Evidence
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Evolution
An orderly succession of
changes.
Biological evolution is the
change of populations of
organisms over generations.
Came from a common ancestor
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Lamarck’s Theory
One of the first
to propose a
hypothesis of
species
modification.
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Lamarck’s Theory
Proposed that species evolve
over time.
Similar species descended from
a common ancestor.
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Lamarck’s Theory (cont’d)
Incorrectly hypothesized that
species modification is the result of
acquired traits and that these traits
can be passed on to offspring.
Acquired traits: one not
determined by genes, but arises
during an organism’s lifetime as a
result of the organism’s
experience or behavior.
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Lamarck’s Theory (cont’d)
Example:
•Lamarck’s theory said that
webbed feet of water birds
resulted from repeated
stretching of the membrane
between the toes.
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Lamarck’s Theory (cont’d)
•Over time, this produced a
broad webbed foot, at trait
that would be preserved by
reproduction (offspring of
parents with webbed feet
would have webbed feet as
well).
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Lamarck’s Theory (cont’d)
•Another example: giraffes
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Lamarck’s Theory (cont’d)
Lamarck’s hypothesis was
widely attacked and was easily
disproved.
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Darwin’s Theories
50 years later (1809-1882)
Began his work
on evolution
when employed
as a naturalist
for a voyage of
the H.M.S.
Beagle.
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Darwin’s Theories
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Darwin’s Theories
Found evidence of species
modification in both modern
and extinct species.
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Darwin’s Theories
(cont’d)
His ideas about evolution and
natural selection are summed
up in two theories:
Descent with Modification
Modification by Natural Selection
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Darwin’s Theories
(cont’d)
Descent with Modification
Newer forms appearing in the
fossil record are actually the
modified descendents of older
species.
•Example: Galapagos finches
(13 Species)
•Each had a distinct bill for
eating.
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Darwin’s Theories
(cont’d)
All species had descended
from one or a few original
types of life.
This explained the
observation that organisms
give rise to others similar to
themselves.
•“Origin of Species”
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Darwin’s Theories
(cont’d)
Modification by Natural Selection
Natural selection is the principal
driving force behind evolution.
Environment may affect
individual organisms in a
population in different ways,
because individuals of a species
are not identical.
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Darwin’s Theories
(cont’d)
Some organisms have traits that
make them better able to cope
with their environment.
Organisms with a great number
of favorable traits tend to leave
more offspring than organisms
with fewer beneficial traits.
Different degrees of successful
reproduction: natural selection.
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Darwin’s Theories
(cont’d)
If a trait both increases the
reproductive success of an
organism and is inherited, then
the trait will tend to be passed on
to many offspring.
A population of organisms adapt
to their environment as their
proportion of genes for a
favorable trait increases.
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Darwin’s Theories
(cont’d)
Resulting change in the genetic
makeup of a population is
evolution.
A single organism’s contribution
to the next generation is termed
fitness.
A favorable trait gives an
organism that has it an adaptive
advantage.
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Darwin’s Theories
(cont’d)
The environment “selects” the
traits that will increase in a
population.
•Example: Peppered Moths
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Peppered Moths
Darwin’s Theories
(cont’d)
Selection conditions change as
the demands of the environment
change.
•If change is too fast,
populations may not adapt fast
enough and will become
extinct.
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Evidence of Evolution
Evidence supporting evolution
is found in the body structures
of living organisms.
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Evidence of Evolution
(cont’d)
Homologous features: similar
features that originated in a
shared common ancestor.
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Evidence of Evolution
(cont’d)
Example: forelimbs in human,
bat, penguin, and alligator
•Look different
•Vary in function
•Very similar in skeletal
structure
•Derived from the same
embryological structures
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Forelimbs of Vertebrates
Evidence of Evolution
(cont’d)
Analogous features: serve
identical functions and look
somewhat alike.
Very different embryological
development
May be different in internal
anatomy.
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Evidence of Evolution
(cont’d)
Example: wings in birds and
insects.
•Share a very remote ancestor
•Wings evolved independently
and differently in more recent
ancestors.
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Evidence of Evolution
(cont’d)
Vestigial features: serve no
useful function.
Examples: human appendix and
tailbone
Were useful to an ancestor, but
no longer useful to modern
organisms.
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Evidence of Evolution
(cont’d)
Evidence that the feature was
functional in some ancestors of
the modern organism.
Modern organism with such
feature, probably shares common
ancestry with an organism that
has a functional version of that
feature.
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Evidence of Evolution
(cont’d)
Similarities in Embryology
Similar embryological
development among species
indicates a common evolutionary
history.
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Evidence of Evolution
(cont’d)
• Early stages of
different
vertebrate
embryos are
very similar.
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Evidence of Evolution
(cont’d)
Similarities in Macromolecules:
Similarity in DNA, RNA, and
proteins indicates a common
evolutionary history.
•The more similar the
macromolecules, the more
closely related the species are
thought to be.
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Patterns of Evolution
Coevolution: two or more
closely associated species
change in response to each
other.
Example: plants and their
pollinators
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Patterns of Evolution
(cont’d)
Convergent Evolution: organisms
that are not closely related
resemble each other because they
have responded to similar
environments.
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Patterns of Evolution
(cont’d)
Example: sharks and
porpoises appear very
similar, but are not
closely related.
Environment selects
similar phenotypes.
Analogous features
associated with
convergent evolution.
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Patterns of Evolution
(cont’d)
Divergent Evolution: related
populations become less
similar as they respond to
different environments.
Can ultimately result in a new
species.
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Patterns of Evolution
(cont’d)
Adaptive
radiation:many
related species
evolve from a single
ancestral species.
• Example:
Galapagos finches
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Patterns of Evolution
(cont’d)
Process can be sped up artificially
through artificial selection.
•Example: dog breeding.
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