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Evolution
What is evolution?
Evolution is genetic change in
a population or a species over
generations.
Genetic change is responsible
for all the changes that have
produced Earth’s diversity of
organisms.
Evolution
„
„
Evolution is a widely accepted scientific theory
that describes the observed changes in living
things over time
Scientists use evolution
to explain the great
diversity of life, but
some dispute its ability
to describe the origins
of life on Earth
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Evolution
„
„
„
Organisms are adapted to their environment; a
good fit
As descendents of a remote ancestor spread into
various habitats over millions and millions of
years, they accumulate diverse modifications
(adaptations) that fit them to specific ways of
life
= descent with modification (evolution)
Evolution
„
Natural variation among individuals is based on
heredity (and mutation). These variations enable
organisms to become adapted to their
environment over time
Natural Selection
„
„
Natural selection is the process by which
favorable, inherited traits become more
numerous in successive generations of a
population of reproducing organisms
Over time, natural selection leads to species that
are well adapted (highly evolved) to their
environments
1 Population with varied inherited traits
2 Elimination of individuals with certain traits
3 Reproduction of survivors
Certain individuals with a distinct, inherited characteristic will be selected against, while others with a (different) distinct, inherited trait will survive
„ Darwin and
Wallace
Proposed a
Mechanism of
Evolution
The voyage of the Beagle
Great
Britain
Europe
North
America
Pacific
Ocean
Atlantic
Ocean
Africa
Galápagos
Islands
Equator
South
America
Australia
Andes
„
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
Figure 13.1B
„
While on the voyage of the HMS Beagle in the
1830s, Charles Darwin observed
„ similarities
between living and fossil
organisms
„ A large diversity of life on the Galápagos
Islands, such as giant tortoises.
How Do We Know That Evolution Has
Occurred? What is the evidence?
1. Fossils Provide Evidence of Evolutionary Change over
Time.
2. Comparative Anatomy Gives Evidence of Descent with
Modification
3. Functionless Structures Are Inherited from Ancestors
4. Some Anatomical Similarities Result from Evolution in
Similar Environments
5. Embryological Similarity Suggests Common Ancestry
6. Modern Biochemical and Genetic Analyses Reveal
Relatedness among Diverse Organisms
1. The study of fossils provides
strong evidence for evolution
„
Fossils and the fossil record
strongly support the theory of
evolution
„
Hominid skull
„
Petrified trees
youngest
rocks
oldest
rocks
Fossils provide strong support for the idea that
today’s organisms were not created all at once but
arose over time by the process of evolution.
If all species had been created simultaneously, we
would not expect
(a)trilobites to be found in older rock layers than
(b)seed ferns, which in turn would not be expected
in older layers than
(c) dinosaurs, such as Allosaurus. Trilobites became
extinct about 230 million years ago, seed ferns about
150 million years ago, and dinosaurs 65 million years
ago.
„
The fossil record shows that
organisms have appeared in a
historical sequence
„
Many fossils link early
extinct species with
species living today
„
These fossilized hind
leg bones link living
whales with their landdwelling ancestors
Figure 13.2G, H
The study of fossils provides strong
evidence for evolution
„
Fossils and the fossil record
strongly support the theory of
evolution
„
Hominid skull
„
Petrified trees
2. Comparative Anatomy Gives
Evidence of Descent with
Modification
„
Homologous
Structures Provide
Evidence of
Common Ancestry.
Human
Cat
Whale
Bat
humerus
ulna
Pterodactyl
carpals
Dolphin
metacarpals
Dog
phalanges
Human
Bird
Bat
FLYING
Seal
Sheep
Shrew
SWIMMING
RUNNING
GRASPING
3. Functionless Structures Are
Inherited from Ancestors
„
Many organisms have vestigial structures that
serve no apparent function. The (a) salamander,
(b) whale, and (c) snake all inherited hindlimb
bones from a common ancestor. These bones
remain functional in the salamander but are
vestigial in the whale and snake.
Salamander
Baleen whale
Boa constrictor
4. Some Anatomical Similarities
Result from Evolution in Similar
Environments
Analogous structures: Convergent
evolution can produce outwardly similar
structures that differ anatomically. The
wings of (a) insects and (b) birds and the
sleek, streamlined shapes of (c) seals and
(d) penguins are examples of such
analogous structures.
5. Embryological Similarity
Suggests Common Ancestry
„
Embryological stages reveal evolutionary
relationships. Early embryonic stages of a (a)
lemur, (b) pig, and (c) human, showing strikingly
similar anatomical features.
6. Modern Biochemical and Genetic
Analyses Reveal Relatedness among
Diverse Organisms
How does evolution occur?
Darwin proposed natural selection as the
mechanism of evolution
„ Darwin
observed that
„ organisms produce more offspring than
the environment can support
„ organisms vary in many characteristics
„ these variations can be inherited
„ Darwin concluded
that individuals best
suited for a particular environment are more
likely to survive and reproduce than those
less well adapted.
„ Darwin saw natural selection as the basic
mechanism of evolution
„ As
a result, the proportion of individuals
with favorable characteristics increases
„ Populations gradually change in response
to the environment