Transcript Ch 22 lecture - D and F: AP Biology

Chapter 22
Descent with Modification: 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
• Book made two major points:
1.Many current species are descendants of
ancestral species
2.Natural selection is a method for this
evolutionary process
Resistance to the Idea of
Evolution
• The Origin of Species
– Shook the deepest roots of Western culture
– Challenged a worldview that had been
prevalent for centuries
The Scale of Nature and
Classification of Species
• Aristotle: species as fixed and unchanging
• Old Testament: species were individually
designed by God and therefore perfect
• Carolus Linnaeus: organismal changes are
evidence that the Creator has designed each
species for a specific purpose
– Linnaeus was a founder of taxonomy, the branch of
biology concerned with classifying organisms
Fossils, Cuvier, and
Catastrophism
• Fossils: remains/traces of organisms,
usually found in sedimentary rock, which
appears in layers or strata
– Paleontology: the study of fossils
• Cuvier: developed paleontology; advocated
catastrophism
– Catastrophism: speculating that each boundary
between strata represents a catastrophe
(disaster)
Lamarck’s Theory of Evolution
• Lamarck hypothesized that species evolve
through use and disuse and the
inheritance of acquired traits
– The mechanisms he proposed are
unsupported by evidence
– Except pertaining to epigenetics
The Voyage of the Beagle
• Charles Darwin had a consuming interest in
nature
• After receiving his B.A. degree, he was
accepted on board the HMS Beagle
– Darwin collected plants and animals from South
American
– He observed changes in plants and animals that
lived in many diverse environments
– His interest in geographic distribution of species
was fuelled by a stop at the Galápagos Islands
England
EUROPE
NORTH
AMERICA
PACIFIC
OCEAN
ATLANTIC
OCEAN
AFRICA
Galápagos
Islands
HMS Beagle in port
Equator
SOUTH
AMERICA
Darwin in 1840,
after his return
AUSTRALIA
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
Darwin’s Focus on Adaptation
• Darwin thought that adaptations to the
environment and the origin of new species
as closely related processes
• From studies made years after Darwin’s
voyage, biologists have concluded that
this is indeed what happened to the
Galápagos finches
Cactus eater. The long,
sharp beak of the
cactus ground finch
(Geospiza scandens)
helps it tear and eat
cactus flowers and
pulp.
Seed eater. The large
ground finch (Geospiza
magnirostris) has a large
beak adapted for cracking
seeds that fall from plants
to the ground.
Insect eater. The green warbler finch
(Certhidea olivacea) used its narrow,
pointed beak to grasp insects.
Descent with Modification
• “Descent with modification” summarized
Darwin’s view of how life is united
– All organisms are related through an ancestor
that lived in the remote past
• In the Darwinian view, the history of life is
like a tree with branches representing life’s
diversity
Sirenia
Hyracoidea (Manatees
(Hyraxes) and relatives)
0
10,000
2
5.5
24
34
Elephas Loxodonta Loxodonta
cyclotis
maximus africana
(Africa)
(Africa)
(Asia)
Natural Selection and
Adaptation
• The work of Darwin has been summarized
into two observations and two inferences
• Observation 1: Members of a population often
vary in their inherited traits
• Observation 2: all species can produce more
offspring than their environment can support and
many of these offspring fail to survive and
reproduce
• Inference 1: Individuals whose inherited traits give
them a higher probability of surviving and
reproducing in a given environment tend to leave
more offspring
• Inference 2: This unequal ability of individuals to
survive and reproduce will lead to the
accumulation of favorable traits in the population
over generations
Artificial Selection
• In artificial selection, humans have
modified other species over many
generations by selecting and breeding
individuals with desired traits
Summary of Natural Selection
• Natural selection: differential success in
reproduction from interactions between
individuals that vary in heritable traits and
their environment
– Produces an increase over time in adaptation of
organisms to their environment
– If an environment changes over time, natural
selection may result in adaptation to these new
conditions
A flower mantid
in Malaysia
A stick mantid
in Africa
The Evolution of
Drug-Resistant Bacteria
• An example of ongoing natural selection
that has had an effect on humans is the
evolution of drug-resistant pathogens
– The evolution of Staphyloccocus aureus into
methicillin-resistant S. aureus or MRSA
– Some bacteria had enzymes that could break
down penicillin and other antibiotics
Homology, Biogeography, and
the Fossil Record
• Evolutionary theories provide a cohesive
explanation for many kinds of observations
Anatomical Homologies
• Homology: similarity resulting from
common ancestry
– Homologous structures: anatomical
resemblances that represent variations on a
structure present in a common ancestor
– Vestigial organs are remnants of structures
that served important functions in the
organism’s ancestors
Human
Cat
Whale
Bat
• Comparative embryology reveals
anatomical homologies not visible in adult
organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
Molecular Homologies
• Examples of homologies at the molecular
level are genes shared among organisms
inherited from a common ancestor
– Anatomical resemblances among species are
generally reflected in their molecules, genes,
and gene products
Species
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Human
100%
Rhesus monkey
95%
87%
Mouse
69%
Chicken
54%
Frog
Lamprey
14%
Biogeography
• Darwin’s observations of biogeography,
the geographic distribution of species,
formed an important part of his theory of
evolution: convergent evolution
– Some similar mammals that have adapted to
similar environments have evolved
independently from different ancestors
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
The Fossil Record
• The succession of forms observed in the
fossil record is consistent with other
inferences about the major branches of
descent in the tree of life
• The Darwinian view of life predicts that
evolutionary transitions should leave signs
in the fossil record
– Paleontologists have discovered fossils of
many such transitional forms