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Transcript
Mechanisms of Evolution
Darwinian Evolution
Descent with modification by means of
natural selection
All life has descended from a common ancestor
The mechanism of modification is natural
selection
• Concept 22.3: Darwin’s theory explains a
wide range of observations
• Darwin’s theory of evolution
– Continues to be tested by how effectively it can
account for additional observations and
experimental outcomes
Natural Selection in Action
• Two examples provide evidence for natural selection
Differential Predation in Guppy Populations
•
Researchers have observed natural selection
–
Leading to adaptive evolution in guppy populations
Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools
EXPERIMENT
and measured the average age and size of guppies at maturity over an 11-year period (30 to
60 generations).
Pools with killifish,
but not guppies prior
to transplant
Predator: Killifish; preys
mainly on small guppies
Experimental
transplant of
guppies
Guppies:
Larger at
sexual maturity
than those in
“pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on large guppies
Guppies: Smaller at sexual maturity than
those in “killifish pools”
Figure 22.12
1
185.6
161.5
67.5 76.1
Males
Age of guppies
at maturity (days)
Weight of guppies
at maturity (mg)
RESULTS
After 11 years, the average size and age at maturity of guppies in the transplanted
populations increased compared to those of guppies in control populations.
Females
85.7 92.3
48.5
58.2
Males
Females
Control Population: Guppies
from pools with pike-cichlids
as predators
Experimental Population:
Guppies transplanted to
pools with killifish as
predators
CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations
in the population (larger size and slower maturation) being favored. Over a relatively short time, this altered
selection pressure resulted in an observable evolutionary change in the experimental population.
The Evolution of DrugResistant HIV
• In humans, the use of drugs
– Selects for pathogens that through chance
mutations are resistant to the drugs’ effects
• Natural selection is a cause of adaptive
evolution
• Researchers have developed numerous
drugs to combat HIV
Percent of HIV resistant to 3TC
– But using these medications selects for
viruses resistant to the drugs
Patient
No. 1
Patient No. 2
Patient No. 3
Weeks
Figure 22.13
2
• Bacteria and viruses are able to evolve
rapidly because they reproduce rapidly
and can pass on advantageous mutations
to vast numbers of new individuals very
quickly.
Selection for beak size in a Galápagos population of the medium ground finch
Lines of Evidence
that Support Natural
Selection as a
Mechanism of Evolution
3
Homology,
Biogeography, and the
Fossil Record
• Evolutionary theory
– Provides a cohesive explanation for many
kinds of observations
Homology
• Homology is similarity resulting from common ancestry
Anatomical Homologies
• Homologous structures between organisms
– Are anatomical resemblances that represent variations on a structural
theme that was present in a common ancestor
Human
Cat
Whale
Bat
• Vestigial organs
– Are some of the most intriguing homologous
structures
– Are remnants of structures that served
important functions in the organism’s
ancestors
4
Embryological Homologies
• Comparative embryology
– Reveals additional anatomical homologies
not visible in adult organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Figure 22.15
Human embryo
Molecular Homologies
• Biologists also observe homologies among
organisms at the molecular level
– Such as genes that are shared among
organisms inherited from a common ancestor
– The more closely related two organisms are,
the more sequences they share
• Anatomical resemblances among species
are generally reflected in their molecules,
their genes, and their gene products
Species
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
100%
Human
Rhesus monkey
95%
Mouse
87%
Chicken
69%
Frog
Figure 22.16
Lamprey
54%
14%
5
• Molecular biology has substantiated
Darwin’s idea that all forms of life are
related to some extent through branching
descent from the earliest organisms.
• Even taxonomically distant organisms
have some proteins in common.
• The common genetic code has been
passed through all branches of life since
its beginning in an early form of life.
DNA Sequence Cytochrome C
• Cytochrome C of different orders of mammals and
birds differs in 2 - 17 amino acids, classes of
vertebrates in 7 - 38, and vertebrates and insects
in 23 - 41; and animals differ from yeasts and
molds in 56 - 72 amino acids.
• We can calculate the minimum numbers of single
mutations needed to change the cytochrome C of
one species into that of another. # of mutations
between cytochrome C of humans versus other
living beings are:
– Monkey1, Chicken18, Dog13, Penguin18, Horse17,
Turtle19, Donkey16, Rattlesnake20, Pig13,
Fish(tuna)31, Rabbit12, Fly33, Kangaroo12, Moth36,
Duck17, Mold63, Pigeon16, Yeast56
Homologies and the Tree of
Life
• The Darwinian concept of an evolutionary
tree of life
– Can explain the homologies that researchers
have observed
6
Phylogeny of the major groups of extant vertebrates
Species
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
100%
Human
Rhesus monkey
95%
Mouse
87%
Chicken
69%
Frog
Figure 22.16
Lamprey
54%
14%
Biogeography
• Darwin’s observations of the geographic
distribution of species
– Formed an important part of his theory of evolution
– The biogeographical patterns he observed only made
sense in the context of evolution
– Review the material from lecture one pertaining to
species on the continent of South America and the
Galapagos Islands
Biogeography
• Is the study of the geographical distribution of
species.
• Islands have many endemic species which are
closely related to species on the nearest
mainland
• The occurrence of identical late Paleozoic fossils
of plants and animals in Africa and South
America is explained by continental drift
7
• Some similar mammals that have adapted
to similar environments
– Have evolved independently from different
ancestors
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
Figure 22.17
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
Figure 25.1 A gallery of fossils
8
Fossil evidence: supported
by other lines of evidence
• Prokaryotes are placed as the ancestors
of all life by evidence from cell biology,
biochemistry and molecular biology
• The fossil record shows the chronological
appearance of vertebrates as sequential
with fish first, followed by amphibians,
reptiles and then mammals and birds
• 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
Figure 22.18
Many lineages are largely
complete
• Planktonic organism lineages spanning
100 million years, including such groups
as foraminifera, radiolaria, diatoms and
coccolithophorids
• Horses
• Whales
• Elephants
9
Figure 24.24 The branched evolution of horses
Systematics
• Taxonomy and Classification as used in
the science of Systematics often reflect
actual evolutionary relationships as
verified by other lines of evidence
• Darwin realized the connection between
his Tree of Life and Linnaeus’
classification hierarchy
What Is Theoretical about
the Darwinian View of
Life?
• “Theory” does not mean the same thing in science that it
does in everyday language
• In science, a theory
– Is based on laws, hypotheses, observations and inferences
– Accounts for many observations and data and attempts to
explain and integrate a great variety of phenomena
– Must be testable
10
Examples of Scientific
Theories
•
•
•
•
•
•
•
Gravitational Theory
Heliocentrism
Cell Theory
Germ Theory
Electromagnetic Theory
Quantum Mechanics
Plate Tectonics
The criterion of the scientific status of a theory is
its falsifiability, or refutability, or testability.
• Darwin’s theory of evolution by natural selection
– Integrates diverse areas of biological study and stimulates many
new research questions
– Has been the reigning paradigm in biology for the past 150 years
• Every question in biology and medicine is an
evolutionary question
• We may discover new mechanisms of evolution, but the
fact that the diversity of life on Earth has evolved from a
common ancestor will not change.
• In science "fact" can only mean "confirmed to such a
degree that it would be perverse to withhold provisional
consent."
• View the video: Isn’t Evolution Just a
Theory at the PBS Website below
http://www.pbs.org/wgbh/evolution/educator
s/teachstuds/svideos.html
11