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The Theory of Evolution
Ch. 13
Biology
Ms. Haut
Lamarck’s Theory of
Acquired Inheritance
(early 1800s)
• Jean Baptiste Lamarck observed fossil
records and the current diversity of life
and formulated his theory
• Suggested giraffes acquired long necks
because ancestors stretched higher and
higher into the trees to reach leaves
– Lengthened neck was passed to offspring
Charles Darwin
• Compared South American fossils
with living species there and
elsewhere
• Observed organisms and their
distributions on Galápagos Islands
Darwin’s Theory of Natural
Selection
• Observations:
– Overproduction of offspring leads to competition
of limited resources (food, space, breeding
partners)
– Individuals of a population vary in characteristics,
and many such traits are passed on to offspring
• Conclusions:
– Individuals with inherited characteristics make
them best adapted to survive in their environment
and reproduce and leave more offspring than less
fit individuals
Natural Selection
• Prominent force in nature
• Support in the results of artificial
selection—selective breeding of
domesticated plants/animals
• Populations tend to evolve in response to
environmental conditions
Populations are the Units of
Evolution
• Population=group of individual organisms
living in the same place at the same time
• Evolution is measured as the change in
frequency of a given characteristic within a
population over a succession of generations
What is a species?
• Biological Species Concept
– Species—group of organisms that have the
potential to interbreed and produce fertile
offspring
– Reproductively isolated by various factors
preventing mixing with other species
Geographic Isolation can lead to
Speciation
Subspecies of Deer mice
Islands are Living Examples of
Speciation
• Adaptive Radiation
– Evolution of many diversely adapted species
from a common ancestor
– Example: Darwin’s Finches
• Finches with different beak shapes fit
different ecological niches
1. Seeds blown over from mainland
and form small colony
2. Gene pool isolated—evolves into
new species B
3. Storms/other agents blow seeds to
nearby island and evolve into
species C
4. Some of species C recolonize the
first island and cohabit with species
B and some populate a new island
5. Speciation continues between new
areas and previously colonized
areas
Overview: Theory of Evolution
1. Variation exists within the genes of every
population or species (due to random mutation)
2. In a particular environmnet, some individuals of
a population/species are better suited and have
more offspring (natural selection)
3. Over time, the traits that make certain
individuals of a population able to survive and
reproduced tend to spread in that population
4. There is clear evidence from fossils and many
other sources that living species evolved from
organisms that are extinct
Evidence of Evolution
•
•
•
•
•
Fossil Record
Biogeography
Comparative anatomy
Comparative embryology
Molecular Biology
Fossilization
• Most fossils are actually casts of animals or plants.
• Animal dies and sinks to the sea floor.
• Tissue begins to decay and is buried under layers of
sediment such as mud or sand.
• These layers become rock.
• The hard parts of the animal are
replaced with minerals such as
iron
pyrites or silica.
• These minerals form the fossil.
• Usually fossils show the hard parts of the
animal or plant - such as shell or bones.
• Trace fossils—evidence of living plants or
animals, such as worm burrows or dinosaur
footprints.
• Most fossils are found in sedimentary rocks rocks which were created when shells or
small loose bits of rock are laid down in
layers (limestone, sandstone, clay and chalk)
Fossil Record
Trilobite
510 million years ago
Chancelloria eros
543 million years ago
Keichousaurus hui
250 million years ago
Knightia humilis,
Diplomystus dentatus,
Mioplosus
54 million years ago
Plantanus
wyomingensis
(sycamore)
Determining Age of Fossils
• Relative age—determined by position in
sedimentary rock
• Absolute age—determined by radiometric
dating (radioactive isotopes)
– Based on half-life of an isotope—period it takes
for half the radioactive material to decay
Carbon-14 (C-14)
Up to 50,000 yrs
Potassium-40 (K-40) Up to 1.28 billion yrs
Number of Half-Life
0
C-14 Remaining
(atoms)
100
1
50
2
25
3
12.5
4
6.25
5
3.13
Number of Atoms of C-14
Half-Life of Carbon 14
120
100
80
60
40
20
0
1
2
3
4
Number of Half-Life
5
6
Evidence: Biogeography
• Geographical distribution of species
suggests organisms evolve from common
ancestors
• Island forms are most similar to forms
found on the closest mainland, rather than
forms on ecologically similar, but more
distant islands
Comparative Anatomy
• Comparison of body structures between
different species
– Similarities give signs of common descent
• Homologous structures—features that have
similar structure but have different
functions
Comparative Anatomy
• Comparison of body structures between
different species
– Similarities give signs of common descent
• Homologous structures—features that have
similar structure but have different functions
• Vestigial structures—Small body structures that
may have been functional in the ancestors of a
species, but has no real function at the present
time (appendix, tail bone)
Comparative embryology
• Different organisms go through similar
embryonic stages
• All vertebrates have an embryonic stage in
which gill pouches appear in the throat
region—evidence of a common ancestor
Molecular Biology
• Study of molecular basis of genes and gene
expression
• Universality of genetic code
• Conservation of amino acid sequences in
proteins such as hemoglobin
Causes of Microevolution
• Mutation—random change in organism’s DNA
that creates a new allele
– Rare events
– Ultimate source of the genetic variation that
initiates evolution
Insecticideresistant
Populations
Modes of Natural Selection
• Original population demonstrates the
continuum of shell color (light to dark)
Modes of Natural Selection
• Divergence
– Accumulation of
differences between
groups
– Leads to
Speciation—process
by which new species
form
Reproductive Barriers Keep Species
Separate
• Prezygotic barriers—prevent mating or
fertilization between species
– Habitat isolation—species live in same general
area but not the same places
– Behavioral isolation—special signals
recognized
– Temporal isolation—breeding occurs at
different times
– Mechanical isolation—anatomically
incompatible
– Gametic isolation—gamete recognition
Reproductive Barriers Keep Species
Separate
• Postzygotic barriers—Prevent the
hybrid zygote from developing into a
viable, fertile adult
– Reduced hybrid viability—embryo
aborted
– Reduced hybrid fertility—offspring
sterile
– Hybrid breakdown—offspring of
hybrids sterile
Overview: Natural Selection
1.
2.
3.
4.
5.
All species have genetic variation
The environment presents many different challenges
to an individual’s ability to reproduce
Organisms tend to produce more offspring than their
environment can support; thus, individuals of a
species often compete with one another to survive
Individuals within a population that are better able to
cope with the challenges of their environment tend to
leave more offspring than those less suited to the
environment
The traits of the individuals best suited to a particular
environment tend to increase in a population over time