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Biology 1 Notes
Chapter 15 (pages 368-386)
Darwin and Evolution
Darwin’s Theory of Evolution
•
•
15–1 The Puzzle of Life’s Diversity
•
A. Voyage of the Beagle
B. Darwin’s Observations
1. Patterns of Diversity
2. Living Organisms and Fossils
3. The
15–2 Ideas That Shaped Galápagos Islands
C. The Journey Home Darwin’s Thinking
A. An Ancient, Changing Earth
1. Hutton and Geological Change
2. Lyell’s Principles of Geology
B. Lamarck’s Evolution Hypotheses
1. Tendency Toward Perfection
2. Use and Disuse
3. Inheritance of Acquired Traits
4. Evaluating Lamarck’s Hypotheses
C. Population Growth
15–3 Darwin Presents His Case
A. Publication of On the Origin of
Species
B. Inherited Variation and Artificial
Selection
C. Evolution by Natural Selection
1. The Struggle for Existence
2. Survival of the Fittest
3. Descent With Modification
D. Evidence of Evolution
1. The Fossil Record
2. Geographic Distribution of
Living Species
3. Homologous Body Structures
4. Similarities in Embryology
E. Summary of Darwin’s Theory
F. Evolutionary Theory Since Darwin
The Diversity of Life
• BRAINPOP- Charles Darwin
• Humans share the Earth with millions of
other kinds of organisms of every
imaginable shape, size, and habitat.
• The process by which modern organisms
have descended from ancient organisms is
evolution.
• Evolution is the change in populations
over time.
• Many explanations about how species
evolve have been proposed, but the ideas
first published by Charles Darwin are the
basis of modern evolutionary theory.
• A theory is a well-supported testable
explanation of phenomena that have
occurred in the natural world.
Darwin on HMS Beagle
• It took Darwin years to
develop his theory of
evolution.
• He began in 1831 at age
22 when he took a job as
a naturalist on the
English ship HMS
Beagle, which sailed
around the world on a
five-year scientific
journey.
• Darwin studied and
collected biological and
fossil specimens from
several continents and
many remote islands.
• His observations and data led Darwin to propose a revolutionary
hypothesis about the way life changes over time.
Darwin in the Galápagos
• On the Galápagos Islands, Darwin studied
many species of animals and plants that
are unique to the islands but similar to
species elsewhere.
• The Galapagos Islands were unique in that
although they were close together, each
island had very different climates.
• Darwin observed that the characteristics
of many animals and plants varied
noticeably among the different islands of
the Galapagos.
• Many of the fossils that Darwin
discovered resembles living
organisms but were not identical
to them.
• The glyptodon, an extinct animal
known only from fossil remains
is an ancient relative of the
armadillo of South America.
Giant Tortoises of the Galápagos Islands
• Among the tortoises, the shape of the shell corresponds to different habitats.
• The Hood Island tortoise (right) has a long neck and a shell that is curved and
open around the neck and legs, allowing the tortoise to reach the sparse
vegetation on Hood Island.
• The tortoise from Isabela Island (lower left) has a dome-shaped shell and a
shorter neck. Vegetation on this island is more abundant and closer to the
ground.
• The tortoise from Pinta Island has a shell that is intermediate between these
two forms.
• These observations
led Darwin to
consider the
possibility that
species can change
over time.
Influences on Darwin’s Work
• Influenced by the work of many others, Darwin worked to refine his
explanation for how species change over time.
• Hutton and Lyell helped scientists recognize that Earth is many millions of
years old, and the processes that changed Earth in the past are the same
processes that operate in the present.
– This led Darwin to think that if the Earth could change over time the
organisms on it probably changed over time as well.
– Also, if it took the Earth many, many years for life to change, then the
Earth must be extremely old.
• An English economist Thomas Malthus believed that the human population
grows faster than Earth’s food supply.
– Applying this concept to biology, Darwin knew many species produce large
numbers of offspring and that these species had not overrun Earth.
– He concluded that individuals struggle to compete in changing
environmental conditions.
– Also, only some individuals survive the competition and produce offspring.
• Unfortunately not all scientists that influenced Darwin were completely
accurate in their beliefs.
Acquired Characteristics and Use/Disuse
1
• Lamarck was one of the first
to develop a theory about
evolution and realize that
organisms adapted to their
environment.
• He believed that selective use
or disuse of a body part would
cause it to change and that this
change would be passed on to
offspring.
3
2
1) The male crab uses its small claws in front to attract mates and ward off
predators.
2) Lamarck believed that because it was used repeatedly it became larger.
3) According to Lamarck’s theory , the acquired characteristic, a larger claw,
would be passed on to the crab’s offspring.
This theory has been shown to be incorrect!
Inherited Variation and Natural Selection
• Darwin observed that the traits of individuals vary in populations.
• Variations are then inherited.
• Breeding organisms with specific traits in order to produce offspring
with identical traits is called artificial selection
• Darwin hypothesized that there was a force in nature that worked like
artificial selection.
• Natural selection is a mechanism for change in populations.
– It occurs when organisms with favorable variations survive, reproduce, and
pass their variations to the next generation.
– Organisms without these variations are less likely to survive and
reproduce.
– As a result, each generation consists largely of offspring from parents with
these variations that aid survival.
• Alfred Russell Wallace, another British naturalist, reached a similar
conclusion.
Darwin explains natural selection
• Darwin proposed the idea of
natural selection to explain how
species change over time.
• In any population,
individuals have
variations. Fishes, for
example, may differ in
color, size, and speed.
Darwin explains natural selection
• Individuals with certain
useful variations, such as
speed, survive in their
environment, passing
those variations to the next
generation.
• Over time, offspring with
certain variations make up
most of the population and
may look entirely different
from their ancestors.
Adaptations: Evidence for Evolution
• Recall that an adaptation is any variation that aids an
organism’s chances of survival in its environment.
• Darwin’s theory of evolution explains how adaptations may
develop in species.
• Brainpop!!- Mimicry and Camouflage
Structural adaptations arise over time
• According to Darwin’s theory,
adaptations in species develop over
many generations.
• Learning about adaptations in molerats can help you understand how
natural selection has affected them.
• The ancestors of today’s common
mole-rats probably resembled
African rock rats.
• Some ancestral rats may have
avoided predators better than
others because of variations
such as the size of teeth and
claws.
Structural adaptations arise over time
• Ancestral rats that
survived passed their
variations to offspring.
• After many generations,
most of the population’s
individuals would have
these adaptations.
• Over time, natural selection
produced modern mole-rats.
• Their blindness may have
evolved because vision had
no survival advantage for
them.
Structural adaptations arise over time
• Some other structural adaptations are subtle.
• Mimicry is a structural adaptation that enables one species
to resemble another species.
• In one form of mimicry, a harmless species has adaptations
that result in a physical resemblance to a harmful species.
• Predators that avoid the harmful looking species also avoid
the similar-looking harmless species.
• In another form of mimicry, two
or more harmful species resemble
each other.
• For example, yellow jacket
hornets, honeybees, and many
other species of wasps all have
harmful stings and similar
coloration and behavior.
Structural adaptations arise over time
• Predators may
learn quickly to
avoid any
organism with
their general
appearance.
• Another subtle adaptation
is camouflage, an
adaptation that enables
species to blend with their
surroundings.
• Because well-camouflaged
organisms are not easily
found by predators, they
survive to reproduce.
Physiological adaptations can develop rapidly
•
•
•
•
In general, most structural adaptations develop over millions of years.
However, there are some adaptations that evolve much more rapidly.
Physiological adaptations are changes in an organism’s metabolic processes.
For example, do you know that some of the medicines developed during the twentieth
century to fight bacterial diseases are no longer effective?
1) The bacteria in a population vary in their ability to resist antibiotics.
2) When the population is exposed to an antibiotic, only the resistant bacteria survive.
3) The resistant bacteria live and produce more resistant bacteria.
Non-resistant
bacterium
Antibiotic
Resistant
bacterium
• Today, penicillin no longer affects as many species of bacteria because some
species have evolved physiological adaptations to prevent being killed by
penicillin.
• In addition to species of bacteria, scientists have observed these adaptations in
species of insects and weeds that are pests.
Other Evidence for Evolution
• Physiological resistance in species of bacteria, insects, and plants is direct
evidence of evolution.
• However, most of the evidence for evolution is indirect, coming from
sources such as fossils and studies of anatomy, embryology, and
biochemistry.
Evidence of
Evolution
includes
The fossil record
Geographic
distribution of
living species
Homologous
body structures
Similarities
in early
development
which is composed of
which indicates
which implies
which implies
Physical
remains of
organisms
Common
ancestral
species
Similar genes
Similar genes
Fossils- Clues to the Past
• About 95 percent of the species that have
existed are extinct—they no longer live on
Earth.
• Fossils, which come in many forms such as
leaf imprint, a worm burrow, or a bone, are
an important source of evolutionary evidence
because they provide a record of early life and
evolutionary history.
• For example, fossils can help to predict whether an area had been a river
environment, terrestrial environment, or a marine environment. They
also provide information on ancient climate.
• Paleontologists are detectives of the past that study ancient life and
events
• By studying fossils, scientists learn about the diversity of life and about
the behavior of ancient organisms.
• Although the fossil record provides evidence that evolution occurred, the
record is incomplete.
Camel Evolution
Camel Evolution
Age
Paleocene
65 million
years ago
Eocene
54 million
years ago
Oligocene
33 million
years ago
Miocene
23 million
years ago
Present
Organism
Skull and
teeth
Limb
bones
• For example, you can see how paleontologists have charted the
evolutionary path that led to today’s camel after piecing together
fossil skulls, teeth, and limb bones.
Comparing Relative and Absolute Dating of Fossils Chart
Comparing Relative and Absolute Dating of Fossils
Can determine
Is performed by
Drawbacks
Relative Dating
Absolute Dating
Age of fossil with respect to
another rock or fossil (that is,
older or younger)
Age of a fossil in years
Comparing depth of a fossil’s
source stratum to the position
of a reference fossil or rock
Determining the relative
amounts of a radioactive (C,
K) isotope and nonradioactive
isotope in a specimen
Imprecision and limitations of
age data
Difficulty of radioassay
laboratory methods
Water carries small rock
particles to lakes and seas.
Dead organisms are buried
by layers of sediment, which
forms new rock.
The preserved remains
may later be discovered
and studied.
The Fossil Record
• Earth’s history is divided into the geologic time scale, based on
evidence in rocks and fossils.
• The four major divisions in the geologic time scale are the
Precambrian, Paleozoic Era, Mesozoic Era, and Cenozoic Era.
• The eras are further divided into periods.
• By comparing
older rock
layers (near the
bottom) with
fossils from
younger layers
(near the top),
scientists can
document the
fact that life on
earth has
changed over
time.
Movement of the Earth’s Crust
Sea
level
Sedimentary rocks
form in horizontal
layers.
When part of Earth’s
crust is compressed, a
bend in a rock forms,
tilting the rock layers.
As the surface erodes
due to water, wind,
waves, or glaciers, the
older rock surface is
exposed.
New sediment is then
deposited above the
exposed older rock
surface.
Geographic Distribution of Living Species
Beaver
Beaver
Muskrat
Beaver and
Muskrat
Coypu
NORTH AMERICA
Capybara
Muskrat
• Darwin realized that
similar animals in
different locations were a
result of evolutionary
descent.
Coypu and
Capybara
Capybara
SOUTH AMERICA
Coypu
• Even though animals were on different
continents, if they were living under
similar ecological conditions, they were
exposed to similar pressures of natural
selection.
• Due to the similar selective pressures,
different animals ended up evolving
striking features in common.
Homologous Body Structures
Turtle
Alligator
Bird
Mammal
Ancient lobe-finned fish
• Structural features with a common evolutionary origin are called
homologous structures.
• Homologous structures can be similar in arrangement, in function, or in
both.
Homologous Structures
• Although homologous
structures show common
ancestry, each organism’s
limbs developed according
to their environmental
niche.
• Structures were modified
due to adaptations in their
individual surroundings
over time.
Crocodile
forelimb
Whale
forelimb
•
•
Bird
wing
Bird bones show an adaptation to
flying that the bones of the
flightless organisms, though
homologous, do not have.
Bird bones have evolved to be
delicate, lightweight, and elongated
to make flight much easier.
Analogous Structures
• The body parts of organisms that do not have a common evolutionary
origin but are similar in function are called analogous structures.
• Although analogous structures don’t shed light on evolutionary
relationships, they do provide evidence of evolution.
• For example, insect and bird wings probably evolved separately when
their different ancestors adapted independently to similar ways of life.
• The fangs of a rattlesnake and
the fangs of a spider are
analogous structures. They share
the same function in each
organism, to deliver venom, but
the organisms do not share a
common evolutionary origin.
• Analogous structures show the
way dissimilar organisms
adapted independently to similar
ways of life by developing
functionally similar structures.
Vestigial Structures
• Another type of body feature that suggests an evolutionary relationship is a
vestigial structure—a body structure in a present-day organism that no longer
serves its original purpose, but was probably useful to an ancestor.
• A structure becomes vestigial when the species no longer needs the feature for
its original function, yet it is still inherited as part of the body plan for the
species. Many organisms have vestigial structures.
• Vestigial structures, such as pelvic bones in the baleen whale, are evidence of
evolution because they show structural change over time.
– Pelvic bones are evidence that whales once possessed hind limbs. Since whales now
have no hind limbs, their loss must be the result of an evolutionary change.
• In humans, the appendix is vestigial because
it carries out no function in digestion.
• In some skinks legs have become vestigial.
– They are reduced because they no longer
function because they are no longer used in
walking.
Embryology
• An embryo is the earliest
stage of growth and
development of both plants
and animals.
• The embryos of a fish, a
reptile, a bird, and a
mammal have a tail and
pharyngeal pouches.
• It is the shared features in
the young embryos that
suggest evolution from a
distant, common ancestor.
Pharyngeal
pouches
Pharyngeal
pouches
Tail
Fish
Tail
Reptile
Bird
Mammal
Summary of Darwin’s Theory
1) Individual organism’s differ, and some of this variation is heritable.
2) Organisms produce more offspring than can survive, and many that do
survive do not reproduce
3) Since more organisms are produced than can survive, they compete for
limited resources.
4) Each organism has different advantages and disadvantages in the
struggle for existence.
– Individuals best suited for their environment will survive and
reproduce more successfully.
– These organisms pass their heritable traits to their offspring. Other
individuals die or leave fewer offspring.
– This process of natural selection causes species to change over time.
5) Species alive today are descended with modifications from ancestral
species that lived in the distant past.
– This process by which diverse species evolved from common
ancestors, unites all organisms on Earth into a single tree of life.
Evidence of Evolution Flow Chart
Evidence of
Evolution
includes
The fossil record
Geographic
distribution of
living species
Homologous
body structures
Similarities
in early
development
which is composed of
which indicates
which implies
which implies
Physical
remains of
organisms
Common
ancestral
species
Similar genes
Similar genes
Biochemistry
• Biochemistry also provides strong evidence for evolution.
• Nearly all organisms share DNA, ATP, and many enzymes among
their biochemical molecules.
• One enzyme, cytochrome c, occurs in organisms as diverse as bacteria
and bison.
• Biologists compared the differences that exist among species in the
amino acid sequence of cytochrome c.
• The data show the number of amino acid substitutions in the amino
acid sequences for the different organisms.
Biochemical Similarities of Organisms
• Organisms that
are biochemically
similar have fewer
differences in
their amino acid
sequences.
Comparison of Organisms
Two orders of mammals
Birds vs. mammals
Percent Substitutions
of Amino Acids in
Cytochrome c Residues
5 and 10
8-12
Amphibians vs. birds
14-18
Fish vs. land vertebrates
18-22
Insects vs. vertebrates
27-34
57
Algae vs. animals
Interpreting Evidence after Darwin
• Since Darwin’s time, scientists
have constructed evolutionary
diagrams that show levels of
relationships among species.
• In the 1970s, some biologists
began to use RNA and DNA
nucleotide sequences to
construct evolutionary
diagrams.
• Today, scientists combine data
from fossils, comparative
anatomy, embryology, and
biochemistry in order to
interpret the evolutionary
relationships among species.