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Evolution Notes
Unit 8
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
Land Environments
 Earth formed about 4.6 billion years ago.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
Clues in Rocks
 A fossil is any preserved evidence of an
organism.
 Why are there gaps in the fossil record?
Most organisms decompose before they
have a chance to become fossilized.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
Fossil Formation
 Nearly all fossils are formed in sedimentary
rock.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
Dating fossils
 Relative dating is a
method used to
determine the age
of rocks by
comparing them
with those in other
layers.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
Radiometric Dating
 Uses the decay of
radioactive
isotopes to
measure the age
of a rock
 Radioactive
isotopes that can be
used for radiometric dating are found only in
igneous or metamorphic rocks.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
The Geologic Time Scale
 The geological time scale is a model that
expresses the major geological and
biological events in Earth’s history.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
The Paleozoic Era
 The ancestors of most major animal groups
diversified in what scientists call the
Cambrian explosion.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
 A mass extinction ended the Paleozoic
era at the end of the Permian period.
 Between 60 and 75 percent of the species
alive went extinct.
Chapter
14
The History of Life
14.1 Fossil Evidence of Change
 Plate tectonics describes the movement of
several large plates that make up the surface of
Earth.
Terminology to know!
• Hypothesis An “If…then” statement or
proposal of an outcome of an experiment.
(Ex. If I study, then I will pass the test.)
• Theory A hypothesis that has withstood
extensive testing by a variety of methods,
and in which a higher degree of certainty may
be placed (Ex. Theory of Evolution)
• Law Considered universal and invariable
facts of the physical world
(Ex. Law of Gravity)
Chapter
14
The History of Life
14.2 The Origin of Life
Origins: Early Ideas
 Spontaneous generation is the idea that life arises
from nonlife.
 Francesco Redi, an Italian scientist, tested the idea
that flies arose spontaneously from rotting meat.
Chapter
14
The History of Life
14.2 The Origin of Life
 The theory of biogenesis states that only living
organisms can produce other living organisms.
 Louis Pasteur designed an experiment to show
that biogenesis was true even for
microorganisms.
Chapter
14
The History of Life
14.2 The Origin of Life
Cellular Evolution
 Scientists hypothesize that the first cells
were prokaryotes.
 These would compare to our modern day
bacteria
Chapter
14
The History of Life
14.2 The Origin of Life
The Endosymbiotic Theory
 Eukaryotic cells arose from communities
formed by prokaryotic cells.
 This theory explains the origin of
chloroplasts and mitochondria.
Chapter
14
The History of Life
14.2 The Origin of Life
Chapter
15
Evolution
15.1 Darwin’s Theory of Natural Selection
Darwin on the HMS Beagle
 His job was to collect biological and
geological specimens during the ship’s
travel.
What can explain the large extent
of biological diversity on earth?
• Evolution – change over time
– How life has changed over time
Chapter
15
Evolution
15.1 Darwin’s Theory of Natural Selection
The Galápagos Islands
 Darwin began to collect mockingbirds,
finches, & other animals on the 4 islands.
 He noticed that the different islands
seemed to have their own, slightly different
varieties of animals.
The Galapagos
Islands
• West of South America
• Group of islands each with
different climates
• Tortoises varied from island to
island in neck length and shell
shape
• Finches varied in beak shape
• Characteristics of plants and
animals varied from island to
island
Chapter
15
Evolution
15.1 Darwin’s Theory of Natural Selection
Chapter
15
Evolution
15.1 Darwin’s Theory of Natural Selection
Darwin Continued His Studies
 Darwin inferred that if humans could change
species by artificial selection, then perhaps
the same process could work in nature.
Chapter
15
Evolution
15.1 Darwin’s Theory of Natural Selection
Natural Selection
 Individuals in a population show variations.
 Variations can be inherited.
 Organisms have more offspring than can survive
with available resources.
 Variations that increase reproductive success
will have a greater chance of being passed on.
 “Survival of the Fittest”
Chapter
15
Evolution
15.1 Darwin’s Theory of Natural Selection
The Origin of Species
 Darwin published On the Origin of Species
by Means of Natural Selection in 1859.
 It is a means of explaining how evolution
works.
Lamarck’s Theory
•
•
•
•
•
Pre-Darwin scientist
Inheritance of acquired traits
Organs used a lot could grow and change shape
Organs not used would shrivel and disappear
Theory was incorrect but significant because he was the first
scientist to recognize that organisms had changed over time
Chapter
15
Evolution
15.2 Evidence of Evolution
Support for Evolution
 The fossil record
 Provide a record of species that lived long ago.
 Show that ancient species share similarities with
species that now live.
Glyptodont
Armadillo
Evolution
Chapter
15
15.2 Evidence of Evolution
Support for Evolution
 Geographic Distribution
 The distribution of plants and animals that
Darwin saw first suggested evolution to
Darwin.
Rabbit
Mara
Chapter
15
Evolution
15.2 Evidence of Evolution
 Derived traits are newly evolved features, such as
feathers, that do not appear in the fossils of common
ancestors.
 Ancestral traits are more primitive features, such as
teeth and tails, that do appear in ancestral forms.
Homologous Structures
 Anatomically similar structures inherited
from a common ancestor
Chapter
15
Evolution
Analogous Structures
 Same function but different
structure
 NOT inherited from
common ancestor.
Chapter
15
Evolution
15.2 Evidence of Evolution
Vestigial Structures
 Structures that are the
reduced forms of functional
structures in other organisms.
 Evolutionary theory
predicts that features of ancestors that no
longer have a function for that species will
become smaller over time until they are lost.
Chapter
15
Evolution
15.2 Evidence of Evolution
 Comparisons of the similarities in organisms
are seen in comparative anatomy and in the
fossil record.
 Organisms with closely related
morphological features have more closely
related molecular features.
More Terms
• Fitness – ability of an individual to
survive and reproduce in a specific
environment
• Adaptation – inherited characteristic
that increases an organism’s chance
of survival
–Can be physical traits as well as
behavioral traits
Chapter
15
Evolution
15.2 Evidence of Evolution
Camouflage
 Allows organisms to
become almost
invisible to predators
Leafy sea dragon
Chapter
15
Evolution
15.2 Evidence of Evolution
Mimicry
 One species evolves to resemble another
species.
Western coral snake
California kingsnake
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Natural Selection
 Acts to select
the individuals
that are best
adapted for
survival and
reproduction
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
 Stabilizing selection operates to eliminate
extreme expressions of a trait when the
average expression leads to higher fitness.
 Ex. Siberian Husky
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
 Directional selection makes an organism
more fit.
 Favors the extremes
 Ex. Greyhound Dog
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
 Disruptive selection is a process that splits
a population into two groups.
 Ex. Black, White, & Gray Rabbits
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Mechanisms of Evolution
 Population genetics
 Hardy-Weinberg principle states that when
allelic frequencies remain constant, a
population is in genetic equilibrium.
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Write these down & know these!
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Genetic Drift
 A change in the allelic frequencies in a
population that is due to chance and random
mating
 In smaller populations, the effects of genetic
drift become more pronounced, and the chance
of losing an allele becomes greater.
 Marble Example
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Nonrandom Mating
 Promotes inbreeding & could lead to a
change in allelic proportions favoring
individuals that are homozygous for
particular traits
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Founder Effect
 The loss of genetic variation that occurs
when a new population is established by a
very small number of individuals from a
larger population
Island 1
Island 2
Mainland
Island 3
Evolution
15.3 Shaping Evolutionary Theory
Bottleneck
 a significant percentage of a population or
species is killed or otherwise prevented from
reproducing and can rebound later
 Often caused by a natural disaster
What is a gene pool?
• Gene pool – combined
genetic info of all members of
a population
– Contains two of more
alleles (genes) for the same
trait
– Allele frequency – number
of times an allele occurs in
a gene pool compared to
the number of times
another allele occurs
(expressed in percents)
Relative
Frequencies
of
Alleles
Section 16-1
allele for
brown fur
allele for
black fur
Sample Population
48%
heterozygous
black
36%
homozygous
brown
Frequency of Alleles
16%
homozygous
black
Gene Flow
• Genes entering or leaving a population
• AKA. Migration
– Emigration Genes LEAVING a population
– Immigration INCOMING genes in a population
What are sources for genetic
variation?
• Mutations – random change in the DNA,
may cause evolution in future populations
• Genetic shuffling – occurs in meiosis when
gametes are formed
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
 Sexual selection operates in populations
where males and females differ significantly
in appearance.
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
 Prezygotic isolation
prevents reproduction
by making fertilization
unlikely.
•In behavioral isolation, patterns of
courtship may be different.
•In temporal isolation, different groups
may not be reproductively mature at
the same season, or month, or year.
•In geographic / ecological isolation,
not in the same habitat where they are
likely to meet.
Eastern meadowlark and Western meadowlark
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
 Postzygotic isolation occurs when fertilization
has occurred but
a hybrid offspring
cannot develop
or reproduce.
 Prevents offspring
survival or
reproduction
(hybrid sterility)
Liger
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Allopatric Speciation
 A physical barrier divides one population
into two or more populations.
Abert squirrel
Kaibab
squirrel
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Sympatric Speciation
 A species evolves into a new species
without a physical barrier.
 The ancestor species and the new species
live side by side during the speciation
process.
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Adaptive Radiation
 Can occur in a relatively short time when one species
gives rise to
many different
species in
response to the
creation of new
habitat or some
other ecological
opportunity
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Coevolution
 The relationship between
two species might be so
close that the evolution of
one species affects the
evolution of the other
species.
 Mutualism
 Coevolutionary arms race
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Convergent
Evolution
 Unrelated species
evolve similar traits
even though they
live in different
parts of the world.
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory
Rate of Speciation
 Evolution proceeds in small, gradual
steps according to a theory called
gradualism.
 Punctuated equilibrium explains rapid spurts
of genetic change causing species to
diverge quickly.
Chapter
15
Evolution
15.3 Shaping Evolutionary Theory