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Chapter 14
Evolution: A History and a Process
14.1 Darwin Developed a Theory of
Evolution
Ideas From Darwin’s Time
 Evolution: change over time
 Before mid-1700s:
 Species are permanent, do not change.
 Earth is <10,000 yrs old & unchanging.
 Georges Buffon (mid-1700s)
 Studied fossils
 Believed Earth to be older
 Decided that certain living animals were similar,
but not exact to their ancestors
14.4 Notes…
Ideas From Darwin’s Time
 Jean Lamarck (early 1800s)
 Proposed that life changes
 Changes occur as process of adaptation
 Adaptation: Inherited characteristic that improves
an organism’s ability to survive and reproduce.
 Inheritance of Acquired Characteristics: organism
can pass on characteristics acquired during its
lifetime to its offspring
e.g. Kangaroo’s powerful legs were result of ancestors
jumping & passing leg strength to offspring
-Proven false, adaptation requires modification of DNA
14.1 Notes…
The Voyage of the Beagle
 1831- Voyage around
world
 Chart coastline of S.
America for British navy
 Charles Darwin (22yrs)
on board HMS Beagle
 Study geology, plants &
animals during voyage.
14.1 Notes…
Darwin’s Observations
 Observed thousands of specimens.
 Kept extensive journals & recorded
observations
 Plants & animals in S.A. are different
from European species.
 Interested in Galapagos islands:
 Galapagos species were similar but
different from S.A. mainland species
 Species on some Galapagos islands were
similar to, but different from, species on
nearby islands.
 Concluded that species changed to
adapt to new environments
14.1 Notes
Ideas From Geology
 Darwin reads books by Charles Lyell (geologist)
 Lyell suggested physical changes to Earth result
from geologic processes occurring over long
periods of time.
Example:
erosion of river bed = river canyon
 Darwin experiences earthquake in Chile
 Land below water shifts above water
 Ocean fossils in Andes Mts.
 Concludes that earth is very old and processes over
time cause changes to earth.
14.1 Notes…
Darwin Publishes His Theory
 Darwin becomes famous upon return to England
 Darwin builds his theory
 Reads essay by Thomas Malthus, who believes
populations can grow faster than the rate of
resources, causing species to struggle to
survive
 Writes 200 pg essay about his ideas & gathers
more info.
 Publishes book called The Origin of Species
14.1 Notes…
Darwin’s Two Main Points
 Two Main Points of Darwin’s book
1. Descent with Modification
-All species descended from
ancestral species
-Spread into various habitats
-Accumulated different adaptations
to various ways of life
2. Natural Selection
-Individuals with inherited
characteristics well-suited to
environment leave more offspring
Snowshoe
hare
Jackrabbit
Peppered Moth
14.2 Evolution Has Left Much
Evidence
The Fossil Record
 Evolution has left much
evidence.
 Fossils: preserved
remains or markings left
by organisms that lived in
the past.
 Most fossils are found in sedimentary rock
layers


Sand & silt deposit, pile up, & compress into layers
Organisms become fossils if buried under deposits
14.2 Notes…
The Fossil Record
 Fossil Record: collection of
fossils recorded in rock
layers over time.
 Fossils provide evidence for
earth’s changing life.
 Fossils of extinct species can
help link past & present life
forms.
14.2 Notes
Geographic Distribution
 How organisms are distributed throughout
the world gives clues to how species may
have evolved.
e.g. Many unique species evolved on the
isolated island of Australia
-Marsupials: Kangaroos and Koalas
-Why? Possibly isolated with common
marsupial ancestor.
14.2 Notes…
Similarities in Structure
 Similarities in structure
among species provide
clues to evolutionary
history.
 Homologous
Structures: similar
structures among
related species, but
differing functions.
14.2 Notes
Similarities in Structure
 Vestigial Structures:
structures that have a
major function in one
species but not in a
related species
 No clear function
 May have been
important at one time
e.g. whale & vestigial
hipbones
14.2 Notes…
Similarities in Development
 Comparing the development of different organisms
can give clues about evolution
 Related species have similar embryonic stages
e.g. Vertebrates (fishes, frogs, snakes, birds & primates)
have pouch on side of throat during embryonic stage
 Embryonic structures develop into species-specific
structures
e.g. pouch forms into skull bones or gills
14.2 Notes…
Molecular Biology
 DNA sequences in organisms shows similarities and
differences
 DNA is passed down from parents to offspring
 DNA sequences are similar in similar species &
different in different species.
 Compare # of genes & proteins
14.3 Darwin Proposed natural Selection
as the Mechanism of Evolution
Darwin’s Theory of Natural Selection
 Natural selection helps explain adaptive
evolution
 Population: group of individuals of the same
species living in the same area at the same
time.
 Finches on Galapagos Islands



S.A. finch species colonizes Galapagos islands
Finch populations on different islands adapt to local
environments, diversify & become 13 separate species.
Beaks adapted for specific foods on different island-Why?
Natural selection
How did theses different beaks arise?
Darwin proposes the differences arise through natural selection
14.3 Notes…
Darwin’s Theory of Natural Selection
 Theory based on 2 sets of observations
1. Species tend to produce more individuals
than environment can support
-Members of a population struggle to
survive, only strongest survive.
2. There is variation or differences among
members of the same species
-Passes from generation to generation
14.3 Notes…
Darwin’s Theory of Natural Selection
Population of
Organisms
Overproduction
 Natural Selection:
 Individuals with inherited
traits that are best suited
to the environment are
more likely to survive and
reproduce than less fit
individuals.
↓
Variation
Struggle for
Existence
Differences in
Reproductive
Success
↓
Evolution of
Adaptations
14.3 Notes…
Artificial Selection
 Artificial selection: Selective
breeding of plants and animals to
produce offspring with genetic
traits that humans value
 Change occurs quickly
e.g. diversity of dog species in 500 yrs
 In contrast, natural selection
favors traits that benefit organism,
environment does “selective
breeding”.
14.3 Notes
Pesticides-Natural Selection in Action
 Evolution observable in pesticide
resistance insect species
 By spraying crops with poisons to
kill insects, humans have favored
the reproduction of insects with
inherited resistance.
e.g. Flour beetles that feed on grain
14.4 Microevolution is a Change in
a Population’s Gene Pool
Populations and Their Gene Pools
 A population is the smallest level at
which evolution can occur.
-natural selection is apparent when
populations are tracked over time.
 Gene Pool: all the alleles (alternative
forms of genes) in all the individuals
that make up a population.
14.4 Notes…
Changes in Gene Pools
 Some alleles may be
more common due to
natural selection
 Frequency of alleles=
how often alleles occur
in a gene pool
 Microevolution:
evolution on the
smallest scale-a gen. to
gen. change in the
frequencies of alleles in
population.
 Hardy-Weinberg
Equilibrium: frequency
of alleles in the gene
pool are constant over
time.
-Populations that do not
undergo change are not
presently evolving
 What mechanisms
change a gene pool?
1. Genetic Drift,
2. Gene Flow & Mutation
3. Natural Selection
14.4 Notes…
Genetic Drift
 Genetic Drift: a change in the gene pool of a
population due to chance.
-smaller population = greater impact
 The Bottleneck Effect: Reducing the size of the
population (natural disasters), reduces the size of
gene pool (genetic variation).
E.g. Cheetahs
 The Founder Effect: When few individuals, w/
little gen. variation, colonize an isolated island,
lake or new habitat.
E.g. Finches on Galapagos Islands
Genetic Drift
14.4 Notes…
Gene Flow & Mutation
 Gene Flow: the exchange of
genes with another population
when fertile individuals or
gametes migrate between
populations
e.g. Windstorm blows pollen from
neighboring white flowers into a
red-flowered population
 Reduces the genetic differences
between populations
14.4 Notes…
 Mutation: is a change in an organism’s
DNA.
 If the mutation is carried by a gamete, the
mutation enters the population’s gene pool.
 Natural selection can affect the frequency
of the mutation in a population.
e.g. albino deer
 Mutations are an important source for
variation in asexually reproducing
organisms
14.4 Notes…
Natural Selection & Fitness
 Genetic Drift, Gene Flow & Mutation cause
microevolution or changes in allele
frequencies. Only Natural Selection leads to
adaptation!
 Natural Selection = blend of chance & sorting
 Fitness: the contribution that an individual
makes to the gene pool of the next generation
compared to the contributions of others.
a.k.a “survival of the fittest”
14.4 Notes…
Natural Selection & the
Galapagos
 Peter & Rosemary Grant have
studied finches in Galapagos
for 30 years. Documented
several cycles of natural
selection.
e.g. finches eat large seeds
during dry years, those with
large beaks are more
successful, tend to survive &
pass on trait
14.5 Evolutionary Biology is
Important in Health Science
Natural Selection and Sickle Cell Disease
 Sickle Cell Disease
 Only homozygous individuals have the
disease: caused by a recessive allele inherited
from both parents.
-1 out of 25 individuals in some African
populations have the disease
 People suffer symptoms including: weakening,
pain, damage to organs & death.
 Heterozygous individuals (one copy of allele)
do not have disease but can pass it on.
Benefit = Resistant to malaria.
 Sickle Cell Disease is common in areas with
highest amount of malaria parasite due to
natural selection
14.5 Notes…
Evolution of Antibiotic Resistance in Bacteria
 Antibiotics: medicines that kill or slow the growth
of bacteria.
Benefit: Saved lives of millions of people
Risk: Caused evolution of antibiotic-resistant
bacteria by natural selection
 Drugs kills most of bacteria except those that can
survive. Resistant bacteria multiply & become the norm.
e.g. New York City & Tuberculosis Bacteria
 Overuse of drugs is speeding the evolution of resistant
bacteria