What is
Evolution
???
= a generalized
change
in the proportion of
certain inherited genes in a
population
over
time
(many generations)
Early Ideas (before Darwin)
Old Ideas to explain life:
*The Earth is only 10,000 years old and
unchanging
Darwin’s influences
Buffon
: Recognized earth is older than previously thought
–
Recognized similarities in fossilized remains and
modern species
Lyall
: Recognized gradual physical changes in earth
formed current geological landscape. Earth is old.
Malthus
: The earth has finite resources and
Darwin’s influences
Carolus Linneaus
: naming/classification system
of living things. Recognized related species.
Darwin’s influences
Lamarck
: first proposed that organisms evolve/ adapt
(species are NOT permanent/ unchanging)
Adaptation
: inherited characteristic that aides an
organism’s ability to survive and reproduce in a
given environment
Inheritance of acquired characteristics
: individuals
can acquire traits over their lifetime and pass
*
Aquired inheritance
was later disproved by studies of
genetic inheritance:
*Inherited traits must be based on
genetic
changes
that are passed on via gametes
Inheritance of acquired characteristics:
Reproduction of 1st generation;
2nd generation
is born with slightly longer necks
1st generation giraffes stretch necks
during life 2nd generation giraffes stretch necks during life
Reproduction of 2nd generation;
3rd generation
is born with slightly longer necks than 2nd
generation
3rd generation giraffes stretch necks
during life
Reproduction of 3rd generation;
4th generation is
born with slightly longer necks than 3rd
generation
Charles Darwin: Father of
Evolution
Mid 1800’s:
Beagle (ship)
voyage
around the
world influenced his ideas on
geology, animals, plants:
•Observed and studied existing and
fossilized animal/plants
•Found evidence of adaptations
•Darwin observed evidence of geological
changes to Earth
Artificial Selection:
Hints for explaining Evolution
Darwin observed how
human breeders/
farmers
could cause
changes in traits of
animals/plants
Artificial selection
:
Breeders (humans)
directly choose which
individuals to reproduce
and pass on traits
Darwin’s Ideas
*Darwin theorized that
in nature
, environmental
pressures select which individuals survive/reproduce
1844
started to collect/write down ideas
1858
Alfred Russell Wallace shared similar ideas with
Darwin
“Origin of Species”
Theories
1.
Descent with modification
:
All modern species are
descended from more ancestral species
*Species from common (shared) ancestors spread to different habitats and adapted to changes in their environments
2.
Natural selection
is mechanism of evolution
*Individuals with inherited characteristics better suited to
survival in a particular environment will reproduce and pass on their genes more successfully
14.1 Review Questions
1. What ideas about geology and adaptation influenced
Darwin’s ideas?
2. How were Darwin’s ideas different from older ideas?
3. Which of the following is an adaptation: the sharp
teeth of a house cat, or a scar on the cat's ear?
Explain.
Evidence for Evolution: Fossil Record
Fossil
= a preserved
marking/ remain left by a
past organism
*Give clues about ancestors of modern organisms
Oldest Fossil evidence:
3.8 billion years ago:organic chemicals 3.5 b.y.a.: prokaryotes
Evidence for Evolution: Fossil Record
Fossil record
: position of fossils
in different layers of rock is a
clue to their age
*Fossils of
extinct
species
help reconstruct
biological
history
on Earth
*Fossil record/history
is
incomplete (so is our
knowledge of the evolution
of species)
*Fossils give clues to how modern species evolved from ancestors:
Example: Whale ancestors
*Fossils show that ancient whale ancestors had small hind limb structures
*Evidence of whale’s evolution from land animals
Evidence for Evolution: Geographic
distribution of species
Clue to how modern organisms evolved
Example: Marsupials in Australia (Kangaroo, Koala) vs. other mammals
*Rear young in pouches (rather than a placenta, as most mammals do)
*Evolved differently from other
Evidence for Evolution: Similar
structures in different species
Homologous structures: structures similar in shape/ arrangement but with different functions
*Indicate a common ancestor among several species
*Support idea of descent with modification
Vestigial Structures
:
important in ancestral
species, but not important
in modern species
– Show evidence of evolution from ancestor with more developed version of trait
– Natural selection favors individuals with reduced versions of these structures
Examples: human tail bones,
whale/snake hind limbs
,
Wings on dodo bird/
Evidence of Evolution: similarities in
developmental structures
Related species
develop in similar
ways because of
their common
ancestry
Example:
Gill pouches
,
tail
structures in
human embryos/
other animal
Evidence of Evolution: Molecular
similarities among species
Related species have similar genes and proteins
Example: Human and Gorilla hemoglobin proteins differ in only 1 amino acid
Concept Check 14.2
1.
Why are older fossils generally in deeper rock layers
than younger fossils?
2.
How can evolutionary theory explain why Australia is
home to relatively few native placental mammals?
3.
What are homologous structures?
Natural Selection causes changes
in populations
Populations
: group of
individuals of same
species in same area at
same time
*Populations in diff.
areas adapt and change
to different
Natural Selection causes changes
in populations
Example: Darwin’s finches
• Each population evolved to have different beaks according to environmental
conditions where they lived
Natural selection acts on variation
among individuals
Variation: differences among members of
the same population
Much variation is heritable (passed on via genes from parent to offspring)
Not all individuals can survive
Some individuals survive better, produce more offspring, pass on their genes
Cause overall evolution of the population towards certain adaptations
Environmental Pressures
Artificial Selection:
Hints for explaining Evolution
Darwin compared artificial selection to natural selection
Artificial selection:
Breeders (humans) -rather than natural conditions- select individuals to reproduce and pass on traits (desirable to humans)
Both artificial and natural selection lead to changes in populations
Natural Selection may act quickly
in some populations
Example: pesticide resistance in beetles
*Pesticide treatment “selects” for individuals with resistance to the pesticide.
over several generations percentage of resistant individuals increases
(Evolution occurs)
Adaptation of Pesticide Resistance
Variation:
Pressures:
Differential Reproductive Success:
Adaptation of Pesticide Resistance
Adaptation of Pesticide Resistance
Adaptation of Pesticide Resistance
Adaptation of Pesticide Resistance
Adaptation (result):
The resistance gene
increases in frequency.
Initial
population (33%
resistance)
Final
population (100%
PBS Evolution Website. Video 4:
“How does Evolution Actually Work?”
http://www.pbs.org/wgbh/evolution/educators
/teachstuds/svideos.html
or
http://www.teachersdomain.org/resource/tdc0
2.sci.life.evo.howreally/
14.3 Analysis Questions
1. What general conditions lead to a struggle for
survival among individuals in a population?
(Name at least two)
2. What is the goal of artificial selection?
3. Why is artificial selection different from natural
selection?
4. Why might a specific pesticide become less
effective over time?
14.3 Analysis Questions
1. What general conditions lead to a struggle for
survival among individuals in a population? (Name at
least two)
Overproduction; Environmental Pressures
2. What is the goal of artificial selection?
14.3 Analysis Questions
3. Why is artificial selection different from natural
selection?
Artificial: Humans decide which individuals survive/
reproduce
Natural: Environmental pressures affect which
individuals survive/reproduce
4. Why might a specific pesticide become less
effective over time?
MicroEvolution
Microevolution:
change in
allele frequency
in a
population’s gene pool
Gene pool
: all the alleles in a population
–
Source of groups genetic variation
–
Genes mixed via meiosis, fertilization
*natural selection acts on
individuals
but
populations
Hardy-Wienberg equilibrium
= condition of no change in gene pool.
*When allele frequencies change, microevolution
has occurred
Causes of microevolution
Genetic drift
: change in gene pool due to chance
Genetic Drift
caused by:
1. Bottleneck affect
: Population size is randomly
reduced by a natural disaster, etc., allele
frequencies change
Smaller gene pool in surviving population
often less variety of alleles
decreased ability of population to adapt to disease, other
Genetic Drift
caused by:
2. Founder effect
: gene pool limited to alleles of
founding members of new population
Example: Afrikaner population of Dutch settlers in South
Africa- higher than normal frequency of allele causing
Huntington’s Disease
because many original founding
Founder effect
Example
: Small groups of
Galapagos finches were isolated on different
islands
–
Each island contains unique finch species with
Gene flow and mutation also cause
micro-evolution
Gene flow
= exchange of genes with
another population (migration and
breeding)
– Mixing alleles may reduce genetic diversity between populations, or blend two populations into a single population
Example: Ancestral Homo sapiens
populations may have experienced some gene flow with Neanderthal
populations.
Gene flow and mutation also cause
micro-evolution
Mutation
: change in DNA. Mutated genes enter
gene pool only if passed from parent to
offspring in gametes
–
Provide source of new variety in gene pool
*Example: bacteria mutate to become resistant to a
drug, and pass the resistance gene to other
Natural Selection determines
fitness and causes adaptations
Micro evolution from: genetic drift,
gene flow, mutation.
Cause non-adaptive changes in a population’s gene pool
Natural selection
acts on the
variation in a population to
cause adaptation
Individuals with certain alleles tend to survive and reproduce better
Natural Selection determines
fitness and causes adaptations
Fitness: contribution an individual makes to next generation’s gene pool (compared to other individuals)
Individual must reproduce healthy, fertile offspring to improve fitness
*Example: A horse and a donkey do NOT improve their fitness by having offspring (mule) because mules are sterile animals.
Case Study: Natural Selection of Galapagos
Finch beak characteristics
Medium Ground Finch prefer small seeds (easier to crush) vs. large seeds (hard to crush). Some variation in beak size exists.
Dry years: small seeds rare (large seeds
common)
– Larger beaked birds eat large seeds more easily
Wet year: small seeds more common – Smaller beaked birds forage more
Chart: Beak depth (size) over time
Predict:
After a dry year
which type of
bird will become
more common in
the population?
Larger Beaked!
After a wet year?
14.4 Analysis Questions
1. What processes or events can change the gene frequencies in a gene pool?
2. Are there any possible negative effects from having a limited gene pool?
3. How could a weak, scrawny, unattractive individual be considered more fit than a strong, attractive looking individual?
4. Describe an example in nature of a microevolution event in a specific population.
A. Who is the group?
Natural Selection and Sickle Cell
Disease
Sickle cell disease: caused
by inheriting
abnormal
hemoglobin gene
Causes weakness, pain, organ damage, sometimes death
Natural Selection and Sickle Cell
Disease
Carriers for sickle cell (one copy of allele) have unexpected survival benefit:
– Resistance to malaria
Malaria: a disease which causes many infant deaths in
underdeveloped countries
The parasite which causes
malaria is carried by mosquitos
Nat. Selection and Sickle Cell Disease
Frequency of sickle cell allele higher than average (1 in 3 people) in areas where malaria-carrying mosquitos are common (hot, moist, poor sanitation/healthcare access)
Evolution of antibiotic resistance in
bacteria
Antibiotics are used to treat many disease-causing bacteria
Overuse/misuse of antibiotics selects for antibiotic-resistant bacteria which may cause untreatable infections in humans (i.e. MRSA)
– Patients should carefully follow doctors directions for use
– Doctors should avoid prescribing antibiotics except when absolutely necessary
Antibiotic Resistance Animation:
**Understanding evolution relates
to specific human concerns:
Why are certain human alleles (i.e. sickle cell) more common in certain groups? (Why have these groups adapted in this way?)
How do bacteria develop drug- resistance? (Explain the process of natural selection)
How can we artificially create animals or crops/plants with desirable traits?
14.5 Review Questions
1. How does natural selection encourage the sickle cell allele to persist in certain human populations?
– population affected:
– variety in the population: – environmental pressure:
– which individuals have a heritable characteristic that gives a
survival advantage?:
– adaptation made by the population:
2. Why is it important for humans to understand how bacteria evolve?
