# Is There Evidence?

Document Sample

LAB:Variation in a Species
•   What is the purpose of Part 1?
•   (Measuring Pumpkin seeds)

•   There is variation in size in Pumpkin plants.
Variation can be measured.
LAB:Variation in a Species
•       What is the purpose of Part 2?
•       (Calculate how long it takes pumpkin plants to take over
the Earth)

•   There are reasons to explain why pumpkin
plants have not ever taken over the Earth
LAB:Variation in a Species
•   What is the purpose of Part 3?
•   (Effect of predators on sweet cute Bonitos)

•   There are reasons to explain why the
population of bonitos on one island look
different from bonitos on another island
What is a species?
•       A group of living things that
•       are similar,

•   and can breed together in nature

•    to produce fertile offspring.
What is a population?
•       A group of living things that
•       belong to the same species,

•   live in the same area,

•    and can reproduce together.
What is a gene pool?

•   The total collection of genes in a population
at any one time.
Hardy & Weinberg
•   What is allele frequency?

•   1908: Hardy and Weinberg invented the
term “allele frequency” to describe the
percentage of dominant and recessive
alleles found in a populaton.
Hardy & Weinberg
•   How is allele frequency measured?

•   Example: a lizard population might have the
following allele frequency for the alleles F
and f:
•   FF = 0.64      (64%)
•   Ff = 0.32      (32%)
•   ff = 0.04      (4%)
Hardy & Weinberg
•   What is genetic equilibrium?

•   1908: Hardy and Weinberg invented the
term “genetic equilibrium” to describe a
population in which the frequency of
alleles stays the same from one generation
to the next.
Hardy & Weinberg
•   How was genetic equilibrium measured?

•   Hardy-Weinberg equations:
•   p2 + 2pq +q2 = 1
•   p+q=1
Hardy & Weinberg
•    Hardy-Weinberg Equations

•       Where p2 is the frequency of homozygous
dominant individuals
•       Where 2pq is the frequency of heterozygous
individuals

•   Where q2 is the frequency of homozygous
recessive individuals
Hardy & Weinberg
•       What causes genetic equilibrium?
•       There must be…….
•       A large population
•       Members mating at random
•   No mutation
•   No migration
•   No natural selection
Hardy & Weinberg
•       What can cause allele frequency to change?

•       Migration (also called gene flow)
•       Mutation
•   Mate selection (non-random mating)

•    Predators, disease, famine, drought, storms,
accidents.
Observing Variation
•   (1) Variation exists in living populations.

•   (2) Some variations are helpful and increase
life span.

•   (3) Some variations are harmful and
decrease life span.
Observing Variation
•   (4) A population may become physically
separated, so two groups form.

•   (5) As mutations and meiosis occur, new
variations will appear.
•   (6) Some offspring will survive better than
others.
Observing Variation
•       (7) Offspring that survive in one area may
not survive in another area.

•   (8) Over time, more variations will
accumulate in the two populations.

•       (9) The two populations will become
different because different variations occur
in the two groups.
Observing Variation
•   (10) Individuals that die out do not get to
reproduce.
•   (11) In some cases, the two groups become
so different from each other that they can no
longer interbreed.

•   (12) Sometimes, a new species has formed.
What is this Process?
•   Evolution of species

•       A set of natural processes that causes
change in a population of living things over
time.
•       Biological evolution, simply put, is descent
with modification.

Source: http://www.swarthmore.edu/NatSci/cpurrin1/textbookdisclaimers/CobbDisclaimer.jpg
Understanding Evolution
•   Scientists study natural processes and look
for natural explanations.
•   I will introduce you to some of the evidence
that leads biologists to view evolution as the
great unifying theory of the field.
•   Science cannot answer every question.
•   What if you disagree with photosynthesis?
Evolution by Natural Selection
•   Variation exists in every population.
•   Sources of inherited variation: meiosis,
crossing over, mutation.
•   Natural selection (predators, disease,
drought, cold, famine, flood, heat…..)
causes some individuals to survive while
others do not.
•   Allele frequency change is called evolution.
Sometimes it causes speciation.
Charles Darwin
•   Age 25: set sail on 5 year voyage on HMS
Beagle as “naturalist”.
Darwin’s Voyage of Discovery

A reconstruction of the HMS Beagle sailing off Patagonia.
The Voyage of the Beagle
Cape Verde and Galapagos Archipelegos
Galapagos Islands and South American Mainland
Intra-Galapagos Variability:
Darwin’s Finches
Darwin saw patterns among a diverse,
extensive array of fossils & specimens
(worked on it for a couple decades!)

Charles Darwin observed animals and plants
in the Caribbean, South America, the
Galapagos, Hawaii, Indonesia, Africa and
Europe.
•   He took massive notes in several notebooks.
•   He wrote three books about his experiences.
Common Ancestor
The central idea of biological evolution is that all
life on Earth shares a common ancestor, just as
you and your cousins share a common
grandmother.
Darwin’s Notebook
Darwin’s Ideas Did Not Develop in a Vacuum

Contributor’s to Darwin’s thinking included:

Charles Lyell – uniformitarianism.

1797-1875

Georges Cuvier – species extinction.

1769-1832
Darwin’s Ideas Did Not Develop in a Vacuum

Contributor’s to Darwin’s thinking included:

Thomas Malthus – struggle for existence.

1766-1834

Jean Baptiste de Lamarck – evolution by
acquired characteristics.

1744-1829
Jean Baptiste de Lamarck
•       Animals face a need to change.

•       Animals make themselves change

•   Animals pass on the changes to offspring.

•   “Inheritance of Acquired Characteristics”
Alfred Russel Wallace Independently Drew the Same
Conclusions as Darwin

Papers from Wallace and Darwin were jointly presented (with little
impact) to the Linnaean Society in 1858.
Evolution by Natural Selection
•   Variation exists in a population. (Darwin
did not know how the variation was
passed…genetics was not yet understood)
•   Some organisms survive and pass on
genes…some do not.
•   Causes of this evolution: migration,
“heredity”, mate selection, predators,
disease, famine, drought,
Lamarck and Wallace: How would
they explain these observations?
•   In 1960, a pesticide was sprayed at Tybee
Island, GA, killing 97% of all mosquitoes.
•   In 1979, the same pesticide killed less than
30% of all the mosquitoes.
•   Lamarck:               Wallace:
Darwin’s Observations and Inferences

Observation 1: Left unchecked, the number of
organisms of each species will increase
exponentially, generation to generation.

Observation 2: In nature, populations tend to
remain stable in size.

Observation 3: Environmental resources are limited.

Inference 1: Production of more individuals than can be supported by the
environment leads to a struggle for existence among individuals, with
only a fraction of offspring surviving in each generation.
Darwin’s Observations and Inferences

Observation 4: Individuals of a population vary extensively in their
characteristics with no two individuals being exactly alike.

Observation 5: Much of this variation between individuals is heritable.
Darwin’s Observations and Inferences

Inference 2: Survival in the struggle
for existence is not random, but
depends in part on the heritable
characteristics of individuals.
Individuals who inherit
characteristics most fit for their
environment are likely to leave
more offspring than less fit
individuals.
Darwin’s Observations and Inferences

Inference 3: The unequal ability of individuals to survive and
characteristics accumulating over generations (natural selection).

Taken together, these three inferences are a statement of Darwin’s
Theory of Evolution.
Genetics and the Modern Synthesis

A major problem in Darwin’s theory was the lack of a
mechanism to explain natural selection.
How could favorable variations be transmitted to later
generations?
With the rediscovery of Mendel’s work and its vast
extension in the first half of the 20th century, the missing
link in evolutionary theory was forged.

Darwinian theory supported by genetics is known as the modern synthesis.
The Modern Synthesis
1932-1953

1)   Mutation and segregation result in
large variability within populations
2)   Individuals pass alleles to offspring
3)   Differential reproductive success
How can allele frequency
change?
•   Migration
Mutation
•   Meiosis and crossing over
•   Natural Selection (predators, disease,
famine, drought)
•    Non-random mating (sexual selection)
•   Genetic drift (luck)
How can evolution occur?

•   Migration
Mutation
•   Meiosis and crossing over
•   Natural Selection (predators, disease,
famine, drought)
•    Non-random mating (sexual selection)
•   Genetic drift (luck)
Evidence that evolution takes
place
•   Biogeography

•   Homologous or vestigial structures

•   Homologous DNA and proteins

•   Evolution observed right now

•   Fossil evidence
Homologous skeletal structure

Why use the same skeletal plan for these very
different appendages?
Homologous Structures

Bees, ants and wasps have stingers which are
modified ovipositors…which explains why only
females can sting!
Vestigial whale pelvis bones

Vestigial anthers and pollen:
Dandelions are asexual
Why should different organism possess related genes?

Evidence of
Evolution –
Conservation and
Diversification at
the Molecular Level
Why does the degree of
relationship of genes
match their degree of
relationship established
by other methods?
Embryo Homology
Evidence for Evolution - Comparative Embryology

Why do embryos of different animals pass through a
similar developmental stage?
Recent discoveries of the conservation of molecular
mechanisms of development are even more compelling.
Plant embryo homology
Evidence for
Evolution
– Evolution Observed

Evolution of pesticide
resistance in response to
selection.

Explain how this is
perceived as an example of
evolution.
Evidence for Evolution – Evolution Observed

Evolution of drug-resistance in HIV.
Interpret this example of evolution.
Bear evolution based on homologous DNA genes
Whale and
dolphin
evolution
based on
DNA
homology
Evolution: Changes in allele
frequency over time
Phylum Annelida segmented worm evolution
based on fossil and DNA homology
Evolution of Turtles, with massive fossil evidence
Biogeography
Hawaiian Monk Seals
Common Ancestor
Evolution: Changes in allele
frequency over time
Whale evolution
Hardy-Weinberg genetic equilibrium

•   Allele frequency will not change as long as:
•   There is no migration (gene flow)
•   There is no mutation
•   There is random mating
•   There is no natural selection
•   The population is large, so there is no
genetic drift
Genetic Drift: The Founder Effect
•   A few individuals are separated from the
original population.
•   All the descendants resemble the founders,
even if those traits are not best for the
environment.
•   EXAMPLE: island tortoises
Genetic Drift: Bottleneck Effect

•   A large population declines rapidly.
•   The survivors reproduce and the population
goes up in number, but the new population
resembles the survivors.
•   The genes of the new population are often
more uniform, with less variation
•   EXAMPLE: cheetahs
Natural Selection
•   Stabilizing Selection: natural selection
removes organisms at the extremes of a
population….like Goldilocks.
Natural Selection
•   Directional selection: natural selection
removes organisms at one extreme and in
the middle, favoring one extreme.
Natural Selection
•   Disruptive selection: natural selection
removes organisms with the average form
of a trait, favoring both extremes.
How to form new SPECIES?
•   Reproductive isolation is required.
•   Allopatric speciation:
– Geographic barrier divides the population
(ocean, canyon, mountain)
•   Sympatric speciation
– Organisms all live in same area, isolated
by song, timing, mutation
single species evolves into several different
forms that live in different ways

Songbirds from South America    Honeycreepers from
Hawaii
Convergent
Evolution –
process by which
unrelated
organisms
independently
evolve similarities
similar
environments.
Nothing in biology
makes sense except in
the light of evolution.
Theodosius Dobzhansky

Charles Darwin in later years

DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 10 posted: 9/10/2012 language: simple pages: 75
How are you planning on using Docstoc?