Download Darwin_and_Evolution_3

Drill

Define
• Theory
• Law
• Hypothesis
How did life begin?
Ideas as to the Origin of Life
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Extraterrestrials
Divine
Intervention
(God)
Oparin
Hypothesis
Oparin
• Hypothesized about conditions on
early earth
• Known as primordial stew or soup
• No Oxygen
• Lots of Nitrogen
• Methane
• Lightning
• Ozone from lightning
• Formed amino acids from his
experiment
Background

What is an organism?
• A living thing is an organism.

What is an offspring?
• Your kids are your offspring. (babies)

What is a species?
• Two organism are the same species when they
can have fertile offspring
• Grizzly and a polar bear

What is a population?
• Group of organisms of the same species.
Where do new species come
from?
Evolution

Evolution is a set of ideas which
explain how populations change over
time.
Evolution is NOT

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
Origin of life
A law
Opinion
A hypothesis
Directional
Ideas Relating to Evolution

Aristotle
• Things are unchanging

Couvier
• Deeper Fossils are older
• Deeper you go the more dissimilar fossils are

Lamarke
• Use Disuse Theory
• Giraffe

Malthus
• Organisms make a lot of offspring (babies)
• Some will not survive.
Evolution as the Cornerstone of Biology
Nothing in biology
makes sense except
in the light of
evolution. –
Theodosius
Dobzhansky
Charles Darwin in later years
Darwin’s Global Circumnavigation of the Globe on the HMS
Beagle Provided a Rich Source of Observations and Experiences
A reconstruction of the HMS Beagle sailing off Patagonia.
Darwin’s Observations for Natural Selection
1: The number of organisms
of each species will increase,
generation to generation.
(Malthus)
2: In nature, populations tend
to remain stable in size.
(Darwin)
3: Environmental resources are limited.
Production of more individuals than can be supported by the
environment leads competition. Not everyone will live
Darwin’s Observations and Inferences
4: Individuals of a population vary
extensively in their characteristics with no
two individuals being exactly alike.
5: Much of this variation between individuals
is heritable.
Darwin’s Observations and Inferences
So…
Survival is not random, but depends
the heritable characteristics of
individuals.
Individuals who inherit characteristics
that make them good enough to
survive are likely to leave more
offspring.
Natural Selection


Those best suited to the environment
will survive.
Survival of the fit enough
Forms of Natural Selection
Microevolution

Change in the frequency of
alleles in a population over
generations (short time
period)
Ketterwells Moths

Industrial Revolution
• Darkened Trees
• City moths observed to be darker
• Country moths observed to be lighter

Selection Pressure
• Trees Darker in the city by Soot.
Evolutionary
Timeevents
Scales
Microevolution:
Short time scale
(generation-to-generation) that change the
genotypes and phenotypes of populations.
Evolution in Action - Antibiotic Resistance in “TB Bacteria”
Initial population
has rare resistant
mutant
First round of
incomplete
antibiotic treatment
Most cells are resistant
After second round of
antibiotic treatment
population expands and
all cells are resistant
Surviving cells are
all resistant
Second round of
antibiotic treatment
Antibiotic treatment
discontinued
Population expands
in absence of
antibiotic
Population Genetics
Microevolution

A population is a
group of
interbreeding
organisms
present in a
location at a
time.
Human phenotypic variation.
Forces Which Cause
Microevolution
Natural Selection
 Mutation
 Gene Flow (Migration)
 Genetic Drift
 Non-Random Mating

Mutation
Mutation is the only source of new alleles in a species.
Mutation provides the raw material of evolution.
Mutation acting alone works too slowly to drive evolution.
With an average mutation rate,
it takes ~ 70,000 generations,
far more than the existence of
modern humans, to reduce
allele frequency by 50%.
Gene Flow or Migration
Gene flow makes separate populations more similar genetically.
The effects of gene flow are seen in many human populations.
Gene flow in plants –
wind-dispersed
pollen moving
between Monterey
pines.
Genetic Drift
Genetic drift is random fluctuation in allele frequency between
generations. Its effects are pronounced in small populations.
Non-Random Mating

If people over 6 feet tall only have
offspring with people 6 feet tall a
change in alleles is likely to happen
A Genetic Bottleneck
A genetic bottleneck is one form of genetic drift in which a population
“crashes” then rebounds.
Animals known to be affected by genetic bottlenecks include the
northern elephant seal, cheetah, and some human populations.
The Founder Effect
The founder effect is another form of genetic drift in which a small
portion of a population migrates to a new area then expands in number.
In this case, the allele frequencies in the
expanded population are often very
different from those of the founder
population.
The Founder effect accounts
for the high frequency of
Ellis-van Crevald syndrome
in Amish, retinitis
pigmentosa on Tristan da
Cunha, and colorblindness
on Pingelap.
Inbreeding – One Form of Non-Random Mating
Inbreeding occurs when related individuals mate.
Inbreeding reduces the proportion of heterozygotes and increases
the proportion of homozygotes in a population.
This is a bad idea when considering recessive genetic disorders.
Example: A mating between first cousins
increases the risk of albinism 10-fold.
Inbreeding, genetic bottlenecks and
founder effects all come into play in
conservation genetics.
Albinism – a recessive
genetic condition.
Evidence for Evoltuion
Evidence
for
Evolution?
The fossil
record
Transitional forms in
the evolution of whales.
Evidence for Evolution?
Comparative anatomy
Homologous structures in vertebrate limbs
Evidence for Evolution?
Comparative embryology
What’s the Evidence for Evolution?
Molecular
biology
To be continued….
Darwin’s Observations and Inferences
Inference 3: The unequal ability of
individuals to survive and reproduce
leads to a gradual change in a
population, with favorable
characteristics accumulating over
generations.
These three inferences are a
statement of Darwin’s Theory of
Evolution.
What is Evolution?
The kind we’re talking about is sometimes
called organic evolution to distinguish it from
non-biological changes over time.
Working definition: Evolution is the
progressive change in organisms over time.
What is Natural Selection?
Natural selection is the process in which more fit
organisms produce more offspring than less fit organisms.
For natural selection to be of evolutionary significance, at
least some of the superior fitness of parents must be
heritable.
Natural selection produces organisms better adapted (more
fit) to particular environments.
Evolution in Action - An Increase in DTT-Resistance
Following the Institution of Spraying Programs
Evolutionary Time
Scales
Macroevolution:
Long time scale
events that create
and destroy species.
The weak
link inGenetics
Darwin’s
was
Population
andtheory
Microevolution
understanding how traits were transmitted.
The rediscovery of Mendel’s
work and the development of
population genetics in the first
decades of the 20th century
greatly strengthened
evolutionary theory, leading to
the so-called synthetic theory of
evolution.
Population Genetics and Evolution
Taking a reductionist approach,
evolution can be considered as
changes in allele frequencies
over time.
What causes allele frequency
change?
“Forces” of Allele Frequency Change
Natural Selection

The force that changes allele
frequency so that a population
becomes better adapted
An Evolutionary Force That Does Not
Change Allele Frequency
One force changes genotype frequency without changing allele
frequency.
This is:
Non-random mating
Natural Selection
Natural selection leads to adaptation – an increase in the fitness of a
population in a particular environment.
Natural selection works because some genotypes are more
successful in a given environment than others.
Successful (adaptive) genotypes become more common in
subsequent generations, causing an alteration in allele frequency
over time and a consequent increase in fitness.
Stabilizing Selection of Human Birth Weight
Stabilizing Selection for the Sickle Cell Allele
In heterozygous form, the sickle cell allele of -globin confers resistance
to malaria. Therefore, the allele is maintained, even though it’s harmful
in homozygous form.
Directional
Selection
Hominid Brain Size
An Outcome of Strong Artificial Selection
Does Selection Create the Perfect Organism?
No, only better organisms as evolution
is constrained by history and buffeted
by random events.
Macroevolution and Speciation
What is a species?
The definition we’ll use – A species is a group of individuals capable
of interbreeding to produce fertile offspring.
This is the biological
species concept. Like all
attempts to define a
species, it has many
problems.
How Do
Species
Arise?
One important way
is initiated by
geographic
separation of
populations.
This leads to
reproductive
isolation, which is
the key force
driving
speciation.
Geographic Separation and Reproductive Isolation
Two species of ground squirrel descended from a common ancestral
population separated by the formation of the Grand Canyon.
There Are Many
Different
Mechanisms of
Reproductive
Isolation
Mass Extinctions Have Been a “Fact of Life” on Earth
The Dynamics of Speciation - Gradualism or
Punctuated Equilibrium?
A current debate is whether
new species arise gradually
at a constant rate or in
bursts of speciation that
may coincide with
environmental change.