Transcript Theories of Evolution A. Development of Theories

II. Theories of Evolution
A. Development of Theories
Observations Lead to a Question
• 13 species of finches unique to Galápagos islands
• ALL most closely resemble 1 finch species
living on the South American mainland.
• The hypothesis: the islands were colonized
by a single finch species that strayed from
the mainland -- This bird adapted differently
to the different habitats on each island
• key characteristic of the finches -- beaks
– adapted to the foods available on the each island
• How did these different beaks arise? -through natural selection
1. Jean-Baptiste Lamarck (1744-1829)
First person to suggest that life evolved
a) The law of Use
and Disuse
b) Inheritance of
acquired
characteristics
Lamarck believed that giraffes stretched their necks to reach
food. Their offspring and later generations inherited the
resulting long necks
Charles Darwin
2. Darwin’s Theory: Natural
Selection (Based on his observations)
a)
b)
c)
d)
Variation exists within all species
Populations always tend to increase
The amount of resources is limited
There will be a struggle for the
available resources
e) Organisms who are most fit will live
longer and have more offspring. (The
offspring will inherit advantageous
traits)
Most giraffes used to have short necks, but some had slightly
longer necks. When the food on the lower branches was eaten,
many of the giraffes with shorter necks died of starvation,
leaving the ones with slightly longer necks to survive and
reproduced. Through many generations, the giraffes with longer
necks became the most common.
Pesticides = Natural Selection in
Action
• Pesticides: poisons used to kill insects
• 100’s of insects have developed pesticide resistance
• Survivor bugs after the first pesticide treatment had
genes that somehow enabled them to resist the
chemical attack.
• Survivor’s offspring inherited the genes for pesticide
resistance.
• A pesticide does not create resistant
individuals, but selects for resistant insects
that are already present in the population.
Artificial Selection
• selective breeding of plants / animals
produce offspring w/genetic traits that
humans value
• plant breeders improve traits -- grain
production, disease resistance, protein
content
• animal breeders select for growth rate or
temperament
• Breeders play the role of the environment,
allowing only those plants or animals with
desired traits to reproduce.
Artificial Selection
• Darwin observed that artificial selection
could produce a great deal of change in a
species in a short time.
• He reasoned that over thousands of
generations, natural selection could also
cause major change.
• Artificial Selection = humans choose
• natural selection favors traits that benefit
the organisms in their particular
environment
• environmental conditions do the "selective
breeding."
3. Origin of Variation
• Genetic Recombination
(Sexual reproduction. Meiosis,
Crossing over and random
fertilization)
• Mutation (Produces New
Genes)
B. Mechanisms of Evolution
1. Species and Populations
• Evolution cannot be seen in
an individual because their
genes do not change.
a) Evolution is a change in the
genetic make up of a
population
b) Gene Pool- all the different
alleles (gene forms) in a
population
2. Hardy-Weinburg principle
Gene Pool
2.
Population Genetics Or
Fun with Hardy-Weinburg!
The Math!
Let P = the frequency of Dominant Genes in a population
Let q = the frequency of Recessive genes in a population
Therefore:
P+q=1
All the dominant genes + all the recessive genes = all the genes
Individuals can be:
Genotypes
Hardy-Weinburg Notation
Homozygous Dominant
Heterozygous
Homozygous Recessive
Therefore:
PP or P2
p
Pq + qP or 2Pq
q
qq or q2
p
q
P2
Pq
qP
q2
P2 + 2Pq + q2 =1
All the Homozygous Dominant + All the Heterozygotes + All the
Homozygous Recessives = All the Population
With these formulas, you can solve all Hardy-Weinburg problems
C. Factors which Change Genetic
Equilibrium (ie. Cause Evolution)
1. Natural Selection: Favoring one genotype
over another. Ex. H. B. Kettlewell
In England, before the industrial revolution, tree bark was a lighter
color and lighter moths out numbered darker moths 9:1
Coal caused the tree bark to darken during the industrial revolution. The
darker moths then numbered the lighter moths 9:1
Types of Selection
a) Directional
Selectionconstant genetic
change of one
type. Ie. Giraffe’s
necks getting
longer. Dinosaur
size increasing
Types of Selection
b) Stabilizing
SelectionSelection that
favors the average
and eliminates the
extremes. The
population
becomes more
alike
• Siberian Huskies – sled dogs (35-60 lbs.)
• Too heavy – too slow and potentially sink in
snow
• Too light – not strong enough to pull sleds
• The population all becomes similar to each other
Types of Selection
c) Disruptive
selectionSelection that
favors the extremes
and eliminates the
average.
Population
becomes more
different. This can
lead to new species
• Meteor hit Earth 65 mya
• Food was depleted, dust blocked the sun,
tsunamis and wildfires were plentiful.
• Larger (average) animals who need lots of
oxygen and food, died out quickly.
Types of Selection
C. Factors which Change Genetic
Equilibrium (ie. Cause Evolution)
2) Gene flow- Movement of organisms in or
out of a population
3) Mutation- change in a gene form that is
unequal. Ie. Change form gene A to a more
than a to A.
4) Genetic Drift- change in gene frequency
due to random chance (some genotypes
may mate more than another just due to
chance)
5) Isolation- separation of a population so it
can’t interbreed. Either genetic or
geographic
Patterns of Evolution
1. Divergent evolution-Two separate
species becoming more different due to
different selective pressures in different
environments (human foot vs. ape foot)
a) Adaptive Radiation- process by which
species adapt to a variety of habitats
b) Speciation- formation of two separate
species from one
SPECIATION
2. Convergent
Evolution- the
process by
which distantly
related
organisms
become more
similar due to
similar selective
pressures in
similar habitats