Transcript ppt

Why do organisms ‘match’ their
environment?
fitness
Natural selection:
differential survival and reproduction of individuals
based on genetic differences in some trait(s)
adaptation
• The ‘match’ is genetic and induced by
environment.
Charles Darwin figured out how natural
selection could lead to adaptive evolution.
• offspring resemble parents
• variation in traits can be inherited
• life is full of challenges!
• variation in traits  variation in fitness
Fitness:
- ability to survive and reproduce
- depends on the environment
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
mutation!
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
Generation 4: 0.12 not resistant
0.88 resistant
Natural selection – key points
differential survival and reproduction of individuals
based on genetic differences in some trait(s)
For adaptations to evolve:
- differences in the trait must cause differences in fitn
- differences in the trait must be heritable
Fitness depends on the environment.
local adaptation
Natural Selection
• Directional Selection: natural selection
removes organisms at one extreme and
in the middle, favoring one extreme:
– The peppered moth
– Bacterial resistance to antibiotics
– Insect resistance to pesticides
Natural Selection
• Stabilizing Selection: natural selection
removes organisms at the extremes of a
population:
– Birth weight in humans (heaviest and
lightest babies have the highest mortality)
Natural Selection
• Disruptive selection: natural selection that
favors two extremes of a characteristic
– Grass plants in Welsh copper mines
– Sickle cell heterozygotes in Africa
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.
Why was this little sticker so controversial?
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 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
“Inheritance of Acquired
Characteristics”
• Animals face a need to change.
• Animals make themselves change
• Animals pass on the changes to
offspring.
Darwin observed
animals and plants in
the Caribbean, South
America, Galapagos,
Hawaii, Indonesia,
Africa & Europe.
• He wrote three books
about his experiences.
• He took massive notes
in several notebooks,
working on Origin of
Species 20 years!
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 Voyage of Discovery
A reconstruction of the HMS Beagle sailing off Patagonia.
The Voyage of the Beagle
Galapagos Islands and South American
Mainland
Intra-Galapagos Variability:
Darwin’s Finches
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 Darwin: 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:
Darwin:
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 heritabl
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
reproduce leads to a gradual change in a population, with
favorable characteristics accumulating over generations
(natural selection).
Taken together, these three inferences are a statement of
Darwin’s Theory of Evolution.
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
4) Adaptation increases allelic fitness
How can allele frequency change?
1. Migration
2. Meiosis and crossing over
3. Mutation
4. Natural Selection (predators, disease,
famine, drought)
5. Genetic drift (chance changes to small
populations)
How can evolution occur?
1. Migration
2. Meiosis and crossing over
3. Mutation
4. Natural Selection (predators, disease,
famine, drought)
5. Genetic drift (chance changes to small
populations)
Evidence evolution
•
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?
Vestigial whale pelvis bones
Vestigial anthers and pollen:
Dandelions are asexual
Why does organism X have a feature
which looks exactly like a weakened,
not fully effective, overly-complex
version of an organ found in its
evolutionary ancestors, if not for
common descent via natural selection
and mutation?
Why should different organism possess related genes?
Why does the degree of
relationship of genes
match their degree of
relationship
established by other
methods?
Evidence for Evolution
– Evolution Observed
Evolution of pesticide
resistance in response
to selection.
Explain how this is
perceived as an example
of evolution.
Biogeography
Evolution of new species
• A population becomes divided by a physical
barrier (water, mountains, desert, or just a
large distance.
• The two populations experience different
selection pressures and will evolve
separately.
• Even if the two populations meet again, they
are now so different that they can no longer
interbreed. They are reproductively isolated
and are two distinct species.
Convergent
Evolution –
process by which
unrelated
organisms
independently
evolve similarities
when adapting to
similar
environments.
Nothing in biology
makes sense
except in the light of
evolution. Theodosius
Dobzhansky