Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Evolution: Fact or Theory?
Tuesday, October 4, 2016

11:22 AM

Fact! Species change through time
Established long before Darwin
Easily observed in fossil record, modern populations, domesticated plants and
animals, diseases, and crops
Definition: change in the genes (morphology) of a population of organisms (species) over
time
Theory! Natural Selection explains this pattern
Charles Darwin published hypothesis in 1859
On the origin of species by means of natural selection
Theory of natural selection is very strongly supported by facts and tests
Different evolutionary mechanisms proposed since then
Mechanism of Natural Selection
Four Facts: V + I + S = A(adaptation)
All individuals vary
Many traits are inherited
Populations have the potential to over-reproduce
Resources are limited
Many individuals will perish before reproducing in the struggle for existence
Some variations enable some individuals to survive and produce more offspring than
others
These variations are more fit
Conclusion
Those populations of individuals better suited to (more adapted to) their environment
(because of inherited traits) will leave more descendants (on average)
Populations will become better adapted to their environment
Adaptation and the Environment
Adaptation (verb) is the process by which populations becomes better suited to their
environment
Adapted traits (adaptations, noun) increase an organism's fitness
Fitness = number of offspring in lifetime (Fecundity)
The environment is the agent of selection!
Environment is:
Biotic: competitors, predators, prey, mates
Abiotic: Climate, physical habitat, water depth, physical conditions
An adaptation in one environment could be detrimental in another
Convergent adaptations are strong evidence for natural selection
Convergence is a strong indication of natural selection
Theories make testable predictions about the future
Natural Selection makes predictions:
1
...
Environmental change will have a predictable effect on populations
a
...
Similar environmental pressures should cause similar adaptations (convergence)
3
...
If change is too rapid, species will go extinct
What Evolves?
Individuals cannot evolve
An individual is born and later dies
No evolutionary change occurs within lifetime
(only mutations in sperm and eggs can be inherited by offspring)
Only populations of individuals can evolve!
Individuals are replaced
Evolution occurs in populations (lineages) of individuals
Artificial - Human Selection
Selective Advantage measured by number of dark mice that survive for every 100 light mice
that survive
Only 1% selective advantage = 101 dark for 100 light
How fast can natural selection occur?
Depends on:
Availability of beneficial variants
Depends on rates of population
Reproduction rates of population
Size of population
Selective advantage of particular variants
Determined by environment!
Sexual Selection
Darwin originated idea
"The advantage which certain individuals have over other individuals of the same sex and
species, in exclusive relation to reproduction
...
Mutation
BIOL 197 Page 2

1
...
New genetic variants form because of changes in DNA
2
...
Caused by dramatic environmental and population changes
i
...
Involves bottleneck events and founder effects
3
...
Natural selection and sexual selection
b
...
Some variants are more fit than others in some environment
ii
...
Mutations
Random Outcomes
2
...
Selection
Nonrandom Outcome (adaptation)
Hardy-Weinberg Principle
Hardy-Weinberg Equilibrium
In the absence of evolution, gene frequencies will remain constant and predictable
through time
Null hypothesis for population genetics
Also how know how many AA, Aa, and aa in a population
Assumption of H-W:
1
...
Random mating (No sexual selection)
3
...
Assumes no genetic drift
4
...
No selection occurs
IF a population is not a H-W equilibrium, we can conclude evolution is occurring
Additional tests needed to identify what evolutionary mechanism is occurring
Allopatric Speciation
Speciation requires reproductive isolation
BIOL 197 Page 4

Speciation requires reproductive isolation
Allopatric (branching) speciation
1
...
Populations become geographically isolated
2
...
Overtime, populations diverge into two species
ii

---