Download Theories of Evolution

Theories of Evolution
1) Lamarck
- French scientist
- Late 1700’s- early 1800’s
- “acquired traits” (use it or lose it) theory
traits are not determined by genes but
by “need”
EX: giraffe necks grow longer because they
stretch to reach the leaves higher up.
2) Charles Darwin
• English scientist
• Developed his theory of “natural selection”
in the mid 1800’s
• His theory was based on descent with
modification.
• Was a naturalist on the HMS Beagle
(traveled around the world, mostly the
southern hemisphere) for 5 years.
Voyage of the HMS Beagle
Darwin
Noticed organisms had some similarities
even when they lived far apart.
* Darwin’s Finches
Kept records & collected specimens
Published “The Origin of Species…”
Darwin’s Finches
Darwin read other published works and was
influenced by:
1) Lamarck’s Theory
2) Lyell’s book on Geology
3) Malthus’ book on human population
& economics
Natural Selection
Nature selects those that are best adapted
to survive.
“Survival of the Fittest”
Adaptive advantage = a favorable trait
What is fitness?
“Measure of a trait’s relative contribution to
the following generation”
Ability of a trait to lead to reproductive
success…more babies = more “fit”.
Darwin’s Theory of Natural
Selection has 4 principles
1) Individuals in a population have
differences
2) The differences of individuals are
inherited
3) Organisms have more offspring than can
survive
4) Differences that increase reproductive
success are more likely to stay in a
population
Patterns of Evolution
1) Coevolution
2 species in close association evolving
together. ( or a species evolving as a
result of evolution in another species)
These organisms may depend exclusively
on each other & be highly specialized!
2) Convergent Evolution
unrelated species becoming more similar
over time.
EX: Dolphin (mammal) and fish.
3) Divergent Evolution
related species becoming more different
over time.
Can be the result of:
1) artificial selection – humans selecting
the traits and breeding for those traits
(purebred dogs)
2) adaptive radiation – many species
evolve from one species (Darwin’s
finches)
The Peppered Moth – an
example of how human’s can
affect a species
Which colored moth has the
advantage?
Genetic Equilibrium
What is genetic equilibrium?
A balance of alleles within a population
Genetic equilibrium does not exist!
5 reason genetic equilibrium does
not exist…
1) Mutations – random mutations alter
genetic information
Sometimes new traits can develop.
Harmful traits are usually eliminated
over time.
2) Migration
Immigration – movement INTO a population
Emigration – movement out of a population
When individual organisms move in or out of
a population their genes go with them!
3) Genetic Drift
Changes in a population that are caused by
chance or random events.
EX: large volcano, fire, flood, disease
Genetic drift will have more effect on a small
population more than on a large
population.
4) Non-random Mating
Non-random mating would lead to less
“selection” and all alleles would have an
equal chance of being passed on.
Some populations do have random mating,
many animals do not.
5) Natural selection
“Bad” traits are usually eliminated from a
population as a result of natural selection.
3 ways natural selection affects
populations & their traits
1) Stabilizing selection – the “middle” trait is the
most favorable. There will be few organisms at
the extremes.
2) Directional selection
One of the “extreme” versions of a trait is the most
favorable. Most individuals will have that trait.
3) Disruptive selection
Both “extreme” traits are favorable, but the
“middle” trait is not.
Hardy - Weinberg
Shows genetic equilibrium
p2 + pq + q2 = 1
(p = dominant allele, q = recessive allele)