Transcript Evolution Part II

Evolution Part II
Microevolution – change in a population
over time
Lamarck – a French naturalist who
worked in Paris at the Natural History
Museum.
Lamarck’s Hypothesis
1. Organisms constantly strive to improve
themselves
2. The effort to improve causes the most
used structures to improve and the
others to waste away
3. Once a structure is advanced, the trait is
passed to the offspring.
Lamarck Disproven
August Weismann – 1889 –
disproved Lamarck
Experimented with mice – cut the
tails off, but offspring still were born
with tails.
Darwin’s Voyage
1831 traveled aboard the HMS Beagle to
make maps
Read a book by Charles Lyell – Lyell
reasoned that the Earth was very old.
Darwin also studied economist, Thomas
Malthus. Malthus reasoned that without
disease, starvation, and disasters, the
human population would outgrow its
resources. Darwin thought this of all
species.
Natural Selection
There is variation in populations
(mutations)
Some mutations are favorable
More young are produced each
generation than can survive
Those that survive and reproduce
have favorable mutations
Over a long, long time small changes
accumulate and populations change
Wallace
Alfred Russel Wallace – Presented
the same theory as Darwin, but
papers and journals were lost in fire
Mechanisms of Natural Selection
Variations occur by mutation,
recombination during sexual reproduction,
and random fertilization
Niche – an organism’s way of life and its
use of the environment
The niche includes whether or not the
animal is a predator and things the animal
needs to survive – light, temp., moisture
When the niche changes, the organisms
with the most favorable characteristics will
survive and reproduce
Peppered Moths
English peppered moths live in the forests.
Before the industrial revolution, the trees in the
forest were covered with gray lichen.
The moths were speckled light gray.
Occasionally there were black moths born in the
population because of mutations
During the industrial rev., the lichen died and the
trees became darker in color
The black moths thrived and reproduced because
they were better suited to the niche.
Charles Darwin
Voyage of the Beagle
Types of Selection
Types of Selection
1. Directional – when one extreme is
selected for (Ex. Moths)
2. Disruptive – when both extremes
are selected for (ex. Weeds)
3. Stabilizing – when the average is
selected for (human height)
4. Sexual – male competition and
female choice
Genetic Equilibrium
Gene pool is the combined genetic
makeup of a population
Genetic equilibrium occurs when a
population is NOT evolving and the
allele frequency is constant
1. No natural selection, random
mating, no mutations, no migration
Hardy-Weinberg equilibrium
Genetic Drift
Genetic drift – an accidental change
in gene pool. Can cause drastic
changes in small populations. Can
be caused by reproductive isolation
or catastrophe.
Genetic Drift
Bottleneck effect
• Drastic reduction in population size
• Ex. Population of cheetahs
• Inbreeding occurs when population
size drops
• This decreases genetic variability
• Makes them less “fit”
Founder Effect
Type of genetic drift
When a few individuals colonize an
island, lake, or other new habitat
What Darwin observed with finches
on the Galapagos
Founder effect on humans
Ex. In 1814, 15 people founded a
British colony on a group of islands
in the Atlantic
One colonist carried the recessive
allele for retinitis pigmentosa blindness
Of the 240 residents in 1960, 4 had
the disorder, and 9 were carriers
That is a higher frequency than in
Britain
Gene Flow
Gene flow is the loss or gain of
alleles in a population
USA is an example
Mutations
A mutation is a change in someone’s
DNA
Single mutations don’t have much of
an effect on a gene pool, but those
with mutations that make them more
successful will be selected for and
pass the mutation on to offspring
Mutations are the raw material for
evolution
Survival of the fittest
The individuals who work best in the
habitat leave the most offspring
Their alleles have the most impact
on the gene pool
Evolution of Cardiovascular
Disease
Rare among small populations of
humans whose diets resemble that of
early humans
Early humans who had the tendency
to eat fatty foods were more likely to
survive famine
Maybe that is why we have the taste
for fatty, sweet foods
Antibiotic resistance
Some mutated bacteria can survive
antibiotics
Tuberculosis-causing bacteria
Just like the pesticide-resistant
plants in the web activity
Speciation
Species – an interbreeding
population of organisms that produce
healthy, fertile offspring
Speciation usually begins by
reproductive isolation
Allopatric and Sympatric
Allopatric Speciation
Patterns of Evolution
Divergent evolution – when two isolated
population evolve independently (Ex.
Brown and polar bears)
Adaptive radiation – rapid evolution of a
variety of species from a single ancestor
(ex. Darwin’s finches)
Convergent Evolution – when two
organisms without a common ancestor
occupy the same niche, so they have the
same characteristics. (ex. Porpoise and
penguin)
Adaptive Radiation