Transcript Evolution

Evolution
What is evolution?
• Biological evolution is NOT just a change
over time.
• The definition of evolution is
Descent with Modification
Some sort of change within a
lineage.
What is a species?
• Biological species concept: This
concept states that "a species is a group
of actually or potentially interbreeding
individuals who are reproductively isolated
from other such groups."
Mechanisms of Evolution
• How does evolution work?
• What are the selective forces that cause
evolution to occur?
• How can we get genetically DIFFERENT
organisms that come from the SAME
common ancestor?
Descent with Modification
• Recall, there needs to be some long
term change of the gene frequency over
time.
More beetles have genes
A
Drought causes
a decrease in
food.
B
for green color and years
later more brown beetles
than green ones.
Modes of evolution
1.
2.
3.
4.
Genetic Variability
Mutation
Genetic Drift
Natural Selection
Genetic Variation
Gene Flow
Movement of genes
from one population
to another.
Mutation
Sex
Sexual reproduction
causes new
combinations of
genes.
Changes in DNA
Mutations
Causes:
Mutations are
RANDOM
2 Types:
Somatic-not in gametes
so they are not heritable.
Germ-found in gametes
so they are heritable.
1. DNA copying error
2. Environment
Effects of Mutation
• Negative effects
– Persist in very low frequencies
– Could be a lethal mutation or cause sterility
• Positive effects
– Beneficial mutations spread rapidly
– Individuals with a beneficial mutation have a
selective advantage
Genetic Drift
• Frequencies of
particular alleles may
change by random
chance
• Prevalent in small
populations
Bottleneck Effect
• Drastic reduction in population
• High risk of mutation
• Little Variability
Founder Effect
• Founder effect – few
individuals in a new
population
• High risk of mutation
• Little Variability
Natural Selection
• Natural selection is the
process by which individual
organisms with favorable traits
are more likely to survive and
reproduce.
From Theory to Reality
• There is no magic threshold when a new
species is “made”
• Evidence Supports Theory of Evolution
– Vestigial Elements
• Elements that have appeared to have lost any
usability
• Eyes in cave organisms
• No light = no eyes, but organisms still have eye
sockets
Making new species
• New species are made when...
– Isolation of two populations
– Reduced gene flow between them
– Selection/Genetic drift
– Altered genetic composition
Once Isolation Occurs
• Selection – different pressures driving
different phenotypes/genotypes
• Genetic Drift – change in genetic makeup
of a population to do random changes
• ***Isolation of “populations” allows these
random changes to accumulate***