The document discusses key concepts related to evolution including natural selection, descent with modification, mutations, adaptations, genetic variation, genetic drift, microevolution, macroevolution, speciation, and coevolution. It explains how small gradual changes over extremely long periods of time through various evolutionary mechanisms like natural selection can result in major changes within populations and the formation of new species through the process of descent with modification.

1. Origins of Life
Mechanisms of Evolution
- Natural Selection -

2. What is Evolution?
 Simple:
"change over time"
 Less Simple:
"descent with modification"
• many, many, MANY small changes
over LOOOOOOOOONG periods of
time that result in the formation of
many DIFFERENT types of organisms

3. Descent with
Modification
 Given enough time, many
small changes could add
up to big changes within
populations of organisms
 Mechanisms of change:
• mutation
• migration
• natural selection
• genetic drift
 Requires a very, very,
very, very, VERY long
time to happen

4. Gene Frequency
 Evolution occurs when there is
a change in gene frequency
within a population over time.
• Gene frequency:
the percentage of
a particular allele
compared to the
total of all other
alleles of the
same gene in a
given population

5. Mutations
 A mutation is a change in DNA
sequence that alters the trait a specific
gene controls
• Only one nucleotide pair in a thousand is
randomly changed every 200,000 years
• Some genes control many traits or affect
the expression of many other genes
 Caused by:
• Copying errors in the genetic material
during cell division
 Deletion
 Insertion
 Translocation
• Increased by exposure to ultraviolet
or ionizing radiation (x-rays),
chemical mutagens, or viruses

6. Results of Mutation
 Results:
• most mutations are neutral
 have no effect on
survival/reproduction
• many are harmful
 detrimental to fitness or lethal
• VERY small percent are
advantageous
 result in a change in phenotype that
improves reproductive success
 Cell type matters:
• germ cell (reproductive/sex cell)
mutations are passed on to offspring
• DNA of somatic cells aren't passed
to offspring (mutations stay local)

7. What Changes are Passed On?
 Inherited Traits:
• characteristics determined
by genes (DNA)
 eye color, height, tongue-
rolling ability
 NOT Environmental/Learned Traits:
• things your circumstances teach you
 language, how to play piano, love of cheese

8. Adaptations
"Fitness" = an organism's ability
 Adaptations are inherited to survive and reproduce
traits that improve help an
organism survive and
reproduce
• "I was born with rugged good
looks and easily found a wife,
even though there were very few
women in the Jamestown colony."
 Adaptations are NOT learned
behaviors or characteristics
• "Our family moved to the Alaska
and eventually adapted to the
climate."

9. Adaptation & Environment
 A given trait may or may not be an adaptation, depending
on the environment in which the organism lives.
Would these cats' long fur be an adaptation in...
Sahara Desert?
Alaska?

10. Gene Flow
 Gene flow occurs when organisms migrate
- new genes are introduced when an organism travels to
join a different population
- only creates
change when
populations are
isolated
• geographically
or
• reproductively

11. Natural Selection
 A mutation may improve
"fitness" (chance of
survival/reproduction)
• competition for resources
• health/hardiness
• reproductive success
• predator evasion
 Only the fittest (best adapted
to survival) can reproduce
 Traits passed on are those with
best adaptations to the current
environment

12. Case Study
 White Peppered Moth populations
dwindled and black phenotype
flourished
 Assumed bird predation
diminished the less-camouflaged
white moths
 Individuals less adapted to their
environment dwindle and may
eventually become extinct
 Experiment flaws:
• variables not accounted for:
 migration may have affected numbers
 time of release, landing behavior, diet
 the artificially high numbers released might have
created a predatory magnet

13. Speciation in Darwin’s Finches
 In the 1830’s Darwin sailed around the world and
observed incredible diversity in the population of
finches on the Galapagos Islands

14. Galapagos Finch Migration
 Natural selection
occurred as the birds
competed for food and
resources.
 Adaptations selected
by new surroundings
when they migrated
from mainland to
islands
 Geographic and then
reproductive isolation
kept the species distinct

15. Genetic Drift
 Random changes in
allele frequency
• random circumstances
cause an allele to become
more common (or extinct)
Freak
Lawnmower
Accident!
 What if the
mower-gone-
crazy takes out
all but two rose
bushes, wiping
out all the
recessive
alleles in a
population?

16. Genetic Variation
 Evolutionary change
cannot happen without a
change in genes and gene
combinations.
 Sources of variation:
• Mutation
• Gene Flow
 genetic exchange due to
the migration
 without isolation,
reduces differences
between populations
(acts against genetic
variation)
• Sexual Reproduction

17. Meiosis & Genetic Variation
 Sexual Reproduction increases genetic variation
• Crossing Over
 segments of DNA swap places during prophase 1 of meiosis
• Independent Assortment
 chromosomes line up randomly during meiosis

18. Types of Evolution
 Microevolution
• small changes within a species'
set of genes that result in
phenotypic differences
• hundreds of years (short time)
 Macroevolution
• descent with modification
• the process by which modern
organisms have descended from
ancient ancestors
due to many small
changes over
hundreds of
thousands of
years (long time)

19. Speciation
 a lineage-splitting event
that produces two or more
separate species is called
speciation
• produced in lab experiments
• populations change so much that
they no longer can interbreed and exchange genes
• seems to require geographic isolation
 Macroevolution = speciation on steroids
 Individuals DO NOT evolve over time.
...but POPULATIONS do!

20. Coevolution
Evolution in which two different
species affect each others'
adaptations.
Occurs between organisms that have
close ecological relationships:
• Competitive
 fight each other for limited
resources
• Mutualistic
 live together in a way that
helps them both survive
easier
• Predator/prey
 one hunts/eats the other as
food
• Parasite/host
 one lives off the other,
without killing it completely