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Evolution
A history of Evolutionary Thought
Humans did NOT come from apes
Early Philosophies
• Plato: organisms existed in an ideal form
– Unchanging
• Aristotle: categorized living things
– Ordered scheme called Ladder of Nature
• Primitive animals at the bottom
• Humans at the top
Evidence – Before Darwin
• Exploration of new land
– New creatures existed
• Similarities existed
• Differences apparent
• Fossil organization
– Bottom rock layers contain more primitive
fossils
– Top rock layers contain fossils that lived later
Mechanisms of Evolution –
Before Darwin
• Jean-Baptiste Lamarck’s Theory of
Inheritance of Acquired Characteristics
– Organisms could change themselves in life
– Organisms gain traits they need
– Pass on these changes to offspring
Lamarck
• Theory ultimately discarded
• There is no conscious or thought in
evolution
• Think about it...
– If you lose an arm, will all your kids have one
less arm?
– If you are born with a birthmark, will all your
kids have it to?
Darwin’s Journey
• Traveled on the HMS Beagle
• Traveled many places
• Made many observations of new species
not yet documented
Darwin’s Observations
• Snakes with rudimentary hind limbs
• Snakes with no rattle that shook their tails
like rattlesnakes
• Penguins using wings to paddle, not fly
Darwin’s Observations
• Many species on the Galapagos Islands
unlike species on the mainland
• Vast amount of finches on the island that
were similar, but had different eating
habits and therefore different beak
structure
Darwin’s Ideas
• Proposed that evolution occurs by natural
selection
• Studied ideas about 4 0 years
Competition?
• Wallace in America
– Came up with the
same ideas
– Wrote to Darwin
– Darwin rushed his to
publication first
Natural Selection
• Both naturalists came up with the idea
independently of the other
– Both published their findings in 1858
• Logically some organisms would be able
to survive better than others
– They would pass on their traits to their
offspring
So What is Evolution?
• Evolution means change
• More than change over time
– Trees lose their leaves
– Mountains rise and erode
• Evolution involves descent with genetic
inheritance
• Descent with modification!
Questions to ask
• How can one explain all these makeshift
arrangements?
• How are there so many similarities and at
the same time so many differences?
• What causes these differences?
What Darwin was saying
• Evolution occurs by natural selection
• Evolutionary Theory was proposed
• Today there are many evolutionary
theories
What will we talk about?
• Briefly discuss the Theory of Evolution
– Science trying to explain how life began using
natural methodology
• Investigate evolution
– Science explaining why and how organisms
change through time
– Organisms pass on these changes
– Has been observed in labs and in nature
Evolutionary Theory
How did life begin?
• Early life began 3.5 – 4 billion years ago
• Early organic compounds present
– Made of carbon
• Conditions were very different then
• Spontaneous generation possible then
– not known to be possible today
Time
• Geologists estimate Earth to be about 4
billion years old
• Life was not on Earth in its beginnings
Beginnings of Life:
First PROKARYOTES:
1. Accumulation of small organic molecules
•
Monomers such as amino acids &
nucleotides
2. Joining of monomers to make polymers
•
Proteins & nucleic acids
3. Joining of polymers into droplets
4. Able to pass on these characteristics
•
Heritability
Miller & Urey Experiment
• Attempted to simulate conditions on early
Earth
• Mixed water vapor, hydrogen, methane,
ammonia with energy
• Amino acids & other organic compounds
formed
See the experiment See the experiment
Hmm???
•
The first organisms on Earth were
probably
a.
b.
c.
d.
Autotrophic, aerobic eukaryotes
Heterotrophic, aerobic eukaryotes
Autotrophic, anaerobic prokaryotes
Heterotrophic, anaerobic prokaryotes
First Organisms
• Very primitive
• Prokaryotic
– Single celled
– Circular DNA
First Eukaryotes
• Theory of Endosymbiosis
– One prokaryote absorbed (endo) another
prokaryote (mitochondria)
– Instead of digesting it, they began to work
together (symbiosis)
– Different DNA in mitochondria, chloroplast,
and nucleus
See it happen
How might Evolution happen?
• Mutations in DNA
– Changes code
– Can change characteristics
– Random
– Many times lethal
– Can be helpful
Mutations
• Passed on to offspring = evolution
• Not passed on = just a mutation
Example: Antibiotic Resistance
• Antibiotics kill bacteria
• Mutation happens in bacteria
– Antibiotic does not kill that 1 bacteria
– That one bacteria divides into 2 (passes on
mutation)
– Those 2 into 4, etc.
• Now there is a population of bacteria that
are resistant to that antibiotic
• Great for the bacteria; bad for humans
Darwin’s Natural Selection
• Organisms produce more offspring than
can survive
• Populations tend to remain constant over
time
• Organisms in a species will show
differences due to different genes
Darwin’s Natural Selection
• Some variations passed on to offspring
• Not all organisms survive
– Predators
– Disease
– Competition
• Organisms that are the most fit for the
environment will survive and make more
like themselves
Evolution
• Organism
Population
Community
Ecosystem
• Smallest unit in which evolution occurs is
population
Adaptations
• Adaptation
– A certain trait arises from a mutation that
makes that organism more fit for its
environment
• Examples
– Camel
• Broad feet, little sweat/urine, sandy color
– Polar bear
• Blubber, white hair, big feet
How Organisms Change
• Species
– Like organisms capable of interbreeding
naturally
• Evolution
– Genetic change in a population over a long
period of time
• Gene pool
– Sum of all genes in a population
How Organisms Change
• Genetic Drift
– Small populations more effected by random
chance
• Adaptive Radiation
– Slow change of genotype and phenotype of a
species from common ancestor
– Become more diversified over time
Points on Evolution
• Natural Selection
– Does NOT cause genetic changes in
individuals
– Befall individuals, but occurs in populations
• Evolution
– Change in genotype frequency
– Not necessarily “good” or “progressive”
Mechanisms of Evolution
1.
2.
3.
4.
5.
Mutation
Migration
Small population
Nonrandom mating
Natural selection
Natural Selection
• When nature ‘selects’ for ‘better’ traits
• NOT done consciously
• If it works better, it will most likely:
– Survive longer
– Reproduce more
– Spread its genetics more
• Bacterial resistance
• Peppered moths
Types of Natural Selection
• Directional selection
• Stabilizing selection
• Disruptive Selection
Directional Selection
•
•
•
•
Individual have extreme values of a trait
Populations move in a certain direction
Example
Climate get colder, moves to favor those
with thicker fur
Stabilizing Selection
• Favors average
• Against those who are extreme
• Example
– Large lizards more subject to predation
– Small lizards difficult in defending territory
– Average size best of both worlds
Disruptive Selection
• Adapts individuals in a population to different
habitats
• Favors either extreme
– Llike directional selection, but favors more than one
• Areas that provide different resources
• Example
–
–
–
–
Galapagos finches had different food choice
Small bird feeds on smaller seeds
Large bird feeds on larger seeds
Average size bird competes with both
Terms
• Adaptation
– Trait/s that help an organism survive and
reproduce
• Coevolution
– Evolve together
– Usually between predator and prey
– Fastest wolf catches the deer; fastest deer
gets away
Terms
• Speciation
– The rise of a new species
• Gene pool
– The genes in a population
Mutations in Common Animals
• Rabbit story: Big ears vs. small ears
– Short-eared rabbits
• Roaches: How did they survive
– Big, fat, cockroach
• Antibiotic resistant bacteria
– We are helping by not using antibiotics
correctly
Evidence of Evolution
•
•
•
•
•
•
•
•
Fossil record
Comparative Anatomy
Homologous Structures
Vestigial Structures
Embryonic Development
Biochemical & Genetic Analysis
Artificial Selection
Observed Natural Selection
Fossil Record
• Progressive – from ancient to modern form
• Not complete
– Some better represented than others
• Fossil forms
– Bones, teeth, shells
– Petrification of softer parts
• Replaced by minerals
– Whole animals
• Glaciers, amber
Fossil Record
•
•
•
•
What creatures looked like
How long ago they lived
The deeper the fossil, the older it is
Shows how species have changed over
millions of years
• Incomplete
– Very few plants & animals become fossils
Comparative Anatomy
• Organisms that evolve in similar
environments develop similar structures
• Natural selection drives species to develop
structures best suited for their environment
Comparative Anatomy
• Convergent evolution
– 2 similar species have similar forms
• Whale & shark
• Analogous structures
– Outwardly similar function
• Wing of fly and wing of bird
Homologous Structures
• Similar in structure regardless of use
– Forearm of vertebrates
• Human, cat, whale, bat
• Derived form same common ancestor
Vestigial Structures
• Structures with no apparent purpose
– Pelvic bones of whales
– Human tail bone
– Human appendix
– Emu wing
Embryonic Development
• All vertebrates look similar in early
development
• All have gill slits and a tail (even humans)
– Gill slits are skin folds in early developing
organisms
Biochemical & Genetic Analysis
• Similarities between organisms’ DNA and
protein structures
• DNA sequencing allows us to tell which
organisms are more closely related
Artificial Selection
• Selective breeding
• Produce wanted traits in offspring
– Plump chickens
– Dairy cow that produce more milk
• Select the best offspring and breed them
together
• Reduces the number of gene in a
population’s gene pool
• Lessens diversity
Causes of Extinction
• Drastic changes in environments
– Food source is removed
• Populations have trouble adapting
• Interactions with other organisms
– Competition for resources
• Habitat change
– Leading cause of extinction!
– Catastrophic events
• Human activities
Hmm???
• Why is genetic homozygosity dangerous
to a nearly extinct species (small
population)?