Evolution
Chapter 16, 17, and 19 in textbook
Darwin’s Theory of Evolution
Evolution: the process by which all living organisms have
developed and diversified from earlier forms over
time.
Evolution is Just a Theory
– Scientific theory: well-substantiated explanation of
some aspect of the natural world that is confirmed
through observation and experimentation
– A scientific theory can be supported or disproven,
but never proven.
– Other scientific theories: Cell Theory, Theory of
Plate Tectonics, Collision Theory
Darwin’s Theory of Evolution
Darwin set sail on a voyage around the
world and made many observations.
• Organism in similar environments
around the world had similar
characteristics
– Australia has different plants and
animals than Africa
– Australia and Africa have similar
grassland environments.
– The plants and animals in both
grasslands have similar characteristics
even though they are different.
Darwin’s Theory of Evolution
• Species always seemed well-suited
for their environment
– At the Galapagos the
environment on each island is
very different.
– The animals found on each island
seemed to had changed to match
the environment.
– What can you infer about the
environments on Hood and
Isabella island by observing the
tortoises?
Darwin’s Theory of Evolution
• Ancient organisms resemble
modern organisms.
– Fossils: preserved remains or
traces of ancient organisms
– By studying fossils you can
infer why the ancient
organism no longer exist.
– What modern organism
Australopithecus and
Neanderthal resemble. Why
did they go extinct?
Idea’s That Shaped Darwin’s Thinking
Geology
• In Darwin’s time, most people believed
the Earth was a few thousand years
old.
• Geologists began to gather evidence
that the continents have been forming
for millions of years.
• How did this information help Darwin
form his theory on evolution?
Idea’s That Shaped Darwin’s Thinking
Selective Breeding
• How could a farmer use selective
breeding to get cow with larger horns?
– In order for selective breeding to
work you need natural variation.
– Natural Variation: individual
organisms of the same species can
have different characteristics.
– Darwin called this process artificial Selection
– Artificial Selection : nature provides the variation and
humans select those they find useful.
– How did this information help Darwin form his theory of
evolution? (Darwin did not know about heredity)
Idea’s That Shaped Darwin’s Thinking
Population Growth
• Economist Thomas Malthus
realized that the human
population was growing.
– If the population
continued to grow, we
would run out of
resources.
– Once we run out of
resources many people
would die.
• How did this information help Darwin develop his theory
on evolution?
Darwin’s Theory of Evolution
Darwin proposed natural selection as the mechanism of
evolution.
– Natural selection: the process by which organisms
with variations most suited to their environment
survive and produce more offspring.
3 criteria for natural selection to occur:
1. Natural Variation
2. Struggle for Existence
3. Survival of the Fittest
Darwin’s Theory of Evolution
1. Natural Variation
– There must be diversity among the
individuals of a population (the
have different characteristics).
– The traits must be heritable
2. Struggle for Existence
– Species must compete for limited
resources and avoid predators.
– Fitness: the organism’s ability to
survive and reproduce.
Darwin’s Theory of Evolution
• Survival of the Fittest
– Only the most “fit” individuals will
be able to survive and reproduce to
pass on their adaptations.
– Adaptation: any inherited
characteristic that increases an
organism’s fitness (ability to survive
and reproduce)
– Which insect has the highest
fitness?
Lamarck’s Theory of Evolution
Lamarck proposed a theory of
evolution 50 years before Darwin’s
theory.
Lamarck’s Two Ideas
1. The inheritance of acquired traits.
• Lamarck thought that traits
acquired during an organisms
life could be passed on to the
next generation.
• How would Lamarck’s explain
the evolution of a giraffe’s long
neck?
Lamarck’s Theory of Evolution
2. Use and Disuse
– Lamarck thought that body parts that were not being
used were gradually disappearing.
– How would
Lamarck
explain the
evolution of a
cave fish’s lack
of eyes?
Pattern’s of Evolution
Adaptive Radiation
• Adaptive Radiation: When a single species evolves
into several different species over time.
•
All organisms share a common descent:
– All living organism evolved from a single common
ancestor that lived billions of years ago.
– Over time, that organism evolve in different ways
to give to rise to all of the modern living
organisms.
– Organisms are closely related if they share a
recent common ancestor.
Pattern’s of Evolution
How long ago did
human and
chimpanzee’s
share a common
ancestor?
What is the
chimpanzee’s
closest living
relative?
Pattern’s of Evolution
How are new species formed
during adaptive radiation?
Speciation: The formation of
a new species through
evolution.
– Populations must be
reproductively isolated
from each other
– Populations can be
isolated by geography,
behavior or time.
Pattern’s of Evolution
2. Convergent Evolution
–
–
–
Unrelated organisms evolve similar
adaptations because they live in
similar environments
Sharks and dolphins do not share a
recent common ancestor.
They have similar characteristics
because they share a similar
environment.
Pattern’s of Evolution
3. CoEvolution
–
–
–
The evolution of two or more species, each adapting
to changes in the other
Occurs when species interact closely with each other.
Ex: Cheetah and Gazelles have co-evolve to become
the fastest and 2nd fastest land animals
Pattern’s of Evolution
4. Punctuated Equilibrium:
– Species do not evolve for long
periods of time and then go
through short period of rapid
evolution.
– What causes the period of
rapid evolution?
• Mass Extinctions: A large
number of species die out
in a short time.
•
Isolation: A group of individual gets isolated from
the main population.
Pattern’s of Evolution
5. Gradualism
– Organisms have evolve
at a slow and steady
rate.
– This theory is in contrast
with punctuated
equilibrium.
Evidence of Evolution
Homologous Body Structures
– Body structures shared by related species that have a
similar structure but different functions.
– Supports the theory that organisms evolved from a
common ancestor.
Evidence of Evolution
Analogous Body Structures
– Body parts in different
species that is similar in
function but not in
structure
– Structures evolved in
response to a similar
environmental challenge.
– Supports convergent
evolution
Evidence of Evolution
Embryology
– Closely related organisms look more
similar in the early stages of
embryonic development.
Genetics
– All living things have the exact same
genetic code.
– A group of 3 DNA nucleotides will
code for the same amino acid in all
organisms.
– Closely related organisms have a
similar DNA sequence.
Evidence of Evolution
Geologic Time Scale: a timeline
of earth’s history.
– Major changes in fossils
separate segments of time
(periods).
– The end of each “Era” is
usually a mass extinction.
– 99% of all species that ever
lived on Earth are extinct
Evidence of Evolution
Scientists must determine the age of the fossil to determine
where the organism fits in the geologic time scale.
2 Methods of Determining Age of Fossils
1. Relative Dating
– Where is it in the rock layer?
– Deeper layer = older fossil
– Can’t tell you exactly how old
the fossil is, just that it is
older or newer than another
fossil
Put the fossils in order from most modern to oldest.
Evidence of Evolution
2. Radioactive Dating
– Calculate the age of the
sample based on the
amount of radioactive
isotopes it contains.
– half life: the time
required for half of the
radioactive isotopes to
decay.
– Half life of carbon-14 is
5,715 years.
How old is a fossil if 25% of the
carbon 14 is remaining?
Origin of Life
How did life begin on Earth?
• Miller and Urey conducted an
experiment to determine if
organic molecules could be
formed under the conditions of
early Earth?
– They placed water in a flask
and they added the gases
that made up the
atmosphere at that time.
– They boiled and electrocuted it many time.
– Eventually this process produced amino acids.
Origin of Life
• The earliest forms of life had to
be anaerobic. Why?
• Most living organisms need
oxygen for cellular respiration.
• What is the main purpose of
cellular respiration?
• Anaerobic organisms used
fermentation produced energy
without oxygen.
• Cyanobacteria: the first
organism to do photosynthesis.
• How did photosynthesis change
the atmosphere?
Origin of Life
Endosymbiotic Theory: The mitochondria and chloroplasts
of eukaryotic cells were once independent prokaryotic
cells.
• The prokaryotic cells were engulf by larger cells:
– One engulfed cell became the mitochondria
– One engulfed cell became the chloroplast
• Evidence: The mitochondria and chloroplasts have their
own membranes and DNA.
Evolution as Genetic Change
Evolution, in genetic terms, is a
change in the allele frequency a
population over time.
– Gene Pool: the combined
genetic info. of all the
members of a population
– Relative Frequency: the
number of times that an allele
occurs in a gene pool compare
to the total number of alleles
What is the allele
frequency of the black
and brown alleles?
Evolution as Genetic Change
Natural selection affects polygenic traits differently than
single gene traits.
• Single-Gene Trait
• Polygenic Trait
– Controlled by one gene
that has two alleles
– Two distinct phenotypes
– Ex: Tall or Short Pea Plants
– Controlled by more than
one gene with many alleles
– Many possible genotypes
and phenotypes
– Ex: Human Height
Evolution as Genetic Change
Natural selection can affect the distributions of polygenic
phenotypes in any of 3 ways:
1. Directional Selection
– When individuals at
one end of the curve
have higher fitness
than individuals in the
middle or other end.
– Entire curve shifts
– Favors one of the
extreme variations
Evolution as Genetic Change
2. Stabilizing Selection
– Individual in the center
of the curve have
higher fitness than
those at the ends of
the curve.
– Center remains stable
but narrows entire
graph
– Favors average
individuals
– Ex: weight of human
infants
Evolution as Genetic Change
3. Disruptive Selection:
– When individuals at
each end of the curve
have higher fitness than
those in the middle
– Favors both extreme
variations
– Creates two distinct
phenotypes (can lead to
speciation)
Evolution as Genetic Change
• Genetic Drift: random change in allele frequency of a
small population due to chance.
– Does not increase the overall fitness of the population
– More likely to occur in small populations.
Evolution as Genetic Change
• Genetic Equilibrium:
when the allele
frequencies in a
population remain
constant over time.
– The population is
not evolving
Hardy-Weinberg Principle
A population will not
evolve if the following
conditions are met:
1. Random Mating
2. Large Population
3. No Migration
4. No mutations
5. No natural selection
Evolution as Genetic Change
Lamarck’s Theory of Evolution
Evaluating Lamarck’s Theory
• Lamarck was one of the
first to recognize that life
changes over time
• He also realized that
organisms were adapt to
their environment
• He didn’t know how traits
were inherited (acquired
traits cannot be inherited)
Coevolution
Darwin vs. Lamarck
Lamarck vs. Darwin