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Module 10
Evolution
Abiogenesis
• Life first arose from
non-living material in
a “primordial soup”
• Experimentally
tested by Miller and
Urey
• Also called
SPONTANEOUS
GENERATION
H2S
CO
Heterotroph Hypothesis
• Explains evolution of
prokaryotic cells
• Earliest cells had to
take in nutrients
(heterotrophic)
• Earliest cells had to
live in oxygen free
conditions (anerobic)
Heterotroph Hypothesis
• Photosynthetic
prokaryotic cells
evolved, allowing for
release of free
oxygen
• Led to ozone layer
O2
Heterotroph Hypothesis
• Oxygen led to
evolution of aerobic
cells
O2
Endosymbiont Hypothesis
• Explains the evolution of
eukaryotic cells
• A symbiotic relationship
formed between larger
and smaller prokaryotic
cells – smaller cells
became mitochondria
and chloroplasts
•
YouTube - The Evolution of
Eukaryotic Organisms:
Endosymbiotic Theory
Multicellular Life
• Multicellular organisms
are made of eukaryotic
cells
• The evolution of
eukaryotic cells allowed
multicellular life to
evolve, and eventually
colonize land
Biogenesis: Life comes from life
• Although life may have arisen
spontaneously, life continues
through other life!
• Spontaneous generation has
been disproven by scientists
Biogenesis: Life comes from life
Disproven by: Francesco Redi
Biogenesis: Life comes from life
Disproven by: Louis Pasteur
Evolution = CHANGE over time
Occurs through the process of
NATURAL SELECTION
Nature “selects” the best adapted
organisms to survive and
reproduce
Natural Selection Stated Clearly
(10 min)
What is an Adaptation?
• A “heritable” trait
• Makes an organism
better suited to its role
in the ecosystem
• May be structural,
behavioral, or
physiological
Structural:
defensive structures, camouflage,
mimicry
Behavioral:
Herding, schooling, growling
Physiological:
enzymes, oxygen transport, sight
Theory of Natural Selection
• Proposed by Charles Darwin
• 4 “Requirements”
Variation
Different
phenotypes in
the population
Overproduction
Leads to
competition
Natural
Selection
Nature
“selects” the
best adapted
Survival of the
“fittest”
Best adapted
individuals have
greater reproductive
success
Individuals DON’T EVOLVE!
Individuals don’t evolve –
populations do!
This requires a change in
the “gene pool”
MUTATION:
The raw material for change
Can be
selected
FOR
Can be
selected
AGAINST
3 Selection Mechanisms
Stabilizing
Directional
Disruptive
Speciation
Speciation:
The development of a new species
Geographic
Isolation
Natural
Selection
Reproductive
Isolation
Timeframe for Evolution
Gradualism
GRADUALISM:
Occurs over a long period of time
with the accumulation of small
changes
PUNCTUATED EQUILIBRIUM:
Occurs with speciation in rapid
bursts with 1000’s of years of
stability between changes
Punctuated
Equilibrium
Evidence for Evolution
Fossil Record
May give exact age or relative age
Evidence for Evolution
Biochemical Evidence
Comparing amino acid sequences
REMEMBER…
If amino acids are
similar, DNA is
similar because
DNA is a code for
making proteins!
Evidence for Evolution
Homologous Structures
Similar bone arrangement, but
different functions
REMEMBER…
Analogous
structures do not
give evidence of
evolution from a
common ancestor!
Evidence for Evolution
Vestigial Structures
Not functional, but may have been
important in an ancestor
Vestigial Structures - SciShow
Evidence for Evolution
Comparative Embryology
Similar embryos give evidence of a
common ancestor
Evolution Today
Evolution is still happening!
However, it’s usually too slow to observe…
EXCEPT:
1) Pesticide Resistance
Evolution Today
Evolution is still happening!
However, it’s usually too slow to observe…
EXCEPT:
2) Antibiotic
Resistance