Evolution V:
Macroevolution & the Origin of
Life
AP Biology
Macroevolution
• Macroevolution describes patterns of
evolution for groups of species over
extended periods of geologic time
• There are two distinct theories:
– Phyletic Gradualism
– Punctuated Equilibrium
Theories
L
gradual evolution
and speciation
stasis
extinction
Phyletic Gradualism
L
extinction
rapid evolution
and speciation
Punctuated Equilibrium
Phyletic Gradualism
• This theory argues that evolution occurs
by the gradual accumulation of small
changes.
• Individual speciation events or major
changes occur over long periods of time.
• Fossil evidence provides snapshots of
the evolutionary process, but that is
considered a testament to the
incompleteness of the available fossil
record
Punctuated Equilibrium
• This theory argues that evolutionary
history consists of geologically long
periods of stasis with little or no
evolution, interrupted, or “punctuated”
by geologically short periods of rapid
evolution
• This theory attempts to explain why
few fossils of intermediate stages are
found, since they only occur in short
bursts of evolutionary time
The Origin of Life
• The study of how life began is called
Chemical Evolution
• Heterotroph Theory: proposes that the
first cells were heterotrophs (couldn’t
make their own food)
• The theory of the origin of live can be
outlined in the following 9 steps
Origin of Life
• 1. The earth and its atmosphere are
formed
– The primordial atmosphere originated
from outgassing of the molten interior of
the planet (through volcanos) and
consisted of CO, CO2, H2, N2, H2O, S,
HCl and HCN, but little or no O2
Origin of Life
• 2. The primordial seas formed
– As the earth cooled, gases condensed to
produce primordial seas consisting of
water and minerals
Origin of Life
• 3. Complex Molecules Synthesized
– Energy catalyzed the formation of organic
molecules from inorganic molecules
– Organic “soup” formed
– Complex molecules included acetic acid,
formaldehyde, and amino acids
– These molecules are monomers that
would become the building blocks for the
synthesis of polymers
# 3 Evidence
• A.I. Oparin and J.B.S. Haldane
independently theorized that simple
molecules could only form in the absence of
the highly reactive oxygen
• Stanley Miller tested the theories of Oparin
and Haldane by simulating an experiment
under primordial conditions. He applied
electric sparks to simple gases (not oxygen)
connected to a flask of heated water. After
1 week, the water contained various organic
molecules including amino acids.
Origin of Life
• 4. Polymers and self-replicating
molecules were synthesized
– Monomers combined to form polymers.
Some made by dehydration condensation
(removal of water)
– Protenoids are abiotically produced
polypeptides. They can be
experimentally produced by allowing
amino acids to dehydrate on hot dry
substances
Origin of Life
• 5. Organic molecules were
concentrated and isolated into
protobionts
– Protobionts were the precursors of cells.
They could carry out chemical reactions
enclosed within a border across which
materials can be exchanged, but couldn’t
reproduce
– Microspheres and coacervates are
experimentally (and abiotically) produced
protobionts that have some selectively
permeable qualities
Origin of Life
• 6. Primitive Heterotrophic Prokaryotes
Formed
– Heterotrophs are living organisms that
obtain energy by consuming organic
substances (i.e. pathenogenic bacteria)
– The organic “soup” was a source of
organic material for the heterotrophic
cells to consume for energy
– As the cells reproduced, competition
drove natural selection to favor those
cells most successful at obtaining food
Origin of Life
• 7. Primitive Autotrophic Prokaryotes
were Formed
– As a result of mutation, a heterotroph
gained the ability to produce its own food.
As an autotroph, it had a successful
advantage
– Autotrophs make their own organic
compounds using light energy or the
energy of inorganic substances (i.e.
cyanobacteria)
Origin of Life
• 8. Oxygen and the Ozone Layer Formed
and Abiotic Chemical Evolution Ended
– As a by-product of the photosynthetic activity
of the autotrophs, oxygen is released and
accumulates in the atmosphere
– Ozone layer formed when O2 interacts with
UV light.
– Ozone layer blocks UV light and ends a
major source of energy for the abiotic
synthesis of organic molecules
Origin of Life
• Eukaryotes Formed (endosymbiotic
theory)
– Endosymbiotic Theory states that
eukaryotic cells originated from a mutually
beneficial association (symbiosis) among
various kinds of prokaryotes
– Mitochondria, chloroplasts, and other
organelles established residence inside
another prokaryote, producing a
eukaryote
# 9 Evidence
• A) Mitochondria and chloroplasts possess
their own DNA (circular and “naked”)
• B) Ribosomes of mitochondria and
chloroplasts resemble those of bacteria
• C) Mitochondria and chloroplasts reproduce
independently of their eukaryotic host cell
(binary fission)
• D) Thylakoid membranes of chloroplasts
resemble the photosynthetic membranes of
cyanobacteria