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

Phyletic Gradualism Punctuated Equilibrium

gradual evolution and speciation

extinction

L L

extinction

rapid evolution and speciation

stasis

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