The Emergence of Complex Life

1
The Emergence of Complex Life

• It is an error to imagine that evolution
  signifies a constant tendency to increased
  perfection. That process undoubtedly involves a
  constant remodeling of the organism in adaptation
  to new conditions but it depends on the nature
  of those conditions whether the direction of the
  modifications effected shall be upward or
  downward
• Thomas Henry Huxley (1823-1913)

2
The Emergence of Complex Life

• We wish to learn
• What evolutionary advances have taken place at
  the level of the cell?
• What are the major events in the history of life?
• What causes extinctions, and how are extinctions
  related to opportunities for new evolutionary
  advances?
• Are rates of extinction and rates of evolution
  uniform or variable?

3
The Emergence of Complex Life
Every individual alive today, the highest as
well as the lowest, is derived in an unbroken
line from the first and lowest forms - August
Weismann
4
Lifes Origins A Chronology

• 4.6 bya formation of primitive earth and
  atmosphere
• 3.8 bya first chemical evidence of life
• 3.5 bya first fossils of procaryotic cells
• 3 bya advent of photosynthesis
• 2.5 2 bya communities of procaryotes
  (stromatolites)
• 2 1.5 bya oxygen accumulation
• 1.5 bya eukaryotic algae
• 0.6 bya Cambrian explosion

5
Evolution of Earths Atmosphere
6
Lifes Origins The Questions

• Where did the raw material for life come from?
• How did monomers develop?
• How did polymers develop?
• How did an isolated cell form?
• How did reproduction begin?

7
Lifes Origins Best Answers

• Where did the raw material for life come from?
• Early earths atmosphere
• How did monomers develop?
• Miller-Urey experiment
• How did polymers develop?
• Polymerization on clays, evaporation
• How did an isolated cell form?
• Enclosed membrane of lipid cells
• How did reproduction begin?
• RNA has the ability both to self-replicate and
  catayze reactions

8
Oparins Hypothesis

• In the atmosphere of the early Earth, energy in
  the form of ultraviolet light from the sun or
  lightning discharges could have created complex
  organic molecules from gasses such as CH4, NH3,
  and H2.
• These complex molecules might have been similar
  to the building blocks of life the amino acids
  which, when strung together in long chains, from
  proteins.
• Once formed, the complex organic molecules could
  have somehow clumped together in larger units,
  eventually taking on the characteristics of
  primitive cells.
• The gradual synthesis would have taken place in
  the early ocean, which he described as a soup
  of organic molecules.

9
Millers Experiment

• Millers classic experiment produced the organic
  building blocks of life from a simulated
  primitive atmosphere of methane, ammonia, and
  hydrogen.
• Using a high-energy electrical spark to simulate
  natural lightning, amino acids were formed.
• More recent experiments indicate that the ammonia
  and methane (though to be uncommon in the
  primordial atmosphere) can be replaced by carbon
  dioxide, which was abundant in the early
  atmosphere.
• Recent experiments also show that the electrical
  discharge mechanism can be replaced by using
  energy from ultraviolet light.

10
Findings Since Miller

• Amino acids can be replaced from other, more
  common pre-cursors, and using UV light instead of
  an electric spark
• Molecules able to catalyze chemical reactions
  have been formed
• RNA has been shown to have catalytic as well as
  self-replicating capability

11

• How did polymers develop?
• Polymerization on clays, evaporation
• How did an isolated cell form?
• Enclosed membrane of lipid cells

aggregation of macromolecules
Lipids in an aqueous solution form coacervates
12
Molecular Clues
Molecules of living organisms are rich in carbon
compounds containing hydrogen suggests little
or no free oxygen on primitive earth Only 20
amino acids of the left-handed variety are used
by living things in proteins suggests a single
origin of life DNA and RNA are the universal
basis of all life forms suggests great advantage
of this molecular machinery for reproduction and
growth ATP is the universal energy currency of
all living things suggests a common origin for
metabolism In all cells, the first steps of
carbohydrate metabolism involve fermentation, and
the last steps in aerobic organisms use oxygen in
respiration suggests that aerobic respiration
evolved from anaerobic
13
Which came first?

• DNA
• RNA
• Protein
• Carbohydrates
• Lipids

Lifes origin requires a molecule that can both
store information and catalyze the synthesis of
other molecules. RNA can catalyze simple
reactions and can help as a template for protein
synthesis and for more RNA synthesis. This
suggests that RNA was probably the first genetic
molecule to start life. Later we suspect that DNA
evolved to be a more stable molecule, and
proteins evolved to be more efficient enzymes.
RNA with catalytic activity is referred to as
ribozyme.

• DNA ? RNA ? PROTEIN
• (Genetic (Information (Catalytic and
  Information) and catalytic) Structural)

14
Crises and Innovation in Early Life
Heterotrophy (consuming organic compounds) almost
certainly evolved before autotrophy (producing
organic compounds from inorganic
materials) Innovation autotrophy. The
earliest autotrophs likely derived their H from
H2 or H2S (akin to chemosynthesis by bacteria of
deep sea vents) Crisis the H source became
exhausted Innovation Photosynthesis (using
energy of sunlight to cleave H from H20) Crisis
the resulting O2 poisoned the atmosphere (after
more than one billion years of earth
rusting) Innovation aerobic respiration
15
Advent of the Eukaryotic Cell

• Prokaryotic cell
• - lacks internal membranes
• - little internal organization
• - bacteria, blue-green algae
• Eukaryotic cell
• - nucleus (internal membrane)
• - sub-cellular organelles
• -chromosomes
• -mitochondria
• -chloroplasts
• - plants, animals, protozoans, fungi

16
Eukaryotic and Prokaryotic Cells

17

• The Probable Origin of Mitochondria and
• Chloroplasts in Eukaryotic Cells

• Endosymbiont origin
• accidental?
• Benefit was efficiency?
• Benefit was ability to become larger (to
  escape being engulfed)?

18

• Symbiosis Within a Modern Cell
• The ancestors of the chloroplasts in today's
  plant cells may have resembled Chlorella, the
  green, photosynthetic, single-celled algae living
  symbiotically within the cytoplasm of the
  Paramecium pictured here.

19
Multicellularity

• Size limits on how large a single cell can grow
  and still function efficiently
• One solution form colonies (filamentous green
  algae, sponges, etc.) Functions are not
  coordinated.
• Advanced multicellular organisms show cell
  differentiation. Specialized cells form tissues,
  different tissues to act collectively as organs,
  and different organs coordinate within the
  organism
• Evolved more than one billion years ago

20
The four eons of earth history.
Bya billion years ago, mya million
years ago
21
The three Eras of the Phaneozoic, further divided
into periods. Major events and mass extinctions
are noted
22
Major Events in the History of Life

• The history of life involves enormous change
• On occasion many species went extinct in a short
  time mass extinctions
• Over time, life has become more diverse and more
  complex
• Extinction is commonplace average species lasts
  2 - 10 million years on average, 1 2 species go
  extinct per year.
• The Earths geological and biological histories
  are intertwined.

23
(No Transcript)
24
New Arrivals, Diversification, and Decline
25
Punctuated Equilibrium

• Two views of evolutionary change
• - gradual and steady, verses
• - long periods of stasis interrupted by episodes
  of rapid change?
• Raises key questions
• - rate of evolutionary change
• - nature of process
• Fossil record not precise enough for definitive
  answers

26
The Burgess Shale provides an exceptional view of
lifes diversity at the beginning of the
Paleozoic. Some forms survive today, others are
very ancient history. If one could rewind and
re-play the tape of life, would the outcome be
the same?
27
Causes of Extinctions

• Not just species, but families and phyla
  disappear
• Most taxa that ever lived are extinct
• Causes include
• - evolution into descendent form
• - due to changes in physical environment
• - due to appearance of biologically superior
  life forms (predaton, competition)
• These are surface answers

28
Mass Extinction

• a relatively brief period of time in which more
  species go extinct than usual.
• Five major ME mark end of
  Ordovician, Devonian, Permian, Triassic,
  Cretaceous
• K T event is best known
• - end of age of reptiles
• - 63-66 mya
• - asteroid evidence iridium, crater
• Opportunity adaptive radiation

29
This Iridium signal led a Berkeley physicist to
propose that the impact of a huge meteor some
60-65 mya caused the K-T extinction event and the
extinctions of the dinosaurs.
30
(No Transcript)
31
Clocks in Molecules
32
Evolution and Natural Selection

• The history of life involves enormous change
• Over time, life has become more diverse and more
  complex
• Extinction is commonplace
• The Earths geological and biological histories
  are intertwined