The Origin and Evolution of
Life
The Nature of Life
• Life
– During last 4 by adapted to many environments and
physico-chemical conditions
– Most organisms live at 1 atm and 0-40oC; Some
Bacteria can live up to 1400 atm or -18 to 104oC
– Unicellular Organisms vs Non Living Molecules
(Amino acids, RNA (ribonucleic acid)
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reproduction
growth via nutrients and energy
responds to outside stimuli
Share same genetic code
chemical uniformity
– C, O, H, N, P >> nucleic acids, proteins, carbohydrates, fats
The Nature of Life
• Prokaryote vs. Eukaryote
– small (1-10 um) vs large (10-100um)
– No nucleus vs Nucleus
– DNA in nucleoid vs Membrane bounded nucleus
containing chromosomes made of DNA, RNA
– Cell division direct (binary fission) vs mitosis
and miosis
– Rare multicellular forms vs Multicellular
organism with extensive development of tissues
Building Blocks: Pattern shared by all life
• All Life: DNA => RNA => Protein
• DNA architect plans for building (instructions to build
proteins in the ribosome) transcribes information into
RNA (Blueprint)
• RNA messenger translates blueprint into proteins in
the ribosomes
• Genes code for specific proteins (enzymes)
• Enzymes are proteins that control all chemical
reactions
• Order of nitrogenous bases (read in groups of 3) {A,
T, C, G} determines the type of proteins made
• Each group of 3 codes for a specific amino acid
DNA: Our Genetic
Code
Spiral double helix of sugars and
phosphate linked together by
nitrogenous bases such as Thymine,
Cytosine, Adenine and Guanine.
A Gene is a portion of the DNA
molecule that includes approximately
1500 base pairs and a Chromosome
contains many genes
The Origin of Life
• 19th Century Ideas
– life created supernaturally
• cannot be proven scientifically
– continually being formed by
spontaneous generation of nonliving
matter
• untenable by numerous experiments
• 20th Century
– life generated spontaneously and
evolved through different steps
The Origin of Life
• Origin of life is NOT an event
• Origin of life is a continuous process
• Stages
– inorganic production of key simple organic molecules
– production of more complex molecules that can synthesize
more of the same molecule
– development of a genetic code of self-replicating molecules
(RNA,DNA,proteins)
– production of the first cell by separation of these codes
from the outer world by a membrane
• Ocean environment by 4.0 by- fossils evident at
3.8by
The Origin of Life
• Many complex organic molecules must
have formed before an organism produced
• The process of life took many steps over
the first 600 my
• Probability theory would dictate that at
least one random event would have
produced a result
• This process cannot occur on Earth today
because the simple organism would be
destroyed by oxidation or predation
Steps in the Origin of Life
• Aerobic vs. Anaerobic
– oxygen poisons living cells so early life was
anaerobic
• Lack of free Oxygen >> No Ozone layer
– UV radiation kills cells so life had to originate at
depth
– Water depths of 10m or more
• Models
– non-oxidizing secondary atmosphere rich in the
constituent chemicals for life--H2O, CO2, N
– Energy in the form of UV radiation & Hot springs
Steps in Origin of Life
• Before the first cell>>Chemical Evolution
– production of significant molecules necessary for life
• Phosphoric acid crucial to cell chemistry>> phosphoric
acid can bond molecules and promote long chain
molecule formation
• Amino acids formed first since they do not form if
oxygen present
– probably formed on clay surfaces since they are attractive
and absorptive, also protection from UV
• Larger Molecules
– amino acids are linked together by dehydration synthesis
(water loss), clays have potential to absorb water, thus
amino acids could be linked on clay surfaces
Experimental Studies
• A. I. Oparin- 1930s
– Produced sugars and fatty acids from the constituents of
an early atmosphere
• Urey and Miller- 1953
– Production of cyanide, formaldehyde and 4 different amino
acids from water vapor, methane, hydrogen and ammonia
and electrical sparks
• Subsequent Experiments
– Production of 18 of the 20 known amino acids and
extremely simple forms of DNA from gases rich in water
vapor, CO2, and nitrogen and UV radiation
– S.W. Fox (1959) produced protein-like (protenoids) chains
from a mixture of 18 amino acids at 70oC in the presence
of phosphoric acid
The Environment for Life
• Volcanic Hot Springs
• Oceanic hydrothermal
vent system
• Deep (below the level
of UV penetration)
• Clays and/or Zeolites
as templates
• Similarity with present
day chemosynthetic
heterotrophic
organisms
The First Cells
• All cells use the same genetic code
• Archaeobacteria- most primitive
– Heterotrophs: obtain energy from surroundings by
some chemical reaction
– Obtain energy by converting CO2 and H2 to CH4 or by
the reduction of sulfur compounds
• Eubacteria
– 10 Phyla, including cyanobacteria (Autotrophs:
manufacture their own food source)
• First Cells poorly developed metabolic
systems
– absorbed nutrients directly
– fermentation
Life
• Prokaryota
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Appear 3.8-3.6 by
no nucleus
single loop chromosome with all genes
reproduction-binary fission
• Eukaryota
– Single cell appear 2 by
– Multicellular appear as trace fossils 1by and as body
fossils 700my
– Nucleus with 2 pairs of chromosomes (2 copies of all
genes)
– Asexual and SEXUAL reproduction>> more combinations
Endosymbiotic Theory- Evidence the
observation that mitochondria and chloroplasts
posses their own genetic apparatus
• Stromatolites:
laminated structures
composed of layers
of cyanobacterial
(Prokaryotic
photosynthetic
bacteria) filaments
and sediment
• Foraminifera:
Calcium carbonate
secreting unicellular
eukaryotic organisms,
planktonic and
marine
Taxonomic Hierarchy
• Linnean Classification
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Kingdom
Phylum (Phyla)
Class
Order
Suborder
Superfamily
Family
Genus (genera)
Species
• Example
– Animalia, Chordata,
Mammalia, Primate,
Anthropoidea, Hominoidea,
Hominidae, Homo sapiens
Organic Evolution
• Challenge to special creation in the 18th
century
• Buffon
– Environment involved
– Concept of species
• Lamarck
– “inner want”
• Inherited characteristics
• Little used structures dissappear
How Evolution Works
• Organic Evolution is the change in populations
of species with time
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between species
within a species
during the lifetime of an individual
at the chromosomal level
at the molecular DNA level
• Species produce more offspring than can survive to
maturity
• Individual species have different genetic combinations,
thus also different anatomical attributes
• Some individuals better suited to their environments
How Evolution Works
• Organic Variation and Heredity
– individuals look like their parents but are not
exactly like them
– sexual reproduction design to produce many
and varied combinations
– random mutations in gene replication 1 in
10,000
– mutations due to chemical reactions and
radiation
• Reproductive Potential
• Natural Selection
(A) mitosis, (B)
meiosis, and (C)
fertilization.
How Evolution Works
• Reproductive Potential
– potential for rapid expansion of a species in a
given geographical area
– a species will fill a niche until it reaches a
climax
• Natural Selection (Darwin)
– interaction between genetics and environment
– “survival of the fittest” (H. Spencer)
– certain individuals are better suited
(engineered) for the habitat they inhabit
Physical Factors Controlling Natural
Selection
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Temperature (land and sea)
Water Depth (sea)
Altitude (land)
Rainfall (land)
Humidity (land)
Salinity (sea)
Light Intensity (land and sea)
Substrate (sea and land)
Seasonality (land)
Tidal Range (sea)
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Biological Factors: The Trophic
Relationship
Food web sets limits on
the number of species
• Elements govern the
structure
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predation
parasitism
competition
symbiosis
• Pyramid structure
– each trophic level
must have a lower
biomass than the
level below it (as
much as 90% drop)
Modes of Evolution
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Transformation
Speciation
Extinction
Adaptive Radiation
Divergent, Parallel and Convergent
Evolution
Modes of Evolution: Transformation
• Gradualism (Darwinian
concept)
• Change of properties
(morphological) so that over
time it warrants to be called
something else
• Transitional forms
• This mode occurs in
species with a relatively
small breeding population
• Common in vertebrates of
small isolated populations
that are broad ranging
• Adaptations to changing
environments
Gradualism
• Evolution of the Horse
• Fossils preserved in
consecutive formations
exhibit sequential
morphologic changes
• Paleocene: small browsing
animal the size of a dog,
with 4 toes on the front feet
and 3 on the back, low
crown and weak enamel on
teeth (woodland-leaves)
• In progressively younger
rocks the fossils exhibit
larger size, reduction of side
toes, increase in height and
complexity of teeth
(grasslands-grasses w/ silt)
Fig. 3.15a
An example of
progressive
evolutionary
change in a group
of Permian
ammonoid
cephalopods.
(From Spinosa,C. Furnish, W.
M., and Glenister, B. F. 1975. J.
Paleontol. 49(2): 239-283.)
Modes of Evolution: Punctuated
Equilibria
• 2 species A-B, and C
• A is a widespread species
evolving slowly or not at all
• B is an isolated small part
of species A with a deviant
anatomy
• After extinction event, B is
the only survivor and it
spreads out over a larger
area
• Unless the small population
B is found, then A appears
to change abruptly into C
Modes of Evolution: Punctuated
Equilibria vs Gradualism
• Morphological change occurs
in a sideward direction
• Time is depicted in a vertical
direction
• The short horizontal side
brances of the punctualistic
model depict sudden change,
whereas the inclined
branches of the gradualistic
model suggest slow uniform
change through time
Modes of Evolution: Speciation
• The splitting of a
species into two
or more parts as
the result of some
ecological or
geographic barrier
or due to
migration
• Barriers can be
canyons,
mountain ranges,
isthmus, deserts,
ocean basin
Speciation
• Intercontinental
migrations of
members of the
camel family
• Camels originate
in North America
during the
Eocene
• Migration through
land bridges
• Geographic and
ecological
barriers
EXTINCTION
• The rapid disappearance of a group of
organisms
• As a response to an ecological catastrophe
– Climatic Change
• The extinction of one group releases the
resources for another group to thrive
• Background Rate as a result of random factors:
– competition, predation, changes in temp., changes in
salinity
• Mass extinctions >> Catastrophic
– asteroid collision, rapid oceanic turn-over;
accelerated rates of plate tectonic (volcanism)
Adaptive Radiation
• Organisms rapidly filling new ecological niches
increasing both numbers and diversity
• Typically lasts from 5 to 10 my
• Major expansion in adaptation of one or more
original minor taxa
• Steps
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extinction rate drops
competition is reduced
speciation occurs
species transforms rapidly into different descendants
• Creation of new ecological niches by plate tectonics
Divergent Evolution: Homologous
Structures
• In 4-limbed vertebrates, the
bones of the limbs may vary
in size and shape but they
are fundamentally similar and
in similar relative positions
• Basically similar structures in
dissimilar organisms are
referred to as homologous
• The differences in
homologous structures are
the result of variations and
adaptations to particular
environmental conditions,
similarities >>common
ancestry
c:carpal; h:humerous;
m:metacarpal; r:radius;
u:ulna; 1-5:digits
Parallel Evolution
• Two related species that evolve
similar specializations to the same
sort of habitat but independently
• a) Thoatherium, a Miocene
litoptern
• b) Equus, a modern horse
• Both shared a common 5 toed
hoof mammal ancestor and
independently evolved to a onetoed foot for maximum running
endurance
Convergent Evolution
• Represented by animals with
different ancestry evolving to
similar forms and functions in
different places or at different times
• a) Dinogorgon, a saber-toothed
therapsid from the Permian of S.
America
• b) Thylacosmilus, a saber-toothed
marsupial from the Miocene of
Argentina
• c) Smilodon, a saber-toothed cat
from the Pleistocene of N. America
• The historical development of
groups of organisms so as to
depict descent from ancestors
• The depiction is called a
phylogenetic tree
• Branches on the tree are called
clades
• In cladistic phylogeny
organisms are analyzed on the
basis of characteristics they
share in order to determine
their ancestor-descendent
relationship
• The shorter the links between
groups the closer the
relationship
Phylogeny
Simple cladogram
showing the simple
primitive trait of a
vertebral column
Evolutionary “Laws”
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Haeckel’s Law
Dollo’s Law
Cope’s Law
Williston’s Law
Haeckel’s Law: Ontogeny Recapitulates Phylogeny
In its development
from embryo to
adult, the individual
passes through
(recapitulates) the
evolutionary stages
of its ancestors. Thus
the human embryo
progresses from a
single cell thru
higher invertebrate
stages to resembling
a fish, a reptile and
finally a mammal
Dollo’s Law
• Structures once lost cannot be regained
• Difficulty in duplicating the genetic
mechanism of the development of a
structure
Cope’s Law
• Organisms generally increase
in size from their ancestors
• This is possibly due to
– larger organisms have fewer
predators and a larger size
protects against many smaller
predators
– food utilization is more efficient
– thermal inertia increases, constant
body temperature
• Increase in size >> decrease in
population >> decrease in
biomass
• Leads to extinction and
increases opportunity for others
Williston’s Law
• Common
evolutionary trends
occur in related
organisms with
serially homologous
structures
• Thus structures are
reduced in numbers
• Structures become
more differentiated