Evolution and Systematics:
Biology 2900
Living stromatolites (Shark Bay WA)
Evolution of life
ORIGINS OF LIFE
AND PRECAMBRIAN EVOLUTION
• How did life evolve?
• What were the first living things like?
• What is the tree of life?
(text Fig, 16.1)
• Life arose ~4 Ga (109 years ago)
• No fossils; must reconstruct indirectly
Main questions about:
• Life’s defining attributes
• Earth’s environment
• First cells
EARTH’S EARLY ENVIRONMENT
• Must consider earth’s origins
• Solar system and Earth originated ~4.5 Ga
• Initially inhospitable (too hot, etc.)
• Subject to many and unpredictable impacts
• Cooling  crust
• Cooling  condensation  oceans
RNA: KEY TO EARLY EVOLUTION
• Before 1982: all known enzymes = proteins
• Proteins can perform complex tasks but cannot
propagate themselves
• DNA: can store and transmit information, but does no
“work”
• 1982: RNA as enzymes (ribozymes)
• RNA can store and transmit information and “work”
• Revolutionary for concepts of origins of life
• RNA preceded proteins and DNA on the planet
RNA AS EARLY LIFE FORM
• RNA possesses genotype and phenotype
• RNA genotype: primary ribonucleotide
sequence (single-stranded, unlike DNA)
• RNA with complex folding  3D structure
• Folded state can have active sites for catalysis
• RNA phenotype is its reactivity: catalyzes
chemicals reactions on substrates
RNA can evolve because:
• Can store information that can be propagated
• Experimental evolution of heritable phenotype
• Self-replicability
WHAT IS LIFE?
Living entities have genotype and phenotype:
• Genotype: “ability to store and transmit information”
• Phenotype: “ability to express that information”
• Evolvability
-- (1) “record and make alterations in heritable
information”
-- (2) “distinguish valuable from detrimental changes”
RNA AS EARLY LIFE FORM
• “RNA World Hypothesis”: RNA-based life forms evolved
into extant life
• DNA more stable chemically than RNA, especially when
double-stranded
Evidence for antiquity of RNA (“ghosts of an RNA world”):
• Widespread catalytic functions
• Ubiquity of ribosomes as component of replication
mechanism – framework rRNA
• Ribonucleoside phosphates (e.g., ATP) in intracellular
energy transfers
• RNA not first self-replicating evolving system:
-- evolved from simpler chemical system
• Where did RNA come from?
-- information-bearing biomolecules from inorganic
sources: where are latter from?
-- What were the reactions  large molecules?
-- How did self-assembly (polymerization) happen?
-- How were large biomolecules protected?
• How did RNA-based system  DNA- and proteinbased system?
• Primary source extraterrestrial?
-- Panspermia Hypothesis (Box 16.1);
-- Murcheson meteorite (pp. 629-30)
Early experimentation, e.g., Miller (1950s):
• Boiling water, vapour past CH4 + NH4 + H2 with
electric spark (reducing atmosphere assumed*)
• Organic products inc. glycine, α-alanine
*Less-reducing atmosphere now assumed: domination by CO2
not CH4, N2 not NH4
OPARIN-HALDANE MODEL
1. Nonbiological processes  organic molecules
(“building blocks” like nucleotides, amino acids)
2. These organic molecules in “prebiotic soup” 
biopolymers like proteins, nucleic acids
3. Some biopolymer combinations  self-replicating
organisms “feeding” on organic molecules
1)
2)
3)
(Text Fig. 16.12)
PRECELLULAR LIFE
Oldest informative sedimentary rocks: magnetite
and silicate layers in rock from banded iron formation Apatite crystal
(Akilia Island, Greenland)
(~20 µm across)
40 cm
x
Inclusion (“x”) in
etched apatite crystal
LATEST DATES OF PRECELLULAR LIFE
Inclusions of carbonaceous material within apatite
with high ratios of C12:C13 suggest biological origin:
• 3.85 Ga (Akilia Island, Greenland)
• 3.7 Ga (Ishua, Greenland)
• 3.25 Ga (Pilbara, Australia)
CELLS
• Preceded by DNA-based system of storing
information plus proteins to express
information
• All life is cellular so cenancestor was cellular
• Cenancestor << 2 Ga
Advantages:
• Compartmentalization
• Control over internal environment
(text Fig. 16.15)
CELLS AND EARLY FOSSILS
Oldest at 3.465 Ga (Apex Chert formation, Marble Bar,
Western Australia): colonies of cyanobacteria*
Simple cells stacked end-to-end
as short filaments
*Microfossils of similar age
from Swaziland
EARLIEST CELLULAR LIFE
• Apex Chert and Swaziland fossils differ
and are well differentiated
• Indirect methods necessary to pinpoint
nature of ancestral cellular organism
(text Fig. 16.16)
3.4-billion-year-old cells (South Africa)
Top row: fossils; bottom row living cells
• Stromatolites: earliest fossils = evidence of
cyanobacteria (and other bacteria)
• Evidence  root of Universal Phylogeny > 2 ga
• Cyanobacteria: originated > 3 Ga(?), responsible for
O2 atmosphere (?), ecologically dominant for 2
billion years
Section of stromatolite ~2.1 Ga;
Minnesota (from UCMP site)
(text Fig. 16.18)
Phylogeny of life based on analysis
of nucleotide squences of small-subunt rRNAs
Bacteria
Archaea
Eukarya
Different genes, different phylogenies:
Genes involved in processing/storage of genetic information
agree with small-subunit rRNA-based phylogeny
Bacteria
Archaea
Eukarya
Different genes, different phylogenies:
Genes for proteins involved with metabolism
place Bacteria and Archaea as sister lineages
Bacteria
Archaea
Eukarya
Different genes, different phylogenies:
Genes for proteins involved with metabolism
place Bacteria and Archaea as sister lineages
HORIZONTAL GENE TRANSFER
• Many inconsistencies between phylogenies based on
different gene classes used in analyses
• HMGCoA reductase from Archaeoglobus fulgidus
-- A. fulgidus is archaean based on ss rRNA
-- HMGCoA reductase gene seems to be bacterial
Horizontal (lateral) gene transfer widespread and
important esp. in early evolution: e.g., 18% of
genome of E. coli derived from lateral gene transfer
EARLY (SINGLE-CELLED) EUCARYA
590 Ma (China)*
~900 Ma (Siberia)
1.5 Ga (Australia)
Earliest: 1.85-2.1 Ga (Michigan)
Lyngbya (extant)
Fossil cyanobacteria
and extant relatives
Paleolyngbya
(950 Ma; Siberia)
Spirulina (extant)
Fossil cyanobacteria
and extant relatives (2)
Heliconema
(850 Ma; Siberia)
Gloeocapsa (extant)
Gloeodiniopsis (1.55 Ga; Bashkiria)
Entophysalis (extant)
Eoentophysalis (2 Ga; Canada)
Fossil cyanobacteria
and extant relatives (3)
Combination of inferential and fossil data to
estimate first divergence on Universal Phylogeny:
• Earliest, 4.4-3.7 Ga
• Latest, 3.4-2 Ga
• Earliest Eukaryotes by 1.85-2.1 Ga
ORIGIN OF ORGANELLES
• Evolution by “gradual refinement”: Bacteria and
Archaea
• Eucarya: complicated genomes with non-coding
DNA; complex cells with diverse organelles; much
multicellularity with differentiation of cells, tissues
• Mtochondria and chloroplasts common in Eucarya
but not universal:
-- Giardia has neither; therefore they arose within
Eucarya
(text Fig. 16.30)
Origins of mitochondria
and chlorpolasts within Bacteria
• Mitochondria and chloroplasts possess their own
chromosomes:
-- small and circular in form like in Bacteria
• Margulis: these organelles evolved from
endosymbiotic arrangement involving bacteria
• Evolutionarily speaking:
-- Mitochondria are purple bacteria (Proteobacteria)
-- Branch of interest within Proteobacteria includes
many forms with close associations with other
species – rhizobacteria, agrobacteria, rickettsias
-- Chloroplasts are cyanobacteria
“Once the fundamental life processes of DNA
replication, protein synthesis, respiration,
and cell division had evolved, a spectacular
diversification of life ensued.”
-- text, p. 663
INCREASING COMPLEXITY:
MULTICELLULARITY
• Overall coordination of some key function is
necessary and sufficient condition
• Bacterial colonies can undergo self-organized
patterned growth
-- lack overall coordination, so not multicellular
• Developmentally differentiated cell types in a
colony make it truly multicellular
• Multicellular eukaryotes: by late Proterozoic
Proterozoic (Precambrian)
• Everything before 543 Ma
• >80% of Earth’s history
Late Proterozoic = Ediacaran
• England, Namibia, Newfoundland, Russia
THE FOSSIL RECORD
Fossil: “any trace left by an organism that lived in
the past”
Two important issues for all kinds of fossils:
• Which parts of organisms are fossilized?
• Which habitats produce fossils?
TYPES OF FOSSILS
1. Compression and impression fossils
Material buried in sediments before decomposition;
weight of material  impression
Leaf (Paleocene; Alberta)
Stoma from same
TYPES OF FOSSILS
2. Permineralized fossils
Buried structures dissolve mineral precipitates
in cells (can preserve internal structure).
Includes petrifaction: minerals and fossils
replace organic material  stone.
TYPES OF FOSSILS
3. Moulds and casts
Result from decay or dissolving of parts.
TYPES OF FOSSILS
4. Unaltered remains
Logs saturated with oil in tar sands; dung;
corpses in peat bogs, permafrost, amber
FOSSIL FORMATION
Intact remains rare; other fossil types depend on:
• Specimen durability
• Burial (usually in water-saturated environment)
• Lack of oxygen
Most fossils are hard structures, e.g. teeth, shells
Rich fossil environments: depositional anoxic
environments with fine-grained deposit and little
disturbance
BIASES IN FOSSIL RECORD
• Ecological bias
• Taxonomic bias
• “Parts” bias
• Temporal bias
CONTINENTAL DRIFT
• Cuvier, Lyell and others knew about great sealevel fluctuations, different climates; various
theories proposed
• Lyell suggested crustal lifts/declines triggered
climatic changes
• Antonio Snider-Pelligrini (1858): fit of
coastlines on opposite sides of Atlantic
• Movement championed by
Alfred Wegener (1880-1930);
treatise 1915
from Antonio Snider-Pellegrini (1858)
Late Permian (255 Ma)
Late Jurassic (152 Ma)
Northern:
Laurasia
Southern:
Gondwanaland
Early Late Cretaceous (94 Ma)
PLATE TECTONICS
Plate movements help explain many disjunct
distributions, e.g. Pipidae (Anura)
Pipinae
Xenopinae
PALAEOGNATHAE
Tinamous
Mexico to Patagonia
Elephant birds
Madagascar
Kiwis
New Zealand
Moas
New Zealand
Ostriches
Africa
Rheas
South America
Cassowaries
Australasia
Emus
Australia
NEORNITHES
Paleognathae
Tinamidae (A)
Ratites
Kiwis, moas (B)
Ostrich, cassowaries, emus, etc. (C)
Neognathae
Galloanserae
Megapodes, curassows, pheasants (D)
Screamers, waterfowl (E)
Neoaves (F)
Neornithes = ((A(BC))((DE)F))
NEORNITHES = ((A(BC))((DE)F))
ratites
Paleognathae
Neognathae
AVIAN BIOGEOGRAPHY AND
PLATE TECTONICS
•
•
Origins of modern birds: mainly Gondwana
History of modern birds influenced by
movements of southern continents
Oo
Or
T
O
T
E
Oe
Oc
K
E
T
K
O
E
Oc
Oe
K
EDIACARAN BIOTAS AND BEYOND
• Ediacaran: ~650 to 540 Ma (UCMP)
• Marine bacteria, marine green algae common
• First animals, e.g. Vendian (= Ediacaran) animals
(following images from UCMP)
Ediacaran Fauna (soft-bodied)
• Named after Ediacaran Hills (Australia; 1946)
• Similar faunas worldwide termed “ediacaran”
• First firm evidence of multicellularity: jellyfish,
sponges
• Some Bilateria
Windermeria
Dickinsonia
Ediacaria
Pteridinium
Bradgatia
Tribrachidium
Tribrachidium: cnidarian? echinoderm?
Ediacaran “problematica”
Spriggina: arthropod relative?
Mistaken Point, southern Avalon Peninsula
Mistaken Point: Precambrian fossils
Mistaken Point, southern Avalon Peninsula
• In 1967 MUN grad student S. B. Misra discovered
Ediacara-type fossils (~565 Ma)
• Well-preserved: layers of volcanic ash
• Good samples for different times
• Deep-water fauna, unlike most
• Some resemble sea pens
• Most of uncertain affinity
• Some shared with an English assemblage
-- then: “microcontinent” of E Newfoundland +
S Britain + U.S. east coast
“North American”
Olenellus
“European”
Paradoxides
Cambrian fossil evidence for “ancestral” Atlantic Ocean (Iapetus Sea):
ocean closed during formation of Pangea, later opened on different line.
(From Redfern R. (2000) “Origins: the evolution of
continents, oceans and life.” Weidenfeld & Nicolson)
THE PROTEROZOIC: SUMMARY
• Nearly 90% of Earth’s history before Paleozoic
• Most lineages began in Proterozoic:
-- stromatolites* (shallow waters worldwide);
declined ~700 Ma, rare after ~450 Ma
-- multicellularity (e.g., red algae, green algae,
jellyfish, sponges...)
“Layered...deposit...formed by photosynthesizing colonial cyanobacteria and other
microbes...oldest known fossils [> 3 ga]...common in Precambrian...” (NOAA)
(Text Fig. 2.18)