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Outline
• Evolution
– Origin of Life
– Origin of Species
•
•
•
•
Evolution
Natural Selection
Speciation
Human origin
– References
SCBI 124 General Biology
ORIGIN OF LIFE
Chemical Evolution
• The origin of life
– Abiotic synthesis of small organic molecules
(amino acids and nucleotides)
– The formation of polymers (proteins and nucleic
acids)
– Packaging into protobionts
– The origin of hertitable molecules.
Origin of Earth
• Earth
– 4.6 Billion years ago (BYA)
– 3.9 BYA; forming phase ended
– 3.8 BYA;
• The oldest rock on Earth (Issua, Greenland)
• Atmosphere
– Reducing atmosphere and “primitive soup” (Oparin and
Haldane, 1920)
– The origin of organic molecules (Miller and Urey, 1953) →
amino acids, hydrocarbon compounds
Artist’s conception of Earth
approximately 3 billion years ago
Deep-sea vents
are rich in sulfur
and iron.
Miller and Urey’s experiment using
reducing system of H2, CH4, NH3 and
water.
The Origin of Life
• Abiotic synthesis of polymers
– Polymers formed by dripping amino acid solution on hot
sand, clay or rock.
• Protobionts
– An aggregate of chemicals inside membrane-like
structure. (liposome)
• RNA World
– Ribozyme – RNA with catalytic function
– Natural selection → on protobiont with RNA
– DNA World (stable, more accurate replication)
The Origin of Cells
• Prokaryotes
– Stromatolites 3.5 MYA layers of bacteria
– The origin of electron transport system
– The oxygen revolution (from cyanobacteria) 2.72.2 BYA (10% more than present day)
The Origin of Cells
• Eukaryotes
– 2.7 BYA cholesterol, 2.2 BYA for simple alage, 2.1
BYA most agreed eukaryote
– (Serial) Endosymbiosis: the origin of
mitochondria and chloroplasts
– Cytoskeleton: the origin of sexual reproduction
– “You are what you eat” hypothesis
The origin of
eukaryotic cells
through
endosymbiosis
events.
3.5 BYA fossilized stromatolites;
Shark Bay, Australia
Iron oxide of terrestrial rock suggested
oxygen was in the air.
The Origin of Multicellulars
• Multicellulars
– Algae, plants, fungi and animals
• Early multicellulars
– 1.2 BYA small algae (1.5 BYA by molecular clock)
– 750-570 MYA → severe ice age (Snowball Earth
hypothesis)
• Colonies
– Collections of cells, some become differentiated.
Phanerozoic
Proterozoic
Homo
Mammals
Reptiles
Cretaceous
extinction
65.5 MYA
Permian
extinction
Archaen
Fish
251 MYA
Cambrian
542-488.3 MYA
Earth’s major crustal plates
Laurasia and
Gondwana
Pangaea
Continental drift
SCBI 124 General Biology
EVOLUTION IDEAS AND EVIDENCE
Nothing makes sense in
biology, except in the light of
evolution.
(T. Dobzhansky, 1973)
Introduction
• Natural selection as evolutionary process
– Population changes over time, certain heritable
traits can help organism leave offspring than
other.
• Evolutionary adaptation
– An accumulation of inherited characteristics that enhance
organisms’ ability to survive and reproduce in specific
environment.
Introduction
• Evolution
– Descent with modification
– A change over time in the genetic composition of
a population
• Speciation: new species
– A gradual appearance of all of biological
diversity.
A marine iguana, well-suited to its rocky habitat in the Galapagos Islands.
Historical Context
• Darwinism
– Timing and logic
– Resistance to the idea of evolution
• Western culture:
– Earth is a few thousand years old, populated by unchanging
organisms.
The historical context of Darwin’s life and ideas.
Catastrophism
• Fossils, Cuvier and catastrophism
– Paleontology
• The study of fossils developed by Georges Cuvier
(1769-1832)
• Catastrophism
– Not believe in gradual evolution, strata boundaries came
from catastrophism.
– Sudden and violent changes (flood or drought) that can
destropy many species.
Fossils from strata of sedimentary rock: The Colorado river and the Grand Canyon.
Lamarck’s Theory of Evolution
• Jean-Baptiste de Lmarck
– Evolutionary change explains the fossil record and
organisms’ adaptations to their environments.
• Changes occur, but no extinction.
• Species only transformed.
– How does evolution occur?
• Use and disuse
• Inheritance of acquired characteristics
– Innate drive
Acquired traits cannot be inherited: the bonsai.
Darwin’s Research
• The Origin of Species
– Species change through natural selection
• Darwin
– Shrewsbury (western England)
– University of Edinbrugh (medicine)
– Cambridge University (clergyman)
• John Henslow (botanist)
• Robert FitzRoy (captain of HMS Beagle)
The Voyage of the Beagle
• What did Darwin find?
– Various adaptation of plants and animals
– Ecological diversity, from grassland to high mountain
– South America temperate species are resembled species
in the tropic, rather than Europe temperate species.
The Voyage of the Beagle
• What did Darwin find?
– Fossils were distinct, but resemble those living species of
the continent.
– Geologic processes can change the landscape
• Principles of Geology (Chales Lyell, 1830)
– Galapagos island species
Armadillos (living species)
Megatheres (extinct species)
Capibara (living species, small)
Capibara (extinct species, large)
The voyage of HMS Beagle
Darwin’s Focus on Adaptation
• Adaptation and speciation
– Could a new species arise from an ancestral form
by the gradual accumulation of adaptations to a
different environment?
• Galapagos finches
– Their beaks and behaviours are adapted to specific food
found on their specific islands.
Darwin’s Focus on Adaptation
• The origin of species
– 1840s
• major features done, Darwin was in poor health.
– 1844
• the long essay was written but unpublished.
– 1858
• Alfred Russel Wallace wrote to Darwin
– 1859
• Darwin published “The Origin of Species”
Beak variation in
Galapagos finches
The Origin of Species
• Descent with modification
– Darwin’s view of life
– Tree of life
• Elephant evolution
– Linnaeus taxonomy
• Reflect the branching history of the tree of life as
species descended from their common ancestors.
Descent with modification: evolutionary tree of elephant
Natural Selection
• Definition
– Natural selection is the differential success in
reproduction that results from the interaction
between individuals that vary in heritable traits
and their environment.
• Differential success in reproduction
– The unequal ability of individuals to survive and reproduce.
Natural Selection
• Effects
– Over time, natural selection can increase the
adaptation of organisms to their environment.
• If the environment change or individual move to new
habitat, natural selection could sometimes give rise to
new species.
Camouflage as an
example of
evolutionary
adaptation
Natural Selection
• Unit of evolution
– A population is the smallest unit that can evolve.
• Natural selection occurs through interaction between
individual and environment, but individual do not
evolve.
• Population
– A group of interbreeding individuals belonging to a particular
species and sharing a common geographic area.
Natural Selection
• Life as Darwin see it
– Life evolve through gradual accumulation of
small changes.
• Natural selection operates in various contexts over
time as can be seen in geological evidence and the
entire diversity of life.
• Measuring evolution
– Relative proportions of heritable variations in a
population over a succession of generations.
Evidence of Evolution
• Evolution can help answer questions
– Why certain characteristics in related species have an
underlying similarity even though they may have very
different function.
• Homology
– Anatomical homologies
• Comparative embryology
– Molecular homologies
• Biogeography
• The fossil record
Homology
• Homology
– Similarity resulting from common ancestry.
– Anatomical homologies (comparative anatomy)
• Comparison of body structures between species.
Homology
• Homology
• Homologous structure
– Variation on a structural theme that was present in their
common ancestor.
– Vestigial organs
» Remnants of structures that served important functions
in the organism’s ancestors.
• Comparative embryology
– The comparison of early stages of animal development, not
visible in adult organisms.
Homology
• Homology
– Molecular homologies
• Similarity at the molecular level. All forms of life use
the same genetic machinery of DNA and RNA.
• Many share genes (bacteria vs human)
– Homologies and the tree of life
• Molecular homology can date back to the ancestral
past.
• Some homologies evolved just recently (tetrapods), 5digit limbs → nested pattern.
• Organisms evolved from a common ancestor.
Mammalian forelimbs: homologous structure
Anatomical similarities in vertebrate embryos
Comparision of a protein found in diverse vertebrates
Biogeography
• Biogeography
– The geographic distribution of species.
• Closely related species tend to be found in the same
geographic region.
• Distant region with same ecological niche occupied by
different species (sometimes look similar).
Biogeography
• Biogeography
• Australia
– Australian marsupials have eutherian lookalike. (i.e. sugar
glider and flying squirrel).
– Convergent evolution (not homologous)
• Endemic
– Species that found no where else (Galapagos, Hawaii)
Different geographic regions,
different mammalian brands
SCBI 124 General Biology
SPECIES AND SPECIATION
Outline
• Species and speciation
– What is species?
– Species concepts
– Speciation modes
– Adaptive radiation
– Tempo of evolution
– Macroevolution
– References
What is Species?
• Species
– Latin word, species=kind or appearance
• Real or artificial?
– Real entity as species can recognize its own
species.
– Higher taxonomic levels are artificial.
• Continuous or discrete
– Discrete (morphologically distinct species)
The Biological Species Concept
• Biological species concept (BSC)
– Ernst Mayr (1942)
– Members of the same species are reproductively
compatible.
• A species as a population or group of populations
whose members have the potential to interbreed in
nature and produce viable, fertile offspring, but are
unable to produce fertile offspring with other
populations.
The Biological Species Concept
• Limitations of the BSC
– Fossil (extinct species)
– Asexual organisms
– No information of reproduction = inconclusive
– Has no potential to interbreed (geographically
isolated)
Similarity between different species
(Left) The eastern meadowlark (Sturnella
magna)
(Right) The western meadowlark
(Sturnella neglecta)
Both are distinct species, their song and
behaviour are different prevent
interbreeding if they meet in the wild.
Diversity within a species
All human (Homo sapiens) can
interbreed.
Reproductive Isolation
• Reproductive isolation
– Factors that prevent members of two
species producing viable, fertile hybrid
offspring.
• Many barriers can work together.
• Gene flow restriction
Prezygotic Barriers
• Prezygotic barriers
– Before the hybrid zygotes are formed.
•
•
•
•
•
Habitat isolation
Temporal isolation
Behavioural isolation
Mechanical isolation
Gametic isolation
Postzygotic Barrier
• Postzygotic barriers
– After the hybrid zygotes are formed
• Reduced hybrid viability
• Reduced hybrid fertility
• Hybrid breakdown
Prezygotic isolation
Postzygotic isolation
Prezygotic isolation (cont)
Morphological Species Concept
• Morphological species concept
– Similarity between members of species is greater
than with other species.
• Good for both sexual and asexual species; taxonomists
use this for ages.
• Bad for its subjectivity, lack of reproductive isolation
data
Paleontological Species Concept
• Paleontological species concept
– Morphological discrete characters found from
fossils.
• Good for fossil identification.
• Bad for its lack of reproductive isolation data.
Ecological Species Concept
• Ecological species concept
– Similar ecological niche (what they eat, how they
live, etc.)
• Good for both sexual and asexual organisms.
• Bad for lack of reproductive data and different species
could have similar niche.
Phylogenetic Species Concept
• Phylogenetic species concept
– Same species with a unique genetic history
(belong to the same clade; appear as
monophyletic group)
• Good for both sexual and asexual, even fossils; can
distinguish sibling species (then confirmed with BSC)
• Bad for its requirement of extensive information (time
and money as well as man hours)
Speciation
• Speciation
– The evolution of a biological species.
– The origin of new species.
– There are two ways gene flow between
subpopulations can be interrupted.
• Allopatric speciation
• Sympatric speciation
Allopatric Speciation
• Allopatric speciation
– Greek allos=other, patra=homeland
– Gene flow interruption
– When subpopulation divided with geographic
barrier (or distance)
• Barriers’ effectiveness depending on mobility of
organisms (birds vs turtle vs plants).
• Genetic differences accumulate over time (mutations)
• Allele frequencies altered by selection, drift
Harris’s antelope squirrel
(Ammospermophilus harrisi) of the
southern rim of the Grand Canyon.
White-tailed antelope squirrel
(Ammospermophilus leucurus) of
the northern rim of the Grand
Canyon.
Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon.
Birds and other organisms that can disperse across the Grand Canyon have not
diverged into different species on opposite rims.
Can divergence of allopatric
fruit fly populations lead to
reproductive isolation?
Starch Population
Starch flies tend to
mate with other starch
flies.
The barrier is not
absolute, some flies
mate with other flies
from different
population.
Maltose Population
Maltose flies
tend to mate
with other
maltose flies.
Sympatric Speciation
• Sympatric speciation
– Greek syn=together, patra=homeland
• How can reproductive barriers (reduction in gene
flow) between sympatric populations evolve when
members remain in contact?
– Chromosomal mutation
» Polyploidy, autopolyploidy, allopolyploidy
– Nonrandom mating
» Habitat differentiation
» Sexual selection
Sympatric speciation by autopolyploidy in plants
One mechanism for allopolyploid speciation in plants
Sympatric Speciation
• Polyploid species
– The goatbeard plants (genus
Tragopogon)
• Diploid species
– T. dubius, T. pratensis and T.
porrifolius
• Tetraploid species
– T miscellus (T. dubiusxT. pratensis)
• Allopolyploid species
http://ftp.funet.fi
– T mirus (T. dubiusxT.porrifolius)
– With ongoing hybridization with its
parent species.
The lake Victoria
Only 12,000 years old, but there are 500 species of cichlid fishes. Similar
genetically, suggested that they diverged just recently, probably from food
preferences.
Does sexual selection in cichlids result
in reproductive isolation?
Under normal light,
females of both
species mate with
male of the same
species.
Under
monochromatic
orange light, females
of both species mate
indiscriminately
resulting in hybrid
and viable hybrids.
Males and females of Pundamilia pundamilia and P. nyererei
Mate choice based on male colouration by females is reproductive
barrier. As prezygotic become breached in the lab it suggests that
genetic different is small and the speciation occur just recently.
Adaptive Radiation
• Adaptive radiation
– Evolution of many diverse species
• In new environment with many ecological niches to
occupy.
• Same habitat, but after mass extinction (just what
thought to happen 65 MYA, when dinosaurs gave way
to mammals to diversify.
– Hawaii archipelago
– Australia
Dubautia laxa
Argyroxiphium sandwicense
Dubautia linearis
Dubautia waialealae
Dubautia scabra
Adaptive radiation of the silversword alliance came from only one
species of tarweed about 5 million years ago (molecular analysis).
The Tempo of Speciation
• Gradualism
– Descent with gradual modification (Darwin)
– Little changes accumulate over time.
– Species continuously adapted to the
environment.
• Punctuated equilibrium
– Niles Eldredge and Stephen Jay Gould
– Long stasis, punctuated by sudden change.
Two models for the tempo of
speciation
Gradualism model
Punctuated equilibrium model
Macroevolution
• Macroevolution
– Evolutionary changes above species levels.
– As small differences accumulated, it would
become clear and more pronounced.
• Evolutionary novelties
– Exaptation
• Structures that evolve for one thing, but have
another function sometime later (feather and
flying).
Allometric growth
Differential growth rates in human.
Legs and arms lengthen more than
head and trunk.
Comparison of chimpanzee and human
skull growth.
Similar for both chimpanzee and
human in fetus.
In adult, human skull become rounded
with little sloping whereas chimp skull
become elongated wilth sloping face.
Different
Time
Heterochrony
Salamanders that live on tree
have their digit development
end sooner, giving more
webbing to developed for
tree climbing.
Short, but more webbing
Hox mutations and the origin of vertebrates
Invertebrate with one copy of
Hox complex
First duplication occurred 520 MYA
New set of genes with new role of
backbone development.
Second duplication 425 MYA yielding 4 set
of Hox complexes made jaws and limbs
development possible.
SCBI 124 General Biology
HUMAN ORIGIN
Phylogeny of mitochondrial cytochrome oxidase II alleles
in humans and the African great apes.
129
Hominins
The earliest hominins
Aegyptopithecus sp.
Sahelanthropus tchadensis
Orrorin tugenensis
Ardipithecus kadabba
Ardipithecus ramidus
The Australopithecus genus
Australopithecus anamensis
Australopithecus bahrelghazali
Australopithecus afarensis
Australopithecus africanus
Australopithecus garhi
The Paranthropus genus
Paranthropus aethiopicus
Paranthropus boisei
Paranthropus robustus
The Homo genus
Kenyanthropus platyops
Homo habilis
H. rudolfensis
H. ergaster
H. erectus
H. floresiensis
H. antecessor
H. heidelbergensis
H. neanderthalensis
H. sapiens idaltu
H. rhodesiensis
H. cepranensis
H. georgicus
H. sapiens
Paranthropus boisei (specimen KNM-ER 406, left) and Homo ergaster (specimen
KNM-ER 3733, right) both lived in what is now Koobi For a, Kenya, about 1.7
million years ago.
131
132
Homo ergaster
Homo habilis
Homo rudolfensis
133
Homo sapiens
Homo heidelbergensis
Homo neanderthalensis
Homo erectus
134
Phylogeny of Homo sapiens and
its recent ancestors and extinct
relatives
135
Australopithecus afarensis
Laetoli Footprint
136
Neanderthal’s Last Rock Refuge
• New evidence
published in Nature
http://news.bbc.co.uk/2/hi/science/
nature/5343266.stm
– Neanderthal might have
live up to 24,000 years
ago (thought to be
30,000 years ago).
• Gorham cave, Gibraltar,
Germany.
– Homo sapiens entered
Europe about 40,000
years ago.
Gorham cave
138
Nature (13 Sep 2006) Letters to Editor
Phylogeny of Neanderthals and modern humans
139
Summary
• Evolution
– Darwin: descend with modification
– Mechanism: natural selection
– Resource: genetic variation
– Diversity: speciation
– Unit: population
– Motto:
• Gene mutates, population evolves
References
• Textbooks
– Campbell, N. A. (2008). Biology. San Francisco,
Pearson Benjamin Cummings.
– Department of Biology (2008), Biology 1.
Sukdisopa Publishing. Bangkok.
• Resource and discussion
– Biology Homepage
• http://www.sc.mahidol.ac.th/scbi