BIO 140: EVOLUTIONARY BIOLOGY.

Evolution – Descent with modification over long period of time.Genetics – Heredity and variation.Phylogeny – Evolutionary history of organismSystematics – Study of biological diversity in an evolutionary context.

“Nothing in biology makes sense except the light of evolution”- Dobzhansky, 1977

Evolution- Descent with modification; change in the form and behavior of organism between generation.

- Modifications occur through a lineage of population.~ “ancestors-descendant” series of population

MODIFICATION CAN BE AT DIFFERENT LEVEL- DNA- Morphology- Social Behavior~ DNA sequence divergence

Evolutionary PhenomenaOften divided into:

Microevolution- Process that occur within species

Macroevolution- Evolution above the species level; higher taxa- Evolution on a “Grand Scale”- Major events of life (fossil record)

CHAPTER 1: INTRODUCTIONA. THE HISTORY OF LIFE

Geologic time- Time scale of the distant past (millions to billions of years ago).- Established by geologists mainly from fossils and molecular data - divided into eons, era, periods and epochs.

Clock Analogy for some key events in the Earth’s historyFour Eras:

Precambrian Paleozoic Mesozoic Cenozoic

Archean or Proterozoic eon- Origin of the Earth’s crust- oldest rocks- Origin of life – photosynthetic prokaryotes - Oxygen accumulates – aerobic metabolism- Origin of Eukaryotes (protest – algae and invertebrates)

- Oldest known fossil known

Stromatolites – rocks that contain bacteria microfossils and layered mound

Cambrian Period- Sudden increase in the diversity of major animal phyla (Cambrian explosion)- These animals phyla may have existed earlier (100 mya) based on DNA sequence divergence- Most lacked skeletons or were small, remains have not been found.- Mass extinction at end of period

Ordovician period- Marine algae dominant- origin of plants- Colonization of land by diverse fungi, plants, animal

Silurian Period- Diversification of marine invertebrates- Diversity of jawless fishes (early fishes)- Colonization of land by vascular plants and arthropods.

Devonian Period- Diversification of bony fishes- First tetrapods (amphibian) and insect appear

Carboniferous Period- Extensive forests of vascular plant forms- Firs seed plat appears- Origin of reptiles- Dominance of amphibians

Permian Period- Radiation of reptiles ~ mammal-like reptiles- Origin of modern orders of insect- Extinction of many marine and terrestrial organisms at end of the period.

Triassic Period- Gymnosperms dominate landscape - Radiation of Dinosaurs- Origin of early mammals and birds

Jurassic Period- Gymnosperms

Cretaceous Period- Angiosperms- Dinosaurs become extinct

Tertiary Period: Epochs Paleocene Eocene Oligocene – primate groups including Apes Miocene Pliocene – Ape like ancestors of human appear

Quaternary Periods: Epochs

Pleistocene Epoch – ice age, human appear Recent – recorded history

WHAT ARE FOSSILS??Fossils - Preserved remnants or impressions left by organisms that lived in the past.Fossil record – Ordered array in which fossil appear within layers or strata of sedimentary rocksPaleontology – study of fossils

ROCK FORMATION Igneous – Form from volcanoes or mid oceanic ridges Sedimentary – form from deposition of minerals that precipitate out of water; where most

fossils are found *Silt- very fine Earth particles*

Metamorphic – Form from either igneous or sedimentary rocks under high temperature and pressure.

Formation of Fossils1. Sand and silt are carried by rivers to seas and swamps2. Deposits pile up and compress other sediments hollow into the rock.3. When organisms die, they settle along with the sediments; a tiny fraction preserved as fossils4. Overtime, additional strata are added containing fossils from each time period. 5. As sea levels change and the sea floor is pushed upward, sedimentary rocks are exposed6. Erosion by means reveals strata; older strata contain older fossils

Types of fossils Hard Remnants (shells, bones, teeth) of vertebrates Thin films – retain organic material

e.g. Plant leaves (myo) still green with chlorophyll; pollen. Replicas of organisms (cast formation) Trace Fossils – Footprints, animal burrows, impressions Preserved organism – in resins of trees or in glacial ice caps (mammoth that have been frozen)or

mud pits.

Methods to date Fossils Relative Dating

- Uses Fossils in each stratum of sedimentary rock- Compare or correlate the strata at one location and at another location by the presence of similar fossil called “index fossils”

RECALL!Geologists have established the Geologic Time ScaleHow was this determined?? -The boundaries are marked in the fossil record by:

1. Explosive radiations of new life forms.2. Mass extinctions due to catastrophe

For Relative Dating the record of rocks serve as:

1. Serial that chronicles the relative ages of fossils2. Tells the order in which group of species that are present in a sequence of strata involved3. “Before” and “after” proximation

Absolute dating- Ages given in years (not errorless)

1. Radiometric Dating - Method most often used to determine age of rock and fossils- Fossils contain isotopes of elements that accumulated in the organisms where they were live*Isotopes – forms of an element that differ in the number of neutrons in an atom

- Each Radioactive isotopes has fixed rate of decay; i.e. it can be used to date a specimen*Half-life – Number of years it takes for a 50% of the element or original sample to decay:

unaffected by temperature and pressure and other environmental variables2. Other Methods

L- and D- amino acids form the chemically interconverted (racemization) Living organisms mixture of L and amino acids One can determine how long the organism has died using the rate of racemization

Based on absolute dating- The fossil record is a remarkably detailed document of phylogeny over the vast scale of geologist time.

Half-Life100% 50% 25% 12.5% 6.25% 3.125%

CONTINENTAL DRIFT- Continental plate lies on the Earth’s crust. The crust float on the underlying hot mantle-Crustal movement over long periods of time ~ a few centimeters per year.- Plate Tectonics- Correlated with the geographical distribution of life (biogeography)

~ Mass extinction~ Adaptive radiation (adaptive radiation in biological diversity)

Plate tectonics- refers to the geological processes resulting from plate movements. Convection currents of the hot mantle below contribute to plate movements Plate edges can be zones of violent tectonic activitySubduction Zone- Where the edges of one plate is being pushed over the edge of an adjacent plate - The denser plate plunges beneath its neighbor and portions of it may be melted by the intense heat within the mantle, turning the solid rock of crust into molten magma- The one denser plate pushed down, the less dense pushed upward.

The Marianas trench in the south pacific is a subduction zone over 11,000 m deep. The abrasion on subduction zones causes earthquakes and volcanic eruptions

Oceanic Ridges may also be found on plate boundaries

When the gap separate, molten rock wells up in the gap, the rocks solidify and add crust to both plate on phenomenon called seafloor spreading.

Collision of equally dense plates- When two oceanic plates on two terrestrial plates collide they pile up and build mountains.- e.g. 55 mya, the Indian plate crushed into the Eurasian plate starting the formation of Himalayas Mountain ranges.

Continental Drift – Happens about 250 mya, near the end of Paleozoic are.- Plate movements brought all land masses together into supercontinent called Pangea (all land)

IMPLICATIONS1. Living organisms came together and competed for existence.2. Habitat were destroyed3. Extinctions occurred: but this provided new opportunity for taxonomic groups that survived

the crises

About 135 MYA (mid Mesozoic) Pangea split into Laurasia (north) and Gondwana (south) land masses

RESULT: Each continent became a separate evolutionary arena. Floras and faunas of the different biogeographical areas diverged

About 65 MYA (end of <Mesozoic) Laurasia and Gondwana separated into the present day continents.

Australia isolated for 50 MY, has a unique mammals, i.e. Marsupials About 10 MYA, the Earth’s youngest major mountain range, the Himalayas, had formed (started when India collided with Eurasia) The continents continue to drift today

MASS EXTINCTIONS- two factors that govern diversity in the fossil record:

Extinction – decrease in diversity Radiation – increase In diversity

Extinction is a relatively recent discovery, during the 18th to early 19th century When several neutralists observed that some fossils forms where no longer alive. E.g. the amniotes (marine invertebrate group)

Extinctions have 2 kinds of interest in Evolutionary Biology- Evolutionary Significance

1. The question of Causality- Why do species go extinct?- Can be studied with fossil evidence- Biological and non-biological causes

2. The consequences of extinctions- When a species goes extinct, it vacates ecological space that can be exploited by another species

- The sudden extinction of a larger taxonomic group may vacate a larger space and permit a new adaptive radiation by a competing group

EXTINCTION RATE- A general survey of extinction rates shows a decreasing trend- In terms number of species going extinct per million years- The trend also shows 5 or 6 mass extinctions

MASS EXTINCTION- When extinction rates appear to be exceptionally high- Unusually high numbers of taxa become extinct- Different number of mass extinctions is recognized by different paleontologist

The Largest Mass Extinction events End-Cambrian Late-Ordovician Late-Devonian End-Permian* Later-Triassic End-cretaceous*

*two most important mass extinctions

Mass extinction and Eras- They geologist of the 19th century figured out the main eras of the earth’s history by looking for characteristic fossil faunas- Different characteristic faunas that lasted for a noticeable time (or depth) in the sediments were recognized as different periods

1. End-Cambrian (500 MYA)- Debatable due to insufficient evidence- Trilobites (with > 90 Cambrian families) were greatly reduced- Several classes of echinoderms become extinct

2. Late-Ordovician (440 MYA)- Considered 2nd largest of all times in terms of the proportion of taxa affected - May have been caused by a drop in the temperature and a drop in sea level- At this time, glaciers were present in the polar regions of the continents

3. Late-Devonian (about 360 MYA)- Many species of jawless, armored swimming vertebrates become extinct.

4. End-Permian (250 MYA)- Most devastating mass extinction of all time – biggest in history-It eliminated about 54% of marine families, 84% of genera and 80-90% of species.- Altered taxonomic composition of organisms ON LAND:- Major changes in plant assemblages- Several insect orders become extinct- The dominant amphibians were replaced by new groups of Therapsids (including the ancestors of mammals) and diapsids (including the ancestors of dinosaurs)

Several factors caused radical environment change:

About the time the continent emerged to form Pangea altered climate, the marine and terrestrial habitat.

Massive volcanic eruptions also occurred in what is now Siberia:- Species ash and lava into the atmosphere- Produced CO2 that warmed the global climate- reduced available O2 to marine organisms

5. Late-Triassic (about 200 MYA)- Decimated groups such as ammonoids and bivalves - Cropped out gastropods (e.g. snails) that could drill shelves of bivalves- Greatly affected synapsids (groups to which mammals belong) survivors gave rise to the first true mammals during Jurassic Period.

~Synapsids are characterized by temporal fenestra, a hole behind each eye socket.6. End-Cretaceous (65 MYA)

- Or Cretaceous-Tertiary extinction- Less severe but best-known mass extinction- At least half and maybe 60-75% of species

~ Many marine and terrestrial plants and animals, including the dinosaurs (except for birds)

- Many paleontologists believe this was caused by the impact of an asteroid or some other extra terrestrial body

-Climate become cooler, shallow seas receded -Large volcanic eruptions may also have contributed to the cooling through materials that blocked the sunlight.

Impact Hypothesis Postulated to be the main cause of the cretaceous extinctions Collisions of an asteroid or a large comet with earth A thin layer of clay enriched in Iridium from Cenozoic sediments

*Iridium- an element very rare on earth but common in meteorites and other extraterrestrial debris.

Recent research has focused on the Chixulub crater (65 MYO) on the Yucatan Coast of Mexico

Crater is about 180 km diameter ~ about the right size to have been caused by an asteroid with a diameter of about 10 km.

Impact may have darkened the Earth for years resulting in reduction of photosynthesis. Food chain collapsed

Released hot white debris that causes fire storm.

Causes of Mass Extinctions (Factors) Asteroid impact Changes in sea level and climate High levels of volcanic eruption (volcanism, Vulcanism) Changes in the shapes of Continents due to plate tectonic movements

* All the factors are not mutually exclusive, they could had happened all at the same time.

Effects of Factors1. Habitat Destruction

2. Change in environment unfavorable to the species.

Adaptive radiation When taxonomic groups diversify extensively Especially high after mass extinctions

~ survivors become the stock for new radiation~ sheer luck or novel characteristics or evolutionary novelty adaptive quality

Organisms fill many of the adaptive zones (ecological space) vacated or newly created by the extinctions

Adaptive Zones – a set of new living conditions and resources that present many new opportunitiese.g. Evolution of wings allowed insects to invade new niches (treetops, other islands, new

feeding and new breeding areas) New adaptive zones allowed evolution of hundreds of thousands of variation on the basic insect

body plane.g. The rise of mammalian diversity during the early Cenozoic are may have been

associated with the opening of adaptive zones after the extinction of the Dinosaur Lineages

B. EARLY EARTH AND THE ORIGIN OF LIFE

The Origin of the Universe (before life began) About 14 BYA, the universe came into being (according to astronomers and physicists) Through an explosion from an infinitely dense point (the big Bang) Hydrogen was formed shortly after and gave rise to other elements About 10 MYA, Milky Way Galaxy was formed from the collapse of a cloud of dust and gasses About 4.6 BYA, the sun was formed as a second or 3rd generation star from a stellar explosion

(supernova) giving rise to the solar system including the Earth.~ based on radiometric dating of meteorites and moon rocks

The earth formed a solid crust as it cooled and the oceans were formed about 4.5 BYA About 4 BYA, small protocontinents may have risen leading to large landmasses by about 3 BYA The oldest known rocks are younger ~ 3.8 BYA only formed later form geological processes such

as subduction of crust.

General theories on the Origin of life on Earth1. Special Creation theory2. Spontaneous generation3. Chemical Origin of Life4. Extraterrestrial Origin5. Deep Sea vents

1. Special Creation Theory - God made the Universe and the Earth in 7 days- Big-bang implied- 7 days = 7 biblical days?- All organisms created simultaneously at the same point in time No change ~ fixity of species

2. Spontaneous Generation (Abiogenesis)- Life from non-lifee.g.- Rats from dirty rags or shirt- Insects from rice grains- Flies or maggot from rotten meat Disproved by L. Pasteur

3. Chemical origin of life- First living cell arose from aggregation of inorganic elements to form primitive organic molecules- given the condition of the primitive Earth life originated between 3.5 and 4.1 BYA (the time which the earth’s crust began to solidify)- Life arose by spontaneous generation- Inorganic to organic molecules to cells…RAW MATERIALS1. Water2. Nitrogen3. Ammonia4. Carbon dioxide5. Carbon Monoxide6. Methane7. Hydrogen Gas8. Reducing atmosphere

CHEMICAL EVOLUTION IN 4 STAGES1. Abiotic synthesis and accumulation of small organic molecules2. Joining of monomers into polymers 3. Formation of protobionts (due to aggregation of abiotically produced molecules)4. Origin of heredity during or before protobiont appearance.

I. Oparin and J.B.S. Haldane postulated that the reducing atmosphere and greater UV radiation enhanced reactions joining simple molecules to produce the first organic molecules

Not possible today since O2 affects chemical bonds aerobic respiration.

Stanley Miller and Harold Murey made an apparatus with H2O, H2, CH4, and NH3 to create organic molecules. Resulted to amino acids, sugras, lipids, ATP, purines and pyrimidines

First Cells are the Protobionts – Abiotically produced moleculesProtenoids – Abiotocally synthesized polypeptides

- Can be made by dripping organic monomers onto hot sand, rock or clay- clay – substrate for abiotic synthesis of polymers since:

1. Monomers bind to charged site in clay2. Metal ions could act as catalysts of dehydration reactions in clay3. Binding sites in clay assisted in forming polymers4. Pyrite – Provides a charged surface and electrons freed during its formation

could support bonding between molecules. Iron Pyrite – fool’s gold; consist of Iron and Sulfur

- al alternative to clay as substratum of organic synthesisLaboratory Evidence for Protobionts

1. Proteinoids assemble into microspheres surrounded by a selective permeable membrane2. Liposomes can form spontaneously from phospholipids

Coacervates (named by Oparin) One type of protobionts formed from a suspension of macromolecules is shaken Colloidal aggregates or droplets of polysaccharides, nucleic acids and polysaccharides

Origin of Genetic Information RNA- first genetic material Amino acids aligned along RNA molecules by a primitive mechanism Proteins and enzymes evolved RNA chains base pair with each other to produce DNA DNA replace RNA as the genetic material because it is more stable

Features of RNA1. RNA polymers can replicate (Replicability)2. Can serve as template on which polypeptide form (code for information, NA Protein)

Hypothesis for the origin of polypeptide synthesis and the genetic code (Smith et.al. 1995) Ribozyme H links specific small nucleotides to amino acids forming a cofactor The RNA ribozyme ancestor of mRNA, binds to the cofactor Ribozyme R, evolves into ribozyme R2, which can link amino acids together

Several evidences suggest that RNA preceded DNA:1. Single stranded RNA is simpler trhan DNA which can is always double-stranded.2. RNA can take on many different structures depending on its nucleotide sequence

~ Same structural forms allow RNA to act as enzyme (or Ribozyme) catalyzing biochemical reactions e.g. Replication of RNA

3. “Pre-biotic” soup experiment has readily yielded the nucleotide U rather that T.

Transition from RNA to DNA Possibly because RNA has a high mutation rate More complex life forms could not evolve until the mutations rate reduced The evolution of DNA would have led to a reduction of mutation rate

The minimum Criteria for a living cell1. It can capture energy from environment2. It can use energy to replicate itself3. It can carry out metabolism

In living organisms, they said functions are carried out by: Nucleic Acid – carry information which can be replicated Proteins – help replicate nucleic acids, transducer energy and generate or constitute the

phenotype Lipid Membrane – hold the components together in compartments

Protobionts exhibit some life properties such as:

1. Metabolism2. Self-replication3. Excitability (presence of stimulus)4. Main of an internal environment different from their surroundings

4. Extraterrestrial origin of life or PanspermiaHypotheses:

1. Through meteorites and comets2. Brought by intelligent extraterrestrial aliens

~Proofs Earth’s crater

5. Deep Sea vents Source of hot water and minerals – may have provided the energy and chemicals needed for

the early protobionts

Water Dynamics in Deep-sea Vents:1. Cold water seeps down into tiny fissures in an oceanic ridge2. Hot rocks get shocked by the cold water and crack causing little earthquakes to occur

(opening more fissures)3. Water in the cracks picks up heat from magma4. Hot water forced through hydrothermal vents brings nutrients melted from the rock below

Early Earth cycles in the sea:1. Volcanic vents under the sea release gates enclosed in bubbles2. The gases inside the bubbles reached to form simple organic compounds 3. Some bubbles to rise to the surface and pop releasing contents of the air4. The simple organic molecules released from the bubbles reacted to form more complex

compounds in the presence of radiation lightning and other energy source5. The more complex molecules fell back (as raindrops) into the sea enclosed in bubbles and

the process begins again

The Early Cell The first cells were most likely anaerobic since the early Earth’s atmosphere had little oxygen

(heterotrophic) 3.5 BYA, the oldest bacteria, like microfossils were found in layered mounds ~ stromata

Similar to the structures formed today along sea edges by cyanobacteria (blue-green algae)

These fossils appear to be photosynthetic indicating the life evolved prior to the time of the “Fossils”

Evolution of Eukaryotic CellsEarly Cells (prokaryotic, heterotrophic) Photosynthetic bacterial cells 2.2 BYA (O2) in atmosphere started to increase aerobic metabolism ~2 BYA first eukaryotic cells.

Origin of Eukaryotic cells Require the following events:1. Origin of mitochondria and chloroplast2. Origin of the nucleus3. Evolution of mitosis and meiosis4. Origin of multicellular life for more complex eukaryotes

Eutogenous Model- Infolding of the membrane led to the formation of nucleus

Endosymbiotic Model- Host cell engulfed mitochondria-like organism

Modern Symbiosis- Yeast cells in Paramecia

DEVELOPMENT OF EVOLUTIONARY THOUGHTStages:

1. Pre-Darwinian concepts: Early beliefs2. Darwin’s Theory (1859)3. Post-Darwinian: The modern synthesis

PRE-DARWINIAN Prior to 1700s Prevailing concepts had originated with Plato and Aristotle (Greek Philosophers)

PLATO – Philosophy of essestialism “Each species has an ideal form (essence) and variation arose due to accidental imperfections”

ARISTOTLE – Fixity of species“Each species had been created with fixed properties perfectly adapted to their environment”

Also believed that diving forms could be arranged in a scale or ladder of increasing complexity

Scale of nature Simple to complex In this view of life, species are fixed and do not evolve Prevailed for 2000 years

Upto 1700’s: Creationism Each species was created individually by God Earth was the center of the universe Man stood atop Creation

Those who helped lay the GroundworkA. Carl Von Linne (Swedish Doctor and Botanist, 1707-1778)

“I will sort and name many things” Sought order in the diversity of the life hoping to discover the pattern of creation Established the frame work for modern classification in his Systema Naturae (1735) ~

Animals and plants Binomial Nomenclature Established the concept of types Group species into Genera … Believed in the Fixity of Species Taxonomic groups did not imply evolutionary relationship (artificial classification) since

he believed that species were permanent creationB. Count G. L. Buffon

“I will describe and explain everything”

Wrote books that ultimately ran to 44 volumes Histoire Naturelie, Generale et Particulaire (description and life of plants and animals,

astronomy, age of earth, processes of life) His book on natural history of Animals suggested the possibility of evolution

e.g. Limb n=bones of mammals were remarkably similar might all have been inherited from a common ancestor

Differences among individual species not fixed Creation provided a relatively small number of founding species that evolved through

natural processesC. James Hutton (Scottish Geologist)

“The world is older than you think” His curiosity about the origin of minerals on the Earth’s surfaces led to the conclusion

that present day rocks had been churning and remaking themsileves again and again over an unaccounted period of time

“Gradualism” – Geologic processes occur at a slow rate that they are not readily perceived

“Uniformitarianism” – Geologic processes taking place now are the same as those that have always taken place; Popularized by Charles Lyell

Geologic processes are so uniform that their rates and effects must balanced out through time e.g. Mountain building balances erosion.

D. Jean Baptiste Lamarck (French Scientist) Species change they do it by striving Flore Francaise – Semi amateur field guide to French plants Marine invertebrates and marine fossils Believed that evolution was drive by an innate tendency toward increasing complexity

which he equated with perfection As organisms attained perfection, they become better adapted to their environment (For Lamarck) evolution responded to organisms’ sentiments interrevis “felt needs”

Specific adaptations evolve through:1. Use and Disuse – Body organs extensively become lerge and stronger while those

not use deteriorate.2. Inheritance of Aquired characteristics – modification acquired by an organism

during its life span be passed onto their offspringsE. Thomas Malthus (Englsih Clergymen, 1766-1834)

“Life is a struggle and only the fittest survive” Helped Darwin (Through selection, evolutionary change will occur) Essay on the principles of population populations tend to increase geometrically

while food supply in contrast increases arithmetically Steady threat of starvation , later on only the strongest survive

F. G. Cuvier (Paleontologist. Morphoanatomist) Reconciled the fossil evidence with his belief that species were immutable Theory of Catastrophism – Speculated that boundaries between fossil strata

corresponded in time to catastrophe events such as floods and drought. Multiple Strata indicated many catastrophes

Cuvier’s Theory of Catastrophism- Elaborated on by Louis Agassiz (Zoologist, 1807-1873)- New creation after each catastrophe

- Proposed at least 50 separate Catastrophe and creation

DARWINIAN Charles Robert Darwin (1809-1888)

Son of a physician Medicine in Edinburgh Career clergymen at Cambridge University but become more interested in natural history

The HMS Beagle Mission: To chart the oceans and collect oceanographic and biological information around the

world. Darwin (age 22) was recommended as the ship’s naturalist by John Henslow in 1831

In the course of the voyager, Darwin became an accomplished naturalist: Collected many specimens Made geological and biological observations Recorded observation (notebooks) Formulated theories to explain observation

Some important observations of Darwin The species he saw in South America differed strikingly from those in Europe Most of the animal species at Galapagos Islands were similar to those of mainland South

America Dispersal of organisms to nearby Islands The birds ~ finches, he observed varied from island to island; also the giant tortoises different

species that might have come from a common ancestor

Charles Darwin, shortly after the Beagle returned to England In 1844, Darwin wrote a long essay on natural selection and the origin of species but did not

publish it: He wanted to assemble more evidence first. Also because the subject was controversial

In 1838; Darwin read Malthus’s essay on population “Human Population grow at a faster rate than supplies of food can provide”

Leads to struggle for existence Variation and overproduction make natural selection possible

About 20 years after the voyage, In June 1858, Darwin received a manuscript from another travelling British naturalist, Alfred

Russell Wallace (1823-1913) who: Studied plants and animals in the Malay Archipelago (East Indies) Had independently concerned of natural selection almost identical to Darwin

Darwin and Wallace’s concept of Natural Selection Darwin’s Friend Charles Lyell and Joseph Hooker arranged for a simultaneous presentation of

Darwin’s 1894 essay and Wallace’s manuscript at Linean society of London on July 1, 1858. Both were given credit

The Origin of Species was published the next year, 1855:“On the Origin of the Species by Means of Natural Selection or the preservation of favoured races in the struggle for life”

Significance: Presented the first convincing case for evolution.

Provided on enormous amount of evidence from many fields to support both the concept of natural selection and evolution itself

United the field of Biology into a cohesive science The book also gave Darwin the edge over Wallace; It made the concepts more closely

associated with Darwin

DARWIN’S TWO MAJOR POINTS1. Species evolve from ancestral species and were not specially created (Descent with

modification)2. Natural selection is a mechanism that could result int eh evolutionary change (Natural selection

is the causative agent of evolution)Requirement:

1. Reproduction2. Hereditary Variation

Darwinism“Descent with modification”

Viewed history of life as a tree with many branches – some with dead ends (99% of all species that ever lived are extinct)

Most of Darwin’s book focused on how populations of individual species become better adapted to their local environment through natural selection.Variation Natural Selection adaptation

Ernst Mayr (1928) – Dissected the logic of Darwin’s theory into 3 inferences based on 5 factsFact 1: All particle species will increase in population size if their offspring give birth to other fertile speciesFact 2: Populations tend to remain stable in size except for seasonal fluctuations Fact 3: Environmental resources are limitedInference 1: production of individuals more than the environment can support leads to struggle for existenceFact 4: No 2 individuals are exactly the sameInference 2: Survival in the struggle for existence is not random but depends on the hereditary constitution of the surviving individuals Fact 5: This variation among individuals is heritable. Those individuals that are better fit to their environment leave offspring than less fit individuals Inference 3: This unequal ability of individuals to survive and reproduce will lead to gradual change in a population, with favorable characteristics accumulating over the generation

In Summary:1. Natural selection is differentiated success in reproduction2. Natural selection occurs from interaction between environment and the inherent variability in a

population3. The product of natural selection is the adaptation of populations to their environment

Great Gap In Darwin’s Theory

Darwin could not explain hereditary variation Prevailing belief the was:

- Blending inheritance ~ variation should decrease not increase- Because offspring are often intermediate between their parents in terms of feature

The Theory of Natural Selection was not accepted for the next 60 years Darwin Never New that Gregor Mendel had provided the answer in a paper published in 1865

Mendel’s Theory of particulate inheritance Inheritance is based on particles (not blending fluids) that pass from generation to generation – Thus variation can persist

The concept of “Mutation” such particles (later called Genes) developed only after 1900 (Hugo de Vries)

POST-DARWINIAN: THE MODERN SYNTHESI S Huxley (1942) called this the “modern synthesis” or evolutionary synthesis For geneticists, systematists, and paleontologist forged from the contribution They Reconciled Darwin’s theory with the fats of genetics

NATURAL SELECTION AND REPRODUCTIVE ISOLATION Act upon the resource of variability to guide populations of organisms into adaptive channels

Synthetic Theory – built around Darwin’s essential concept

After Modern Synthesis – Neutral Theory Neutralist held that most genetic variant, e.g. allozymes are determined largely by genetic drift

and gene flow Genetic Drift – Random fluctuations in gene frequencies in populations

Selectionist vs. Neutralist Most of the molecular evolution (e.g. of Protein structure) occurs by Genetic drift and the

observable genetic variation does not confer any selective advantage to individuals in the population

The neutral theory points out that an entirely neutral mutation is being fired (or maintained) in a population

Since there are many mutable sites at a locus, it is expected that any time a number of alleles is in various stages of drift toward gain or loss

Neutralist Hypothesis Called by some as non-Darwinian evolution. Appears to be supported by findings of large

amounts of enzyme and protein polymorphism

”After evolutionary biologists will be mentioned in the chapter dealing with populations”