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Evolution . Chapters 22 - 26. Evolution. Processes by which living organisms originated on Earth and have been diversified and modified through sustained changes in form and function. The earliest known fossil organisms are single-celled forms resembling modern bacteria (3.4 bya)

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Chapters 22 - 26


  • Processes by which living organisms originated on Earth and have been diversified and modified through sustained changes in form and function.

  • The earliest known fossil organisms are single-celled forms resembling modern bacteria (3.4 bya)

  • Evolution has resulted in successive radiations of new types of organisms, many which have become extinct…and some which are present day flora and fauna…extinction & diversification continue today!

Origin of life on earth
Origin of Life on Earth

  • Steps Proposed in the Origin of Life

    • Formation of the Earth ~4.6 bya and its acquisition of volatile organic chemicals by collision with comets and meteorites (precursors of biochemical molecules)

    • Prebiotic synthesis and accumulation of amino acids, purines, pyrimidines, sugars, lipids and other organic molecules in the primitive terrestrial environment

    • Prebiotic condensation reactions involving synthesis of polymers of peptides (proteins), and nucleic acids (RNA/ ribozymes) with self-replicating and catalytic abilities

Origins continued
Origins continued…

  • Steps Proposed in the Origin of Life

    • Synthesis of lipids, their self-assembly into double-layered membranes and liposomes, and the “capturing” of prebiotic (self-replicating and catalytic) molecules within their boundaries

    • Formation of a protobiont; this is an immediate precursor to the first living systems. Such protobionts would exhibit cooperative interactions between small catalytic peptides, replicative molecules, proto-tRNA, and protoribosomes. Ex., Liposome

    • RNA (PNA, more stable early form) arose before DNA

Scenarios to the origin of life
Scenarios to the Origin of Life

  • Ocean Surface (Tidal Pools) – This popular hypothesis suggests life arose in a tidepool, pond or on moist clay on the primeval Earth. Gases from volcanoes would have been energised by UV light or electrical discharges to form the prebiotic molecules in froth (Miller-Urey Expt)

Scenarios for the origin of life
Scenarios for the Origin of Life

  • Panspermia – Cosmic ancestry is a serious scientific hypothesis that proposes living organisms were “seeded” on Earth as passengers aboard comets and meteors. Such incoming organisms would have to survive the heat of re-entry.

  • http://www.nasa.gov/mission_pages/cassini/media/cassini-20080326.html Probe Finds Organic soup on Saturn Moon (Enceladus)

  • http://geology.com/nasa/life-on-saturns-moon-enceladus.shtml

Scenarios for origin of life
Scenarios for Origin of Life

  • Undersea Thermal Vents – A recently proposed hypothesis suggests that life may have arisen at ancient volcanic vents (called smokers). This environment provides the necessary gases, energy, and a possible source of catalysts (metal sulfides).

Origin of eukaryotic cells know the endosymbiotic theory
Origin of Eukaryotic Cells(know the endosymbiotic theory)

Geologic time video
Geologic Time (video)

  • Life originated 3.4 bya Early Earth Environment lacked free oxygen (Urey-Miller Experiment)  concentrations of molecules led to synthesis of active chemical groupings of molecules and interactions of chemical compounds  rudimentary genetic system  Natural Selection  Anaerobic Prokaryotes (bacteria) Blue-Green Algae and aerobic photosynthesis Amalgamation of distinct cell types (first eukaryotes; endosymbiotic theory) blue-green algae evolved into chloroplasts & aerobic bacteria evolved into mitochodria DNA may have arisen through prokaryotic symbionts  single-celled eukaryotes developed complex modes of living and advanced types of reproduction multicellular plants and animals w/ free oxygen and food supplies abundant (700 mya) basic body plans of modern animals developed with a remarkable burst of evolutionary diversity (700 – 570 mya)  jellyfish and burrowing worm skeletons (570 mya)fishland plants (400 mya)arthropods (some evolving into insects) (360 mya)Dinosaurs and mammals (135 mya)extinction of dinosaurs (65 mya)human evolution (2 mya) *Know general steps (See pbs evolution web site!)

  • http://www.pbs.org/wgbh/nova/origins/

Landmarks in the origin of life
Landmarks in the Origin of Life

  • 4.6 bya Formation of the Earth and acquisition of volatile organic chemicals

  • 4.0 bya protobiont

  • 3.5 bya oldest microbial community now known is from Apex chert of northwestern Australia (cyanobacteria fossils and stromatolites)

  • 2.7 bya Compounds of oily residue squeezed out of Australian Shale suggests presence of eukaryotic cells (1 by before original prediction)

  • 2.5 bya Molecular fossil of cyanobacteria, 2-methylhopane, is abundant in organic rich sedimentary rocks from the Mount McRae shale in western Australia

  • 2.1 bya fossil imprints appear in the geological record that are so large they can only be eukaryotic cells

  • 1.1 bya Grooves in sandstone fron the Vindhyan Basin (central India) may be burrows of ancient worm-like creatures (500 my before other previous evidence)

  • 0.55 bya fossils of more complex, multi-celled creatures (e.g., fossils 1 meter across have been found in Ediacara Hilles, Finders Ranges, South Australia)

  • To present Fossil history of large eukaryotic organisms is well documented

  • Do Activity on PBS Evolution Website- Deep Time

  • Extra Credit: Go to Ocean Journey, Prehistoric Journey and/or new A&P exhibit or Ecology extra credit, DMNS

Evidence for evolution see word table
Evidence for Evolution (See Word table)

  • Paleontology (fossil record)

  • Comparative anatomy

  • Vestigial Structures

  • Comparative Embryology (developmental stages)

  • Comparative Physiology (similar enzymes, hormones, etc…)

  • Taxonomy (classification…see overhead schemas)

  • Biogeography (isolation mechanisms)

  • Genetics (gene mutations, chromosomal rearrangements, chromosome segment doubling produce variations)

  • DNA, RNA, Protein comparative analysis

  • Artificial Selection (See “Dog Evolution” video)

  • See: http://www.pbs.org/wgbh/evolution/

  • See: Campbell Powerpoint 22-09 to 22-15

  • Video Clips: Evidence for Theory of Evolution and Agents of Evolution

Fossil formation
Fossil Formation

  • Fossils are remains of long-dead organisms that have escaped decay and have, after many years, become part of the Earth’s crust.

  • Preserved remains such as an impression (cast), or marks made during lifetime (trace fossils)

  • Rapid burial of the organism usually in water-borne sediment where minerals are added and removed

  • Provide a record of the appearance and extinction of organisms; calibrated against a time scale (dating techniques-relative v. radiometric)…build a picture of evolutionary changes over time.

Fossil formation1
Fossil Formation

  • Modes of Preservation

    • Silification- silica weathered volcanic ash is gradually incorporated into partly decayed wool (petrification)

    • Phosphatisation- bones and teeth are preserved phosphate deposits

    • Pyritisation- Iron pyrite replaces hard remains of the dead organism

    • Tar pit- animals fall into and are trapped in a mixture of tar and sand

    • Trapped in Amber- gum from conifers traps insects and then hardens

    • Limestone- Calcium carbonate from the remains of marine plankton is deposited as a sediment that traps te remains of sea creatures

    • Show fossils!

Transitional Fossils- a mixture of traits that are found in 2 different, but related, taxonomic groups (e.g., Archaeopteryx)

Walking with the Dinosaurs: Genetics Video

Dating fossils
Dating Fossils

  • Fossils are rarely dated directly; the rocks in which they are found are dated

  • Methods using Radioisotopes:Fission Track (U-235); Radiocarbon (C-14); Potassium/Argon (volcanic rocks above or below fossil strata); Uranium series (U-235, U-238) into thorium (th230) and U-234

  • Non-Isotopic methods:Palaeomagnetism (alignment of Earth’s magnetic field at the same time rock sample was last heated above critical level); Thermoluminescence (measures the light emitted by a sample of quartz and/or zircon grains); Electron Spin Resonance (measures microwave energy absorbed by samples); Amino Acid Racemisation (measures the gradual conversion of Left to right handed aas); Varve (measures the distinct, annual deposits of sediments in lakes); Tree-ring (measures annual growth rings of trees and can be cross-referenced with C-140; Relative (position in rock strata)

Historical background
Historical Background years ago…

Early evolutionary studies see more notes on line
Early Evolutionary Studies years ago…(see more notes on-line)

  • Erasmus Darwin (1731-1802): Evolution of “inheritance of acquired characteristics”

  • Georges Cuvier ( 1769-1832): catastrophic extinctions explained unique sets of fossil species between successive strata

  • James Hutton (1726-1797): theory of Gradualism, profound change is the cumulative product of slow but continuous processes

  • Reverand Thomas Malthus (1766-1834): “An Essay on the Principles of Population” attempted to justify the squalid conditions of the poor by stating that poverty and starvation were merely a consequence of overpopulation

  • Charles Lyell (1797-1875): “Principles of Geology” proposed that the geological processes we observe today have always been occurring and the Earth is therefore very old

  • Hebert Spencer (1820-1903): proposed “survival of the fittest”

  • Alfred Wallace (1823-1913): “Theory of Natural Selection”

  • Gregor Mendel (1822-1884) model of inheritance

  • August Weisman (1834-1914) chromosomes as the basis of heredity (demolishes acquired characterisitcs)

  • R.A. Fischer (1890-1962), J.B.S. Haldane (1898-1964), Sewall Wright (1889-1988) Founding of population genetics and mathematical aspects of evolution and genetics

  • Julian Huxley (1887-1975), Ernst Mayer (1904-2005), T. Dobzhansky (1900-1975) helped form the mordern or synthetic theory of Darwinian Evolution incorporating developments in genetics, palaeontology, and other brances of biology

Early evolutionary studies
Early Evolutionary Studies years ago…

  • No scientific explanations of evolution were given until the 18th Century

  • The growth of natural history led to increased knowledge of fossils & living organisms

  • Jean Baptiste Lamarck (1744-1829): “Philosophe Zoologique”: patterns of resemblance found in various creatures arose through evolutionary modifications of a common lineage…environmental changes evoke in individual animals direct adaptive responses that are passed on as inheritable traits (ex. Giraffe’s long neck); idea of use and disuse and inheritance of acquired characteristics

  • May have some merit with epigenome and immune system inheritance

Early evolutionary studies1
Early Evolutionary Studies years ago…

  • Charles Darwin (1859) published his theory…offspring inherit a resemblance to their parents not solely due to environment…in nature individual’s with traits that made them better adjusted to their environments or gave them higher reproductive capacities…”higher fitness!”

  • Tenets: 1) more individuals are born than survive; 2) when environmental changes occur, populations require new properties to maintain their fitness; 3) traits are inheritable; 4) either adaptation or extinction occurs

  • Alfred Wallace had the same ideas!

What was darwin like
What was Darwin like? years ago…


Early evolutionary studies2
Early Evolutionary Studies relate to Natural Selection?

  • Mendel discovered that characteristics are transmitted across generations in discrete units, now known as “genes,” in a predictable manner

  • Inheritable changes can occur without regard to environment…evolution is driven onward by the random accumulation of favorable mutational changes

Early evolutionary studies3
Early Evolutionary Studies relate to Natural Selection?

  • Hugo de Vries, Thomas Morgan, & William Bateson : natural selection, evolution directed by adaptive fitness, minor role (“mutationists”)

Early evolutionary studies4
Early Evolutionary Studies relate to Natural Selection?

  • Sewall Wright & J.B.S. Haldane, population geneticists, and several others independently developed arguments that when a mutation is immediately favored, its spread within a population depends on: 1) size of population; 2) length of generations; 3) degree to which mutation is favorable; 4) rate at which the same mutation reappears in the descendants

Early evolutionary studies conclusions
Early Evolutionary Studies Conclusions relate to Natural Selection?

  • A gene is favorable only under certain environmental conditions

  • The total number of genes available for the next generation can be large: genetic variability & the gene pool

  • Sexual reproduction ensures that the genes are rearranged in each generation: recombination

  • When a population is stable, the gene frequency remains the same (even though the genes in individuals may be recombined in different ways)

  • When the gene frequencies in the pool change in a sustained manner, evolution is occurring!

  • Mutations provide the gene pool with a continuous supply of new genes; through natural selection, gene frequencies change so that advantageous genes occur in greater proportions

What is considered to be an advantageous gene

What is considered to be an “advantageous” gene? relate to Natural Selection?

Are all acquired traits good, bad, or somewhere in-between?

Early evolutionary studies5
Early Evolutionary Studies relate to Natural Selection?

  • Mathematical support by Hardy and Weinberg (1908)

  • (p + q)2 = p2 + 2pq + q2 = 1, where p = allelic freq. of A and and q = allelic freq. of a in a population

  • Conforms to a Punnet square

Hardy weinberg theorem
Hardy – Weinberg Theorem relate to Natural Selection?

  • The frequency of alleles in a population will remain the same regardless of the starting frequencies (“equilibrium”) if: 1) population is large; 2) matings are random; 3) there are no net changes in gene pool due to mutation; 4) there is no migration of individuals into and out of the population; 5) there is no selection…all genotypes are equal in reproductive success

  • Hence, evolution does occur if one of the above is violated!

  • See Population Genetics Lab: H-W Theorem

Nothing in biology makes sense except in the light of evolution
“Nothing in biology makes sense except in the light of evolution…”

  • Theodosius Dobzhansky in the “Genetics and Origin of Species,” extended the mathematical arguments with experimental and observational evidence

  • Demonstrated adaptive genetic changes in large populations of fruit flies as a result of controlled environmental changes…compatible with Darwinian natural selection

Modern synthesis or synthetic theory
Modern Synthesis or Synthetic Theory evolution…”

  • Ernst Mayer (zoologist) showed that new species usually arise in geographic isolation often following a genetic “revolution” that rapidly changes the gene pool

  • George Simpson (paleontologist) showed from the fossil record that rates and modes of evolution are correlated

  • G. Ledyard Stebbins (botanist) showed that plants display evolutionary patterns similar to those of animals

  • The Modern Synthesis or Synthetic Theory is strongly supported by observation and experiment!

Modern synthesis or synthetic theory1
Modern Synthesis or Synthetic Theory evolution…”

  • James Watson, Francis Crick, and Rosalind Franklin demonstrated that DNA is the genetic molecule of inheritance

  • Mutations are known to be changes in the position of a gene, or the information coded in a gene, that can affect the function of the protein for which the gene is responsible.

  • Natural Selection can then operate to favor or suppress a particular gene according to how strongly its protein product contributes to the reproductive success of the organism

Punctuated equilibrium
Punctuated Equilibrium evolution…”

  • Stephen Jay Gould and Niles Eldredge: Theory of Punctuated Equilibrium (1972)…species undergo most of their morphological modification as they first separate from the parent species showing little change as they produce additional species…gradual change is replaced with stasis punctuated with episodes of speciation (See additional handout)

Mechanism of evolution
Mechanism of Evolution evolution…”

  • Peppered moth example: light v. dark variants; frequency changes due to environmental conditions

  • Mechanisms of: 1) Geographic Isolation (Darwin’s Galapagos Finches & Hawaiian Fruit Flies); 2) Genetic Drift (gene freq. Change by the chance failure of progeny to reproduce to the exact gene proportions of their parents…natural disaster); 3) Founder effect (migration of individuals to an isolated population); 4) Mutations (seems to be the chief agent); 5) Gene Flow (change in gene pools due to migration of individuals between populations); 6) Nonrandom matings (inbreeding, mate selection); 7) Natural Selection via differential reproductive success (increases freq. Of some alleles and diminishes others)

Paths of speciation

Speciation evolution…”- microevolution is changes to a single gene pool; macroevolution is changes above the species level (feather appearance)

Anagenesis-phyletic evolution- accumulation of changes that gradually transform a given species into a species with different characteristics

Cladogenesis-branching evolution- is the splitting of a gene pool into two or more separate pools, which give rise to one or more new species

Allopatric- gene flow is interupted when a population is divided into geographically isolated subpopulations (ex., squirrels in Grand Canyon); “Other country”

Sympatric- a small population becomes a new species without geographic isolation; polyploidy or autoploidy (more than 2 sets of chromosomes due to failure to complete cell division); “Same country”

Hybridization- mating or crossing of 2 true-breeding varieties

Adaptive radiation- evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges

Paths of Speciation

Results of evolution
Results of Evolution evolution…”

  • Speciation: anagenesis v. cladogenesis (See Speciation PPt.)

  • Allopatric Speciation: a process thought to have been responsible for a great many species formation; when an ancestral population becomes segregated by a geographic barrier or is divided into 2 populations geographically (Geographical fragmentation important- 1) moving to new environments, 2) geographical isolation, 3) different selection pressures, 4) reproductive isolation)

  • Sympatric Speciation: new species may be formed even where there is no separation of the gene pools by physical barriers, but separation due to radical change in the genome- 1)speciation through niche differentiation, either niche isolation or reproductive isolation; 2) speciation by polyploidy or allopolyploidy (doubling of chromosomes)

  • Reproductive barriers separate species (prezygotic, habitats, behavioral, temporal, mechanical, gametic, reduced hybrid viability, reduced hybrid fertility, hybrid breakdown, & introgression); see p.474-475

  • See bio.kimunity Ppts. 1 and 2

Pathways of evolution not goal orientated
Pathways of Evolution…Not Goal Orientated evolution…”

  • Divergent evolution (diversification of an ancestral group into 2 or more species in different habitats)

  • Covergent evolution (common selection pressures bring about similar adaptations; analogous structures)

  • Coevolution (describes cases where two or more species reciprocally affect each other’s evolution)

  • Adaptive radiation (diversification both structural and ecological among descendants of a single ancestral group to occupy different niches)

  • Parallel evolution

  • Extinction

  • Macroevolution- changes can accumulation through many speciation events such as changes in rate and timing and spatial patterns; allometric= different growth rates for different parts of the body determine body proportions; paedomorphosis= sexually mature form of species retains features that were juvenile structures in an ancestral species; ex., growth rates of humans, comparison of chimp and human skulls, ground v. tree- dwelling salamanders; axolotl; Hox genes and evolution of tetrapod limbs; Hox mutations and the origin of vertebrates

Acknowledgements evolution…”

  • Pictures and graphics from google.com

  • Information supplemented by: Campbell, et al Biology, Encarta, and Professor Farabee’s web site and explorebiology.com

  • (http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html)

  • http://www.pbs.org/wgbh/evolution/