Evolution/Origin of Life• What is life? Where does life come from?

• The Biogenesis/Abiogenesis Debate: Abiogenesis also known as Spontaneous Generation• Ancient Times (Aristotle): frogs from mud puddles• 17th C (Jean Van Helmont): “mouse recipe” Presence of the “active principle”• 17th C (Francisco Redi): maggots from decaying meat 1st scientist to use a control Gauze let air into the jar, and “caught” eggs on top

• 18th C (John Needham): boiled meat broth in loosely sealed flasks

Presence of “vegetative force”

• 18th C (Spallanzani); melted glass at top of flask• 19th C (Pasteur): used swan-necked flasks to end the

Biogenesis/Abiogenesis Controversy Pasteur-Pouchet Debate

• Virchow : coined the term “biogenesis”

Origin of Life:• Oparin’s Hypothesis (1936)• 14.6 billion years ago (“Big Bang”) Sun formed from explosion of a small volume of matter and energy

• 4.6 billion years ago: Earth, other planets formed Heavy elements in the center of the earth (Fe, Mg) Lighter elements form primitive atmosphere (CHON) Evaporation of H2O; Clouds formed; Rained for millions of years;

Lightning

• Formation of the oceans• Polymer formation in the oceans (“organic soup”) Heterotrophs (1st cells) dependent on food source in the ocean

(anaerobic) Autotrophs (2nd cells) independent; able to produce their own food

by photosynthesis (aerobic); release of O2 (formation of the Ozone Layer)

• Stanley Miller (1953): proved Oparin’s Hypothesis in his lab

Substituted electricity for lightning Filled a vat with H2O, CH3, NH3

• Result: (2 weeks later) – amino acids Amino acids are in all living things – “building blocks of

proteins”

• Life came from chemical changes in the ocean.

• Why is this explanation not considered to be spontaneous generation?

It took millions of years If lightning occurred…If it rained…If certain chemicals

were present…, then it is a possibility.

Evolution:

• Gradualism: A gradual change in a species over millions of years (Charles Darwin)

• Punctuated Equilibrium: periods of stability and periods of drastic changes within a species (Stephen Jay Gould)

Proofs of Evolution:

• Fossils in sedimentary rocks

• Homologous Organs: same structure but different function; examples: bird’s wing, horse’s front leg, whale’s fin, human’s arm, bat’s wing

Common ancestor Divergent evolution (Adaptive radiation): adapt to different

environments

• Analogous Organs: same function but different structure: examples: bat’s wing, butterfly wing

No common ancestor Convergent evolution (organisms come together in the same

environment)

• Vestigial Organs: organs with no apparent function; examples: tone, wisdom teeth, ear muscles, appendix, 3rd eyelid, little toe, cave-dwelling fish with eyes

• DNA-RNA-ATP Similarities

• Similarities in Embryos

Charles Darwin (1809-1882)

• Naturalist on the Beagle (5 year voyage)• Galapagos Islands (100 km. west of Ecuador) Variety of finches (13), tortoises, iguanas

• Influences on Darwin: Charles Lyell (Principles of Geology) Thomas Malthus (Essay on the Principle of Population)

• Work of Alfred Wallace• 1859: On the Origin of Species

• Darwin’s Theory of Evolution: Overproduction of the species Observations of Thomas Malthus

Constant struggle to survive Competition greatest among members of the same species

Uniqueness (variety) Organisms produced sexually show a variety among offspring

Natural Selection Nature/environment chooses which organisms will survive

Survivors pass on genes “Survival of the Fittest”

LaMarck (1744-1829)

• Theory of Need Organisms have an inner need to change

• Theory of Use and Disuse Organs not used weaken and eventually disappear

• Inheritance of Acquired Traits Acquired abilities/traits are passed on to offspring

• Giraffe Story:• How did giraffes get longer necks? Giraffes stretched their necks ---Led to longer necks---Organisms

change to survive in their environment (L) Variety of giraffes with different neck sizes---Nature or

environment determines which organisms will survive (D)

Natural Selection and Adaptation:

• A result of environmental change

• Story of English Peppered Moths: 1800’s: 2 species of peppered moths in

Northern England (light – dark) Trees covered with light gray lichens What happened to the light-colored moths? What happened to the dark-colored moths?

Industrial Revolution : soot on blackened tree bark What happened to the light-colored moths? What happened to the dark-colored moths?

Natural Selection Distribution Curves:

• Stabilizing Selection: Selection against the

extremes

When individuals near the

center of the curve have

higher fitness than

individuals at either end

of the curve

Intermediate phenotype

(average) favored

• Directional Selection: When individuals at one end

of the curve have higher fitness than individuals in the middle or at the other end

Evolution causes an increase in the number of individuals

with the trait at one end of the

curve

• Disruptive Selection: When individuals at the

upper and lower ends of the curve have higher fitness than individuals near the middle of the curve

Selection acts against individuals of an intermediate type (average)

Adaptation:

• The fitness of an organism for its environment (able to survive and reproduce)

• Structural: involves body parts Camouflage: hiding by blending in with

background Mimicry: copying body parts Monarch butterfly (bitter) and Viceroy butterfly

(good tasting); Viceroy survives possible predators by copying Monarch

• Physiological: organism changes its metabolism to survive

Bacteria adjusts to different doses of penicillin

• Behavioral: organism changes its behavior to survive Courtship and mating behaviors

Mechanisms of Evolution:• Gene Pool: all the genes for a population

• Genetic Equilibrium: all of the genes coming into a population equal all of the genes coming out of the

population (in=out)

• What causes changes in the genetic equilibrium? Mutations (DeVries), Genetic Drift (chance occurrence), Gene

Flow (immigration and emigration), Natural Selection

• Hardy-Weinberg Law (1908): A constant population exists if there are no mutations, no genetic drift, no gene flow (immigration or emigration), random mating, and a large population

Speciation:

• Species: a group of interbreeding organisms that share a gene pool

• Geographic Isolation: members of the same species separated by a physical boundary (mountain, river) Darwin’s finches

• Reproductive Isolation: formerly interbreeding organisms prevented from reproducing (seasonal – different breeding seasons)

Evolution vs. Creationism:• A belief in a scientific explanation for the creation of life

vs. a literal interpretation of the Biblical story of Genesis• 1925 Scopes Trial (Tenn.)• John Scopes (a substitute biology teacher) violated Butler Act• Wm. Jennings Bryant (Prosecutor) – Clarence Darrow (Defense)• Scopes found guilty (fined $100)

Scopes Trial: