Biology-Unit 15Biology-Unit 15

The Theory of EvolutionThe Theory of Evolution

• Evolution- Evolution- The process of change The process of change over timeover time

• Theories of evolution assume that Theories of evolution assume that modern life forms have evolved modern life forms have evolved (changed) from previously existing (changed) from previously existing life forms.life forms.

1. Evidence of Evolution1. Evidence of Evolution

• Attempts to describe the Attempts to describe the mechanisms by which organisms mechanisms by which organisms change over time have formed the change over time have formed the basis of the evolutionary theory.basis of the evolutionary theory.

includes

Evidence of Evolution

Physical remains of organisms

Common ancestral species

Similar genes Similar genes

which is composed of which indicates which implies which implies

The fossil record

Geographic distribution of living species

Homologous body

structures

Similaritiesin early

development

Theories of EvolutionTheories of Evolution

• Attempt to explain the diversity of Attempt to explain the diversity of life forms on earthlife forms on earth

• Species diversity is actually based on Species diversity is actually based on the variety of the variety of ADAPTATIONS that ADAPTATIONS that different species may possess.different species may possess.

• Adaptations - any Adaptations - any structural, structural, functional, or behavioral functional, or behavioral characteristic of a species that helps characteristic of a species that helps it to better survive in its environmentit to better survive in its environment

Evidence of Evolution continued:Evidence of Evolution continued:

A. Comparative CytologyA. Comparative Cytology

-Organisms with very similar cell -Organisms with very similar cell structures are usually structures are usually considered to considered to be more closely related.be more closely related.

B. Comparative B. Comparative BiochemistryBiochemistry

-Analysis of -Analysis of enzymes and other enzymes and other proteins show that a proteins show that a great deal of great deal of similarity similarity exists in exists in organisms known to organisms known to be related be related genetically.genetically.

C. Comparative C. Comparative AnatomyAnatomy-Similar organisms -Similar organisms can be shown to have can be shown to have limbs, limbs, internal internal organs, or other organs, or other structures that are structures that are constructed similarly.constructed similarly.

-These structures are -These structures are known as known as homologous homologous structures.structures.

D. Comparative D. Comparative EmbryologyEmbryology

-Reproductive -Reproductive processes in many processes in many different organisms different organisms reveal patterns of reveal patterns of similarity among similarity among closely related closely related organisms.organisms.

E. Geologic RecordE. Geologic Record

Fossils are commonly discovered in Fossils are commonly discovered in sedimentary rock layers.sedimentary rock layers.

Water carries small rock particles to lakes and seas.

Dead organisms are buried by layers of sediment, which forms new rock.

The preserved remains may later be discovered and studied.

-The oldest fossils of the simplest life -The oldest fossils of the simplest life forms are generally found in the forms are generally found in the bottom layers.bottom layers.

-While the younger fossils of more -While the younger fossils of more complex organisms are found in the complex organisms are found in the top layers.top layers.

-This is an example of relative dating.-This is an example of relative dating.

Scientists can determine the age Scientists can determine the age of fossils of fossils through radioactive dating.through radioactive dating.

Sedimentary rocks form in horizontal

layers

When part of Earth’s crust is compressed, a bend in a rock forms, tilting the rock layers.

As the surface erodes due to water, wind, waves, or glaciers, the older rock

surface is exposed.

New sediment is then deposited above the exposed older

rock surface

• F. Vestigial Structures: structures that do not F. Vestigial Structures: structures that do not seem to have any use (are also reduced in seem to have any use (are also reduced in size) but are size) but are remains of structures that were remains of structures that were probably functional in ancestral organisms.probably functional in ancestral organisms.

• Human examples: appendix, tailbone Human examples: appendix, tailbone (coccyx), (coccyx), wisdom teeth, muscles that move wisdom teeth, muscles that move the ears and nosethe ears and nose

• Animal examples: whales and pythons have Animal examples: whales and pythons have vestigial hind leg bones embedded in body vestigial hind leg bones embedded in body wallwall

2. Evolutionary Scientists:2. Evolutionary Scientists:A. John Lamarck - Proposed the idea of A. John Lamarck - Proposed the idea of evolution that included two main ideas: evolution that included two main ideas: 1. Use and Disuse 1. Use and Disuse

-The more a structure was needed, -The more a structure was needed, the the more efficient it would more efficient it would

become.become.-A structure that was not used -A structure that was not used would would

eventually disappear.eventually disappear. 2. Transmission of Acquired Traits 2. Transmission of Acquired Traits

-Traits developed as needed -Traits developed as needed within the within the life of an organism.life of an organism.

• An organism could An organism could pass these pass these “acquired traits” to “acquired traits” to future generations future generations through the process through the process of reproduction.of reproduction.

• The favorable The favorable “adaptations” “adaptations” would result would result in in improved survival improved survival ability for the ability for the species.species.

•Lamarck’s theories were an Lamarck’s theories were an important important First StepFirst Step in the in the development of a scientific view development of a scientific view of the evolutionary process.of the evolutionary process.

•Later Experiments conducted by Later Experiments conducted by August Weismann and others August Weismann and others failed to support Lamarck’s failed to support Lamarck’s theories.theories.

C. Charles DarwinC. Charles Darwin• 19th Century naturalist 19th Century naturalist

from Englandfrom England• Devised a theory of Devised a theory of

evolution based on evolution based on variation and natural variation and natural selection.selection.

• His theory forms the His theory forms the basis basis of the modern of the modern theory of evolution.theory of evolution.

Darwin’s Five Main Ideas:Darwin’s Five Main Ideas:1.1. Overproduction: species have a tendency Overproduction: species have a tendency

to produce to produce far more offspring than can far more offspring than can possibly survive.possibly survive.

2.2. Competition: Within each species there Competition: Within each species there is a struggle for survival that may is a struggle for survival that may eliminate many eliminate many individuals before they individuals before they reach reproductive maturity.reach reproductive maturity.

3.3. Variation: Darwin noticed variation within Variation: Darwin noticed variation within a species even though he could not a species even though he could not explain. He knew nothing of genes.explain. He knew nothing of genes.

4. Survival of the Fittest: Animals better 4. Survival of the Fittest: Animals better able to resist disease, withstand able to resist disease, withstand environmental conditions, environmental conditions, and produce and produce more offspring are more likely to more offspring are more likely to survive.survive.

5. Reproduction: Adaptive advantages of 5. Reproduction: Adaptive advantages of one generation may be passed on to one generation may be passed on to the next, perpetuating them in the the next, perpetuating them in the species.species.-This process is -This process is known as SPECIATIONknown as SPECIATION

Lamarck and Darwin Lamarck and Darwin comparedcompared• Lamarck: Giraffes have Lamarck: Giraffes have

long necks due to years long necks due to years of stretching to reach of stretching to reach leaves on tall trees and leaves on tall trees and the passing on of the the passing on of the long necks to offspring.long necks to offspring.

Lamarck and Darwin Lamarck and Darwin comparedcompared• Darwin: Giraffes necks naturally vary in Darwin: Giraffes necks naturally vary in

length. Those giraffes that possess a long length. Those giraffes that possess a long neck were able to reach the leaves on the neck were able to reach the leaves on the tall trees and survive. tall trees and survive. They then passed They then passed the gene for a long neck on to their the gene for a long neck on to their offspring.offspring.

D. Modern Evolutionary TheoryD. Modern Evolutionary Theory

• Based primarily on Based primarily on Darwin’s theory Darwin’s theory of natural selection.of natural selection.

• In addition it incorporates the In addition it incorporates the information available from information available from the the mechanisms of genetics.mechanisms of genetics.

Five Main Ideas:Five Main Ideas:1. Production of variation1. Production of variation

-The reproductive process, meiosis and -The reproductive process, meiosis and fertilization provide the method by which fertilization provide the method by which new combinations of new combinations of both old and new both old and new traits may be “tried out” as new varieties traits may be “tried out” as new varieties within a species.within a species.

-Mutation -Mutation -An important process in providing -An important process in providing the the

new genes that may lead to the production new genes that may lead to the production of new traits.of new traits.

2. Natural Selection2. Natural Selection• Individuals that survive are Individuals that survive are

“selected” and are assumed to be “selected” and are assumed to be those best adapted to survive those best adapted to survive under under the particular set of environmental the particular set of environmental conditions.conditions.

• Survivors tend to pass on the genes Survivors tend to pass on the genes associated with their adaptive associated with their adaptive advantages.advantages.

3. Speciation3. Speciation

• When enough unique When enough unique adaptations have adaptations have been been accumulated, in a species’ accumulated, in a species’ population, population, a new species arises a new species arises from from the parent species.the parent species.

4. Reproductive Isolation4. Reproductive Isolation

• If two populations of species are If two populations of species are geographically separated from each geographically separated from each other for a sufficiently long period, other for a sufficiently long period, they may change so greatly that they may change so greatly that even even if geographic barriers are if geographic barriers are removed the two species will not be removed the two species will not be able to interbreed and reproduce.able to interbreed and reproduce.

or, another example… the “Founder or, another example… the “Founder Effect”Effect”

Time Frame for EvolutionTime Frame for Evolution– Gradualism – Assumes that Gradualism – Assumes that

evolutionary change evolutionary change is slow and is slow and gradual, and continuous.gradual, and continuous.

-Supported by fossil records-Supported by fossil records

-Gradual change of -Gradual change of organisms organisms seen seen from each sedimentary from each sedimentary layerlayer

• Punctuated Equilibrium – Assumes Punctuated Equilibrium – Assumes that species experienced long that species experienced long geographic periods geographic periods of stability of stability (millions of years or more) in which (millions of years or more) in which little or no change occurred.little or no change occurred.

• This stability is “punctuated” by brief This stability is “punctuated” by brief periods periods (a few thousand years) in which (a few thousand years) in which dramatic changes occur within a species.dramatic changes occur within a species.

• Punctuated equilibrium is supported by Punctuated equilibrium is supported by fossil evidence in which little change is fossil evidence in which little change is noted between most sedimentary layers noted between most sedimentary layers but sudden “bursts” of change are but sudden “bursts” of change are evident in the fossils of a few evident in the fossils of a few sedimentary layers.sedimentary layers.

Heterotroph Hypothesis – how life Heterotroph Hypothesis – how life beganbegan

-Assumes that the first primitive life -Assumes that the first primitive life forms were not able to manufacture forms were not able to manufacture their own food.their own food.

-Heterotrophs… (they had to eat)-Heterotrophs… (they had to eat)

Conditions of the Early EarthConditions of the Early Earth

Earth formed from clouds of Earth formed from clouds of cosmic dust and gas cosmic dust and gas over 5 billion over 5 billion years ago.years ago.

After condensing to a semi-After condensing to a semi-solid form, the earth required solid form, the earth required hundreds of millions of years to hundreds of millions of years to cool.cool.

During that period, the earth remained a During that period, the earth remained a hot environment filled with simple inorganic hot environment filled with simple inorganic substances substances such as H2O, NH3, CH4, such as H2O, NH3, CH4,

and H2and H2

-These substances were mixed together in the -These substances were mixed together in the primitive atmosphere and oceans to form primitive atmosphere and oceans to form

a a

““HOT, THIN SOUP” in which random HOT, THIN SOUP” in which random chemical reactions could occur at a rapid rate.chemical reactions could occur at a rapid rate.

• It is believed that these random It is believed that these random chemical reactions led to the chemical reactions led to the synthesis of synthesis of simple sugars, lipids, simple sugars, lipids, and amino acids which then formed and amino acids which then formed larger molecules.larger molecules.

• The large molecules came together The large molecules came together to form aggregates which are to form aggregates which are assumed to have assumed to have formed the first formed the first simple cell-like organismssimple cell-like organisms “living” “living” able to reproduce.able to reproduce.

• Stanley MillerStanley Miller

-Set up a controlled environment that -Set up a controlled environment that simulated the hot, thin soup theorysimulated the hot, thin soup theory

-He was able to -He was able to make simple organic make simple organic substances.substances.

Mixture of gases simulating atmospheres of early Earth

Spark simulating lightning storms

Cold water cools chamber, causing droplets to form

Liquid containing amino acids and other organic compounds

Water vapor

Water vapor

-The natural by-products of living cells -The natural by-products of living cells is is CO2.CO2.

-Organisms evolved to use the CO2 to -Organisms evolved to use the CO2 to make make their own organic food. These their own organic food. These were the first were the first autotrophs!autotrophs!

-These pioneer autotrophs produced free -These pioneer autotrophs produced free O2 O2 which which was released into the was released into the atmosphere. atmosphere.

-This is the first photosynthesis!-This is the first photosynthesis!

Evolution of LifeEvolution of Life

• Early Earth was hot; atmosphere Early Earth was hot; atmosphere contained poisonous gases.contained poisonous gases.

• Earth cooled and oceans condensed.Earth cooled and oceans condensed.

• Simple organic molecules may have Simple organic molecules may have formed in the oceans.formed in the oceans.

• Small sequences of RNA may have Small sequences of RNA may have formed and replicated.formed and replicated.

• First prokaryotes may have formed First prokaryotes may have formed when RNA or DNA was enclosed in when RNA or DNA was enclosed in microspheres.microspheres.

• Later prokaryotes were Later prokaryotes were photosynthetic and produced photosynthetic and produced oxygen.oxygen.

• An oxygenated atmosphere capped An oxygenated atmosphere capped by the ozone layer protected Earth.by the ozone layer protected Earth.

• First eukaryotes may have been First eukaryotes may have been communities of prokaryotes.communities of prokaryotes.

• Multicellular eukaryotes evolved.Multicellular eukaryotes evolved.

• Sexual reproduction increased Sexual reproduction increased genetic variability, hastening genetic variability, hastening evolution.evolution.