Development of Development of Evolutionary Evolutionary ThoughtThought

Isn’t evolution “just” a Isn’t evolution “just” a theory?theory?

•Scientific theories are Scientific theories are explanations that are based on explanations that are based on lines of evidence, enable valid lines of evidence, enable valid predictions, and have been predictions, and have been tested in many ways.tested in many ways.

Evolve – change over Evolve – change over time time

What is What is Evolution?Evolution?Evolution - a change in Evolution - a change in the genetic the genetic composition of a composition of a population over time.population over time.

Paleontology & Paleontology & EvolutionEvolution Older layers of sedimentary rock (the Older layers of sedimentary rock (the

layers on the bottom) contain fossil layers on the bottom) contain fossil species very dissimilar from modern species very dissimilar from modern life.life.

Each layer (stratum) is characterized Each layer (stratum) is characterized by a unique group of fossil species.by a unique group of fossil species.

As you move upward through the As you move upward through the layers, you find species more and more layers, you find species more and more similar to modern life.similar to modern life.

James Hutton - 1795James Hutton - 1795 A Scottish geologistA Scottish geologist proposed that it was possible to proposed that it was possible to

explain the various landforms by explain the various landforms by looking at mechanisms looking at mechanisms currentlycurrently operating in the worldoperating in the world

Proposed that the earth was much Proposed that the earth was much more than a few thousand years more than a few thousand years oldold

Jean Baptiste LamarckJean Baptiste Lamarck Theory of evolution in 1809Theory of evolution in 1809 mechanism:mechanism:

– use and disuse - the idea that the parts used use and disuse - the idea that the parts used the most grow stronger; the parts that don’t the most grow stronger; the parts that don’t get used deteriorateget used deteriorate

– inheritance of acquired characteristics - the inheritance of acquired characteristics - the modifications that an organism acquires during modifications that an organism acquires during its lifetime can be passed along to its offspringits lifetime can be passed along to its offspring

recognized adaptation to environment as a recognized adaptation to environment as a primary product of evolutionprimary product of evolution

Charles Darwin (1809-Charles Darwin (1809-1882)1882)

Father of modern Father of modern

evolutionary theoryevolutionary theory Born in EnglandBorn in England HMS BeagleHMS Beagle Galapagos IslandsGalapagos Islands

The Galapagos FinchesThe Galapagos Finches

What is an adaptation?What is an adaptation?

An inherited characteristic that An inherited characteristic that increases an organism’s ability to increases an organism’s ability to survive and reproduce in its survive and reproduce in its specific environment.specific environment.

Darwin’s ObservationsDarwin’s Observations

Darwin noticed that every bird on the Darwin noticed that every bird on the Galapagos Islands was a modified Galapagos Islands was a modified finch. finch.

The only differences in the birds were The only differences in the birds were their beaks and what they ate.their beaks and what they ate.

These finches looked very similar to These finches looked very similar to one type on South American continent, one type on South American continent, but none of these were found in S.A.but none of these were found in S.A.

““How did one species change into a How did one species change into a different species?”different species?”

He wrote He wrote On The On The Origin of SpeciesOrigin of Species (1859) after 20 years (1859) after 20 years of study.of study.

Darwin’s Four Darwin’s Four PostulatesPostulates Individuals within a population Individuals within a population

vary in their traits.vary in their traits. Some of these traits are heritable.Some of these traits are heritable. More offspring are produced than More offspring are produced than

can survive because of limited can survive because of limited resources.resources.

Individuals with advantageous Individuals with advantageous traits will survive and reproduce.traits will survive and reproduce.

What is natural What is natural selection?selection?

Natural selection - a population of Natural selection - a population of organisms can change over organisms can change over generations if individuals having generations if individuals having certain heritable traits leave more certain heritable traits leave more offspring than othersoffspring than others

Natural selection is the Natural selection is the mechanismmechanism by which evolution is by which evolution is proposed to occurproposed to occur

What is “artificial What is “artificial selection”?selection”? Nature provides the variation Nature provides the variation

among different organisms, and among different organisms, and humans select variations that humans select variations that they find useful.they find useful.

Example: breeding cows, horses, Example: breeding cows, horses, hogshogs

Darwin used this to help support Darwin used this to help support his case for natural selection.his case for natural selection.

Descent with Descent with modificationmodification

the history of life is like a tree, with the history of life is like a tree, with multiple branching and re-branching multiple branching and re-branching from a common trunk all the way to from a common trunk all the way to the tips of the youngest twigsthe tips of the youngest twigs

most branches of evolution are dead most branches of evolution are dead ends; about 99% of all species that ends; about 99% of all species that have ever lived are extincthave ever lived are extinct

Figure 22.7 Descent with modificationFigure 22.7 Descent with modification

Survival of the FittestSurvival of the Fittest

• Another name for Darwin’s theory Another name for Darwin’s theory of natural selection.of natural selection.

•Biologists use the word Biologists use the word fitnessfitness to to describe how good a particular describe how good a particular genotypegenotype is at leaving offspring in is at leaving offspring in the next generation relative to how the next generation relative to how good other genotypes are at it.good other genotypes are at it.

Mechanisms of Mechanisms of EvolutionEvolution

Natural Selection & Natural Selection & Survival of the FittestSurvival of the Fittest

(already discussed with Darwin)(already discussed with Darwin)

Modern IdeasModern Ideas

Darwin + Mendel’s work and the Darwin + Mendel’s work and the work of others, have lead to work of others, have lead to modern ideas about evolution. modern ideas about evolution.

Another mechanism of evolution is Another mechanism of evolution is Genetic DriftGenetic Drift (random changes (random changes in genes) which occurs through in genes) which occurs through natural selection.natural selection.

Modern IdeasModern Ideas

SpeciationSpeciation – formation of new – formation of new species is due to gradual genetic species is due to gradual genetic changes, and that large scale changes, and that large scale evolution is the result of a lot of small evolution is the result of a lot of small scale evolution.scale evolution.

MicroevolutionMicroevolution – process – process responsible for the variations that exist responsible for the variations that exist within a species, or a change in the within a species, or a change in the allele frequency.allele frequency.

Modern IdeasModern Ideas

MacroevolutionMacroevolution – evolution – evolution that occurs between species. that occurs between species.

Examples: the separation of a Examples: the separation of a species to form two distinct species to form two distinct species or the development of a species or the development of a new species from many small new species from many small changes within an existing changes within an existing speciesspecies

Gene FlowGene Flow

The change in occurrence of The change in occurrence of genes in a population. This occurs genes in a population. This occurs when an individual leaves a when an individual leaves a population (emigration) or new population (emigration) or new individual joins a population individual joins a population (immigration).(immigration).

Genetic DriftGenetic Drift

Random changes in the occurrence of Random changes in the occurrence of genes through chance events.genes through chance events.

Can occur when a few individuals of a Can occur when a few individuals of a population break off from the original population break off from the original group and start their own population group and start their own population (founder effect).(founder effect).

Large number of population is killed Large number of population is killed due to disease, starvation, natural due to disease, starvation, natural disaster, etc. (bottle necking)disaster, etc. (bottle necking)

Punctuated Punctuated EquilibriumEquilibrium Darwin felt that biological change was Darwin felt that biological change was

slow and steady as indicated in the fossil slow and steady as indicated in the fossil record.record.

Modern scientists see that this pattern Modern scientists see that this pattern does not always hold. (Darwin’s finches)does not always hold. (Darwin’s finches)

The term punctuated equilibrium is used The term punctuated equilibrium is used to describe a pattern of long, stable to describe a pattern of long, stable periods interrupted by brief periods of periods interrupted by brief periods of more rapid change. This is still more rapid change. This is still controversial today.controversial today.

Evidence of Evidence of EvolutionEvolution

Fossil EvidenceFossil Evidence

Fossils provided a detailed record Fossils provided a detailed record of evolution.of evolution.

Fossils formed in different layers Fossils formed in different layers of rock were evidence of gradual of rock were evidence of gradual change over time.change over time.

Homologous Body Homologous Body StructuresStructures Structures in different species that Structures in different species that

may perform different functions may perform different functions but are similar because of their but are similar because of their common ancestry common ancestry

Vestigial organs - structures of no Vestigial organs - structures of no apparent function to an organism; apparent function to an organism; leftover from ancestry; ex - snakes leftover from ancestry; ex - snakes have leg & pelvis boneshave leg & pelvis bones

Figure 22.14 Homologous structures: anatomical signs of descent with Figure 22.14 Homologous structures: anatomical signs of descent with modificationmodification

More homology…More homology…

Molecular homology - similarity in Molecular homology - similarity in DNA sequence between an ancestor DNA sequence between an ancestor and its progenyand its progeny

Embryological homology - similarities Embryological homology - similarities only apparent in embryological only apparent in embryological developmentdevelopment– ex: all vertebrate embryos have ex: all vertebrate embryos have

“pharyngeal pouches” which later “pharyngeal pouches” which later become gills or Eustachian tubesbecome gills or Eustachian tubes

Patterns of Patterns of EvolutionEvolution

Adaptive RadiationAdaptive Radiation

When a single species or a small When a single species or a small group of species has evolved into group of species has evolved into several different forms that live in several different forms that live in different ways.different ways.

Example: Darwin’s finches (more Example: Darwin’s finches (more than a dozen evolved from a than a dozen evolved from a single species)single species)

Convergent Convergent EvolutionEvolution Explains how unrelated species Explains how unrelated species

can develop similar can develop similar characteristicscharacteristics

Porpoise (mammal) & Shark (fish)Porpoise (mammal) & Shark (fish) Unrelated animals, but share Unrelated animals, but share

similar characteristics to suit their similar characteristics to suit their environmentenvironment

Analogous structuresAnalogous structures

Show similarity in structure Show similarity in structure based on adaptation for the based on adaptation for the same function, not common same function, not common descent.descent.

Divergent Divergent EvolutionEvolution

Suggests that many species Suggests that many species develop from a common ancestordevelop from a common ancestor

Penguins (wings for swimming) & Penguins (wings for swimming) & vultures (wings for flying)vultures (wings for flying)

Both are birds, diverged from a Both are birds, diverged from a common ancestorcommon ancestor

Co-evolutionCo-evolution

When two or more organisms in When two or more organisms in an ecosystem evolve in response an ecosystem evolve in response to each other.to each other.

Example: Flowers and their Example: Flowers and their pollinatorspollinators

Camouflage – an animal Camouflage – an animal looks like its looks like its environment.environment. http://rainforests.mongabay.com/

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Mimicry- when animals Mimicry- when animals have coloring and have coloring and markings to look like markings to look like another animalanother animal