Theories for Evolution

Mr. Young

Evolution

• The process of change within a living system over a period of time

• Genotype changes vs. Phenotype changes

• Micro vs. Macro Evolution• Many different scientists have proposed

theories about this process….…

MicroevolutionMicroevolution: Small-scale evolutionary changes, usually on the molecular level, that occur over the span of a few generations and can therefore be detected in living populations.

Macroevolution:Macroevolution: Large scale evolutionary changes, speciation events, that may require many hundreds of generations and are usually only detectable in the fossil record

Natural SelectionNatural Selection:: The differential reproductive success of certain phenotypes within a given environment

“Survival of the Fittest”

Jean Lamarck1744-1829

“Acquired Traits”

• Theory of use and disuse• If an organ is used , it becomes stronger

and better developed• If an organ is not used, it becomes weaker

and withers away

Lamarck

• An organism acquires traits from its experience (not genes) and those traits are passed down, or inherited by their offspring

• Example: Lamarck believed that giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks.

To Lamarck this means…

• If you have a nose job, your kids will inherit the new nose!

• In real life, what nose will your kids get? (the old one or the new one?)

• Answer: the old one!

Is this logical?

• What determines that traits are passed to their children?– DNA

• If you change your appearance, will your children inherit the new appearance

– No, because your DNA did not change

Natural Selection

• Environmental Selection

• Role of the Environment

• Acquired traits???? (Lamarck)

Who’s Your Daddy?• Charles Darwin

– Theory-descent w/ modification– Theory-natural selection-main principles:

Charles Darwin1809 - 1882

• A naturalist (studied and preserved biological specimens that he collected)

• 5 year voyage around the world aboard the HMS Beagle

Charles Darwin

• Theory of evolution by natural selection– Nature will select the organisms that have

variations that allow them to better survive (survival of the fittest)

– Descent by Modification– Darwin collected different species that were

very similar and hypothesized that they shared a common ancestor

insects

finches

Darwin’s Book: Origin of Species by Natural Selection

• Described his theory of evolution• Caused a lot of controversy and angered

the church• The church initially believed that evolution

is a sin against God• Before Darwin died, the church accepted

his theory and he was buried in a famous church in England

Charles Darwin

• Darwin’s theories are accepted today as the most accurate explanation for evolution

Darwin explains why giraffes have longer necks than their ancestors

• Overproduction – too many giraffes• Struggle or compete for food• Variation in length of neck exists naturally• Longer neck…reach food...survive• Longer necked giraffes survive and

reproduce to eventually originate a new species of giraffes

Hugo De Vries

• Added the concept that mutations in DNA are what cause organisms to change or have variations

• Evolution is changes in DNA that is then inherited(microevolution)

Variations in organisms

• Each species has organisms with varying characteristics for example:– some are taller– some have bigger feet– some run faster– some have better vision– some smell better

Struggle for existence

• Overproduction of a species causes competition for resources to survive – food – water – shelter – space

Survival of the fittest by means of natural selection

• Variations may give certain organisms advantages to survive, while other organisms died

• Nature selects those organisms that will die or survive

Evidence for Darwin's theory

• Fossil record• Biogeography• Comparative

Anatomy–Embryology–Biochemistry

Evidence for EvolutionHomologous structures

• Similar shape• Different function• Shared origin• Example: arms of human, wings of bats,

wings of penguins, arms of alligators• Divergent evolution

Evidence for EvolutionAnalogous structures

• Different shape• Similar function • Different origins• Example: wings of a humming bird and

wings of a moth, both allow the organism to hover

• Convergent evolution

Vestigial Structures

• A structure that had a use in an ancestor but has no use in a particular organism

• Examples: – Appendix in humans– Tail bones in humans… we have no tails– Tiny leg bones in snakes…they have no legs– Wings in penguins…they do not fly– Nipples on boys…they do not produce milk

Embryology

• The study of an organism from creation to birth

• Embryos have – tails that vanish into their spines– gill slits, like fish to breath that vanish into

ears– coats of hair that fall off at birth

Embryos go through stages of heart development

• 2 chambers like fish hearts• 3 chambers like reptiles• 4 chambers like birds and mammals

Adaptations

• A trait that increases an organisms chances of survival

What forces cause evolution?1. Mutation2. Migration (gene

flow)3. Genetic drift

– Random events– Small populations

4. Non-random mating5. Natural selection-4

types;

Types of natural selection

• Stabilizing• Directional• Disruptive

– Aka diversifying

• sexual

Natural Selection?• What leads to these

changes?– Random mutations

• Organisms w/ shorter generation times have higher mutation rates & so evolve quicker than animals w/ longer generation times

• Examples:• Industrial Revolution

vs. Peppered Moth

Natural selection results from Selection Pressures

• those aspects of the environment that can have a notable impact on the reproduction of members of a particular species over evolutionary time.

• adaptations

Defense Mechanism

• Different ways for organisms to defend themselves

• Example: thorns on rose bush

Mimicry

• Copying the appearance of another, more dangerous specie

• Example, the fat bumble bees do not sting, but they copy the yellow/black appearance of thin bumble bees that do sting

Camouflage

• The ability of an organism to blend into their environment

• Example, fish have pale bottoms and dark tops

• Frogs are shades of green

Let’s play name that adaptation!!!