Unit 8 Evolution

What is Evolution?

A well-supported scientific theory stating that organisms change over time

Evidence in stone

Preserved remains of a once living organism is called a FOSSIL

Fossil evidence supported that organisms changed gradually

Anatomical Evidence

Comparative Anatomy: study of similarities and differences between organismsHomologous StructuresAnalogous StructuresVestigial Organs

Homologous Structures

As similar organisms adapt to different environments, the function of their appendages changed

A bird’s arms became wings to flap

A human’s arm is used to pick-up, carry, grasp, etc…

A horse’s arm became a fore-leg to run on

Analogous Structures

Different organisms began living in similar environments, their appendages evolved to perform the same function

A butterfly has wings to fly that are made from an exoskeleton

A sparrow has wings to fly that have an endoskeleton

BirdButterfly

Vestigial Structures

Structures which remain in organisms but have no obvious function Leg bones in snakes and whales Appendix in humans ** Ear muscles in humans

Comparative Embryology

Examining the embryos of organisms

Organisms with similar embryos are thought to be more closely related

Biochemical Evidence (aka Molecular Biology)

Comparison of the amino acid and DNA sequencesChimp and human hemoglobin are VERY similar

Genetic Evidence

DNA passes on traits When mutations occur the genes and

chromosomes can changeHumans have imposed change

through selective breedingThe higher the percentage of

similarities the closer the relationship between two organisms

Jean Baptiste de Lamark

First to recognize that organisms change

Published his hypotheses in 1809

Theory was disproved!

3 Key Assumptions:Desire to Change: organisms have an

inborn urge to better themselvesLaw of Use and Disuse: body parts

that are used will develop; those not used will become smaller/disappear

Inheritance of Acquired Characteristics: organisms pass on traits acquired during their lifetime

Jean Baptiste de Lamark

Charles Darwin

Credited for the theory of evolutionHMS Beagle sailed in 1831 – Galapagos

IslandsPublished Origin of Species in 1858

Darwin’s Observations

Observed tortoises, iguanas, and finches

The islands had different climates and vegetation

The animals were similar… but had noticeable differences

WHY?

Darwin’s Assumptions Variations

Differences among members of the same speciesStruggle for Existence

Predation and competitionOverproduction

More offspring are produced than will surviveSurvival of the Fittest (Natural

Selection) Individuals best suited for the environment will

survive, reproduce, and pass on traits to their offspring

Descent with ModificationPrinciple that species change but descend from

common ancestors

Lamark’s Giraffes

Darwin’s Theory of Natural Selection

Variations help members of a species to survive in a given environment

The environment selects the beneficial adaptation and over time this trait will become more prevelant

Darwin’s Finches

Fossil Formation

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

The preserved remains may later be discovered and studied.

Water carries small rock particles to lakes and seas

Fossil Record

Preserved remains of a once living organism is called a FOSSIL IE: amber, sedimentary rock, tar, and ice

Fossil record is incomplete

Relative Dating

Used to ESTIMATE the age of fossils

Older fossils are in deeper layers of rock

Genes and Evolution In terms of genetics, evolution is the change in

frequency of alleles in a population’s gene poolNatural selection leads to change in gene frequencyMolecular clocks use mutation rates to estimate

how recent a common ancestor was

Hox Genes

Genes which control an organism’s basic body plan Anterior/posterior ends Limbs, wings

Genetic Drift

Changes in the gene pool of a small population due to random chance ex: small group

colonizes a new habitat – founder effect

Speciation

Gradualism – change in species is slow and steady

Punctuated Equilibrium – long periods of stability followed by short periods of rapid change

Punctuated Equilibrium vs. Gradualism

Speciation – Isolating Mechanisms

For new species to form, reproductive isolation needs to occur

Organisms don’t interbreed- gene pools become separate

- Behavioral, Geographic, Temporal

Adaptive RadiationA single species evolves into many speciesOften occurs when a niche opens up

Convergent Evolution

Organisms come to resemble one another but evolved differently

Analogous structures!

Examples: Dolphins and sharks Marsupials and

mammals

Coevolution

Organisms with close ecological relationships evolve together Pollinators and flowers

Ancient Earth

Atmosphere was composed of gases:

CO2, N2, water vapor, CH4, H2S

No O2

Earth formed ~4.6 billion years ago

First Organic Molecules

1950’s Miller & Urey reproduced conditions of ancient Earth

Electric sparks simulated lightning

Amino acids began to form

First Cell

Oxygen Accumulation in Atmosphere

What is a Primate?Binocular VisionDeveloped brainLong fingers & toesRotating shoulders

What makes us Human?

Characteristics of the Hominine Family Bipedal Opposable

Thumbs Larger Brains

Did we evolve from chimps?

Hominine Evolution

Ardipithecus ramedus “Ardi”, 4.4 myaAustralopithecus afarensis “Lucy”, 3.2 myaHomo habilis “handy man”, ≈ 2 mya

Used tools, first of the genus Homo

Homo erectus, “Java Man”, ≈ 1.6 mya 1st to use fire

Homo neanderthalensis ≈ 200,000 years ago

Homo sapien Modern Human ≈ 100,000 years ago

Family Tree or Bush?