AP Biology

EvolutionUnit

What is Evolution?• Change in the genetic makeup of a population

over time.• Fitness – those with favorable variations for

survival and reproduction.– Populations can evolve, not individuals.

• Diverse gene pool good for long-term survival of a species. Genetic variations are important!

• How do genetic variations occur?– Mutation, sexual reproduction, artificial selection,

genetic technology

Genetic variation in a population

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Essence of Darwin’s ideas Natural selection

heritable variation exists in populations over-production of offspring

more offspring than the environment can support competition

for food, mates, nesting sites, escape predators differential survival

successful traits = adaptations differential reproduction

adaptations become more adaptations become more common in populationcommon in population

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Lamarckian vs. Darwinian view

LaMarck in reaching higher

vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring

Darwin giraffes born with longer

necks survive better & leave more offspring who inherit their long necks

Natural Selection• Major mechanism of evolution • Environment is always changing • Acts upon the phenotype of the population• Based on Darwin’s idea that resources are limited

and that there is competition for those resources.• Adaptation = a genetic variation favored by

natural selection.• When allele frequencies shift, speciation occurs

– Thus, the frequency change is NOT RANDOM

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Effects of Selection Changes in the average trait of a population

DIRECTIONALSELECTION

STABILIZINGSELECTION

DISRUPTIVESELECTION

giraffe neckhorse size

human birth weight rock pocket mice

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Natural selection in action

MRSAMRSA

Resistance…NOT immunity!

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Hidden variations can be exposed through selection!Terminalbud

Lateralbuds

Brussels sprouts

Cabbage

Flower cluster Leaves

Cauliflower

Flowerandstems

Broccoli Wild mustard Kohlrabi

Stem

Kale

Artificial selection

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In addition to natural selection, evolutionary change is also driven by random processes…

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Genetic Drift Chance events changing frequency of

traits in a population not adaptation to environmental conditions

not selection founder effect

small group splinters off & starts a new colony it’s random who joins the group

bottleneck a disaster reduces population to

small number & then population recovers & expands again but from a limited gene pool

who survives disaster may be random

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Ex: Cheetahs All cheetahs share a small number of alleles

less than 1% diversity as if all cheetahs are

identical twins

2 bottlenecks 10,000 years ago

Ice Age last 100 years

poaching & loss of habitat

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Conservation issues Bottlenecking is an important

concept in conservation biology of endangered species loss of alleles from gene pool reduces variation reduces adaptability

Breeding programs must consciously outcrossBreeding programs must consciously outcross

Peregrine Falcon

Golden Lion Tamarin

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Human Impact on variation How do we affect variation in other

populations? Artificial selection/Inbreeding

Animal breeds Loss of genetic diversity

Insecticide usage Overuse of antibiotics

resistant bacterial strains

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Evidence Supporting Evolution

2006 Fossil Discovery of Early Tetrapod“Tiktaalik”“missing link” from sea to land animals

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Evidence for Evolution• Paleontology – fossils show change in a

species over time• Biogeography – Similar species are found in

similar ecosystems around the world• Morphology – Comparing structures

– Homologous structures – body parts with similar structure but possible different function. Shows common ancestry

– Analogous structures – similar structure develops in organisms that share a common ecosystem but not a common ancestry

• Biochemical or Molecular– Similarities in gene sequences, proteins, DNA

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Fossils Preserved remains of living things Paleontology is the study of the fossil

record Most organisms do not leave a fossil after

death Explains the “missing links”

Sedimentation Fossils As the organism decomposes the

spaces will be filled with the minerals from the silt

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The Archaeopteryx Fossil

Avian Features

Vertebrae are almost flat-faced.

Impressions of feathers attached to the forelimb.

Belly ribs.

Incomplete fusion of the lower leg bones.

Impressions of feathers attached to the tail.

Forelimb has three functional fingers with grasping claws.

Reptilian Features

Lacks the reductions and fusions present in other birds.

Breastbone is small and lacks a keel.

True teeth set in sockets in the jaws.

The hind-limb girdle is typical of dinosaurs, although modified.

Long, bony tail.LEFT: Archaeopteryx lithographicaFound in 1877 near Blumenberg, Germany

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How old is that fossil? Relative Dating

Age of fossils based according to their location in strata

Absolute Dating Age of fossils determined by analyzing the

content of radioactive isotopes found in the fossil.

Half-life: The length of time required for half of the radioactive elements to change into another stable element.

Unaffected by temperature, light, pressure, etc. All radioactive isotopes have a dependable half

life. Ex: C14 decays into N14

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Relative Dating

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Anatomical evidence

Homologous Structures

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Analogous structures

Solving a similar problem with a similar solutionSolving a similar problem with a similar solution

Does this mean they have a

recent common ancestor?

Don’t be fooledby their looks!

Those fins & tails & sleek bodies are

analogous structures!

Convergentevolution

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Vestigial organs

Why would whaleshave pelvis & leg bones

if they were alwayssecreatures?

These areremnants of

structures that were

functional inancestral species

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Coevolution Two or more species reciprocally

affect each other’s evolution predator-prey

disease & host competitive species mutualism

pollinators & flowers