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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
AP Biology
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
AP Biology
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
AP Biology
Effects of Selection Changes in the average trait of a population
DIRECTIONALSELECTION
STABILIZINGSELECTION
DISRUPTIVESELECTION
giraffe neckhorse size
human birth weight rock pocket mice
AP Biology
Natural selection in action
MRSAMRSA
Resistance…NOT immunity!
AP Biology
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
AP Biology
In addition to natural selection, evolutionary change is also driven by random processes…
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
Evidence Supporting Evolution
2006 Fossil Discovery of Early Tetrapod“Tiktaalik”“missing link” from sea to land animals
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
Relative Dating
AP Biology
Anatomical evidence
Homologous Structures
AP Biology
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
AP Biology
Vestigial organs
Why would whaleshave pelvis & leg bones
if they were alwayssecreatures?
These areremnants of
structures that were
functional inancestral species
AP Biology
Coevolution Two or more species reciprocally
affect each other’s evolution predator-prey
disease & host competitive species mutualism
pollinators & flowers