Evolution
Mar 22, 2016
Evolution
Evolution
• What is evolution?– It is the process of biological change by which
descendents come to differ from their ancestors
Scientists
• Scientists who began studying evolution:– Linnaeus (1700’s)• Developed classification system of organisms• Proposed that organisms arose from hybridization
Scientists
• Buffon (1700’s)– Used evidence of past life– Proposed that species shared ancestors instead of
arising separately– Proposed earth was much older than 6000 years
Scientists
• Erasmus Darwin (1731)– Proposed all living things were descended from a
common ancestor– Later expanded upon by his grandson
Scientists
• Lamarck (1809)– Didn’t believe in
extinction– Species evolved instead– Proposed that changes
in environment caused behavior to change
– Organism passes on these traits to offspring
– “Inheritance of acquired characteristics”
Charles Darwin
• Darwin took a trip to the Galapagos Islands aboard the HMS Beagle
• He studied the inhabitants of the island
What did Darwin find?
Charles Darwin
• Findings and conclusions:– Variation among species– Led him to believe species
adapt to their environment
– Adaptation- feature allows an organism to better survive in an environment
– Leads to change in populations over time
Examples of Adaptations
horned lizard
pistol shrimp
aye aye
archer fish
Charles Darwin
• Natural Selection– Individuals inherit beneficial adaptations and
produce more offspring than others
Charles Darwin
• 4 principles of natural selection:1. Variation
- Differences among organisms2. Overproduction
- More offspring increases chance for survival3. Adaptation
- Certain variations allow to survive better4. Descent with Modification
- Over time, more individuals in the population will have the beneficial traits
Natural Selection
Variation
Adaptation
Overproduction
Descent with Modification
Fossil Evidence
• No fossil evidence that contradicts evolution has been found
• Allows us to see transitions of species over time
Anatomical Evidence
• Homologous structures– Features that are similar
in structure, but different in function in different organisms
– Supports common descent
Anatomical Evidence
• Analogous structures– Structures that perform
similar function
Anatomical Evidence
• Vestigial structures– Unused features– Structure had a function
in early ancestor– Helps support common
ancestry and evolution
Molecular Evidence
• All living things have DNA• Organisms carry
pseudogenes– Genes that do not
function (vestigial)• Cells have very similar
proteins– Marine worms have same
proteins in the eye as vertebrates
Comparison of milk protein in whales and hippos:
• HippoTCC TGGCA GTCCA
GTGGT• Humpback WhaleCCC TGGCA GTGCA
GTGCT
Match the structureHomologous, analogous, or vestigial
A
C
B
Population Distributions
• Normal Distribution– Frequency of a certain
phenotype is near the mean
Population Distributions
• Directional Selection– Selection favors
phenotypes at one extreme
– Population shifts toward advantageous trait
Population Distribution
• Stabilizing Selection– The intermediate is
favored and becomes the most common
Population Distribution
• Disruptive Selection– Both extreme
phenotypes are favored
Genetic Drift
• Bottleneck Effect– Occurs after an event
greatly reduces the size of a population
– Ex. Overhunting of elephant seals
Genetic Drift
• Founder Effect– Occurs after a small # of
individuals colonize a new area
– Ex. Emerald ash borer
Sexual Selection
• Occurs when certain traits increase mating success
• Two types:– Intrasexual
• Physical competition among males
– Intersexual• Displays among males
• Examples:– Intrasexual
– Intersexual
Giraffe fight
Bird display
Long-tailed Widowbird
Male Female
Evolutionary Classification
• Cladogram– Evolutionary tree that
proposes how species may be related to each other through common ancestors
• Clade – Group of organisms that
share certain traits
Evolutionary Classification
BicycleCarMotorcycleAirplaneOn foot
Cladogram for modes of transportation:
walking bicycle motorcycle car airplane
wheels
motor
Passengersenclosed
wings