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