Descent with Modification and Natural Selection

Darwin’s InspirationsGeology Earth’s current features are the result of billions of years of gradual change

Darwin’s Inspirations Fossil Record Extant species are not the only ones to have existed on Earth

Fossil Record Some fossils indicate missing links between extant groups Darwin’s Inspirations

Morphology Homologous structures’ underlying similarities indicate common ancestry Homologous Analogous structures have a similar function but are likely coincidental Analogous Vestigial structures are remnants of ancestors that have no apparent use in a particular current organism. Vestigial

Homologous Structures

Analogous Structures

Vestigial Structures

 Embryological Homologies Similarity in early development indicates common ancestry Similarity in early development indicates common ancestry Beyond Darwin Sponge Jellyfish Clam Insect Human

Molecular Homologies Molecular comparisons indicate relations (closer match = closer relation) Molecular comparisons indicate relations (closer match = closer relation)  DNA Hybridization AB A+B Beyond Darwin

Hybridization Data 98.8% 96.9% 93% 85% 75% 60%

Protein Homologies Organism # of Cytochrome C amino acids that differ from human Cytochrome C Chickens18 Chimpanzees0 Dogs13 Rattlesnakes20 Rhesus monkeys1 Yeasts56 A B C

Mechanisms of Change How did giraffes get such long necks?

Natural Selection E nvironment determines success of traits Overproduction of offspring and scarcity of resources

Natural Selection E nvironment determines success of traits 2. Genetic variation within populations

Natural Selection Environment determines success of traits 3. Organisms with adaptations will survive and reproduce in greater numbers.

4. Subsequent generations will contain more orgs with these adaptations. Natural Selection Environment determines success of traits

 Inherited trait Adaptation  Increases chance of survival/reproduction  Environment-specific

Natural Selection The environment determines success of traits 1.Overproduction 2.Genetic variation 3.Struggle for survival 4.Differential reproduction

Natural Selection

Modes of Selection  Stabilizing Environment is stable Environment is stable Initially adaptive form becoming more numerous from many generations of natural selection Initially adaptive form becoming more numerous from many generations of natural selection RANGE OF PHENOTYPES MOST ADAPTIVE FORM

Modes of Selection  Directional Environment is changing (or has changed) Environment is changing (or has changed) Formerly adaptive form is no longer adaptive Formerly adaptive form is no longer adaptive Pop evolves toward newly adaptive form Pop evolves toward newly adaptive form MOST ADAPTIVE FORM RANGE OF PHENOTYPES

Modes of Selection  Disruptive (Diversifying) Intermediate form is undesirable and decreases in # Intermediate form is undesirable and decreases in # MOST ADAPTIVE FORMS