Lesson OverviewLesson Overview Evidence of EvolutionEvidence of Evolution

Lesson OverviewLesson Overview16.4 Evidence of Evolution16.4 Evidence of Evolution

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of Evolution

Biogeography– study of where organisms

live now and where they and their ancestors lived in the past.

– Two biogeographical patterns are significant to Darwin’s theory.

1. a pattern in which closely related species differentiate in slightly different climates.

Ex. variation in shell shape among the giant land tortoises that inhabit the Galápagos islands.

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of EvolutionSpecies Vary Globally

2. a pattern in which very distantly related species develop similarities in similar environments.

Ex. similar ground-dwelling birds (rheas, ostriches, and emus) inhabit similar grasslands in Europe, Australia, and Africa.

emu. ostrichesRheas

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of EvolutionHomologous Structures – Structures shared by related species and that have been

inherited from a common ancestor are called homologous structures.

– Darwin proposed that animals with similar structures evolved from a common ancestor

– Biologists test whether structures are homologous by (1)studying anatomical details the way structures develop in embryos, (2)the pattern in which they appeared over evolutionary history.

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of EvolutionHomologous Structures –Ex. the front limbs of reptiles and birds are more similar to each other to than either is to the front limb of an amphibian or mammal. –Scientists say that this similarity is used to show that the common ancestor of reptiles and birds lived more recently than the common ancestor of reptiles, birds, and mammals.

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of EvolutionAnalogous Structures –Another example used by scientists are analogous structures body parts that share a common function, but not structure. –Ex. The wing of a bee and the wing of a bird are analogous structures.

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of EvolutionVestigial Structures

–inherited from ancestors, but have lost much or all of their original function due to different selection pressures acting on the descendant.–Ex. The hipbones of bottlenose dolphins

Pelvic bone of a whale

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of Evolution

Other Examples of Vestigial Structures

–The wings of a flightless cormorant –The legs of an Italian three-toed skink cormorant

three-toed skink

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of Evolution

Embryology

–Some scientists use the similar patterns of embryological development as evidence that organisms have descended from a common ancestor.

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of Evolution

Life’s Common Genetic Code

– Some scientists believe that the strongest evidence supporting evolutionary theory comes from genetics.

Lesson OverviewLesson Overview Evidence of EvolutionEvidence of Evolution

Life’s Common Genetic Code

– This genetic code is nearly similar in almost all organisms, including bacteria, yeasts, plants, fungi, and animals

– This compares a small portion of the DNA for the same gene in three animals—a mouse, a whale, and a chicken.