Homologous structures n Structures on different organisms are

Homologous structures n Structures on different organisms are homologous when they have similar base structures but have different functions.

Homologous structures Human Arm Bat Wing Whale Flipper

Analogous Structures n n n Similar functions but NOT structurally related. Insects are arthropods and birds are vertebrates. The wing of a bird and the wing of a butterfly are examples of analogous structures.

Comparative embryology

Vestigial Structures A structure in an organism that has lost all or most of its original function

Transition fossils

The Panda's Thumb n n A classic example of evolution. The giant panda is a bear that adapted to eating bamboo.

The panda’s opposable thumb q. Giant pandas have a thumb pad on the hand q. This thumb pad is used by the panda to grasp bamboo shoots q. It uses its thumb to hold and manipulate the bamboo while eating

The Panda has not always had this opposable thumb. Fossil evidence shows that this has evolved over thousands of years.

Comparing bones.

Unrelated species evolve similar traits even though they live in different parts of the world, or at different times in Earth’s history

Analogous Structures = Convergent Evolution

Analogous Structures = Convergent Evolution

Analogous Structures = Convergent Evolution

Divergent Evolution: one species gives rise to many species

Divergent Evolution § One species gives rise to many species in response to the creation of new habitat or other ecological opportunity § Gives rise to homologous structures

Geographic isolation: prevents individuals of a species in different populations from mating

Geographic isolation prevents a mix of genes with the original species. n n Example: Kodiak Brown Bears This group of bears have evolved into a sub-species, that is different form all other grizzly bears.

An archipelago is a landform which consists of a chain or cluster of islands.

Adaptive radiation: n many species appear to be related to a single ancestral species.

Reproductive Isolation: prevents individuals from reproducing with each other n n Prezygotic isolating mechanisms : prevent reproduction before fertilization Postzygotic isolating mechanisms: prevent reproduction after fertilization

GRADUALISM n Living things change very slowly in small, gradual steps: GRADUALISM

PUNCTUATED EQUILIBRIUM n n Sometimes species will remain the same for a long period of time and then change very quickly. This is usually the result of some catastrophic disaster like an earthquake or volcano.

GALAPAGOS FINCHES

THE EVOLUTION OF BEAK SHAPE IN GALAPAGOS FINCHES n n Darwin first thought about evolution while studying in the Galapagos 13 species of finches in the Galapagos islands Islands are barriers that separate each group of the species- “Geographic Isolation” size and shape of the beak has an important consequence for fitness. (What is Fitness? )

Darwin’s finches Medium Tree Finch Cactus Ground Finch Medium Ground Finch Warbler Finch

GALAPAGOS FINCHES n n n Each species has a highly characteristic beak shape. Darwin focused his study on the link between the shape of the beak, the food and the habitat of each species. This research of his was to result in theory of evolution and the 14 finches became "stars" in their own right.

The Case of the Galapagos Finches n n n All species of finch derive from the same original species. The observation: despite their strong resemblance, each species of finch has a highly characteristic beak shape. The evolutionary factors: geographic isolation, ecological environment, food sources, competition.