7.4 The Evidence for Evolution

Pages 296-302

biogeography

• The study of the distribution of organisms

Galapagos Islands

Darwin on the HMS Beagle

• 1831-1836• Galapagos Islands, 1000 km off the west coast

of S. America• No large land mammals or amphibians• Strange reptiles, birds, insects and plants,

similar to those found on nearest continent

No fear!!

• Birds land on your head.• Iguanas allow you to pick them up.• Sea lions sit beside you.

loss of instinctive fear?

Unique species

• Arrived by water or air then changed into new species over time

Comparing iguanas

• Mainland iguanas have short claws for climbing trees.

• Galapagos iguanas have long claws for hanging onto slippery rocks.

Homologous Features

• A structure with a common evolutionary origin currently used in different ways.

Mammals

• 7 neck bones

Mammals

• 28 skull bones

Skeletons

• Bat skeleton Human skeleton

Homologous embryonic development

• Human embryoshave gill slits.

Analogous Features

• Body parts that perform the same function but do not share similar origin or structure

fly eye rabbit eye

Analogous features

Dragon fly wing vs. bird wing

Vestigial features

Dew toes in dogs hip bones in whales

Thomas Malthus

The Principle of Population

All populations were limited in size by their environment—and in particular their food supply.