Station #3: Comparative Anatomy

Last updated almost 5 years ago

3 questions

Similarities among different species can show two different kinds of relationships, both of which support evolution and natural selection. These similar structures are known as homologous structures and analogous structures.

Similarities shared by closely related species (species who share many characteristics) are homologous, because the species have descended from a common ancestor which had that trait. Homologous structures may or may not serve the same function. Figure below shows the forelimbs of mammals, considered homologous because all mammals show the same basic pattern: a single proximal bone joins a pair of more distal bones, which connect to bones of the wrist, “hand,” and digits. With this basic pattern, bats build wings for their lives in the air, whales form fins for their lives in the sea, and horses construct long, hoofed legs for speed on land. Therefore, homologous structures support common ancestry.

Similarities shared by distantly related species may have evolved separately because they live in similar habitats. These structures are analogous because they serve similar functions, but evolved independently. Figure below compares the wings of butterflies and bats. Bats evolved wings as mammals and butterflies evolved wings as insects. Their wings are analogous structures, each of which evolved independently, but all of which suit a lifestyle in the air. Butterfly wings are made of chitin, a thin but durable protein, while the internal structure of a bat wing is made of sturdy bones. Because analogous structures are independent adaptations to a common environment, they support natural selection.

The image above shows three types of swimming animals - sharks, penguins, and dolphins. Is this an example of analogous or homologous structures?

The image above shows the limbs of four different organisms, all of which are used for different functions. Are these homologous or analogous structures?

Both the North American opossum and Australian kangaroo carry their young offspring in a pouch until they are fully developed. The fact that these organisms have similar structures suggests which of the following?