Evidence for Common Ancestry

What evidence can scientists use to predict which species share a common ancestor? We talked about 2 types of evidence Friday: Biogeography clues Similar nucleotide sequences Today, we will learn about 4 other types: 3) Fossils 4) Homologous structures 5) Vestigial structures 6) Developmental Biology

What do fossils tell us? Life is old. It has changed over time. Fossils that are deeper down are older and existed before fossils closer to the surface. This happens because of the way that rock layers form.

Processing Piece: True or false? The shell existed before the fish skeleton. The fish existed before the fern.

What are homologous structures? Structures that are similar in different species because they were inherited from a common ancestor Example: limb bones, eyes, ear bones (in mammals)

Processing Piece: Circle the humerus bone in the human arm. Circle the other bones that are homologous structures to the humerus bone in the other animals.

What are analogous structures? Structures that have similar functions (jobs) but were NOT inherited from a common ancestor. Example: wings in birds, and wings in insects

What are vestigial structures? Structures that were important in an ancestor, but are useless in the modern species Example: appendix, eyes in blind cave fish, erector pili (muscles that give you goosebumps), hind leg bones in whales

Vestigial Structures

What are Goosebumps?

What does developmental biology tell us? Developmental biology = how an organism develops from a zygote to an adult Distantly related organisms go through similar developmental stages. This implies that they shared a common ancestor. Example: The embryos of animals that live on land go through a stage where they look like very much like fish embryos, with gill folds and a fish-like tail.

Development of different Species

Exit Ticket: Which type of fossil is probably older: one that is closer to the surface, or one that is deeper down? Define each of the following as homologous structure, analogous structure, or vestigial structure: Eyes on a blind cave fish Similar bones in the arms and legs of different species Wings on birds and wings on insects