1.7.2 Evidence for Evolution: Vestigial Structures

Question 1

vestigial structures

Answer 1

• structures that are present in an organism yet have no apparent function
• example: hipbones found in whales and snakes, and the appendix in humans.

Question 2

ancestors of whales

Answer 2

• were four-footed, landdwelling creatures.
• Fossils of now extinct whales show that they had rear flippers that contained leg bones.
• Present-day whales do not have rear appendages but do have hipbones left from their ancestors.

Question 3

ancestors of snakes

Answer 3

• were amphibian-like creatures that had four legs.
• Boa constrictors have vestigial hipbones where
  legs would have been. There are other types of snakes that have protrusions where vestigial hipbones are.

Question 4

herbivores

Answer 4

• The early mammals were thought to be small
  herbivores (plant-eating animals).
• Herbivores have an organ called the cecum that holds bacteria able to digest cellulose, a material found in the cell wall of plants. Herbivores cannot digest cellulose, and thus, it is beneficial for them to have a cecum where bacteria can live and digest cellulose for them.

Question 5

carnivores

Answer 5

• (meat eaters and plant and meat eaters) have a reduced cecum.
• The cecum was selected against in carnivores
  because it wasn’t necessary and was an additional body part with additional risks (it holds bacteria). The remnant of the cecum is the appendix

Question 6

Which of the following is not an accurate explanation for the existence of the indicated vestigial structure?

Answer 6

• The tail on a peacock was once used as a weapon and distraction during confrontation but no longer serves a purpose.

Question 7

Anatomical features that are fully developed and functional in one group of organisms but reduced and functionless in another are _____________ structures.

Answer 7

• vestigial

Question 8

True or false?

The presence of a vestigial structure in an embryo is evidence that evolution by natural selection does not occur.

Answer 8

• false

Question 9

Which of the following is not a vestigial structure?

Answer 9

• the eyelashes in humans

Question 10

Vestigial structures occur because

Answer 10

• the structure conferred no adaptive advantage to the species in which it is functionless, and it may have had disadvantages.
• evolution is a slow process, and useless structures do not disappear quickly.

Question 11

A vestigial structure in the python is the

Answer 11

• pelvic girdle