Vestigial Strutures
A vestigial structure is a structure or organ that through the course of evolution has either diminished
in size or usefulness. It is believed that the human appendix, wisdom teeth and tail bone are vestigial
structures, because they are diminished in size or usefulness from what they would have been much
earlier on in the course of our evolution.
Analyze the pictures above. Suggest a possible function for each structure and explain why it became
vestigial (why that adaptation became less important for survival). Think about organisms that are closely
related to us and the functions they have for those structures (meaning other mammals or specifically other
primates). Record your answers in the table
Structure
Appendix
Possible Function(s)
Why it is considered vestigial
Muscles that make
hair stand up
Coccyx (tail bone)
Muscles that move
ears
Wisdom teeth
Gradual changes have occurred through time that have in some cases reduced or removed the function of
some body structures and organs. The penguin’s wings and the leg bones of snakes are examples of this
phenomenon.
1) The cave fish and minnow shown below are related, but the cave fish is blind.
a. Explain why eyesight is not an important adaptation to life in a cave. __________________
________________________________________________________________
b. Does the appearance of the cave fish and minnow suggest common ancestry? Why?
________________________________________________________________
________________________________________________________________
Embryology
Many scientists use what an organism looks like as an embryo, or embryology, as evidence for evolution. The
embryos of most vertebrates look very similar and have similar structures. For example, fish, bird, rabbit, and human
embryos are similar in appearance in early stages. They all have gill slits and a tail with muscles to move it. Later as
the embryos develop, they become less and less similar.
Embryology
Using complete sentences, describe how comparing early development can help scientists learn about the
relatedness of species. _______________________________________________________________
_______________________________________________________________
_______________________________________________________________
Homologous and Analogous Structures
These structures are formed in similar ways during embryonic development and share similar
arrangements; however, they have somewhat different forms and functions. They are called homologous
structures.
Homologous Structures
Carefully examine the drawings of the bones shown below. Look for similarities among the various animals.
a) Describe the function of each set of bones below.
Animal
Function
Human
Whale
Cat
Bat
Bird
Crocodile
b) Are the bones arranged in a similar way in each animal? _____________________________________
Analogous Structures
Some apparently unrelated animals have organs with similar functions, yet are very different in structure and
form. These structures are called analogous structures.
1) Examine the butterfly wing and the bird wing shown below.
a) What function do these structures share? ________________________________________________
b) How do these structures differ?
______________________________________________________
________________________________________________________________________
c) Do you think the bird’s wing and the insect’s wing came from a common ancestor? Why or why not?
____________________________________________________________________________________
Some apparently unrelated animals have organs with similar functions, yet are very different in structure and
form. These structures are called analogous structures.
Fossils
s
Fossil Evidence
Darwin discovered many fossils during his journeys aboard the HMS Beagle and compared them to living
organisms in the surrounding areas. The organisms above are from South America, one of the continents
he visited.
1. What are the similarities and differences between the glyptodont (glip•tuh•dahnt) fossil and the armadillo?
2. What inference can you make about their existence?
Fossils
Study the figure at below.
Which rock layer is the oldest? _____
Which rock layer is the youngest? _____
Explain what can scientists learn about evolution when comparing different fossils in different rock layers?
(Use terms like relatedness, extinction, transition etc.) You must write at least two complete sentences.