Name ________________________________
AP Biology
Date_____________________
Lab 8B:
Evidence for Evolution
(April Break Assignment Part 2)
Background Information
In a nutshell, the theory of evolution states that all species on earth developed from a common ancestor through
speciation (the branching of one species into two) driven by the processes of natural selection and genetic drift.
We can break this theory down into a number of important ideas:
 There is variation between individuals in a species (this is the raw material for evolution)
 Species change gradually over time
 Natural selection is a key driver of evolutionary change
 One species can branch into two or more species
 All species share a common ancestor
You have two main objectives for this lab:
(1) Examine, and describe, the different types of evidence for evolution
(2) Use this evidence to support some of the ideas in the list above
Pre-Lab: Some Important Vocabulary
Vestigial structures –
Homologous structures –
Analogous structures –
Divergent evolution –
Convergent evolution –
1. Fossils & vestigial structures - Basilosaurus
If you haven’t seen it before, watch the video on Basilosaurus here:
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html and then look at the picture below.
Pearson 2006
(Biology: Exploring Life, by Campbell, Williamsen, Heyden 2006)
The basic gist of this story is that whales evolved from 4-legged, terrestrial mammals into flippered aquatic
mammals. What’s the evidence?
a. Explain how vestigial structures have provided evidence for this story
b. Explain how fossils have provided evidence for this story.
c. Deceptively, whales show some analogous traits to sharks and other fish, due to convergent
evolution in the same environment. Describe at least one trait that is analogous between
whales and sharks, and explain how you know that it is not a homologous trait.
d. Whales share some homologous traits with terrestrial mammals. Give at least one example (it
could be behavioral or structural) and explain how you know that it is homologous.
2. Homologous limbs
Look at the pictures of the homologous limbs.
a. Describe this evidence. What is homologous about
these limbs? (Ask for a color picture to help see!)
Pearson 2006
3. Embryonic development
Look at the pictures of the embryos.
a. Describe this evidence. How would you categorize this
evidence using some of the vocabulary from the first page of
the lab?
b. Homlogous limbs and similarities in embryonic development both support at least one of the ideas
list on page 1. Identify which idea(s) from the list on page 1 this evidence supports, and explain
how this evidence supports that idea(s).
4. The Vertebrate Tree of Life:
Original phylogenetic trees showing the evolutionary relationships between all the vertebrate classes
(Fishes, Amphibians, Reptiles, Birds, and Mammals) placed mammals and birds as closest relatives. This
was mostly based on the fact that both birds and mammals are endothermic (warm-blooded).
However, it turns out that endothermy in birds and mammals is an analogous trait, not a homologous
one!
The newer, now-accepted tree for vertebrates shows the following relationships between
mammals, birds, and reptiles:
a. According to this tree, what group is
the closest living relative of birds?
b. What type of organisms are birds
direct descendants of?
c. Fossil evidence was important in establishing this
unexpected relationship. Look carefully at the picture of
the Archaeopteryx fossil (ask to see the one in color!).
Note the faint lines radiating out from its limbs these are
thought to be imprints of feathers.
Describe this evidence – what features does
Archaeopteryx share with dinosaurs? With birds?
6. Molecular Data: Cytochrome C sequences
Another important type of evidence for constructing phylogenetic trees is molecular data – DNA and
protein sequences from living organisms that, when compared, gives a measure of the evolutionary
distance between different groups.
For example, the table below shows the number of differences in the amino acid sequence for a
particular protein between pairs of selected species. The sequences compared for this data set are
from a protein called cytochrome c, which is a mitochondrial membrane protein involved in cellular
respiration (this makes it good to use for comparison, because almost all species make this protein).
Horse
Donkey
Chicken
Penguin
Snake
Horse
0
Donkey
1
Chicken
11
Penguin
13
Snake
21
0
10
12
20
0
3
18
0
17
0
a. Briefly summarize how molecular evidence (DNA and amino acid sequences) can be used to
determine evolutionary relatedness between species.
b. According to this table, what is the closest relative (among the species listed) to the horse?
Explain your answer.
c. What about the closest relative (among the species listed) of the chicken? Why?
d. Using the data provided, draw a phylogenetic tree showing the relationships between these
5 species.
e. Double check to make sure that your tree makes sense.
f.
Now, summarize at least 2 other types of evidence (like the ones you’ve explored
elsewhere in this lab packet) that could be used to support the relationships in the tree you just
drew.