Primate Evolution Lab
Instructor Notes / Day 1
Instructions
Background Notes
1. Introduce question
The purpose of this presentation is to introduce
the question “how are humans related to other
primates.”
Show the PowerPoint presentation
to the class. The presentation ends
with the question “how are
humans related to other primates?”
2. Clarify question
Ask the students what it means for
species to be “related.”
The question “how are humans related to other
primates?” is ambiguous unless students
understand what it means for species to be
related.
“Related” does not mean “similar.” Species can
be similar without being related.
Species are closely related if they have recent
common ancestors. The concept is completely
analogous to relatedness among cousins. The only
difference is that a phylogeny shows the “family”
tree of species.
3. Explain the schedule to the
class.
Tell the class that they will be
working with ten primate species:
humans, and nine other primates.
Explain to them that the lab is
divided into two parts. On the first
day, they will figure out how to
answer the question, and on the
second day, they will do the actual
work.
4. How many trees for 10 species?
Ask the class how many possible
evolutionary histories there are for
10 species.
Simplify question.
Ask the class how they might try
This is a very difficult question, and the class will
not be able to answer it. It’s purpose is to show
students how difficult it would be for them to
identify the correct phylogeny for 10 species.
One answer: Start with 3 or 4 species instead of
10 .
begin to answer the question.
5. How many evolutionary trees
are possible for 3 species?
There are three possibilities:
6. How many trees for 4 species?
Ask the class to list all the possible
evolutionary histories there are for
3 species.
There are 15 possibilities. They fall into two
categories. Trees of the form (a,b)(c,d) and trees
of the form ((a,b)c)d.
(a,b)c (a,c)b (b,c)a
Ask the class to list all the possible where (a,b)c indicates that species a and b are
evolutionary histories there are for more closely related to each other than to c. Note:
3 species.
don’t use the notation, (a,b)c with the class—
draw the trees on the board.
There are three possible trees of the first form
(a,b)(c,d) (a,c)(b,d) (a,d)(b,c). These can be
enumerated by realizing: species a has to be
paired with one other species, there are three
possible species it can be paired with, and once it
is paired with another species the other two
species must also be paired.
There are 12 possible trees of the form ((a,b)c)d.
They can be enumerated by noticing that any of
the four species can be the most distantly related
species to the other three—species d in the case
of ((a,b)c)d. And for each of these four cases,
there are three possible ways to rearrange the
other three species. For example:
((a,b)c)d
((a,c),b)d
((b,c)a)d
Millions of trees.
Tell the class that there are
34,459,425 possible trees for 10
species. The formula for m species
2m  3! .
is m  2
2 m  2!


Tell them that this means that
comparing all possible trees is not
feasible, and that they will need a
method.
Chernoff face problem #1
Give the class Chernoff face
After the students have worked on the problem
for a while, ask them what they believe the
problem #1 and tell them to
estimate the evolutionary tree for
these “species.”
answer is, and how they solved it.
Problems 2 &3
Discuss the problems after the class has solved
them.
Give the class problems 2
Problem 4
Give the class Problem #4, DNA
sequence data for three species.
Closing announcement
Remind the class that during the
next lab period, each lab group
will be estimating the phylogeny
for 3 species—and that they will
have to present their preliminary
results to the class.
The problem can be solved by noting that the
human and orangutan sequence are the most
similar.