Evidence for Evolution
Comparing Primates
Pre-Lab Discussion
In The Descent of Man, the English naturalist Charles Darwin formulated the hypothesis that human beings and
other primates have a common ancestor. A hypothesis is a suggested explanation for observed facts. All scientific
hypotheses, including that of Darwin, are based on observations.
Darwin observed that human beings and other primates differ in many important ways. Although all primates have
opposable thumbs, the human hand is capable of more refined and exact movements than those of other primates.
The human braincase, or cranium, has more volume and more mass than those of other primates. In addition, human
beings are bipedal, or able to walk on two limbs. Other primates use all four limbs for locomotion. Being bipedal
frees the arms and hands for other tasks, such as tool making. Darwin regarded these human traits as adaptations,
resulting from natural selection. The adaptations of other primates, he suggested, evolved differently.
More recently, biochemists have determined that certain proteins found in different primates contain many of the
same amino acid sequences. Scientists reason that because proteins are produced by DNA, human beings and other
primates must have a similar genetic makeup. Paleontologists have also found fossil remains that provide evidence
that all primates came from a common ancestor. These and other observations lend support to Darwin's hypothesis
of human origins.
In this investigation, you will develop skill in observing and interpreting data provided by biochemists,
paleontologists, and other scientists.
Problem
How are human beings similar to and different from other primates?
Materials (per student)
Metric ruler
Pencil
Protractor
Procedure
Part A. Comparing Amino Acid Sequences in Vertebrate Proteins
1.
Figure 1 shows the amino acids found in selected sites in the hemoglobin of different vertebrates.
2.
Count the number of molecules of each amino acid in human hemoglobin. Note: Be sure to count the
molecules of amino acid in human hemoglobin in the second section titled Primate as well as in the first
section. Record these totals in the appropriate column in Data Table 1.
3.
Count the number of molecules of each amino acid in the hemoglobin of other vertebrates in Figure 1.
(Remember to count both sections.) Record these totals in the appropriate columns in Data Table 1.
4.
Going from left to right, note the position of each amino acid. Count the number of similarities in the
amino acid positions in human hemoglobin as compared with the hemoglobin of each of the other
vertebrates in Figure 1. Record your observations in Data Table 2.
5.
Reexamine Figure 1 and count the number of differences in the amino acid positions in human
hemoglobin as compared with the hemoglobin of each of the other vertebrates in Figure 1. Record your
observations in Data Table 2.
Part B. Comparing Primate Features
1.
Determine the relative size of the lower jaw of each primate by measuring the length in millimeters of
lines ab and bc in Figure 2. Record these lengths in Data Table 3. Record the product of these lengths in
Data Table 3.
2.
Determine the angle of the jaw by using a protractor to measure the angle xy in each primate skull in
Figure 2. Record your observations in Data Table 3.
3. Examine the teeth of each of the three primates in Figure 3.
4.
Count the number of incisors, canines, premolars, and molars of each primate in Figure 3. Record your
observations in the appropriate columns in Data Table 4.
5.
Examine the two skeletons in Figure 4.
6. Compare both views of skeleton A with those of skeleton B. Answer questions 1 and 2 in Observations.
Observations Data Table 1
Number of Molecules of Different Amino Acids in Some Vertebrates
Amino Acid
Abbreviation
Alanine
ALA
Arginine
ARG
Asparagine
ASN
Aspartic acid
ASP
Glutamine
GLN
Glutamic acid
GLU
Glycine
GLY
Histidine
HIS
Isoleucine
ILU
Leucine
LEU
Lysine
LYS
Proline
PRO
Serine
SER
Three-nine
THR
Valine
VAL
Human
Chimpanzee
Gorilla
Baboon
Lemur
Dog
Chicken
Data Table 2
Similarities and Differences in Amino Acid Positions in Hemoglobin
Organisms
Human and chimpanzee
Human and gorilla
Human and baboon
Human and lemur
Human and dog
Human and chicken
Human and frog
Number of Amino Acid Position
Similarities
Number of Amino Acid Position
Differences
Frog
Data Table 3
Comparison of Three Primate Skulls
Length of Lower Jaw
(mm) (ab)
Skull
Depth of Lower Jaw
(mm) (bc)
Area of Lower Jaw
(mm2) (ab x bc)
Angle of Jaw
A
B
C
Data Table 4
Comparison of Primate Teeth
Type of Teeth
Number of Teeth
A
B
C
Incisors
Canines
Premolars
Molars
1.
Describe three differences between skeleton A and skeleton B
2.
Which type of primate skeleton is considered bipedal
Analysis and Conclusions
1.
a. From your observations in Data Table 2, which primate is most closely related to the human being?
b. Which primate is least closely related?
2.
a. Which nonprimate vertebrate listed in Data Table 2 is most closely related to the human being?
b. Which nonprimate is least closely related?
3.
a. Which of the three primates shown in Figure 2 has the largest brain? What do you think is
the name of this primate?
b. Which of the three primates shown in Figure 2 has the smallest brain? What do you think is the name of this
primate?
4.
What is the relationship between jaw size and brain size in these three primates?
5.
From your observations in Data Table 4, what dental characteristics do the primates have in common?
6.
Reexamine Figure 3. How would the diet of primate A differ from the diet of primate C?
7.
What is an advantage of being bipedal?
Critical Thinking and Application
1. Many primates use tools. For example, chimpanzees often use sticks to probe ant hills when searching for food.
They also use leaves as sponges to collect drinking water. How is the use
of tools by humans different from that of other primates?
2. The brain of the human being is larger than that of other primates. How would this relate to the different methods
of communication displayed by humans and other primates?
3. Certain fossil evidence indicates that the primate ancestors of humans lived in areas where trees were scattered
instead of clustered together. How might this type of environment have affected the development of bipedalism in
humans?
4. Describe three physical characteristics that are unique to human beings.
Going Further / Extra Credit
Visit a local zoo to observe the behavior of gorillas, chimpanzees, baboons, and other primates. Observe the ways in
which the animals communicate and interact with one another. What similarities and differences do you observe
between the behaviors of the primates you studied and those of human beings? Use a notebook to record your
observations.