Judgment Day: Intelligent Design on Trial
Students evaluate a variety of data
for the common ancestry of humans and chimpanzees, and consider their level of
confidence in their conclusions as they review each piece of data.
Students will be able to:
define and differentiate
fact, hypothesis, law, and theory.
explain what a karyotype
describe the similarities
and differences between human and chimpanzee chromosomes.
summarize the chromosomal
evidence showing that humans and chimpanzees share a common ancestor.
- copy of the "Weighing the Evidence" student handout
- photographs of chimpanzees (see sidebar for photo resources)
- copy of the "Hominidae Family Tree" student handout
- copy of the "Karyotype Idiograms: Human and Chimpanzee" student handout
- copy of the "The Chromosome Shuffle" student handout
- copy of the "Comparing Chromosomes" student handout
- 1 light blue and 1 yellow highlighter
- copy of the "Sequence Search" student handout
- optional: printout of "Human Chromosome 2: Region 2q13" (55 pages)
Evolutionary biologists assert that
close biological relationships indicate common ancestry. Humans have long been
classified with the great apes (the orangutans, gorillas, and chimpanzees)
based on their very similar anatomy and physiology. More recently, molecular
genetic data (DNA) has confirmed humans' close biological relationship
with the chimpanzee (and to a lesser extent the other great apes).
In this activity, students evaluate
anatomical and genetic data regarding a shared ancestor for humans and
chimpanzees. Students consider whether each piece of data supports the
hypothesis that humans and chimpanzees share a common ancestor, and reflect on
how confident they are in their conclusions with each piece of data they
review. In this way, they come to understand how scientists become more
confident in their conclusions as confirmation for their hypotheses
accumulates. It is important in this activity to dispel the misconception that
humans descended from apes and to emphasize that humans and chimpanzees share a
common extinct ancestor that was
different from either of them.
This common ancestor likely did not
look like either of the modern species but shared characteristics of both. Both
humans and chimpanzees are equally evolved from this ancestor but in different
ways, like cousins with the same great-great-great grandfather. The attributes of
the cousins come from the grandfather, not one another.
The activity should take one to
three class periods. If students have not learned how to read DNA code, you may
want to do just Part I of the activity that compares karyotypes, explores
phylogenetic relationships, and investigates chromosomal rearrangements. Part
II of the activity further explores the DNA data that supports the fusion of
two ancestral chromosomes to produce a single chromosome in humans. For this
part of the activity, students should be familiar with how DNA bases complement
each other and how DNA fits together (5'–3' orientations).
The following table from the
"Weighing the Evidence" student handout shows how the lesson
progresses. It outlines the evidence students will be considering and shows
when students will rate how confident they are the hypothesis is true based on
common ancestor: An extinct group of organisms that gave rise to
two or more later groups.
evolution: Biological evolution is
descent with modification. It includes both small-scale evolution (the
cumulative changes that occur in a population over time) and large-scale
evolution (the descent of different species from a common ancestor over many
generations). Evolution is a scientific theory, supported by a great
deal of evidence, facts, inferences, and tested hypotheses.
idiogram: A diagram of the chromosome complement of a species,
showing banding patterns, that is often used to compare karyotypes of different
intelligent design: The idea that certain
features of the universe and life are too complex to have arisen by natural
causes and instead are best explained as being the product of an intelligent
complete set of chromosomes that constitutes the entire genome of a species.
Karotypes are usually arranged in pairs by number and size (largest to
mutation: A permanent change in the DNA sequence of a gene. Most
mutations are harmless, though some can be harmful. Occasionally, a mutation
can increase an organism's chance of survival.
selection: A process in which
genetically-based characteristics allow some individuals to survive, giving
them a reproductive advantage in their local environments. These
characteristics tend to increase in frequency in the population over time while
those that are disadvantageous decrease in frequency.
A graphical representation of the evolutionary relationships of a group of
organisms. Phylogenetic trees can be based on different types of evidence, such
as gene sequence, genomic data, or protein analysis. Dates are constantly being
refined as scientists gain more information from fossil and molecular analyses
and develop more sophisticated measuring techniques.
science: A systematic form of inquiry, based on observation,
prediction, reasoning, and testing, that seeks to explain how the natural
universe works. Science operates by means of the scientific method—the
formulation of hypotheses that are consistent with observed phenomena and the
subsequent testing of these hypotheses to determine their validity. Scientific
knowledge is constantly refined or altered by new evidence; if a hypothesis is
not supported by experimentation or observation, scientists reject it and
formulate a new hypothesis that is tested against the observed data. Science involves reasoning about the natural world. It does
not involve supernatural explanations of the physical universe. Authentic
scientific inquiry is based on the things that can be studied and tested.
The Nature of Science
The terms fact, law, hypothesis, and theory are used frequently and sometimes interchangeably in day-to-day
conversations. But for scientists, they have very specific meanings. The
following definitions* were developed by members of the National Academy of
fact: In science,
an observation that has been repeatedly confirmed.
law: A descriptive generalization about how some aspect
of the natural world behaves under stated circumstances.
testable statement about the natural world that can be used to build more
complex inferences and explanations.
theory: In science,
a well-substantiated explanation of some aspect of the natural world that can
incorporate facts, laws, inferences, and tested hypotheses.
science, a theory is often the end product of decades or centuries of
scientific research that incorporates numerous observations about the
scientific phenomenon it is trying to explain. A theory represents the
best present explanation for a scientific phenomenon.
See Scientific Term Examples at right for examples of each term.
*Reprinted with permission from the National Academies Press, Copyright 1998,
National Academy of Sciences.
To get students thinking about
the nature of science, introduce the following engagement activity: Tell
students they have been hired to investigate a crime scene in which someone
appears to have broken into the principal's office the day before and
changed every student's science grade to an "F." In a preliminary
analysis, police found blood on the floor where the principal's office
glass door had been shattered. Ask students what types of evidence they might
look for at the crime scene. (Students might note physical evidence such as
fingerprints, hair, fiber, DNA from the blood sample; or eyewitness reports
from people who saw the crime committed.)
List student responses on the board. Now have students rank their confidence
(from most to least) of each piece of evidence in terms of identifying the
person who broke in. Which evidence would be least convincing by itself? (Fingerprints,
hair, and fiber samples, which could have come from any student visiting the
principal's office.) Which would be
most convincing by itself? (The DNA from the blood sample.) What would strengthen the case? (Additional
evidence that supports the DNA evidence, such as eyewitnesses, additional
physical evidence, or a motive for the person who changed the grades.)
Similar to forensic experts,
research scientists also gather evidence (data) to confirm or refute tentative
explanations (hypotheses) that they have about the natural world. Both forensic
experts and scientists use the word theory.
But while a police investigator may have a theory about who committed a crime,
in science, theory means
something very different. Ask students to define what they think theory means in science. How does a scientific theory
differ from a hypothesis? A law? A fact? (See The Nature of Science above for definitions.) Provide students with
an example of each term. (See Scientific Term Examples at right for some suggestions.) Have students
compare the examples and elaborate on what is different about each of them. To
ensure that students understand the differences, have them come up with
examples of each term on their own.
Evolution is a theory. One of
its core propositions is that organisms alive today can be traced back through
time to a common ancestor. Evolutionary biologists investigate the similarities
among organisms; they might hypothesize, for example, that the more similar
organisms are genetically, the more closely related they are, and the more
likely they are to have evolved from a recent common ancestor. In many ways,
humans are more like chimpanzees than any other animal. Tell students that they
are going to consider data to support or refute the following hypothesis:
Humans and chimpanzees share a common ancestor.
Organize students into pairs and
distribute the "Weighing the Evidence" handout to each team. Review
the activity with students.
Tell students that they will
start the activity with data set 1
(comparing traits). Provide each team with photographs of chimpanzees. Ask
students to create a two-column table on a sheet of paper (humans in one column
and chimpanzees in the other) to compare similarities and differences among
physical traits between the two. Have students consider posture, leg and arm
length, feet, teeth, skull, and facial features. (Similarities include that
both species have legs, feet, and grasping hands; both have eyes, a mouth, and
a nose in about the same areas on the face; both have body hair and no tail.
While some overall major features are similar, many differences exist in how
these features are expressed: Chimpanzees have arms longer than legs (the
opposite of humans); chimps have low foot arches, humans have high arches;
chimps have long canine teeth, humans do not; chimps have a wide nasal opening,
humans have a smaller opening; chimps have very hairy bodies, humans have
relatively little hair. In addition, chimps walk on all fours while humans are
Ask students to consider whether
the physical characteristics comparison supports the hypothesis. Based on this
data alone, have each team record how confident it is that humans and
chimpanzees share a common ancestor (on a scale of 1 [least confident] to 10
students they are now going to consider some genetic evidence for common
ancestry of humans and chimpanzees. Distribute the "Hominidae Family
Tree" handout to teams. Inform student that this is what is known as a
phylogenetic, or family, tree. This tree is based on DNA sequence comparisons
among the species in this family. The resulting branches of the tree are what
scientists infer to be the evolutionary relationships among these species.
The handout also includes the number of chromosomes for
each species. Ask students what similarities and differences they notice among
the number of chromosomes for these species. When students notice that humans
have 1 pair (2 chromosomes) fewer chromosomes than the other species, have them
consider what might explain this.
students to develop two hypotheses that would explain why humans and
chimpanzees—given a hypothetical common ancestor—have a different
number of chromosomes. (Two possible hypotheses for the difference in number
of chromosomes between humans and chimpanzees might be either that one long
ancestral chromosome split to form two shorter chromosomes in the chimp genome
or that two short ancestral chromosomes fused to form one longer chromosome in
the human genome.)
Inform students that they will now look more closely at how the actual
chromosomes themselves compare. Introduce data set 2 (comparing chromosomes) to students—human and chimpanzee
karyotype comparisons. Review what a karyotype is with students. (A karyotype
is a complete set of chromosomes that constitutes the
entire genome of a species.) Distribute the "Karyotype Idiograms:
Human and Chimpanzee" student handout and a set of light blue and yellow
highlighters to each team.
Explain that the idiograms are
graphic representations of actual karyotypes and that, since both members of a
matched pair of chromosomes look alike, only one member of each homologous pair
is represented. Inform students that the banding patterns are created when the
chromosomes are stained with a chemical. The chemical used for this karyotype
is called Giemsa, which always attaches itself to regions of DNA with high
concentrations of adenine-thymine (A–T) pairs. The dark bands are called
G-bands. The bands do not represent genes (there could be hundreds of genes
within one band) but they do give an indication of nucleotide sequences. Point
out to students that the tips of the constricted portion of the chromosome is
called the "centromere."
Assign each team a specific set
of chromosomes to compare (i.e., team A does sets 1,2, and 3; team B does sets
4, 5, and 6; and so on. Have students use a light blue highlighter to mark
banding areas on both chromosomes that are the same and a yellow highlighter to
mark areas on both chromosomes that are different. Have students compare
banding patterns, chromosome length, and positions of centromeres.
After all teams have finished,
ask each team to report to the class the similarities and differences they
should note that there are some banding pattern and centromere differences
between the two karyotypes, that human chromosome 2 is much longer than the
chimpanzee chromosome 2, and that there is an extra chimpanzee chromosome.) Then have each team on its own consider whether the
karyotype comparisons support the hypothesis that humans
and chimpanzees share a common ancestor. The have students—taking
into account both data sets they have reviewed—rate how confident (on the
scale of 1–10) they are that humans and chimpanzees share a common
Tell students they will now
review data set 3 (chromosome shuffle)
to investigate some possible explanations for the banding pattern differences
they noted. Distribute the "Chromosome Shuffle" handout to each
team. Have students read about some of the different types of changes that
chromosomes can undergo and correctly identify the types of changes shown on
Once students have learned
about and identified the changes, distribute the "Comparing
Chromosomes" handout and scissors to each team. Have students work in
their teams to determine whether any of the chromosomal changes they learned
about can account for the differences between these chromosomes (students are
given extra chimpanzee chromosomes to cut out and manipulate if needed).
Students will discover that the two chromosomes they have been given to compare
(4 and 5) differ only in pericentric inversions (inversions that include the
After students have found the
pericentric inversions in chromosomes 4 and 5, explain to students that
pericentric inversions account for most of the differences between the two
karyotypes and that scientists have determined that, when these chromosomal
mutations are taken into account, the two karyotypes are virtually identical
(homologous), with the exception of the longer human chromosome 2. (See Activity
Answer below for details about how the
two karyotypes compare.)
Ask teams to consider whether
this data set supports the hypothesis that humans and chimpanzees share a
common ancestor. Then have students—taking into account all three data
sets they have reviewed—rate how confident they are (1–10) that
humans and chimpanzees share a common ancestor.
Revisit the karyotype
comparison and ask students to consider data set 4 (human chromosome 2) to think about what might be
responsible for the final difference between the two karyotypes (the long human
chromosome 2). Have them refer to their "Chromosome Shuffle"
handouts to identify whether one of the types of mutations could explain the
difference. (Some students may notice that fusion [or even fission] could
have been the type of change responsible.)
To test the idea that fusion is
responsible, have students cut out the extra chromosome on their
"Karyotype Idiograms: Humans and Chimpanzees" handout and see
whether it would create a match with human chromosome 2 if fused with the current
chimpanzee chromosome 2. (Students should discover that the chromosome has
to be inverted in order to match up correctly.)
Ask teams again to consider
whether this fourth data set supports the hypothesis that humans and
chimpanzees share a common ancestor. Then have students—taking into
account the four data sets they have reviewed—rate how confident they are
(1–10) that humans and chimpanzees share a common ancestor.
You can stop the activity here
and use the questions on the "Weighing the Evidence" handout to
guide a final discussion, and ask students which of their hypotheses about why
humans and chimpanzees have a different number of chromosomes is best supported
by the data. Or you can move to Part II of the activity in which students examine
human DNA code for additional evidence regarding the common ancestry of humans
Ask students what further
evidence they could look for to test the hypothesis that the fusion of two
ancestral chromosomes formed human chromosome 2. If students don't
suggest looking at the DNA code for evidence, give them a clue by asking them
what one of the strongest pieces of evidence was in the principal's
office break-in. (Some students will likely remember it was the DNA
evidence.) When students suggest DNA, tell
them that the telomeres found at the tips of all chromosomes contain a unique
sequence of DNA code that could be searched for in human chromosome 2.
Ask students what it would mean
if the sequence were found and what it would mean if it were not found. (If
found, it would provide support for the hypothesis that two short ancestral
chromosomes joined to create human chromosome 2; if not found, it would support
the idea that the two ancestral chromosomes did not join, or if they did, that
their telomeres may have been lost. Not finding the sequence could also suggest
that human chromosome 2 may have represented the ancestral form that split
during chimpanzee evolution, producing the two shorter pieces found in chimps
Tell students that they will now
examine data set 5 (DNA telomere
sequence search) to look for the DNA sequence that would exist if telomere DNA
met and joined. Distribute the "Sequence Search" handout to each
student. Inform students that the letters on the page represent
only one strand of bases from the DNA molecule, since the matching bases in the
complementary strand are a given (A with T, C with G). Dealing with only
one strand simplifies reading the code.
To help students know what to
look for in the sequence where the two head-end telomeres attach, explain that
the DNA molecule in one of the chromosomes needs to rotate on its axis a
half-turn in order to connect properly with the telomere DNA in the other
chromosome. (If your students are familiar with the 5'-3' opposite
orientations of the parallel DNA strands, you could point out that this
rotation is because the 5' end of the strand in one chromosome must join
the 3' end of the strand in the other chromosome.) You can illustrate
this by doing the following demonstration: Hook the curved fingers of one hand
to the curved fingers of the other by rotating one hand, wrist, and forearm a
half-turn. When the DNA rotates, the single strand looks like:
...TTAGGGTTAGGGCCCTAACCCTAA... (going from TTAGGG to CCCTAA, the sequence
students will try to determine).
Point out that the sequence
varies a bit in places due to mutations (i.e., an "A" may be
replaced with a "G" in some sequences so that it reads TTGGGG, or
with a "T" so it reads TTTGGG, and so on).
Have students work by themselves
to determine what the sequence would be at the fusion point and search for a
fusion site on their handout. Circulate among students to help any having
After each student has tried to
determine the sequence and locate the fusion site, as a class review what the
correct sequence would be and why, and point out where the fusion site is if
students have not already found it. Have students color the 2A telomere region
with the light blue highlighter and the 2B telomere portion with the yellow
highlighter. Point out to students that these segments are the remains of the
ends of ancient chromosomes, and that each student has these molecular fossils
in almost all of his or her cells.
Once everyone has located the
site, have students discuss in their teams which of the two hypotheses they
developed about why humans and chimpanzees have a different number of
chromosomes is best supported by the chromosome fusion evidence. (It
supports the hypothesis that human chromosome 2 was formed by the fusion of two
ancestral chromosomes. This would have likely occurred after humans and
chimpanzees branched off from a common ancestor.)
Have students consider in their
teams whether the fifth data set they just evaluated—the fusion
data—supports the original hypothesis they were investigating—that
humans and chimpanzees share a common ancestor. Then have each team record a
final 1–10 rating of how confident they are that humans and chimpanzees
share a common ancestor based on all the
data they have evaluated.
Have each team compare its
original confidence ratings with its final ratings. As a class, discuss whether
each team's confidence about the hypothesis changed as new data was
acquired. Use the questions on the student handout as a guide for the
discussion. (Answers are listed below.) Ask students what it would mean in terms of evolution if humans and
chimpanzees were closely related. (It would mean that humans and
chimpanzees have a relatively recent extinct common ancestor [estimated to be
between five and seven million years ago]. If needed, clarify that humans did
not descend from chimps, but rather most likely share a common ancestor with
chimpanzees [as well as other great apes in a more distant past]. Humans and
chimpanzees have both evolved, or changed, from their extinct common ancestor.)
To help students better understand the role of
genetics in evolution, show the portion of the program at right that explains how
genetics drives natural selection and how an expert witness used chromosome
fusion to support the validity of evolution during the Dover trial. (QuickTime or Windows Media plug-in required.)
As an extension, have students
investigate other lines of evidence supporting common ancestry, including the
fossil record, homology, embryology, anatomical and molecular comparisons, and
biogeography. For more information, see "What Is the Evidence for
Weighing the Evidence Student
Student Handout Questions
Regarding the hypothesis that
humans and chimpanzees share a common ancestor, how much did your acceptance
change from the first to the last piece of evidence you studied? How much did
your confidence in your conclusions change as you accumulated more evidence? Answers
will vary, but it is likely that students were more certain that humans and
chimpanzees share a common ancestor at the end of the activity and more
confident in their conclusions with a larger body of evidence. To date, there
is no generally accepted evidence that contradicts the theory of evolution.
Are you 100 percent sure that
the hypothesis that humans and chimpanzees share a common ancestor is true?
Explain. If any students are 100 percent sure, point out to them that
scientists are never 100 percent sure of the certainty of their hypotheses. The
more evidence that supports a hypothesis or theory, the more confident
scientists can be in it, but there is always the possibility that a hypothesis
or theory will be revised based on new, more compelling evidence.
What data did you find the least
convincing? What data did you find the most convincing? Explain your choices. Students
will likely say that the physical characteristics comparison was the least
convincing and that the telomere DNA evidence was the most convincing.
Could all the data be recreated
by another scientist? Why is this important in science? Yes, all the
evidence could be recreated. Experimental reproducibility is a hallmark of a
strong hypothesis. If an experiment cannot be recreated and results cannot be
reproduced, or observations repeated, a hypothesis remains unconfirmed. Past organisms that cannot be directly measured, such as
dinosaurs or ancestors of humans, can be inferred from fossil or molecular
Karyotype Idiograms Student Handout
According to Jorge Yunis and Om
Prakash, the scientists who authored the study* from which the karyotype
idiograms in this lesson were drawn, human and chimpanzee have 13
"presumably identical" pairs of chromosomes (chromosomes 3,
6–8, 10, 11, 13, 14, 19–22, and XY) when heterochromatin is not
considered. (Heterochromatin is tightly packed chromosomal material that stains
deeply during interphase. It is believed to be genetically inactive.) Another
six chromosomes only differ in pericentric inversions (chromosomes 4, 5, 9, 12,
15, and 16).
* "The Origins of Man: A Chromosomal
Pictorial Legacy," Science, Vol.
214, 19 March 1982, pages 1525–1530).
The Chromosome Shuffle Student Handout
Comparing Chromosomes Student Handout
Sequence Search Student Handout
Fusion point search sequence:
The idealized sequence in the graphic would be
…TTAGGG <fusion point>
Due to mutations, the actual
sequence within human chromosome 2 is
…GGTTAG <fusion point>
The fusion point occurs on the line
with bp 108541 (after the 21st base pair on that line). At the fusion point,
the code turns from being mostly Gs and Ts (and hardly any Cs), to being mostly
Cs and As (and hardly any Gs).
The 2A telomere region (to be
colored light blue) begins at about the 10th base pair on line
108301 and runs to line 108541 (through the 20th base pair). The 2B telomere
region (to be colored yellow) starts at line 108541 (from the 21st
base pair on) and runs to line 109081 at about the 33rd base pair.
NOVA—Judgment Day: Intelligent Design on Trial
articles and multimedia features as well as streaming video of the entire
two-hour NOVA program.
Offers a multimedia library of
video clips, an online professional development course, and lesson plans to
accompany the seven-part PBS Evolution
Evolution on the Front Line
Includes an abbreviated guide for teaching
evolution, talking points for teachers, evolution in the news, the American
Association for the Advancement of Science board resolution on ID, and more
from the AAAS.
Offers brief position statements by three
leading proponents of intelligent design, along with three responses from
proponents of evolution, as well as an overview of the ID movement.
National Center for Science Education
Serves as a clearinghouse for
information intended to keep evolution in public school science education.
The TalkOrigins Archive
Offers a collection of articles and
essays to provide mainstream scientific responses to the frequently asked
questions about evolution. Daily transcripts of the trial and the court's
decision can be found at www.talkorigins.org/faqs/dover/kitzmiller_v_dover.html
Provides media-rich resources that
highlight key issues in evolution and the evolution vs. intelligent design
Provides information about what
evolution is and what evidence supports it, the history of evolutionary theory,
and ways to teach evolution for K–16 educators.
Evolution vs. Creationism: An Introduction
by Eugenie C. Scott. Berkeley, Calif.: University of
California Press, 2005.
Provides an introduction to
evolutionary theory, a history of the controversy, source documents from both
sides of the debate, and additional resources for further exploration.
Finding Darwin's God: A
Scientist's Search for Common Ground Between God and Evolution
by Kenneth R. Miller. New York: Cliff Street Books, 1999.
Analyzes the scientific faults of
ID and presents a religious scientist's accommodation of faith and science.
The Making of the Fittest: DNA and the Ultimate Forensic Record of
by Sean B. Carroll. New York: Norton, 2006.
Explains how DNA provides
compelling evidence for evolution and reveals new details about the
Not in Our Classrooms: Why
Intelligent Design Is Wrong for Our Schools
by Eugenie Scott and Glenn Branch,
editors. Boston: Beacon Press, 2006.
Answers many questions regarding
the teaching of intelligent design, provides historical context for the ID
movement, and offers concrete advice for those seeking to defend the teaching
of evolution in their own communities.
The "Weighing the Evidence" activity aligns with the following National
Science Education Standards (see
• The molecular basis of
• Biological evolution
History and Nature of Science
• Nature of scientific
Classroom Activity Author
Flammer taught high-school biology in San Jose, California, for 38 years. He
now serves as Webmaster for the Evolution and Nature of Science Institutes Web
site, where he and other biology teachers develop lesson plans for the
site's collection. He has written for PBS's Evolution
Teacher's Guide and The American
Biology Teacher. For a version of this
lesson that focuses mostly on chromosome fusion, and includes a PowerPoint