Which Types of Evidence Demonstrate the
Strongest Support For Evolutionary
Relationships?
Hook:
Before proceeding through this document, watch this introductory video with you instructor to
open a discussion on evolution.
https://www.brainpop.com/science/famousscientists/charlesdarwin/preview.weml
Overview:
Evolution is the change in species over time, due to alterations in the allele frequencies in a
population. This can occur when the environment favors certain phenotypes (natural selection),
when new members enter a population (gene flow), or due to random chance events (genetic
drift). Discussions on evolution are not always a topic for consensus, but much of what is
‘known’ about evolution by the layman is not supported by evidence. In science, a theory is a
hypothesis that is supported by multiple sources of evidence. In this DBQ activity, your goal is
to familiarize yourself with the areas in science that offer support for evolution. These come
from multiple areas like anatomy, embryology, molecular and biochemical comparisons,
biogeography, fossil record and transitional species.
Task:
The task of this assignment is to generate a five paragraph, three-pronged essay that answers the
question “Which three areas of evidence provide the most reliable support for relatedness and
evolution?” Analyze each of the 8 documents (A-H) below and answer the analysis questions for each
document. Then, decide which three areas of evidence offer the most convincing and compelling
support for evolutionary relatedness among species. The argument that you make in your essay can be
your opinion, but should be supported by evidence from three or more of the documents.
Understanding the question:
1. What is the analytical question asked in this DBQ?
2. What terms in the question need to be defined?
3. Rewrite the question in your own words
Pre-bucketing
Choose from the documents listed below evidence to support your argument that answers the question
above. You should have three supporting statements from the documents that back up your thesis
which answers the question listed above.
Supporting document
Supporting document
Supporting document
Document A: Homologous Structures
The structures above are referred to as homologous structures. Homologous structures have different
functions in organisms but indicate a common ancestry due to the structural similarity. The upper arm
bone is called the humerus. The two lower bones of the limb are known as the radius and ulna. The
wrist bones are metacarpels, and the extension bones are known as phalanges.
Analysis Questions:
1.
2.
3.
4.
Identify the function (jumping, swimming, flying, grasping, etc) for each structure above.
Describe a similarity in bone structure for each of the limbs listed above.
Classify each organism as amphibian, bird, or mammal.
Which shows relatedness better, function or structure? Explain.
Document B: Analogous Structures
Source: http://www.vce.bioninja.com.au/aos-4-change-over-time/evolution/evidence-forevolution.html
Analogous structures are ones that serve a similar or same purpose in different species yet do not
indicate a common ancestry. Instead, the similarities in body form (like the streamlined bodies of
aquatic animals) are due to adaptations that arise due to similar environments. In this case, similarities
in the environment yield similarities in body form. It does not indicate a close relatedness via
evolutionary ancestry. This is known as convergent evolution and explains why dolphins (mammals),
sharks (fish), penguins (birds), and the extinct marine ichthyosaur (reptile) all have torpedo shaped
bodies.
Analysis Questions:
1. What evolutionary advantage is provided by the torpedo shaped body of these marine animals?
2. The butterfly and the bird both have wings. The butterfly has an exoskeleton made of chitin
while the bird has lightweight hollow bones as part of an endoskeleton. Since they both fly,
must they be related via a common ancestor? Or is there a different explanation for the
presence of wings on both species?
Document C: Vestigial Structures
Source: http://www.yourarticlelibrary.com/biology/organic-evolution-9-main-evidences-of-organicevolution/13238/
Source: http://www.vce.bioninja.com.au/aos-4-change-over-time/evolution/evidence-forevolution.html
Vestigial structures (or vestigial organs) are ones that serve no purpose in the current species, but may
have played a role in a recent ancestral species. For example, humans have a coccyx, a tailbone, but no
longer have the fleshy extension known as a tail. It is now vestigial, or without a purpose.
Analysis Questions:
1. Name five vestigial organs and structures found in humans.
2. Provide a hypothesis for each of the organs listed in #1 above as to a functional role they may
have played in an ancestral species.
Document D: Molecular Evidence- DNA/Nucleotide and Amino Acid Sequence Comparisons
Cytochrome C is a protein found in the inner mitochondrial membrane and whose function is to move
electrons through the electron transport chain during ATP production of cellular respiration. This is a
highly conserved protein (found in many species on earth). The data table above compares the
differences in amino acid sequence for cytochrome C in seven different species. The use of DNA and/or
amino acid data provides a numerical comparison, as compared to anatomical homologies and
analogies, which are based on physical appearances.
Analysis Questions:
1. To which species in the list are humans most closely related?
2. Which species is most distantly related to the others? How do you know?
Document E:Biogeography
Source: http://sciencewithpizzi.weebly.com/29-evidence-supporting-evolution.html
Biogeography is the study of the distribution of living organisms across the landforms on earth. During
his travels on the HMS Beagle mapping the South American coastline, Charles Darwin observed
differences and similarities of living organisms across different continents and different islands along an
island chain. He noted that the rhea, ostrich, emu, and cassowary have similar body structures, even
though they are distributed along many different and distant continents. He also noted at least thirteen
species of finch living on various islands of the Galapagos, each adapted to the food sources on the
specific island on which they were found.
Analysis Questions:
1. What is similar/different about Africa, Australia, and South America as far as their climate and
geography are concerned?
2. What types of food are the different finches suited for? How could so many species diverge
from one common ancestor in the Galapagos?
Document F: Comparative Embryology
Source:
http://en.wikipedia.org/wiki/Ernst_Haeckel#mediaviewer/File:Haeckel_Anthropogenie_1874.jpg
Often, the adult for of an organism does not tell the complete story. A different origin story is told when
examining the embryos (early form) of an animal. Ernst Haeckel studied and illustrated the developing
embryos of several vertebrate animals and noted their similarities. All species, aquatic and terrestrial,
have gill slits in their embryonic stage at some point. All embryos demonstrate the presence of a tail
(fleshy piece that extends beyond the anus) at some point during development. Species that are closely
related remain similar in appearance further along their embryonic development. For example, the
turtle and the duck, a bird and a reptile, look nearly identical throughout the entirety of development.
The same can be said for all mammals as well.
Analysis Questions:
1. Which species likely diverged longest ago from the others according to the diagrams?
2. Snake embryos have arm and leg buds in early development. However, these buds are not
present in the adult, which are legless. What can be inferred from the presence of these
structures during embryonic development?
Document G: Fossil Record
Source:
http://www.globalchange.umich.edu/globalchange1/current/lectures/complex_life/fossil_record.html
The fossil record is a collection of fossils (remnants of life forms formerly on earth) that were
buried shortly after the death of the organism. This prevents the decay of the organism.
Therefore, its hard structures resist decomposition (bones, teeth, shells). This can happen
when an organism is caught in a mudslide, buried in lava, trapped in amber (tree sap), drowned
in a tar pit, or frozen in ice. The deeper the fossil is found in a rock layer (stratum), the older it
is. Fossils can be dated based on the strata in which it was found.
Analysis Questions:
1. According to the diagram, what is the current hypothesis as to the age of the earth?
2. In what type of environment did the earliest forms of life on earth likely evolve?
3. The disappearance of a species from the fossil record would indicate what event?
Document H: Transitional Fossils
Source: http://avonapbiology.wikispaces.com/Nick+Tan+Your+Inner+Fish
Transitional fossils are ones that show an intermediate body form between two known species.
For example, Tiktaliik, a transition between aquatic fish and land-dwelling amphibians, has fins
with wrist joint and eyes placed on top of the head. Archaeopteryx is a transitional fossil that
indicates the missing link between dinosaurs and birds.
Analysis Questions:
1. What three pieces of evidence would a transitional fossil between fish and amphibians need to
demonstrate?
2. What types of evidence would Archaeopteryx have that indicate the link between birds and
dinosaurs?
DBQ Essay Outline Guide
Working Title (for the essay)
Paragraph 1
Grabber
Background
State the question within the paragraph.
Thesis & Roadmap
Paragraph 2
Mini-thesis from Bucket 1
Evidence (supporting detail from documents with document citation)
Argument (connecting evidence to thesis)
Paragraph 3
Mini-thesis from Bucket 2
Evidence (supporting detail from documents with document citation)
Argument (connecting evidence to thesis)
Paragraph 4
Mini-thesis from Bucket 3
Evidence (supporting detail from documents with document citation)
Argument (connecting evidence to thesis)
Paragraph 5
Conclusion (restatement of main idea along with possible insight, connection to other situations,
or counterargument)