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Name: _______________________
Evidence for Evolution
Much evidence has been found to indicate that living things have evolved or changed gradually during their
natural history. The study of fossils as well as work in embryology, biochemistry, and comparative anatomy
provides some of the evidence for evolution.
PART 1: HOMOLOGOUS STRUCTURES
Carefully examine the drawings of bones in Figure 1. Notice that all the limbs, whether wins, arms, legs, or
flippers, are built upon the same basic structure. These structures form in similar ways during embryonic
development and share similar arrangements, but are somewhat different in form and function. We call
these structures homologous structures.
Figure 1
1.
Examine the relative size, shape, number and position of the bones. Then, in the table below,
identify the body part shown for each organisms and describe the function of that body part.
Animal
Human
Whale
Cat
Bat
Bird
Whale
Body Part
Function
2. How are the body parts from the Figure 1 similar? How are they different? List two or more
similarities or differences.
Similarities
Differences
3. How does the arm of a human and the flipper of a whale what show evidence of an evolutionary
relationship?
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PART 2: ANALOGOUS STRUCTURES
Some unrelated animals have organs with similar functions, yet are very different in both structure and
form. These types of structures are called analogous structures.
Figure 2
4. Do the wings have similar or different structures? Hint: Are they made of the same “materials?”
Explain your answer.
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5. Do the wings have similar or different functions? Explain your answer.
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6. Does the structure of the wings suggest that there is a close evolutionary relationship? Why do you
think this?
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PART 3: VESTIGIAL STRUCTURES
Gradual changes have occurred throughout time and have in some cases, reduced or moved the function of
certain body structures and organs. Organs or structures that remain in an organism but have lost their
function and become reduced in size are called vestigial structures. The penguin’s wings and the leg bones
of snakes are examples of this phenomenon. The cave fish and minnow shown in Figure 3 are related, but
the cave fish is blind.
Minnow
Cave Fish
Figure 3
7. Explain why the cave fish’s eyesight is NOT an important adaptation to life in a cave.
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8. Does the appearance of the cave fish and minnow suggest any common ancestry? Give an example.
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9. Read the list of human vestigial structures below. Suggest a possible function for each part (think
about what modern day animals might do with these structures as some may still have them) and
explain why it might have become vestigial in humans. The first one has been done for you as an
example.
Structure
Ancestral Function and
Use in the Wild
Why Vestigial Now?
Appendix
Aided in digestion of grasses, leaves, and other
foliage when our ancestors were herbivores.
Humans eat less raw plant food material now and often
cook their food. Food is more easily digested and so the
appendix is less necessary.
Coccyx
(tail bones)
Assists in balance and mobility as a tail.
Muscles
to move ears
The ability to change ear position to pick up
noises from other animals in the area.
Goose bumps
when under
stress
Reflex to raise body hair to make the body look
larger and more intimidating to predators.
Wisdom
teeth
Used to grind down raw plant tissue and typically
appear later in life. Possibly used to replace teeth
lost or eroded by a coarse diet which may have
included some dirt and sand.
PART 4: CYTOLOGY (Study of Cells)
All organisms—big and small—are made of cells. Cells consist of membranes, genetic material, proteins,
fats, carbohydrates, salts, and other substances. Look at the picture of a typical animal and plant cell
below. Notice that only three structure (in capital letters: cell wall, centriole, and chloroplasts) are unique
to either plant or animal cells.
Figure 3
10. What is inside the nucleus of a plant and animal cell?
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11. Do bacteria have a nucleus?
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12. What do you this means (with regards to #11) in terms of when bacterial first appeared on Earth?
Did they come before or after plant and animal cells? How do you know?
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PART 5: DNA
DNA, our genetic code, is nearly universal in eukaryotes and prokaryotes. Anthropologists compare the
differences in DNA to determine the period in which the splitting of two species from an ancestor
occurred. This is based on the fact that harmless DNA mutations can be passed from parent to offspring
and will build up from generation to generation. Generally, the greater the amount of time that has passed
since two species diverged from a common ancestor, the more different their DNA will be. Measuring the
differences in DNA between species can be used to tell how long ago they split from a common ancestor.
The chart below shoes the percentage difference between the DNA of several primate species. Examine
the chart and answer the questions based on the evidence presented.
Species Compared
Human & Gorilla
Human & Chimpanzee
Gorilla & Chimpanzee
Human & Orangutan
Gorilla & Orangutan
Chimpanzee & Orangutan
Percent Difference in DNA
1.4%
1.2%
1.2%
2.4%
2.4%
1.8%
13. What is the job of DNA?
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14. Which are more closely related?
a.
A chimpanzee & orangutan OR a human & orangutan? ____________________________
b. A human & chimpanzee OR a gorilla & chimpanzee?
____________________________
c.
____________________________
A human & gorilla OR a gorilla & orangutan?
15. If the DNA is very similar, what does that mean for how these related organisms function, behave,
etc. in comparison to each other?
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PART 6: EMBRYOLOGY
As adults, humans, fish, pigs, chickens, and salamanders are very different animals. But, surprisingly, they
look very similar in their early stages of development. Chickens and eggs even retain many similarities until
they are born! As Darwin realized, such developmental resemblances hint at having a common ancestor.
Different animals develop along similar pathways because they have all inherited the same genes for
building limbs or eyes or heads. In fact, swapping the gene that triggers eye development in one animal with
the corresponding gene from another animal has little effect—it’s the same gene! Differences arise among
various species because of changes that affect when and where genes get activated during development.
Ultimately, those variations in timing are the biggest differences between fish, chickens, pigs, and humans!
Figure 5
16. What are some common characteristics that ALL the animals share at some point in their
development?
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17. Looking at the developmental patterns for the animals above, which two animals seem to be the
most closely related?
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18. What did you choose the two animals that you did in #17? Explain what you see.
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19. Why do you think that humans, cows, rabbits, and pigs look similar for so long? What do they have
in common compared to other animals?
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