Name: _
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Evidence for Evolution
Scientists use a variety of techniques to determine if species are closely related or not. All these techniques provide
evidence for evolution. If species are closely related, then they must have come from a common ancestor that
evolved over time into two separate species. Today we will be using data to analyze the relationships between
different species of whales.
1. Scientists use embryos to study the evolution of organisms. An embryo is an unborn organism in the process of
development. This is a picture of a whale
embryo at the right. Look at the embryo
handout given to you and compare the
whale embryo to the embryos of other
animals. Which embryo on the handout do
you think is most closely related to the
whale?
2. Why do you think this animal is most closely related to the whale?
3. Scientists also use vestigial structures to look at how organisms evolved.
Vestigial structures are structures that an organism has but that are no longer
used. For example, humans have a tailbone, but we don’t actually have a
tail! This is because we came from a common ancestor a long time ago that
had a tail. Over time, our tail got shorter and shorter because we didn’t need
it anymore. Look at the picture to the right of a whale showing vestigial
structures (pelvis and femur). Why would a whale have a pelvis (hip bone)
and femur (legs) even though it doesn’t walk?
4. Look at the diagram at the right. The common ancestor is the
organism at the bottom of the “tree”. Would the common ancestor
of all these species have a pelvis and femur?
5. In addition to comparing structures that no longer serve a purpose,
scientists compare structures that still serve a purpose for the organism.
These structures are called homologous structures. Look at the picture
to the right. How are the flipper and the human arm similar?
6. How are the whale flipper and the human arm different?
7. Given what you know about humans and whales, do you think they may have shared a common ancestor a long
time ago? Why or why not?
8. Fossils can provide scientists with clues as to how organisms evolved. Look at the fossils below. Place them in
order by numbering them to show how whales evolved over time.
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____#6_____
9. Scientists use morphology to look at relationships between species. Morphology is the study of physical
structures of organisms (ex: limbs, body parts, shapes). Look at the Whale Species Handout and compare each
species to the Sei Whale. Which species do you think is most closely related to the Sei Whale?
10. List at least two pieces of evidence from the pictures that led you to believe that the species you chose in #9 was
most closely related to the Sei Whale.
11. Scientists also use DNA sequences to figure out which organisms are most closely related to each other.
Compare the B. borealis (sei whale) DNA sequence to the other species of whales. Circle any differences.
B. borealis (sei whale)
AAA CCG TAG GCG TCA CGG TAA ATT CCC
B. bonarensis (mink whale)
AAG CAC TTT GCA TCA CCC
B. physalus (fin whale)
AAG CAC TTG GCA TCA CGG TTT ATT CCG
B. brydei (bryde’s whale)
AAA CCC TTG GCG TCA CGG TAA ATT CCG
TTT ATT CCG
12. Which species of whale seems to be the most closely related to B. borealis (Sei Whale)?
13. Why do you think this whale is most closely related to the B. borealis (Sei whale)? (Hint: how did you use the
DNA to figure it out?
14. Once scientists have determined which species seem most
closely related, they create a diagram called a cladogram
that shows how the species are related to each other.
Which species of whale seems to be the most closely related
to B. borealis (Sei Whale)?
15. How did you determine which species was most closely
related to B. borealis (Sei Whale)?
16. Does your answer from question #14 match your prediction from your DNA evidence in #12?
17. Look at the cladogram of the whales. Which species do you think would be least related to B. borealis (Sei
Whale)?
RECAP:
18. List five things that you used in this lab to determine how the Sei Whale was related to different species: