Download Key for Homework due on February 10 (Skeletons Reveal Human

BIOL 241
Winter 2015
Key for Homework due on February 10
(Skeletons Reveal Human and Chimpanzee Evolution)
1. What is a phylogenetic tree used to illustrate?
It illustrates how species are related through evolution.
2. Based on genetic evidence, humans are most closely related to which two species?
Chimpanzees and bonobos.
3. Are humans more closely related to gorillas or orangutans? State the evidence.
Our genes (and our genome as a whole) are more similar to those of gorillas, indicating that we are more
closely related to gorillas.
4. Charles Darwin proposed that modern humans directly descended from chimpanzees. Support or
refute this statement with evidence from the video clip.
Darwin did NOT think that humans descended from chimpanzees. His notes from 1837 suggested that
modern species had common ancestors, not that some modern species had descended from others. More
formally, his 1871 book The Descent of Man said, “We must not fall into the error of supposing that the
early progenitor of the whole Simian stock, including man, was identical with, or even closely resembled,
any existing ape or monkey.”
5. What is a hominid (or hominin)?
A human – any species on the human side of the “last fork” of the primate family tree, representing the
divergence of animals who would become modern chimpanzees and humans.
6. Australopithecus is an early hominid that is now extinct. Why does Dr. White contend that
Australopithecus is not completely gone?
Dr. White said, “Its gene are present, in altered form, in you and me.” In other words, we evolved from
this ancestor and thus share some of its genetic material.
7. Identify at least TWO sources of data scientists can compare to determine the evolutionary
relationships between two or more species?
DNA sequences; anatomy and physiology
8. Bones are one anatomical feature that can provide a wealth of information. List SEVEN things
scientists can learn about an organism by examining its bones.
Its overall size and shape; its age; the size of its jaw muscles (from ridges on the skull); whether it was a
predator or prey (from eye position); its diet and social behavior (from its teeth); its reproductive
physiology (from its pelvis); and whether it walked on 2 legs or 4 legs (from its spine and pelvis).
9. Once the finger bones of Ardi were discovered, why does the crew begin to excavate and sieve the
surrounding area?
To try to find more bones!
10. What is the point of marking the excavation site with small yellow flags?
To indicate where each bone was found.
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BIOL 241
Winter 2015
11. Why did the excavation site for Ardi need to remain wet?
To avoid expansion and contraction of the clay (from alternate wet and dry periods), which could crush
the fossils it contains.
12. List the key features of each structure in the table below.
Anatomical Structure
Chimpanzee
Ardipithecus
Blunter, small canines;
Large, sharp canines,
less of a difference
Teeth
especially in males
between males and
females
Human-like (shallower,
Ilium
Long and flat
somewhat rounded)
Pelvis
Ischium
Long
Similar to chimpanzee
Divergent toe, flexible
Divergent toe but rigid
Feet
foot for grasping
foot structure
Humans
Similar to Ardi
Shallow, rounded
Shorter
No divergent toe,
rigid food structure
13. State which conclusions can be drawn from each set of information.
a. Conclusions from teeth comparisons …
Ardi males may have been less “violently competitive” than male chimpanzees.
b. Conclusions from pelvis comparisons …
Ardi walked bipedally but also may have climbed trees.
c. Conclusions from feet comparisons …
Ardi walked bipedally but also may have climbed trees.
14. Where does Ardi belong on the tree of life? State the evidence.
Ardi is at least partly adapted for bipedalism (shallow rounded pelvis, rigid foot structure). Since
bipedalism is unique to humans, Ardi probably represents a species from the humans-only branch of the
tree.
15. Based on your answer above, is Ardi the common ancestor to humans and chimps? State the
evidence.
No. Since Ardi shows traits that evolved only in humans, it is not likely to be an ancestor of chimpanzees.
Also, it lived 4.4 million years ago, which is after the point at which human ancestors were thought to
diverge from chimp ancestors.
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