CHAPTER 20 Test Your Knowledge
Driving Question 1
What contributes to human skin color, and why is there so much variation in skin color between different populations?
By answering the questions below and studying Infographics 20.1, 20.2, 20.3, 20.4, 20.9, and 20.10, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
What pigment molecule gives dark skin its color? What cell type produces this pigment?
In the course of human evolution, which of the following environmental factors likely influenced whether populations had mostly light-skinned individuals or mostly dark-skinned individuals?
a. average annual temperature
b. average annual rainfall
c. levels of UV light
d. the vitamin D content of the typical diet
e. mitochondrial DNA inheritance
As hypothesized by Jablonski and Chaplin, darker skin is advantageous in________________UV environments because darker skin_____________.
a. high-; reduces vitamin D production
b. high-; protects folate from degradation
c. high-; increases the rate of folate synthesis
d. low-; allows more vitamin D to be produced
e. low-; allows more folate to be produced
USE IT
If folate were not destroyed by UV radiation, predict the skin color you might find in populations living at the equator; in populations living in Greenland. Explain your answers.
Which of the following would help darker-skinned people who live in low-UV environments remain healthy?
a. folate supplementation
b. sunscreen
c. increased production of melanin
d. vitamin D supplementation
e. calcium supplements
What can you infer about the skin-color genotype and the geographic origins of the ancestors of a light-skinned person and a dark-skinned person?
Our closest primate relatives, chimpanzees, have light-colored skin yet live in tropical (high-UV) environments. How would the Jablonski-Chaplin hypothesis explain this observation?
a. Chimpanzees don’t need folate for successful reproduction.
b. Chimpanzees are not susceptible to skin cancer.
c. The hair of chimpanzees protects their light skin from UV light.
d. Chimpanzees require much higher levels of vitamin D than humans do.
e. In chimpanzees a light-colored pigment offers UV protection.
Vitiligo is a disease in which melanocytes are destroyed, with resulting loss of pigmentation. If a dark-skinned person develops vitiligo and therefore lighter-colored skin, would his or her race change? What factors have led people to classify (or misclassify) themselves or others as members of one race or another?
Driving Question 2
Where did the earliest humans evolve, and how do we know?
By answering the questions below and studying Infographics 20.5, 20.6, 20.7, and 20.8, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
What percentage of DNA sequences do all humans share?
a. 0%
b. 25%
c. 50%
d. 75%
e. >99%
Why is mtDNA a useful tool in the study of human evolution? (Think about how mitochondrial DNA is inherited.)
According to the “out of Africa” hypothesis of human origins and migration, which group of people should show the highest level of genetic diversity?
a. Africans
b. Europeans
c. Asians
d. South Americans
e. Australians
447
USE IT
Rank the levels of genetic diversity you would expect to find within the five populations listed in Question 11 from highest to lowest. Justify your ranking.
If there were many human females living ~200,000 years ago, why do we find that the mitochondrial DNA in all living humans is all related to a single woman from that time?
What kind of evidence could you look for to test your explanation? (Think about all the human fossils that have been uncovered, and consider that it is possible to extract DNA from fossils.)
MINI CASE
A mother with medium skin tone gives birth to a baby with darker skin than she has. Her lighter-skinned husband accuses her of infidelity.
a. How reasonable is this, given the genetics of skin color? (Hint: Refer to Infographic 12.9.)
b. Could an mtDNA analysis be used in a paternity test? Why or why not?
Driving Question 3
What we can learn about human evolution from the fossil record?
By answering the questions below and studying Infographics 20.7 and 20.8, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Of the following traits that are associated with being human, which evolved most recently?
a. upright walking
b. ability to control fire
c. social communication
d. tool use
e. big brain
Place the following ancestors in order of most ancient (1) to most recent (5).
______________Homo sapiens
_______________Last common ancestor of chimpanzees and humans
________________Australopithecus
______________Ardipithecus ramidus
__________________Homo erectus
USE IT
Where would the last common ancestor of gorillas and humans fit into the ordering in your answer to Question 16? Explain.
Why would individual Australopithicines who could make and use tools have had a selective advantage (that is, higher fitness) over individuals who could not make or use tools?
Ardi was partially arboreal (that is, the species could live in trees). The ability to move around in trees was facilitated by an opposable big toe that would help grip branches. Once ancient hominids moved permanently to a grounded lifestyle, would there have been any selective pressure to maintain an opposable big toe? Explain your answer.
Members of the genus Australopithecus walked upright, and their fossilized footprints show no evidence of an opposable big toe.
a. What foot structure and lifestyle might have been selected if early hominid evolution occurred in a forested environment? In a grasslands environment? Would you predict any differences because of the selective pressures in each environment? Why or why not?
b. What other traits would you expect to be favored in a forested environment? In open grasslands?
INTERPRETING DATA
An extensive study of a hominid fossil dating from approximately 2 million years ago was published in 2013. For each of the features described below, consider whether they are closer to an ancestral state or closer to modern humans. On the basis of the features described, where would you place this fossil on the lineage between the chimpanzee–human ancestor and modern humans—what genus is it likely a member of?
The shoulder structure and very long arms suggest the ability to climb and perhaps hang or swing.
The spine and other skeletal features suggest an upright stance.
There is no opposable toe.
The heel is very narrow and pointed (not flat and wide).
The skeleton suggests that the gait would have been rolling, the feet rolling inward with each step.
The skull is very small.
The chest is not cylindrical but wider at the base and narrow at the shoulders, much like a triangle.
BRING IT HOME
The U.S. Census Bureau provides information on classifying race (http://www.census.gov/population/race/about/). What races does the U.S. Census Bureau recognize? What about people of mixed race? What about people who identify themselves as Hispanic? How easy is it for you to identify yourself with respect to race given the racial categories on the U.S. Census?