What differences make a difference?

  1. Approximately how old are modern humans?
    1. 170,000 years
    2. 40,000 years
    3. 70,000 years
    4. 1.2 million years
    5. 5 million years

  2. Which group has the most genetic variation?
    1. Humans
    2. Chimpanzees
    3. Penguins
    4. Fruit flies
    5. Elephants

  3. What is the source of genetic variation in humans?
    1. mutation
    2. genetic drift
    3. natural selection
    4. sexual selection
    5. environment

  4. Which two present-day populations are most likely to be genetically similar?
    1. Italians and Ethiopians
    2. Senegalese and Kenyans
    3. Italians and Swedes
    4. Chinese and Lakota (Sioux)
    5. Saudi Arabians and Ethiopians

  5. What caused differences in skin color to evolve?
    1. The environment
    2. Natural selection
    3. Sexual selection
    4. Tanning oil
    5. We don't know

  6. If you know a person's skin color, what can you predict about them?
    1. their blood type
    2. their height
    3. the likelihood they will get certain inherited diseases
    4. whether or not they have musical talent
    5. none of the above

  7. An individual from which country is most likely to carry the sickle cell trait?
    1. Ireland
    2. Greece
    3. South Africa
    4. Samoa
    5. Mexico

  8. Your ancestors are likely to include:
    1. Nefertiti
    2. Julius Caesar
    3. Qin Shi Huang - first emperor of China
    4. All of the above
    5. None of the above

  9. Which continent has the greatest human genetic diversity?
    1. Europe
    2. Asia
    3. North America
    4. South America
    5. Africa

  10. If a catastrophe wiped out everyone except people in Europe, how much of the total genetic variation in our species would be left?
    1. 50%
    2. 38%
    3. 94%
    4. 21%
    5. 74%


  1. A. 170,000 years
    The earliest hominids evolved from apes about 5 million years ago, but modern humans (Homo sapien sapiens) didn't emerge until about 150,000 to 200,000 years ago in eastern Africa. Our species first left Africa only around 70,000 years ago and quickly spread across the entire world. All of us are descended from these African ancestors.

  2. D. Fruit flies
    Fruit flies have existed for a very long time and they also have a short life span, so lots of genetic mutations have accumulated over many generations. Modern humans are a relatively young species, and we have always moved, mixed and mated, so we are one of the most genetically similar of all species.

  3. A. Mutation
    Genetic drift, natural selection and sexual selection act to distribute traits, but new genetic variants arise only through mutation - copying errors during reproduction. We all have the same 35,000 or so genes, but some genes come in different forms, called alleles. For instance, the gene that governs blood group proteins comes in three variants, resulting in A, B or O blood type. Some mutations are harmful, leading to stillbirth or deadly diseases like spinal bifida. Those that are neutral or create an evolutionary advantage are passed on and spread through successive generations.

  4. E. Saudi Arabians and Ethiopians
    Populations that live near each other geographically tend to be more alike than populations that live far apart. We tend to think of Saudi Arabians and Ethiopians as different races, but they are most similar because there has been more recent "gene flow" - intermixing between these two groups. Often when variation seems to follow "racial" lines, it is more accurately explained by geographic proximity.

  5. E. We don't know
    People in tropical areas tend to be darker, while northern and southern populations tend to be lighter. Some scientists attribute this to natural selection in response to ultraviolet (UV) light. Dark skin blocks some UV radiation. Other scientists believe that superficial physical differences arose from cultural preferences, an evolutionary force known as sexual selection.

  6. E. None of the above
    Most traits are governed by different genes, so they are inherited independently. The presence of one trait doesn't necessarily signal the presence of another trait. We think people come packaged into groups, even - as anthropologist Jon Marks jokes, "color-coded for our convenience" - but it turns out they don't. Visual traits - skin color, for example - tell us nothing about deeper internal differences or abilities.

  7. B. Greece
    We often think of sickle cell as a "racial" disease that affects people of African descent, but it evolved as a trait that confers resistance to malaria. It occurs in people whose ancestors came from regions where malaria was once common, like the Mediterranean, Arabia, Turkey, southern Asia and western and central Africa, but not in areas such as southern Africa. Ancestry, not race, is a better indicator of whether or not one carries the markers for sickle cell, Tay Sachs, porphyria and other genetic diseases.

  8. D. All of the above
    We each have 2 parents, 4 grandparents, 8 great-grandparents. Steve Olson and Joseph Chang point out that if we go far enough back in time, only about 30 generations, we each have a billion potential ancestors, more than the population of the earth at the time. This means that any historical person living 1,600 years ago whose children had children is likely to be among our ancestors. Olson writes that because of human migrations and mating, "the DNA now in our cells consists of bits and pieces of the DNA that was in thousands of people's cells a millennia ago."

  9. E. Africa
    All modern humans originated in Africa, and we spent most of our evolution as a species together there. All the other populations of the world can be seen as a subset of Africans. Every human trait found elsewhere can also be found in Africa, with the exception of a few recent variations favored by the environment, sexual selection, or drift - such as light skin.

  10. C. About 94% of our total human genetic variation would remain
    If only the Swedes or Poles survived, we would still retain about 85% of our genetic variation. This is because most variation is within, rather than between, races. On average, any local population contains 85% of all human genetic variation, and any continent contains 94%. This is because humans have always migrated and mixed their genes. Two random Swedes, for example, are likely to be as different as a Swede and a Senegalese.

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