Human Evolution - Ch. 58 - Natural Selection in Modern Humans

Question 1

What are four examples of natural selection in modern humans?

Answer 1

Skin colour, malaria resistance, lactase persistence, and menopause

Question 2

Did humans evolve from chimpanzees?

Answer 2

No. Chimpanzees (and bonobos) are the group of modern species that we share the most recent common ancestor with.

Question 3

Have humans stopped evolving?

Answer 3

No. Some examples of natural selection that cause human evolution include: malarial resistance, skin colour, menopause, and lactase persistence

Question 4

What is wrong with the statement: “The human mind is too complex to have evolved”

Answer 4

1. Complexity is hard to define.

2. This ‘complexity’ has evolved across many different groups over time.

Question 5

What is the fitness tradeoff for having darker skin vs. fairer skin?

Answer 5

Darker skin offers better UV protection (so against mutations that lead to cancer, and against folate breakdown)

Lighter skin offers better vitamin D absorption

Question 6

Define natural selection in 2 steps.

Answer 6

(1. ) Heritable phenotypic variation among individuals in a population
(2. ) leads to differential survival and reproductive success among individuals in the population

Question 7

What is the name of pigment that determines skin colour? What produces that pigment?

Answer 7

melanin; melanocytes

Question 8

Is folate an essential or non-essential vitamin?

Answer 8

essential

Question 9

Is vitamin D an essential or non-essential vitamin?

Answer 9

non-essential

Question 10

What can folate deficiency result in?

Answer 10

lower reproductive success, or infertility

Question 11

What makes a nutrient essential?

Answer 11

the human body must gain the nutrient by diet, i.e., it cannot synthesize the nutrient

Question 12

What species cause malaria in humans?

Answer 12

5 species of Plasmodium

Question 13

What are two forms of Hemoglobin (Hb)? Which one is the common form, and which is mutant?

Answer 13

Hemoglobin A (HbA) and Hemoglobin S (HbS).
HbA is common, HbS is the mutant form

Question 14

A human with the deadly sickle-cell disease has what two alleles?

Answer 14

Homozygous HbS HbS

Question 15

A human with resistance to malaria has what two alleles?

Answer 15

Heterozygous HbA HbS

Question 16

(In regions where malaria is endemic)
When the HbS allele is rare, natural selection selects (for/against) heterozygous individuals.

When the HbS allele is increasingly common, natural selection selects (for/against) heterozygous individuals.

Answer 16

When the HbS allele is rare, natural selection selects FOR heterozygous individuals.

When the HbS allele is increasingly common, natural selection selects AGAINST heterozygous individuals.

Question 17

What term is described by: “the ability of an individual to contribute viable offspring to the next generation, compared to others within its population”

Answer 17

biological fitness

Question 18

What is “menopause”?

Answer 18

The time in which human females stop menstruating, permanently, or the longevity of an organism long past its reproductive age

Question 19

What are the 3 hypotheses under the Theory for the Origin of Human Menopause?

Answer 19

lifespan artifact hypothesis, grandmother hypothesis, and mating behaviour hypothesis

Question 20

What does the lifespan artifact hypothesis suggest? What is its problem?

Answer 20

The lifespan artifact hypothesis suggests that menopause evolved due to increased longevity in humans (because of tools, cooking, medicine, etc.).

Problem: why did male fertility become extended with longevity?

Question 21

What does the grandmother hypothesis suggest?

What is its problem?

Answer 21

The grandmother hypothesis suggests that a mother contributes care to her children’s offspring, thus increasing the number of her grandchildren who survive to reproductive maturity.

Problem: how many children must be produced by a woman’s offspring to replace each missed opportunity for the woman to produce another child of her own? (how to overcome steep selection gradient?)

Question 22

What does the mating behaviour hypothesis suggest?

What is its problem?

Answer 22

The mating behaviour hypothesis suggests that menopause evolved due to a change in mating behaviour—involving only young adult females and adult males. [Could be male preference (nonadaptive) or intergenerational female competition (sexual selection).]

Problem: The computer simulations suggested that tens or even hundreds of thousands of years would have been required for female-specific late-onset fertility-diminishing mutations to have accumulated and ultimately produce a menopause phenotype. We may not have had an extended lifespan for that long of a time period to accumulate such mutations.

Question 23

Lactose is a disaccharide made up of what two monosaccharides?

Answer 23

glucose and galactose

Question 24

What is milk?

Answer 24

The primary food source for young mammals: a nutrient-rich liquid containing proteins, lipids, carbs, vitamins, and minerals. It is produced by mammary glands

Question 25

Nursing involves what enzyme that metabolizes lactose into its components?

Answer 25

Lactase

Question 26

Why is lactase persistence adaptive in pastoralist populations?

Answer 26

Milk gives a renewable and rich source for nutrients, as well as water

Question 27

What percentage of humans cannot properly digest milk after 2 years age?

Answer 27

75%