Chapter 21 Quiz

. Which trait of humans is not shared by the LUCA?

Nucleic acids as the material basis of inheritance

Eukaryotic cell structure

Metabolism uses l-isomers of proteins exclusively

The codons of the genetic code

Humans share all of the above traits with the LUCA.

. Refer to the figure showing the phylogeny of some of the living apes.

According to the figure, which organism is the closest living relative to humans?

Bonobo

Gorilla

Bonobos and chimpanzees, equally

Gorillas and bonobos, equally

Chimpanzees

. Humans and chimpanzees share several polymorphic loci. Which is the least plausible explanation for this fact?

Balancing selection has maintained polymorphism in both species.

Incomplete lineage sorting left polymorphic loci and those have persisted since the speciation event.

Interbreeding has allowed introgression of alleles at these loci in both directions.

Genetic variation provided by the polymorphic alleles enhances resistance to pathogens.

In both species, individuals heterozygous for alleles at these loci may be at a selective advantage.

. What would be the best clue that a fossil skull was left behind by an ape that walked more or less upright?

The foramen magnum has a position relatively far forward.

The mass of the brain is extremely large, relative to other mammals.

Incisors and canine teeth are reduced compared to most primates.

It has a flat, not-projecting face compared to most apes.

The surface upon which jaw muscles anchor is relatively small.

. Many traits of anatomically modern humans enhanced our tool-use, running, and other abilities. Which of these skills was likely reduced in modern humans (compared to our ancestors) as a result of those changes?

Anatomically modern humans are poorer runners than other apes because of the rigid arch of our foot.

Anatomically modern humans are poorer tree climbers than other apes because of our straightened toes and short, straight fingers.

Anatomically modern humans are less efficient at thermoregulation because of our lack of body hair.

Anatomically modern humans have smaller teeth, reducing the rate we can ingest food, thus limiting reproductive rate.

The shorter arms of anatomically modern humans are less well-suited for holding our babies.

. Which genera is likely the most recent ancestor of the genus Homo?

Ardipithecus

Pan

Sahelanthropus

Paranthropus

Australopithecus

. In 2017, Holen and colleagues announced the discovery of a 130,000-year-old site in California that they claimed contained a mastodon that had been butchered by humans (genus Homo). Why did some in the scientific community express skepticism and caution in accepting the findings?

Humans are not thought to have mastered sophisticated tool use by 130,000 years ago.

Mastodons are thought to have gone extinct long before that.

The level of cooperative hunting needed to take down a mastodon did not appear until much more recently.

It is widely believed that Homo sapiens are the only humans to have occupied North America and they did not arrive until 20,000 years ago.

Homo neanderthalensis, the dominant hominin of the time, was vegetarian.

. Which piece of evidence does not support the theory of recent (ca. 200,000 years ago) African origin of humans?

Mitochondrial DNA sequences coalesce to Africa populations about 125,000 years ago.

Linkage disequilibrium of nuclear genes gets progressively lower as one measures populations farther from Africa.

Haplotype diversity of nuclear genes is greatest in Africa.

Fossils of modern humans older than 60,000 years are found only in Africa.

Non-African populations show reduced heterozygosity compared to African populations.

. Which statement best explains why modern Europeans, Asians, or Africans lack Denisovan DNA in their genome?

Denisovans never interbred with any population of Homo sapiens.

Denisovans DNA was eliminated from those populations by strong purifying selection.

Denisovans interbred only with the population whose ancestors are Melanesians.

Neanderthal genes and Denisovan genes are incompatible, so modern populations have one or the other.

Denisovans are an offshoot of hominins that are unrelated to modern humans.

. Which statement is not a good explanation for the relatively low genetic variability among modern human populations?

There is greater variability within populations than among them.

Human population size has increased drastically in a short period of time.

Ancestral human population sizes were very small.

Humans have a global geographic distribution.

The level of inbreeding within human populations has been high at times.

. According to the social brain hypothesis, we should expect primates living in larger social groups to have

larger brains, specifically, a neocortex of relatively larger size.

larger incisors and canines, to defend against more social competitors.

brains that are more metabolically efficient, to account for less food per group member.

smaller brains, because many individuals can work together to solve problems.

great variation in brain and neocortex size, with the dominant individuals having the largest.

. What preceded hunting as a method that humans used to acquire food?

Domestication of animals for meat and milk

Development of crop agriculture

Scavenging carcasses leftover from other carnivores

Fishing

Development of techniques to process meat (butchery, cooking, etc.)

. Why do many domesticated animals and plants have low fitness when compared to their wild relatives?

Small population sizes allow deleterious alleles to become fixed easily.

Deleterious alleles may be linked to genes favored during artificial selection and hitchhike to high frequency.

Inbreeding in domesticated varieties leads to low heterozygosity.

Both a and b

All of the above

. You extract DNA from human bones in an ancient village buried by volcanic ash. You discover that there is an extremely high frequency of the LCT allele for lactase persistence. What might you conclude about the population?

This population is likely the source of the high frequency of the LCT gene in Northern Europe.

The village could not be more than 4,500 years old.

The members of this population likely used domesticated livestock for their milk.

The villagers had a diet rich in wheat or another domesticated crop.

The population could not have been under strong selection because the gene was not fixed.

. Why do populations farther from Africa have more deleterious mutations in their genome?

Repeated bottlenecks and founder effects made genetic drift more intense more often.

Populations farther from Africa have been exposed to more mutagens in the environment.

Those populations have experienced more intense natural selection, so more deleterious alleles increased in frequency by genetic hitchhiking.

As people migrated over the globe they interbred with Neanderthals and Denisovans.

The populations are younger, so purifying selection has not had time to purge deleterious mutations from the populations.

. Sixty years of data from the Framingham Heart Study showed that people with low cholesterol had 50% more offspring, on average, than those with high cholesterol. Since it is known that cholesterol level is highly heritable, what can be concluded from this specific observation?

High cholesterol reduces an individual's fertility.

The frequency of people with low cholesterol should increase in the U.S. population.

Cholesterol level has a major effect on survival.

Natural selection is largely nullified as an important evolutionary mechanism in modern human populations.

Ethnic groups that traditionally have more children have a greater frequency of genes for low cholesterol.

. The "hygiene hypothesis" is an explanation for what phenomenon?

Low survival rates for medical procedures performed before the development of the germ theory of disease

Increasing rates of allergies and autoimmune disorders as a result of a mismatch between the human immune system and exposure to microbes in the environment

The weakening of human immune system by genetic drift, as a result of reduced strength of natural selection in the face of lower exposure to microbes

Lower infant mortality rates in modern hospitals

Purging of deleterious mutations by purifying selection in human populations with high inbreeding depression

. In the study of cultural evolution, what is a "meme"?

A unit of cultural inheritance

A humorous piece of media that is rapidly spread on the internet

Early attempts at music and art by human ancestors

Information spread as a disease rather than as inheritance of a gene

Genetic memory that we have inherited from our ancestors and use without realizing it

Chapter 21 Quiz

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