Question
A central idea in the theory of evolution is that species may evolve gradually over time from a common ancestor.
Which statement(s) explain(s) the pattern of evolution seen in the diagram?
I. Beak shape shows genetic variability in the common ancestor.
II. Changes in beak shape that occur during the lifetime of an individual bird are passed on to the next generation.
III. Changes in beak shape are heritable and make each species better adapted to its environment.
A. II only
B. I and II only
C. I and III only
D. I, II and III
▶️Answer/Explanation
Answer: C. I and III only
Explanation:
- Evolution is the process where populations change over generations due to genetic differences and natural selection. The diagram shows species evolving different beak shapes from a common ancestor, which is an example of divergent evolution.
- Statement I is correct because genetic variability in the ancestor’s beak shape provides different traits that natural selection can act on.
- Statement II is incorrect because changes in an individual’s beak during its lifetime (acquired traits) are not inherited by offspring; inheritance depends on genetic information in reproductive cells.
- Statement III is correct because changes in beak shape passed genetically can improve adaptation to different environments, showing heritable traits affecting survival and reproduction.
Answer Evaluation:
A. Incorrect – Only II is mentioned, but inherited changes do not come from traits acquired in a lifetime.
B. Incorrect – Includes II, which is false; acquired traits are not inherited.
C. Correct – Includes I and III, both accurate about genetic variability and heritable adaptations.
D. Incorrect – Includes all three statements, but II is incorrect.
Question
The cladogram shows the evolutionary relationships between a number of animal groups.
What can be concluded from this cladogram?
A. Tuna evolved from sharks.
B. Crocodiles are more closely related to birds than to whales.
C. Frogs, humans and whales do not share a common ancestor.
D. Shark and tuna evolved later than humans
▶️Answer/Explanation
Answer: B. Crocodiles are more closely related to birds than to whales
Explanation:
- A cladogram is a diagram that shows evolutionary relationships based on common ancestors. Organisms that share a more recent common ancestor are more closely related.
- Statement A is incorrect because tuna and sharks share a common ancestor but one did not evolve directly from the other; they are separate fish lineages.
- Statement B is correct because crocodiles and birds share a more recent common ancestor, meaning they are more closely related to each other than either is to whales. Birds and crocodiles both belong to the group called archosaurs.
- Statement C is incorrect because frogs, humans, and whales all share a distant common ancestor as vertebrates; they did not evolve independently.
- Statement D is incorrect because sharks and tuna represent older fish lineages, while humans evolved later from land vertebrates.
Answer Evaluation:
A. Incorrect – Tuna and sharks are separate groups, no direct ancestor-descendant relationship.
B. Correct – Crocodiles and birds share a closer common ancestor than crocodiles and whales.
C. Incorrect – Frogs, humans, and whales share a common vertebrate ancestor.
D. Incorrect – Sharks and tuna evolved earlier in evolutionary history than humans.
Darwin described evolution as “descent with modification”. What would make evolution less probable?
A. Stable environment
B. Migration
C. Variation in offspring
D. Random mutation
Answer/Explanation
Answer: A. Stable environment
Explanation:
- Evolution is the process by which populations change over time due to natural selection, acting on heritable variation. For evolution to occur, there must be environmental pressure that favors certain traits over others.
- In a stable environment, there is little or no change in selective pressures, so organisms that are already well adapted are likely to remain unchanged. This reduces the likelihood of evolutionary changes.
- By contrast, migration, genetic variation, and mutations introduce new traits or gene combinations, which increase the chances of evolution when the environment changes.
Answer Evaluation:
A. Correct – A stable environment reduces selective pressure, so there is less need for species to evolve.
B. Incorrect – Migration introduces new genes into a population, increasing genetic diversity and the potential for evolution.
C. Incorrect – Variation in offspring is essential for natural selection to act on and drive evolution.
D. Incorrect – Random mutations are the source of new genetic traits that natural selection can favor or eliminate.
What causes heritable variation in a species?
I. Muscle development through exercise
II. Increased rainfall in the ecosystem
III. Changes in the genome of the species
A. I and III only
B. II only
C. III only
D. I, II and III
Answer/Explanation
Answer: C. III only
Explanation:
- Heritable variation means genetic differences that can be passed from parents to offspring. These variations come from changes in the DNA (the genome), such as mutations, gene shuffling during meiosis, and sexual reproduction.
- Only genetic changes affect heredity. Environmental factors (like rainfall) or acquired traits (like muscle development through exercise) do not alter the DNA in a way that can be inherited by the next generation.
Answer Evaluation:
A. Incorrect – Muscle development is an acquired trait and not heritable; only III is correct.
B. Incorrect – Rainfall is an environmental factor, not a cause of heritable variation.
C. Correct – Only changes in the genome (mutations or genetic recombination) create heritable variation.
D. Incorrect – I and II are not sources of heritable variation.
The long-term exposure of bacteria to antibiotics has led to the spread of resistant strains (for example, of Clostridium difficile). What is this an example of?
A. Convergent evolution
B. Immunity
C. Natural selection
D. Dominance
Answer/Explanation
Answer: C. Natural selection
Explanation:
- Natural selection is the process where organisms with traits that help them survive and reproduce are more likely to pass those traits to the next generation. In bacteria, some individuals may carry mutations that make them resistant to antibiotics. When exposed to antibiotics, non-resistant bacteria die, while resistant ones survive and reproduce, spreading the resistance.
- Over time, the population becomes dominated by antibiotic-resistant strains — a clear example of natural selection in action.
Answer Evaluation:
A. Incorrect – Convergent evolution is when unrelated species develop similar traits due to similar environments, not due to selection within one species.
B. Incorrect – Immunity refers to an organism’s internal defense system, especially in animals, not to genetic resistance in bacteria.
C. Correct – Antibiotic resistance spreads because resistant bacteria survive and reproduce more, which is natural selection.
D. Incorrect – Dominance is a genetics term about alleles, not the evolutionary process causing resistance.
Question
What is an outcome of natural selection?
A. Evolution
B. Mutations
C. Reproductive isolation
D. Variation
▶️Answer/Explanation
Answer: A. Evolution
Explanation:
- Natural selection is the process by which individuals with favorable heritable traits survive and reproduce more successfully than others. Over many generations, this leads to evolution, which is a change in the genetic makeup of a population over time.
- Natural selection does not create mutations or variation; it acts on variation that already exists. It can also contribute to reproductive isolation, but that is not the direct or guaranteed outcome — evolution is.
Answer Evaluation:
A. Correct – Evolution is the long-term result of natural selection acting on heritable traits.
B. Incorrect – Mutations occur randomly and are the source of new variation, not an outcome of natural selection.
C. Incorrect – Reproductive isolation can lead to speciation, but it is not always caused by natural selection.
D. Incorrect – Variation must exist before natural selection can act; it is a condition for natural selection, not an outcome.
Question
What is required for natural selection to occur?
I. Acquired characteristics
II. Advantageous characteristics
III. Genetic variation
A. I only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
Answer: C. II and III only
Explanation:
- Natural selection requires genetic variation within a population so that individuals differ in their traits. Some of these traits must be advantageous, meaning they help individuals survive or reproduce better than others.
- These advantageous characteristics are heritable, so they can be passed to the next generation, increasing their frequency over time.
- Acquired characteristics, such as muscles built from exercise, are not genetic and cannot be inherited, so they do not contribute to natural selection.
Answer Evaluation:
A. Incorrect – Acquired characteristics are not inherited and do not contribute to natural selection.
B. Incorrect – While genetic variation is necessary, acquired traits do not support natural selection.
C. Correct – Natural selection requires both genetic variation and advantageous traits that can be inherited.
D. Incorrect – Includes acquired characteristics, which are not involved in natural selection.