π Descent with modification evolution (11 MCQs)
π From Campbell Biology β’ 1. Evolution and the theme of Biology and Scientific Inquiry β’ 11 questions available
What is Descent with modification evolution?
Definition:
Descent with modification is Darwin's term for evolution, meaning that species are related through common ancestry and have changed over time through the accumulation of heritable variations, where offspring differ slightly from parents, and these differences accumulate over generations, leading to the emergence of new species and the diversity of life observed today.
Working:
This process works through the gradual change of traits in populations, where mutations generate new genetic variants, recombination shuffles existing variants, and natural selection or genetic drift determines which variants become more common, leading to divergence between populations, and this is represented by phylogenetic trees where the branch lengths indicate the amount of change, with the rate of evolution measured as .
Example:
A simple example is the evolution of modern whales from terrestrial ancestors, where fossil evidence shows a gradual transition from land-dwelling mammals like Pakicetus to fully aquatic whales, with intermediate forms showing reduced hind limbs and modifications for swimming, illustrating descent with modification.
Reason:
Descent with modification is the core concept of evolution, explaining the unity and diversity of life, and it is essential for understanding genetics, ecology, and medicine, as well as for predicting changes in species due to environmental changes and human activities.
π All Descent with modification evolution MCQs
Q1. Which observation most directly supports the idea that present-day organisms can share underlying biological features while differing substantially in form and function?
π Explanation: The combination of shared cellular machinery and specialized structures is expected when organisms inherit fundamental features from common ancestors while populations accumulate modifications. This explains both biological unity and the striking diversity observed among organisms.
Q2. A researcher compares a basic protein sequence from four organisms and finds that species A and B differ by 2 amino acids, A and C by 18, and A and D by 21. What inference is most reasonable?
π Explanation: Fewer sequence differences can indicate greater evolutionary relatedness because inherited biological information accumulates changes over generations. However, similarity alone does not prove direct ancestry, so A and B are better interpreted as potentially sharing a more recent common ancestor.
Q3. Two populations inherit the same basic anatomical structure from an ancestral population. One population gradually develops a structure specialized for swimming, while the other develops one specialized for grasping. What best explains this pattern?
π Explanation: Descent with modification predicts that inherited structures can be retained while their details change across populations. Different environmental pressures can favor different modifications, producing specialized structures while preserving evidence of their shared ancestral origin.
Q4. A population of insects contains individuals with slightly different mouthparts. After a long period in which one food source becomes dominant, insects with one mouthpart shape become much more common. Which reasoning best connects the observations?
π Explanation: The scenario requires multiple steps: variation exists within the population, some variation is heritable, the environmental change alters which traits provide an advantage, and individuals with advantageous traits contribute more offspring. Over generations, that inherited trait becomes more common.
Q5. A student claims, If two species have similar body structures, one species must have evolved directly from the other." Which correction is strongest?"
π Explanation: Evolutionary relationships form branching patterns rather than a simple ladder. Two species may resemble each other because they inherited a structure from a shared ancestor and subsequently modified it. Similarity therefore does not establish that one modern species became another.
Q6. Researchers observe that two isolated populations initially have similar trait frequencies. After several generations, their environments differ, and the frequency of a particular inherited trait rises in one population but falls in the other. Which explanation best fits the pattern?
π Explanation: The key is that evolutionary change occurs in populations across generations. When environments differ, the relative reproductive success of inherited variants can also differ, causing trait frequencies to shift in different directions and gradually increase biological divergence.
Q7. A biologist records the proportion of a trait in a population over five generations: 10%, 18%, 31%, 47%, and 63%. Which conclusion is most strongly supported by the trend?
π Explanation: The graph shows a progressive increase in the trait's frequency rather than a sudden appearance in all individuals. If the trait is heritable, such a pattern is consistent with evolutionary change as individuals carrying the trait contribute disproportionately to later generations.
Q8. A student says, Species become different because individuals need new traits, so their bodies produce the necessary changes and pass them on." What is the main error?"
π Explanation: The reasoning incorrectly treats evolution as a purposeful response by individuals. Evolution instead depends on variation among individuals, inheritance of some differences, and unequal reproductive success. Across generations, these processes alter trait frequencies within populations.
Q9. A researcher finds that a trait is common in two species living in similar environments. The student concludes that the species must have inherited the trait from their most recent common ancestor. Why is this conclusion weak?
π Explanation: A shared environment can impose similar functional demands on unrelated or distantly related lineages. Therefore, the same type of trait may evolve independently. Evidence from multiple characteristics and ancestry is needed before inferring recent common descent.
Q10. Suppose a branching evolutionary model shows species P splitting into lineages Q and R, while R later splits into S and T. Which statement correctly interprets the model?
π Explanation: The branching pattern represents successive divergence from shared ancestors. Because S and T arise from the same later branch, they share a more recent common ancestor with each other than either does with Q, while all three trace ancestry back through P.
Q11. Two species possess a nearly identical molecular system for copying genetic information, but their reproductive structures and ecological roles are very different. Which interpretation best integrates both observations?
π Explanation: The two observations are not contradictory. Fundamental molecular systems can remain conserved because they perform essential functions inherited from earlier ancestors, while other inherited characteristics can accumulate modifications. Evolution therefore explains both deep biological unity and extensive diversity.