When the biological species concept is difficult to apply, some investigators use phenotype, an organism’s observable characteristics, instead. Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as skull size or width of teeth. If the distribution of measurements from one group does not overlap with those of another, the two groups might reasonably be considered distinct species.

Based on the above passage, the following assumptions have been made:
1. The observable characteristics of a species are primarily determined by genetic divergence resulting from separate evolutionary paths and are not significantly influenced by environmental factors.
2. The evolutionary processes acting on separated groups, with sufficient time, lead to the accumulation of distinct phenotypic modifications.

Which of the assumptions given above is/are valid?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Question

When the biological species concept is difficult to apply, some investigators use phenotype, an organism&rsquo;s observable characteristics, instead. Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as skull size or width of teeth. If the distribution of measurements from one group does not overlap with those of another, the two groups might reasonably be considered distinct species.

Based on the above passage, the following assumptions have been made:
1. The observable characteristics of a species are primarily determined by genetic divergence resulting from separate evolutionary paths and are not significantly influenced by environmental factors.
2. The evolutionary processes acting on separated groups, with sufficient time, lead to the accumulation of distinct phenotypic modifications.

Which of the assumptions given above is/are valid?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

ONLiNE UPSC · Accepted Answer

Statement 1 is correct: For these measurable phenotypic differences to serve as a reliable proxy for identifying separately evolved groups (i.e., distinct species), it must be assumed that these traits reflect underlying genetic divergence due to separate evolution, rather than just plastic responses to different environments.

Statement 2 is correct: For separate evolution to likely result in measurable phenotypic differences, it must be assumed that the evolutionary mechanisms (like selection adapting to different environments, or random drift) operating on these isolated groups will cause their traits to change and diverge over time.

Evolutionary Biology

Species Concept and Phenotype

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When the biological species concept is difficult to apply, some investigators use phenotype, an organism’s observable characteristics, instead. Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as skull size or width of teeth. If the distribution of measurements from one group does not overlap with those of another, the two groups might reasonably be considered distinct species. Based on the above passage, the following assumptions have been made: 1. The observable characteristics of a species are primarily determined by genetic divergence resulting from separate evolutionary paths and are not significantly influenced by environmental factors. 2. The evolutionary processes acting on separated groups, with sufficient time, lead to the accumulation of distinct phenotypic modifications. Which of the assumptions given above is/are valid? (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2