Darwin Diaries Question and Answer
Answers
Answer:
Question:
An enlarged right ventricle both increases oxygen intake and the risk of pulmonary hypertension. How can natural selection result in an adaption that produces both positive and negative effects?
A.) The positive effects appear after reproductive age in certain environments.
B.) The negative effects appear later in life in certain environments.
C.) The negative effects appear before reproductive age in certain environments.
D.) The positive effects outweigh the negative effects in certain environments.
Another Kind of Selection:
In natural selection, organisms have varying reproductive success according to their ability to survive to reproductive age. This type of evolution is driven by environmental factors. But in species with sexual reproduction there can exist another form of evolution. In sexual selection reproductive success is based on the choice made by another organism (pollinator choice in flowering plants, mate choice in mobile animals). Sometimes this choice is a rational decision. For example, in many baboon species a majority of females noticeably prefer males that are more involved with childcare. Other times mate or flower choice can be purely aesthetic judgements. Animal-pollinated plants, along with animals of the sex (usually male) not involved in childcare, grow elaborate structures requiring substantial resources and which leave them vulnerable to predation. But in an evolutionary context, the reward of more offspring is worth the price.
Answer and Explanation:
D is the correct answer.
Adaptations are rarely perfect. They evolve in the context of an organism's existing anatomy and physiology and are limited by the physical and chemical properties of tissues and other organic substances. But as long as a trait works well enough to give that organism greater reproductive success than organisms without it, that trait will be favored by natural selection.
B is true for the example given, but it is not the correct answer to the question.
The prompt gives an example and then asks a question. In the case of the right ventricle, the negative effects of larger volume rarely show themselves until an age when the individual has been reproductive long enough to have several offspring, so reproductive success is not effected. However, 1) the answer does not explain this, and 2) the question portion of the prompt is phrased generally rather than being specific to the example.
C and A are incorrect
If negative effects become apparent before an individual can reproduce, that individual's likelihood of reaching reproductive age is reduced, and the trait is not favored by natural selection. Positive effects of a trait that emerge after the individual is longer reproducing have no effect on reproductive success and are therefore not subject to natural selection.
Answer:
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