“The strongest survive” can make evolution sound like a contest of size or power. Natural selection instead asks which inherited differences help organisms leave descendants in a particular environment. A feature becoming more common need not even mean that it was advantageous.
The cell guide introduced DNA as a carrier of genetic information. We now move from a cell to a population across generations: what is inherited, and why do proportions change? Follow the conditions for selection, the role of the environment, and the effects of chance.
Connect inherited differences with descendants
The first example selects “Heritable traits that improve reproductive success in that environment.” A trait is a characteristic of an organism. The key is that inherited differences affect how readily organisms leave descendants. A trait passed to more descendants can become more common over generations.
“Every trait an organism works hard to obtain” suggests an individual can choose needed inherited features. “Every trait that makes an organism larger” treats size as sufficient evidence of advantage. “Every new mutation” assumes that a new change must be beneficial. None establishes the required connection between inheritance and reproductive success in that environment.
Advantage depends on the conditions
The second answer is “Which traits are advantageous depends on the environment.” How a feature affects survival and reproduction can change with conditions. There is no universal ranking of the best features.
The other options impose a guaranteed trend toward complexity, deliberate gene changes by individuals, or survival restricted to the strongest. The question concerns inherited features becoming more or less common across generations, rather than an individual turning into a desired form during its lifetime.
Chance matters especially in small populations
The third example asks about genetic drift. An allele is a version of a gene; drift is a change in its frequency in a population caused by chance. Distinguish a version being passed on more often because of an advantage from it being passed on more often by chance.
The effect tends to be stronger in “A small population.” Chance differences in which versions reach the next generation can have a larger effect on overall proportions when the population is small. Drift does not require an absence of mutations, and neither “An infinitely large population” nor “Exactly the same in every species” fits the comparison.
Stronger effects in small populations do not mean that drift is absent from large ones. Selection and drift can also operate together. An increase in frequency alone does not establish that the feature was advantageous.
Mark the condition that decides each answer
On paper, write “Is it inherited?”, “Does it help leave descendants in this environment?” and “Is chance involved?” Revisit the examples: mark inheritance and reproduction in the first, environment in the second, and chance and population size in the third. Explain the condition behind your choice, as well as naming the answer.
The practice button selects standard middle- and high-school questions on evolution and ecology, including other matching questions beyond these three. Return to the cell guide to revisit genetic information, or the related living-things guide for plants and food-chain connections.
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Check your understanding with examples
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Example 1 · Biology: evolution and ecology
Which traits can become more common over generations through natural selection?
Every trait that makes an organism larger
Every new mutation
Heritable traits that improve reproductive success in that environment
Every trait an organism works hard to obtain
Read the answer and explanation
Answer: Heritable traits that improve reproductive success in that environment
Natural selection requires heritable variation that affects survival or reproductive success. Traits passed to more descendants can become more common across generations in that environment. This changes the distribution of traits in a population.
Read reasoning and more detail
It is not an individual deciding to acquire a needed feature, and the relevant advantage depends on the environment.
In which population does genetic drift tend to have a stronger effect?
Exactly the same in every species
Only a population with no mutations
A small population
An infinitely large population
Read the answer and explanation
Answer: A small population
Chance sampling has a greater relative effect in small populations. Genetic drift changes allele frequencies by chance. Its comparison with natural selection concerns the cause: a change need not result from an inherited trait giving an advantage.
Topics: Biology: evolution and ecology. Range: Broader knowledge, General knowledge. Difficulty: Standard. These are selected initially. You can change these on the setup screen.
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