Worked example
In a fictional grass population, plants that already have a heritable deep-root trait leave more surviving offspring during repeated droughts. Over generations, descendants with deep roots may make up more of the population. The explanation uses existing variation and differential reproduction.
Contrast and common error
A trait can become more common through migration or chance as well. A frequency change alone does not identify selection. A larger count can even come with a smaller fraction if the population grows faster than the group with that trait.
Transfer check
A trait occurs in 15 of 50 insects before a wet season and 24 of 120 after it. Did its frequency rise? What extra evidence would support selection? Check: it fell from 30% to 20%. Compare surviving offspring by inherited trait under the same wet conditions.
Try it, then explain it.
Complete a short set without looking at the example. After each answer, explain which evidence or rule supports your decision and why the alternatives do not fit.
Sources & authorship
Original OpenExam explanations and examples. References support the concepts; they are not the source of copied questions. Independent educator review is pending.
OpenStax Biology 2e 19.1 Population Evolution