Which of the following constitutes a gene pool?

Liquid water turns into water vapor at which step in the water cycle

Which of the following best describes the purpose of the parathyroid hormone? a. it decreases the blood calcium level and decreases blood phosphorus level. b. it decreases the blood calcium level and increases the blood phosphorus level. c. it increases the blood calcium level and increases blood phosphorus level. d. it increases the blood calcium level and decreases blood phosphorus level.

In general, characteristics that an organism survive and reproduce become more common in a population over time. what mechanism of evolution cause this change?