Questions: Natural Selection Basics

Question 1

What does 'fitness' mean in the context of natural selection?

• A. Physical strength and speed
• B. The ability to survive and reproduce successfully in a given environment
• C. Being the largest organism in the population
• D. The ability to change traits to match the environment

Answer: (B)

In biology, fitness refers to an organism's ability to survive AND reproduce in its environment. A 'fit' organism is one that passes its genes to the next generation — not necessarily the strongest or fastest. A small, camouflaged insect may be more 'fit' than a large, visible one if it avoids predators and reproduces more successfully.

Question 2

Individual organisms can evolve during their lifetime in response to environmental changes.

• T. True
• F. False

Answer: False

Individuals do NOT evolve. Evolution is a change in the inherited traits of a POPULATION over many generations. An individual organism is born with its genes and cannot change them. Natural selection acts on variation that already exists — organisms with advantageous traits survive and reproduce more, shifting the population's traits over time.

Question 3

Explain the three conditions necessary for natural selection to occur.

Model answer: First, there must be variation — individuals in the population must differ in their traits (for example, some moths are darker and some are lighter). Second, those traits must be heritable — they can be passed from parents to offspring through DNA. Third, there must be differential survival and reproduction — some trait variations must give an advantage in the current environment, making those individuals more likely to survive and reproduce.

Without variation, there would be nothing to select. Without heritability, advantageous traits could not be passed on. Without differential survival, all traits would be equally likely to appear in the next generation. All three conditions must be present for natural selection to drive evolutionary change.