Which of the following statements is true regarding evolution?

• A. Evolution results from changes in the genetic composition of a population over time.
• B. Natural selection is the only mechanism by which evolution occurs.
• C. Evolution always leads to organisms becoming more complex.
• D. Individual organisms evolve during their lifetimes.

Answer: (A)

Verified step by step guidance

1. Understand the concept of evolution: Evolution refers to the change in the genetic composition of a population over generations, driven by mechanisms such as natural selection, genetic drift, mutation, and gene flow.
2. Evaluate the first statement: 'Evolution results from changes in the genetic composition of a population over time.' This is accurate because evolution occurs at the population level, not the individual level, and involves genetic changes over time.
3. Analyze the second statement: 'Natural selection is the only mechanism by which evolution occurs.' This is incorrect because evolution can also occur through other mechanisms like genetic drift, mutation, and gene flow, not just natural selection.
4. Examine the third statement: 'Evolution always leads to organisms becoming more complex.' This is false because evolution does not have a predetermined direction; it can lead to increased complexity, simplicity, or no change in complexity depending on environmental pressures and genetic factors.
5. Assess the fourth statement: 'Individual organisms evolve during their lifetimes.' This is incorrect because evolution occurs at the population level over generations, not within the lifetime of an individual organism.