Concept: Overcrowding results when a population grows faster than its environment can support.
Explanation: High natality means a high birth rate in a population.
When births far exceed deaths, the total number of individuals increases sharply.
This added number concentrates in the available space and resources, causing overcrowding.
In contrast, emigration removes individuals and reduces population density.
High mortality also lowers population size, so it cannot cause overcrowding.
Competition is a consequence of overcrowding rather than its primary cause.
Therefore, the factor that directly leads to overcrowding is high natality.
Answer: C. High natality