Match the key concept of Darwinism with its meaning.
| Column I | Column II |
|---|---|
| (a) Overproduction | (i) Differences exist among individuals and are heritable |
| (b) Variation | (ii) Organisms produce more offspring than can survive |
| (c) Struggle for existence | (iii) Better adapted individuals survive and reproduce more successfully |
| (d) Natural selection | (iv) Competition for limited resources like food, water, and space |