Answer:
We are only given one leaf, but the leaves in layer D of the same species would not be identical. Some of them could have deeper indentations or fewer indentations. A wider leaf surface area lets a plant absorb more sunlight, so it would be an advantage if leaves have fewer indentations.
The plants with fewer indentations will reproduce more, passing on their genes for fewer indentations. This repeats for a long time, then plant leaves overall would only have very small indentations (like the leaf for layer B).
Explanation:
There are mutations and variations that make one organism different from another organism, even if they're the same species.
Natural selection is when the environment "chooses" the organisms that have an advantage in the environment to reproduce. Organisms that are selected to reproduce can pass on their genes to future generations.
The deep indentation leaves from layer D were basically "phased out".
