For speciation to happen reproductive isolation must occur
Because photosynthesis is just backwards cellular respiration. I can elaborate more if you need me to.
Answer: Groundwater.
Explanation:
Groundwater is water that occurs below the Earth's surface at depths where all the pore (open) spaces in the soil, sediment , or rock …
It is a perfect example of a natural selection.
(I'm not sure if this is the exact answer that you are looking for.)