It should be natural selection since there is no external influence implied. (like environment or genetic mutations.)
Red Orange Yellow Green Blue Indigo Violet
<---Longest wave length shortest wave length--->
As you went down the colors of the rainbow the wave length got shorter or faster.
Answer:
In an environmental temperature above optimum temperature will cause the enyzmes to denature (deform), because when they denature the subtrate will no longer fit into the enzyme
