At this farm, most of the beetles in this population are not immune to pesticides, while a few are immune because of a mutation.
Differential Survival and Reproduction
Variation
Immune
Not Immune
Not Immune
Not Immune
Not Immune
Not Immune
Not Immune
AND
Parents that are not immune produce non-immune babies while parents that are immune produce immune babies.
Not Immune
Selective Pressure
Inheritance
Immune
Immune
i
Immune
It didn't really matter which beetles were immune or not until one day a farmer sprayed pesticides all over the crops where the beetles lived.
Environment
Adaptation
x
i
x
Not Immune
The beetles that are not immune cannot fight the pesticides and they die, while the beetles that are immune can fight the pesticides and survive and reproduce.
i
Immune
x
x
Not Immune
Immune
All of the beetles that were not immune died from the pesticides. The beetles that are immune are not affected and they survive. The pesticides are putting selective pressure on the beetles.
x
x
Not Immune
Not Immune
Immune
x
Not Immune
Immune
Not Immune
Over time, the frequency of immune beetles increased because they survived the pesticides and reproduced while the frequency of non-immune beetles decreased because they died.