Answer:
In the first generation, the beetles with the dark spotted trait had a better chance of survival. The trait mutated over time, causing the beetles with that trait to be darker.
Step-by-step explanation:
In the picture that I had, it shows that some of the beetles in the first generation started to develop spots on their back or wings. It shows that later down the line, their backs start to get even more darker which means that is must be a trait that mutated over time that would allow the beetles with that trait to be significantly darker. They can't just change their traits if they want to so it would have to be something like mutation that caused it.