June was upset to find one day that her bonsai was covered in ants and as a result, was worried for the health of her award-winning bonsai. She decides to spray her bonsai with some pesticide to kill the ants. She gave the pesticide some time to kill the ants. She was surprised to find that not all of the ants were killed and some even reproduced! She decided to reapply the pesticide, only to find that it was now ineffective against the offspring. What process occurred in the ant population that explains this change in the ant population?