The correct option is C Natural selection
The given example is of natural selection. According to the theory of natural selection, nature supports the survival of the fittest. It means, only those individuals will survive, who adapt themselves to the change in the environment. In the given case, those ants survived, who adapted the mechanism of chemical signalling and were selected by the nature as fittest. Whereas, those organisms died who didn't adapt the mechanism. So, the correct option is B.