If it changes more rapidly, few adaptive walks will be completed, and the population will be poorly adapted most of the time. If it changes very rapidly selection may be inadequate to restore adaptation quickly enough, and the population will dwindle and eventually become extinct
Not being able to adapt creates competition from those who can adapt. This is called the survival of the fittest. New predators and loss of habitats create environmental pressures that can limit the growth of a population and lead them to extinction if they are unable to adapt. The faster the change occurs, and the more drastic the change is with respect to the way that species lives, the more likely it is that the species will not be able to adapt in time and may disappear. This is also called Natural selection.
