Nature usually finds a way to balance populations. When there is plenty of food populations grow. An increased population means that there are more mouths to feed. This results in a reduction in the available food supply which in turn brings about a fall in the population.
Lemmings are renowned for being suicidal and jumping off cliffs. However this is not what is really happening. When lemming population density reaches a certain point, the population is triggered to migrate, and sets off in search of pastures new. No matter what is in the way they travel until they have found somewhere where food is plentiful. So, if they come to a cliff, they will swarm straight over it and head out to sea, to find new land or drown.
This headlong rush results in either finding a fresh supply of food to support the larger population, or a significant reduction in population so that the available food resources can support it. The cycle repeats itself over the years. This headlong rush to their doom is innate to the lemmings’ mind. A similar foolhardy rush to try new things seems to be inherent to humans, like lemming we seem oblivious to the inherent dangers in what we do.