They multiply to a point where there are so many that they begin to eat foods that would not normally be eaten in order to survive because their numbers are so great all of the good food they like is being eaten before them and they weaken from bad diet.
Then a really long cold hard winter comes along again and the parasites and unnatural foods to them and the cold and it wipes out half the herd and species and then the ones who survive have plenty to eat and become strong again.
This goes on and on and on and again and again throughout history..
Natures perfect balance..
Natures perfect plan..
Cruel as it is..
Millions of years in the making..
Also populations overpopulating from where there would normally be hundreds in the grouping to multiplying to millions in a setting and social structure it becomes devastating without knowing it..
Ruling classes and armies and police and jails and shootings and penitentiaries..
Sexual perversions and god beliefs of brutal killing ruling armies..
Now stimulate the living shit out of all this with dozens of what I call stimulant man made drugs and exaggerate all this a thousand times of what it would have been without the added adrenaline..
We got no chance..
Live love and enjoy and take care of the little ones and do what we can..