Peter Kropotkin theorized in his classic Mutual Aid:

by BeingQuest

All species on Earth, over the course of centuries, exhibit “Mutual Aid and Mutual Support, carried on to an extent which made me suspect in it a feature of the greatest importance for the maintenance of life, the preservation of each species, and its further evolution.”

http://truth-out.org/opinion/item/28279-zombie-apocalypse-and-the-politics-of-artificial-scarcity