Complex systems
Complex systems in nature—for example, ecosystems—involve a dynamic interaction of many variables (e.g. animals, plants, insects and bacteria; predators and prey; climate, the seasons and the weather, etc.) These interactions can adapt to changing conditions but maintain a balance both between the various parts and as a whole; this balance is maintained through homeostasis. Human societies are complex systems, as it were, human ecosystems. Early humans, as hunter-gatherers, recognized and worked within the parameters of the complex systems in nature and their lives were circumscribed by the realities of nature. But they couldn't explain complex systems. Only in recent centuries did the need arise to define complex systems scientifically. Complex systems theories first developed in math in the late 19th century, then in biology in the 1920s to explain ecosystems, then to deal with artificial intelligence (cybernetics), etc.