Emergence is an interesting idea that complex behavior can emerge from group of very simple things that interact using a set of very simple rules. Emergence can be observed in lot of processes of nature. I present some of them here.
Emergence occurs when an entity is observed to have properties its parts do not have on their own. These properties or behaviors emerge only when the parts interact in a wider whole. — Wikipedia
Ant Colonies
A colony of ants do amazing things. They build magnificent ant hills. Ant nests are known to have very organized internal structure with place for resting, place for laying eggs, place for waste produced in the nest, etc.
Regardless of what movies would have you believe, ant colonies do not have a bossy queen that tells other ants what to do. Yes, every ant colony has a female ant we refer to as the “queen”, but its only purpose is to sit in the nesting area and lay eggs.
Then the question is, how does every ant in the colony know what it’s supposed to do at any given time?. Without a single leader dictating the roles, will it not lead to a total chaos ? What if all ants decide they want to be soldiers? Who goes looking for food then? Who builds the nest?
Answer turns out to be a simple set of rules (about 20 simple chemical signals in case of fire ants for example) that each ant is wired to follow and all the colony behavior simply emerges.
Cell Differentiation
We start off as a single cell called a zygote which divides into 2, that divides into 4 and so on. Every resultant cell gets the exact same copy of our DNA, which means every cell has the potential to turn into any particular type of cell and eventually be part of a particular organ. If all the cells are same, how does a cell know that it should specialize to become a neuron or a muscle cell or a red blood cell etc. ? And once it actually specializes somehow, how does that cell know it should become part of the leg or part of the arm etc.?
Again the answer turns out be simple set of rules that each cell follows. Some subset of cells receive cues from the substances that are around them (e.g., yolk in a chicken egg) and produce some specific proteins which will be received by some other cells as cues for yet another type of protein thus setting off a chain reaction.
Fish Schools, Flock of Birds
Certain types of fish and birds move together in a flock at an amazing speed without colliding. It is as if their movements are being coordinated by a central orchestrator. But when we look closely, we find that there is no central leader in the flock/school. It turns out, every fish or bird in the flock follows a simple set of rules and the overall behavior simply emerges.
These are only some of the examples that are available in nature and this list can go on.