fortuitism

from The Century Dictionary.

• noun The doctrine that a tendency in the universe toward a certain direction of development may be accounted for by continual fortuitous changes, combined with an inherent possibility of an indefinite sum of change in the direction which development takes and an inherent impossibility of an indefinite sum of change in the opposite direction.
• noun The doctrine of a fortuity in the action of natural causes, as opposed to design.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The doctrine that chance is involved in natural events rather than absolute determinism.