Wiktionary
n. The theory that some aspects are observable in a high-level view of a complex system but barely deducible from the description of its components.
WordNet
n. the appearance of entirely new properties at certain critical stages in the course of evolution
Wikipedia
Emergent evolution is the hypothesis that, in the course of evolution, some entirely new properties, such as mind and consciousness, appear at certain critical points, usually because of an unpredictable rearrangement of the already existing entities. The term was originated by the psychologist C. Lloyd Morgan (1852-1936).
In the 20th century, the hypothesis was widely criticized for providing no mechanism to how entirely new properties emerge, and for its historical roots in teleology.