  Despite our familiarity with specific technologies, the origin of new
technologies remains mysterious. Are new technologies made from scratch, or are
they built up recursively from new combinations of existing technologies? To
answer this, we introduce a simple model of recursive innovation in which
technologies are made up of components and combinations of components can be
turned into new components---a process we call technological recursion. We
derive a formula for the extent to which technological recursion increases or
decreases the likelihood of making new technologies. We test our predictions on
historical data from three domains and find that technologies are not built up
from scratch, but are the result of new combinations of existing technologies.
This suggests a dynamical process by which known technologies were made and a
strategy for accelerating the discovery of new ones.
