Despite the great complexity of the bacterial flagella the Matzke model shows that it is both reducible and highly modular. Darwin was right when he suggested that cooption of previously existing structures and functions would play an important role in the evolution of complex structures. Widespread cooption is how the flagella evolved by natural selection. [p144]
Are flagella irreducibly complex?
The bacterial flagellum represents the flagship of the Intelligent Design
examples of apparent irreducible complexity and with good reason. They
are truly very complex structures.[p137]
The model proposed by Matzke makes extensive use of cooption or a shift in function
for many of its components. This is a characteristic of a modular system
in which a component serves a different prior function and is then coopted
for use in the evolution of the flagellum. [p138]
