Can Co-option Build Complex Molecular Systems?
A complex molecular system does not necessarily have to originate with every modern component already in place. Evolution can recruit proteins and structures that originally performed other functions and incorporate them into new systems.
Gene duplication, changes in regulation, modification of existing proteins, and co-option can provide material from which new functional arrangements develop.
Why This Matters
This directly addresses the claim that a complex molecular machine must have appeared all at once. If components can perform useful functions before becoming part of the modern system, gradual pathways become possible.
Response
Co-option is a genuine evolutionary mechanism and must be included in any serious investigation of molecular machines. Evidence of shared components and changing functions shows that biological systems can reuse existing parts.
However, identifying components that can be co-opted is not necessarily the same as reconstructing the complete origin of an integrated system. The historical question still includes when components were recruited, what functions intermediate arrangements performed, and how assembly and regulation developed.
Question That Remains
For specific molecular machines, how completely can co-option account for the transition from earlier functional systems to the integrated modern structure?