The Figure Illustrates a Likely Scenario for the Molecular Mechanism

Multiple Choice

The figure illustrates a likely scenario for the molecular mechanism of treehopper helmet evolution. This process demonstrates which explanation for the evolution of complex traits?

A) Traits arise in gradual steps, each of which is fully functional and adaptive for the same reason as the modern trait.
B) Complex traits cannot evolve if they are adaptive.
C) Complex traits arise by eliminating whole developmental pathways.
D) Traits originally selected for one function are co-opted for a different function.