  Answering the titular question has become a central motivation in the field
of quantum biology, ever since the idea was raised following a series of
experiments demonstrating wave-like behavior in photosynthetic complexes. Here,
we report a direct evaluation of the effect of quantum coherence on the
efficiency of three natural complexes. An open quantum systems approach allows
us to simultaneously identify their level of "quantumness" and efficiency,
under natural physiological conditions. We show that these systems reside in a
mixed quantum-classical regime, characterized by dephasing-assisted transport.
Yet, we find that the change in efficiency at this regime is minute at best,
implying that the presence of quantum coherence does not play a significant
role in enhancing efficiency. However, in this regime efficiency is independent
of any structural parameters, suggesting that evolution may have driven natural
complexes to their parameter regime in order to "design" their structure for
other uses.
