rationalskepticism.org

Wortfish wrote:

Rumraket wrote:
I'm sorry this is just what the evidence shows, it's not an assumption. Transducin is just the name for the G-protein activated by the Opsin protein receptor (what in the above quote is known as the 7-transmembrane helical structure common to all GPCRs). Other non-opsin GPCRs have G-proteins too (which is why they are called G-Protein Coupled Receptors), clearly homologous to transducin, and they activate their own transducin-like G-proteins in the same way by conformational change when some extracellular stimuli is detected. So yes, "transducin" G-proteins definitely pre-existed the origin of opsins.

But the putative ancestors of transducins would not have been used for phototransduction in the absence of the opsins. Repurposing them for use in a functional visual system would have required more changes than you are prepared to admit.