Given everythingwe understand about consciousness, it seems pretty clear that the brain isrequired for any kind of conscious experience
That is not a “given”by any stretch of the imagination.
A simpledictionary definition of “consciousness” is an "awareness of the worldaround you", that’s what you lose when you lose consciousness. Ifyou approach the question in a logical, scientific manner, devoidof any philosophical, metaphysical implications, or "religious" presuppositions, then thepresence of “consciousness” can only be observed to be the ability to perceive sensory stimuli and respond bypurposeful movement or by a behavioral change.
If that is the case, then the evolution oflife clearly shows a continuum of consciousness that evolved over time, the ability to respond specificallyto the environment, and to act creatively is a property of life at all levels, obviously present in organisms long before the evolution of anything we can call a brain. Single celled organisms with nothing even resembling arudimentary brain or nervous system show themselves to be sensate beings withcomplex behavior.
Studies have shown that prokaryotes such as bacteria can respond to a broad range of stimuli, demonstrateelementary forms of “memory”, and engage in purposeful activities. They have shownthemselves to be extraordinarily perceptive, demonstrating elaborate behavioralresponses and adaptations to a wide range of attractants and repellants andother environmental stimuli such as light. They have complex signalingcapabilities, show the ability to communicate, and change their behavior basedon population size, which implies some kind of quorum sensing ability andclearly demonstrates social behavior on at least a rudimentary level. They havebeen proven to have some form of memory and a rudimentary ability to learn, andthe discriminatory ability to “choose” among alternatives, regarding amongother things, gene expression. They clearly integrate these capabilities into aself-organized and sensate being that in at least an extremely attenuated wayis perceiving, discriminating, remembering, and even “thinking”, on some levelit is conscious.
Over time, nucleated cells emergedwith a greater range of senses and responses, colonies of single-celled creaturesevolved into multicellular organisms with greater degrees on sentienceand a broader ability to respond.Cells emerged that specialized in sensing different aspects ofthe environment, consolidating into sensory organs, nervous systems evolved toprocess and distribute among multiple sensory organs, processing this data anddistributing to other parts of the organism, eventually the flow of informationrequired a central processing point, and brains evolved. Seen in its entirety, seen the way evolution demands that wesee it; there is a direction to life, it constantly progresses towards greatercomplexity and higher forms of sentience, from inanimate matter, to life, tothought, to self-reflective consciousness. The data and observations clearly demonstrate thatconsciousness is not contingent on brain, the evolution of consciousness began long before the evolution of brains, and therefore cannot be dependent on brain.
