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SPECULATIVE EVOLUTIONARY TIMELINE OF CONSCIOUSNESS

The theory at a glance: from selective signal enhancement to consciousness. 

About half a billion years ago, nervous systems evolved an ability to enhance the most pressing of incoming signals. Gradually, this attentional focus came under top-down control. To effectively predict and deploy its own attentional focus, the brain needed a constantly updated simulation of attention. This model of attention was schematic and lacking in detail. Instead of attributing a complex neuronal machinery to the self, the model attributed to the self an experience of X—the property of being conscious of something. Just as the brain could direct attention to external signals or internal signals, that model of attention could attribute to the self a consciousness of external events or of internal event. As that model increased in sophistication, it came to be used not only to guide one’s own attention, but for a variety of other purposes including understanding other beings. Now, in humans, consciousness is a key part of what makes us socially capable. In this theory, consciousness emerged first with a specific function related to the control of attention and continues to evolve and expand its cognitive role. The theory explains why a brain attributes the property of consciousness to itself, and why we humans are so prone to attribute consciousness to the people and objects around us.

Timeline: Hydras evolve approximately 550 million years ago (MYA) with no selective signal enhancement; animals that do show selective signal enhancement diverge from each other approximately 530 MYA; animals that show sophisticated top-down control of attention diverge from each other approximately 350 MYA. Primates first appear approximately 65 MYA; hominids appear approximately 6 MYA; Homo sapiens appear approximately 0.2 MYA.