麻豆传媒

THE smell of coffee, the blue of the sky, the anticipation of seeing a loved one: it is impossible to imagine our lives without the vivid conscious experiences of our every waking moment. And yet they have vexed philosophers for centuries. 鈥淭he nature of consciousness is extraordinarily difficult to define,鈥� says .

It was once thought of as an immaterial force, a 鈥済host in the machine鈥� separate from physical reality. Today, however, many neuroscientists argue that our felt experience is simply the product of our brain鈥檚 inner workings. That makes the question of 鈥渨hy?鈥� loom large. Many actions controlled by the brain occur unconsciously, beneath the level of our awareness. Why make exceptions?

Grasping this means thinking outside our own box, says Anil Seth at the University of Sussex, UK. 鈥淗uman consciousness is not the only form of being conscious,鈥� he says. We tend to emphasise conscious experiences that make us think we are better and smarter than other animals, like our ability to recognise ourselves in a mirror, he says. 鈥淭his is not very helpful.鈥�

The absolute fundamental of consciousness 鈥� having an actual experience of things 鈥� is something seemingly shared by many other organisms. 鈥淚n my view, there are grades and varieties of awareness, and there is no principled dividing line about which 鈥� SHAZAM! 鈥� the light of consciousness is turned on,鈥� says .

With a broader view of consciousness, we can look back along the tree of life to get an idea about its earliest glimmers. Jablonka, together with , has done this with a concept the pair call unlimited associative learning, a capacity to learn about and connect new stimuli,even when experienced at different times.

They found that the brain structures that could support this learning probably arose about 500 million years ago during the Cambrian period, a time of extraordinary evolutionary innovation 鈥� probably initially in primitive fish and arthropods such as trilobites and crabs, and around 250 million years later also in molluscs such as squid and octopus. By evolving this flexible capacity to learn, animals no longer needed to rely on reflexive, automatic behaviours in particular circumstances, and could devise better ways to evade predators, for instance. 鈥淭his gives an enormous adaptive advantage,鈥� says Jablonka.

鈥淐onscious experiences bring together a large amount of information in a unified way that emphasises the relevance for the survival prospects of the organism. And it all comes together in one unified scene that evolves from moment to moment. I think it is extremely useful for organisms,鈥� says Seth. Put this way, the 鈥渨hy?鈥� of consciousness is just down to the vagaries of natural selection 鈥� just another random experiment that happened to confer a survival advantage (see 鈥淲hy does evolution happen?鈥�).

And so it went on. Eventually, animals with more complicated brain structures evolved, giving rise to different and more complex forms of conscious experience, such as the ability to think about thinking. This may be a uniquely human trait, and it gives us a larger space of options for action and learning, says Dennett. 鈥淚f you can think about your thinking, you can correct errors and devise new ways of doing things,鈥� he says. And, of course, ponder the nature of consciousness.

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