(Originally posted 2007, edited and updated 2014. Also previously posted in Philosophy Forums.)
According to evolutionary biology, homo sapiens is the result of billions years of evolution. For all these thousands of millions of years, our sensory and intellectual abilities have been honed and shaped by the exigencies of survival, through billions of lifetimes in various life-forms - fish, lizard, mammal, primate and so on - in such a way as to eventually give rise to the mind that we have today.
Recently, other scientific disciplines such as cognitive and evolutionary psychology have revealed that conscious perception, while subjectively appearing to exist as a steady continuum, is actually composed of a heirarchical matrix of thousand, or millions, of interacting cellular transactions, commencing at the most basic level with the parasympathetic system which controls one’s respiration, digestion, and so on, up through various levels to culminate in that peculiarly human ability of ‘conscious thought’ (and beyond, although this is beyond the scope of current science.)
Our consciousness plays a central role in co-ordinating these diverse activities so as to give rise to the sense of continuity which we call ‘ourselves’ - and also the apparent coherence and reality of the 'external world'. Yet it is important to realise that the naïve sense in which we understand ourselves, and the objects of our perception, to ‘exist’, is in fact totally dependent upon the constructive activities of our consciousness, the bulk of which are completely unknown to us.
When you perceive something - large, small, alive or inanimate, local or remote - there is a considerable amount of work involved in ‘creating’ an object from the raw material of perception. Your eyes receive the lightwaves reflected or emanated from it, your mind organises the image with regards to all of the other stimuli impacting your senses at that moment – either acknowledging it, or ignoring it, depending on how busy you are; your memory will then compare it to other objects you have seen, from whence you will (hopefully) recall its name, and perhaps know something about it ('star', 'tree', 'frog', etc).
And you will do all of this without you even noticing that you are doing it; it is largely unconscious.
In other words, your consciousness is not the passive recipient of sensory objects which exist irrespective of your perception of them. Instead, your consciousness is an active agent which constructs reality partially on the basis of sensory input, but also on the basis of an enormous number of unconscious processes, memories, intentions, and so on. And this is the way in which the ancient philosophy of 'idealism' does indeed recieve support from modern science.
"...this thing we call “the world” isn’t something wholly outside ourselves, something we experience in a detached and objective way. It’s something we create moment by moment in our minds, by piecing together the jumble of unconnected glimpses our senses give us—and we do the piecing according to a plan that’s partly given us by our biology, partly given us by our culture, and partly a function of our individual life experience.
That point is astonishingly easy to forget. I’ve long since lost track of the number of times I’ve watched distinguished scientists admit with one breath that the things we experience around us aren’t real—they’re just representations constructed by our sense organs and brains, reacting to an unimaginable reality of probability waves in four-dimensional space-time—and then go on with the very next breath to forget all that, and act as though matter, energy, space, time, and physical objects exactly as we perceive them are real in the most pigheadedly literal sort of objective sense, as though the human mind has nothing to do with any of them except as a detached observer. What’s more, many of those same scientists proceed to make sweeping claims about what human beings can and can’t know and do, in blithe disregard of the fact that these very claims depend on the same notion of the objective reality of the world of experience that they’ve just disproved."John Michael Greer