And if you can perform that trick in some objective fashion, you’ll be getting an early morning phone call from some guys in Sweden about attending a banquet and taking some money off their hands.
Consciousness is an extremely, almost intractibly difficult process, and despite the o.p.'s statement that “There are no states in-between (correct me if I’m wrong),” in fact we have every reason that there is a vast spectrum of states inbetween sapience and insensibility. Indeed, your own experience is one of consciousness on various levels, from a morning post-coffee hyperalertness to mid-afternoon somnambulism to deep REM sleep at night, and yet it remains a constant or repeatable enough process that you only rarely experience a severe discontinuity.
It’s also not appropriate to attribute consciousness only to humans; certainly, other members of genus Homo experienced significant degrees of consciousness, as does arguably the Great Apes; they certainly display other characteristics of awareness and cognition, including remorse, guilt, fear, enjoyment, pranksterism, et cetera, and to a lesser degree we can say this of many other domestic and wild species like dogs, equines, cetaceans, which enjoy social relations with humans. It also seems very likely, based upon behavior, that other non-social species like octopus or ursines also enjoys a significant degree of congitive capability and no small amount of self-awareness. The notion that only humans think and feel is one emergent of prejudice about our station in life, and is not bourne out in detail studies of other animals.
While the title is misleading, Dennett’s Consciousness Explained is about the best take on consciousness from an evolutionary philosophy point of view. If you want to get more into the technical neurological detail of the brain and the processes of consciousness, I recomment Ian Glynn’s An Anatomy of Thought. (Warning, this is pretty technical, despite being a nominally pop-science book, and you’ll need a basis knowledge in biochemistry and neurology to make good headway through many sections of the book.)
Be prepared to be disappointed, however, in obtaining an authoritative answer; as Nobel laureate Eric Kandel notes in his autobiography, In Search of Memory: The Emergence of a New Science of Mind (also a very good read, and he gets into some of the details about the simple functions that form the basis of memory, which is his area of research), cognition and consciousness are overarching processes that are just too complex to study as a gestalt at this time; we need to understand the fundamental processes of the brain and how they segue together to build larger, more expansive and abstract functions which eventually feed into what we think of as consciousness. It’s not that it’s impossible to understand, merely that we’re as yet too ignorant right now in what we know.
Now, someone (I won’t name any names) is likely to come along and do some kind of handwaving to assert that because we don’t know how it works that it must be some kind of obscure, supernatural, non-biological process that gives rise to sapience, which is a textbook case of argumentum ad ignorantiam. It’s true that we can’t replicate or comprohensively model the processes and so can’t ruled out some kind of ascientific explanation on an experimental a posteriori basis, but as our knowledge of neurology has increased, especially in the last twenty five years, it’s been very clear that many of the things about the nature of mind that seemed formerly inexplicable, like permanent memory, are the result of observable and purely biological mechanisms that don’t require any hazy obtusity about mind/brain duality, nor do they support any hand-waving relationships between consciousness and quantum mechanics. (The only established comparison between the two topics is our vast ignorance of the underlying causes of both.)
Consciousness/sapience/sentinence, however you care to define it, isn’t a single mutant gene that gets turned on or off, but a vast array of orgnaized processes that are seen in greater or lesser degrees in any organism with a large central nervous system, and seems to be an inescapable result (and likely an adaptive benefit) of increasing complexity. We could go on for pages of this thread on the benefits of consciousness, but most are obvious and a reading of the above references plus the many other trestiese on the topic will develop this in a far more regular and organized manner.