Virtually all of these adaptations are cascade effects that— while resulting from a variety of proximate causes— can ultimately be traced back to a paracentric inversion mutation on the Xq21.3 block of the X-chromosome [5]. This resulted in functional changes to genes coding for protocadherins (proteins that play a critical role in brain and central nervous system development). While this provoked radical neurological and behavioral changes, significant physical changes were limited to soft tissue and microstructures that do not fossilise. This, coupled with extremely low numbers of vampire even at peak population levels (existing as they did at the tip of the trophic pyramid) explains their virtual absence from the fossil record.
Significant deleterious effects also resulted from this cascade. For example, vampires lost the ability to code for e-Protocadherin Y, whose genes are found exclusively on the hominid Y chromosome [6]. Unable to synthesise this vital protein themselves, vampires had to obtain it from their food. Human prey thus comprised an essential component of their diet, but a relatively slow-breeding one (a unique situation, since prey usually outproduce their predators by at least an order of magnitude). Normally this dynamic would be utterly unsustainable: vampires would predate humans to extinction, and then die off themselves for lack of essential nutrients.
Extended periods of lungfish-like dormancy [7] (the so-called «undead» state)—and the consequent drastic reduction in vampire energetic needs— developed as a means of redressing this imbalance. To this end vampires produced elevated levels of endogenous Ala-(D) Leuenkephalin (a mammalian hibernation-inducing peptide [8]) and dobutamine, which strengthens the heart muscle during periods on inactivity [9].
Another deleterious cascade effect was the so-called "Crucifix Glitch" — a cross-wiring of normally-distinct receptor arrays in the visual cortex [10], resulting in grand mal-like feedback siezures whenever the arrays processing vertical and horizontal stimuli fired simultaneously across a sufficiently large arc of the visual field. Since intersecting right angles are virtually nonexistent in nature, natural selection did not weed out the Glitch until H. sapiens sapiens developed Euclidean architecture; by then, the trait had become fixed across H. sapiens vampiris via genetic drift, and—suddenly denied access to its prey—the entire subspecies went extinct shortly after the dawn of recorded history.
You'll have noticed that Jukka Sarasti, like all reconstructed vampires, sometimes clicked to himself when thinking. This is thought to hail from an ancestral language, which was hardwired into a click-speech mode more than 50,000 years BP. Click-based speech is especially suited to predators stalking prey on savannah grasslands (the clicks mimic the rustling of grasses, allowing communication without spooking quarry) [11]. The Human language most closely akin to Old Vampire is Hadzane [12].
The Human sensorium is remarkably easy to hack; our visual system has been described as an improvised "bag of tricks" [13] at best. Our sense organs acquire such fragmentary, imperfect input that the brain has to interpret their data using rules of probability rather than direct perception [14]. It doesn't so much see the world as make an educated guess about it. As a result, «improbable» stimuli tends to go unprocessed at the conscious level, no matter how strong the input. We tend to simply ignore sights and sound that don't fit with our worldview.
Sarasti was right: Rorschach wouldn't do anything to you that you don't already do to yourself.
For example, the invisibility trick of that young, dumb scrambler— the one who restricted its movement to the gaps in Human vision— occured to me while reading about something called inattentional blindness. A Russian guy called Yarbus was the first to figure out the whole saccadal glitch in Human vision, back in the nineteen sixties [15]. Since then, a variety of researchers have made objects pop in and out of the visual field unnoticed, conducted conversations with hapless subjects who never realised that their conversational partner had changed halfway through the interview, and generally proven that the Human brain just fails to notice an awful lot of what's going on around it [16, 17, 18]. Check out the demos at the website of the Visual Cognition Lab at the University of Illinois [19] and you'll see what I mean. This really is rather mind-blowing, people. There could be Scientologists walking among us right now and if they moved just right, we'd never even see them.
Most of the psychoses, syndromes, and hallucinations described herein are real, and are described in detail by Metzinger [20], Wegner [21], and/or Saks [22] (see also Sentience/Intelligence, below). Others (e.g. Grey Syndrome) have not yet made their way into the DSM [23]—truth be told, I invented a couple— but are nonetheless based on actual experimental evidence. Depending upon whom you believe, the judicious application of magnetic fields to the brain can provoke everything from religious rapture [24] to a sense of being abducted by aliens [25]. Transcranial magnetic stimulation can change mood, induce blindness [26], or target the speech centers (making one unable to pronounce verbs, for example, while leaving the nouns unimpaired) [27]. Memory and learning can be enhanced (or impaired), and the US Government is presently funding research into wearable TMS gear for—you guessed it— military purposes [28].
Sometimes electrical stimulation of the brain induces "alien hand syndrome" — the involuntary movement of the body against the will of the «person» allegedly in control [29]. Other times it provokes equally involuntary movements, which subjects nonetheless insist they «chose» to perform despite overwhelming empirical evidence to the contrary [30]. Put all this together with the fact that the body begins to act before the brain even «decides» to move [31] (but see [32, 33]), and the whole concept of free will—despite the undeniable subjective feeling that it's real—begins to look a teeny bit silly, even outside the influence of alien artefacts.
While electromagnetic stimulation is currently the most trendy approach to hacking the brain, it's hardly the only one. Gross physical disturbances ranging from tumors [34] to tamping irons [35] can turn normal people into psychopaths and pedophiles (hence that new persona sprouting in Susan James's head). Spirit possession and rapture can be induced through the sheer emotional bump-and-grind of religious rituals, using no invasive neurological tools at all (and not even necessarily any pharmacological ones) [21]. People can even develop a sense of ownership of body parts that aren't theirs, can be convinced that a rubber hand is their real one [36]. Vision trumps propioreception: a prop limb, subtly manipulated, is enough to convince us that we're doing one thing while in fact we're doing something else entirely [37, 38].