Chimpanzees with an extra gene or two – that's all we are. The sense of having agency is really an illusion, as is the sense of self. All "love" actually comes to is neurones firing in the caudate nucleus. Why Donne moves us is just because certain linguistic tropes stimulate certain neuronal pathways. According to claims made by supposedly respectable neuroscientists, reported by supposedly respectable newspapers, it is possible actually to pinpoint the locus of love, wisdom or whatever as parts of the brain that "light up" under functional magnetic resonance imaging (brain scans).

All nonsense, according to Raymond Tallis, professor of geriatric medicine at the University of Manchester, poet, novelist, and all-round polymath. When neuroscience and Darwinism trespass into the humanities, they become, he says, "neuromania" and "Darwinitis" – unhealthy, mad and malign.

He himself uses fMRI on his patients, so is well equipped to explain that what the scanning actually shows is widespread brain activity, which is marginally more prevalent in some areas than others. And usually the same areas – areas that incessantly crop up in different experiments, and are cited as serving quite different functions ("You could be forgiven for thinking of the brain as being managed by a crooked estate agent letting out the same bit of real estate simultaneously to different clients").

Anyway, argues Tallis, even if the scans could in theory, and did in practice, reliably isolate specific brain states to match up with specific psychological states, what would such matching amount to? Is the brain state supposed to coincide with, cause, or be the very same as the psychological state? Sometimes neuromaniacs, in cunning or confusion, shift between these alternatives; sometimes they brazenly opt for a third – the idea that nerve impulses, "by moving from one material place to another… are mysteriously able to be the appearance of things other than themselves".

But if a psychological state (say, an experience of seeing yellow) and a brain state "were the same thing, the least one might expect is that they would appear as if they were the same thing" – appear to be yellow, for instance. They don't; not, anyway, to the neuroscientist observing the brain. But in principle the person whose brain is being observed could (via mirrors and advanced technology) observe their own brain while observing a daffodil outside it; and then their electrochemical activity would simultaneously provide an experience of grey sparking brain stuff and of a yellow flower. Electrochemical activity in the brain, in fact, is required to have "two sets of appearances", but its "inside" appearance is only available to the brain owner. "Inside" is surely illegitimate for neuromaniacs, as is "brain-owner", since they deny a unified self, yet in fact they do precisely what they accuse believers in immaterial mentality of doing. They smuggle a miniature inner observer (a homunculus) into the head. It is just that their homunculus is better disguised; it is broken up into a whole lot of tiny homunculi – neurons, circuits or bits of brain.

Like the clever child who shouts "it's in his pocket" at the bad conjuror, Tallis brilliantly exposes the portentous fraudulence of memes, and the way cod-sci metaphors, such as "information", manage, in anthropomorphising machines, to mechanise humans. Less convincingly, he defends free will from the Libet experiments which purport to disprove it. His goal is to "reaffirm humanity" – and without appealing to mysterious "mind-stuff". What, then, is his alternative to the scientistic account? Each of us, he says, is lifted from the organic events of our self-contained bodies and "stand-alone brains" by "a trillion cognitive handshakes" – the way humans have jointly built up a world of transmittable meanings which transcend biology.

But how did that come about? Tallis makes various explanatory gestures towards the evolution of the hand as flexible tool, but these seem incongruously biologistic. And what about subjective consciousness, the perspectival view which both unites and differentiates a human's multiple experiences? He does not pretend to explain it, but we can be grateful that he shows up the pretensions of those who think they can, and who reduce the glory of being human to brain circuitry and the survival tactics of early hominids. With erudition, wit and rigour, Tallis reveals that much of our current wisdom is as silly as bumps-on-the-head phrenology.