What is it about the cat? Of all the animals we call ‘domestic’, the cat has a unique status; one often hears it said that cats domesticated us. They also arouse far more polarised views than most animals; you love them or hate them – and people often do either of those things with a frankly weird passion. They are associated with women more than men, and it’s certainly true that there are more men among the ailurophobes. It also seems to be the case that people with pretensions to creativity are more likely to be cat lovers (I’ve often wondered if this is because self-reported artistic types are less domestic than the general population, so have more problems with mice and rats).

Evidence of our love, even reverence, for cats goes back at least 9,000 years. Presumably, they were around us even earlier, as one of the species naturalists call synanthropes – those animals and other species that thrive around human settlements. Likely that’s because mice and rats are also synanthropes. But by 7,500 BC, we can find evidence of cats being given the same funerary respect we give ourselves. When you consider that only a small proportion of the population at that time was buried with any dignity, it makes the love and respect implied by feline burial all the more strange.

The ancient Egyptians were famously fond of felines; thousands of mummified cats have been found (along with dogs, jackals, cheetahs, and bulls, among others; but cats in the greatest numbers), and there is of course Bastet, the cat goddess (there was even a city called Bastopolis) whose temples were full of cats. Apparently it was a crime to harm or kill a cat, punishable by death. Herodotus, who spent time in Egypt, reports that he saw, on more than one occasion, people making more effort to rescue their cats from house fires than actually putting out the fires.

The numerous examples of egregious cruelty to cats, cultural as well as personal, throughout recorded history only serve to confirm their special, if ambiguous, status. The witch’s familiar had a particularly bad press in mediaeval Europe, hounded by the Church, but cats have also been associated with Catholicism (in Elizabethan England, for instance, where anti-papists burnt them in wicker baskets). Poets have written homages to them since time immemorial, from the anonymous Irish poet of ‘Pangur Bàn’, through the feline devotions of Christopher Smart, to T S Eliot. In our own age of spurious creativity, as part of the equally peculiar cult of self-expression (don’t get me started on that concept) the world is awash with terrible doggerel about cats.

For cat lovers, the relationship between cats and humans is a practically sacred mystery. Search online for cat-oriented web sites and you will be inundated in a cascade of gushing nonsense about the esoteric, erotic, emotional qualities of cats. In all this torrent of mystical worship, you will search in vain for any objective analysis; no cat lover seems even dimly aware of the possibility that they are projecting a good deal onto an animal that is ultimately no more mysterious than any other small predator.

For good or for ill, the cat has become a cultural fixture. This true of other animals, of course; but those others usually have an obvious function in human society; either that, or they are big and dangerous enough to scare the hell out of us. Only the cat has risen to the status of cultural icon without doing a thing to earn it. So what is it about the cat?

At this point, let me introduce you to Toxoplasma Gondii. T Gondii is ‘an intestinal coccidium that parasitizes members of the cat family as the definitive hosts and has a wide range of intermediate hosts’. Those ‘intermediate hosts’ include most of the species that are predated upon by cats: mice, rats, birds, and shrews, for instance. They also include us. The life cycle of Toxoplasma Gondii has two elements; in intermediate hosts, it reproduces asexually, but in its definitive host, the cat, it reproduces sexually.

Infection by these pesky little protozoa can lead to an illness, toxoplasmosis. While toxoplasmosis is mostly a fairly innocuous illness, characterised by symptoms not unlike a cold or a mild allergy, it can on occasion be a serious risk to human health, especially if it is contracted in pregnancy or old age, or by someone whose immune system is weak. Contracted in pregnancy, it can lead to encephalitis in babies.

T Gondii has recently been in the news as a possible trigger for dementia (there are also a number of studies suggesting that it may lead to suicidal behaviour in some cases, which may perhaps be explained by what follows); this is because it tends to migrate towards the amygdala of its intermediate hosts – and thereby hangs, it seems to me, an explanation for our fascination with felines. The amygdala is the part of the brain that produces the well-known ‘fight or flight’ response; when rats or mice, or any other species that counts as feline food, is infected in this way, the animal loses its fear of cats – not a recipe for survival. Thus the cat gets re-infected by eating its suicidally unworried prey, and T Gondii gets to reproduce sexually again.

The same trigger in humans produces a markedly different response. We are not a realistic lunch for your average tabby (though I’ve occasionally noticed Boban and Lily, the feline king and queen of our house, eying me in a decidedly epicurean way). We react by exaggerating our response to cats; that is to say, we start to love or hate them. Our longstanding affection turns out to be an inveterate infection.

So there you have it. For thousands of years we have imagined that the cat has some kind of mystical (or manipulative) hold over us. In fact, the cat is a passive victim of this relationship, just as we are. The whole grand cultural edifice of feline worship is nothing but a base biological smokescreen; it has been erected so that a bug can have sex in a cat’s intestines.

I wonder if this elaborate joke on nature’s part might have lessons for us elsewhere. How many of the relationships between humans and the animal world, or our cultural and religious attachments to elements of the natural world, are predicated on the behaviour of creatures too small to be noticed? Microbes make up more than fifty per cent of the world’s biota; it’s a sobering thought (and not a little amusing) that they may be more in control of the planet than we ever imagined.