In this beguiling book, Chris Lavers pursues the unicorn across two and a half millenniums, from the bas-reliefs of ancient Persia to the royal coat of arms of the United Kingdom by way of medieval tapestry. As a scientist, his main purpose is to find out what zoological truths lie behind the myth. But he is also a careful explorer of folklore, sifting fact from fiction.

The first known description of a unicorn comes in 398BC from the Greek doctor Ctesias of Cnidus, who in a book called Indica wrote about “certain wild asses which are as large as horses” and “have a horn on the forehead which is about a foot and a half in length”. This first unicorn was a colourful beast, white with a dark red head, blue eyes and a crimson, white and black horn. Lavers concedes that Ctesias was “a library type of fellow” who had never actually seen what he was describing, but that doesn't mean he was a fantasist. He was right, for example, about elephants, which must have seemed equally implausible to him, and about talking birds (which we now know as parrots).

Lavers thinks that the most obvious real-life candidate for Ctesias's unicorn, the rhinoceros, was not the true source and traces this early version of the legend back instead to three other animals. The horn came from the chiru, or Tibetan antelope, whose slender pair of antlers in the male look from a distance like a single horn (distantly being the only way most people ever see these shy beasts). The kiang, or wild ass, gave it its colouring, and the yak was the source of its legendary ferocity. All three creatures can be found on the Tibetan plateau, the site of another, equally resonant myth, Shangri-La.

More details were added to Ctesias's original picture over time, but for more than six centuries the legend of the beast whose single horn, if you could catch one, had curative properties remained in essence unchanged. The very different creature of later western myth - symbolic, semi-sacred - was born when the unicorn “popped up”, as Lavers puts it, most unexpectedly, in the Greek Old Testament. This beast of savage power, whose name in the Greek is translated from the curious Hebrew word “reem”, rampages through the books of Numbers, Deuteronomy, Job and several Psalms. “The unicorns shall come down with them,” Isaiah warns the enemies of God, “and their land shall be soaked with blood.”

Opinion divided sharply among early scholars as to what this Hebrew word “reem” might have meant. St Jerome in the 4th century was among those who thought it might perfectly well be a rhinoceros, and so it appeared in the Vulgate. To the more metaphysically inclined, though, something less lumbering and more spiritual seemed appropriate. Tertullian of Carthage saw the unicorn as a precursor of Christ that “pierces every race with faith”.

From now on the unicorn had more than one life and more than one history. As a real animal, it was pursued by hunters: Samuel Bochart, the 17th-century French biblical scholar thought it was an Arabian goat, and after 1835, when Henry Rawlinson deciphered cuneiform, it gradually assumed the shape of the auroch, a now extinct species of cow. Meanwhile, the less literal-minded admirers of the unicorn, led by St Ambrose, followed the symbolic beast. By the Middle Ages, when every natural phenomenon was read as a tissue of allegory, the unicorn, usually accompanied by a virgin, who is sometimes Mary, had been installed in the bestiary as the animal we now know from tapestries and books of hours. The medieval myth, however, was as hybrid as Ctesias's original. Early pagan stories about ladies whose behaviour with unicorns was anything but virginal got caught up in later Christian texts and lingered as if, as Lavers puts it, the male chroniclers were simply reluctant to give up “the good bit” of the story.

With commendable monomania, Lavers ignores great swathes of history when unicorn scholarship was in abeyance. The entire Enlightenment goes by as merely a “cooling-off period” and only the most dedicated unicornologists will follow his dense and lengthy chapter on “khutu”, the substance that may or may not be the same thing as unicorn horn. It is in the 19th century, when we encounter the romantics and then the Victorian empire-builders, that the story picks up again with the hunt for a real beast to account for the legend. British explorers in India were regularly told that whole herds of unicorns were to be found over the next hill. In the late 1840s a Frenchman, Louis Ducoret, claimed to have seen some grazing near Lake Chad. After obtaining generous sponsorship from the French government to search for them, he spent the money most enjoyably without setting foot outside Algiers.

The only adventurer to obtain any sort of result in his search for the unicorn was Harry Hamilton Johnston, who penetrated the Congolese forest accompanied by seven pygmies and a taxidermist named Doggett. What Johnston found, however, turned out to be the okapi, which, if not a unicorn, was still applauded as the most remarkable zoological discovery of the 20th century. That was in 1901. The following year an army officer, Lieutenant Anzelius, became the first European to kill one. Soon the Belgian government had to put a ban on zoological expeditions and museum scouts to preserve the new-found species from extinction.

Pursuit and capture are essential to the unicorn story that, like all enduring myths, embodies a changing truth that reflects back each age to itself. The reality Lavers finds himself exploring today is humankind's relationship with other species, a relationship from which we do not emerge well. By the end of this wise and entertaining book, his unicorn has ceased to be the quaint motif of nursery rhyme and heraldry, and has become instead a symbol of the vulnerability and co-dependence of species, including our own. As the Looking-Glass unicorn said to Alice in Lewis Carroll's book, “If you'll believe in me, I'll believe in you.”

The Natural History of Unicorns by Chris Lavers
Granta £18.99 pp272

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