Two thick black hairs found on a mountainside in remote northwest India have prompted a new wave of speculation about one of the oldest, most famous and most elusive celebrities in natural history. Yeti, Sasquatch, the Abominable Snowman, Big Foot - he comes by many names, and whether he actually exists or not, he is a vital part of human society.

The hairs, discovered and sent to the British primatologist Ian Redmond this year, do not seem to match those of any other creature known to live in the West Garo mountains. The bristles may belong to an undiscovered species, a survivor of the giant ape called Gigantopithicus thought to be extinct, or to a lost pig. They may be the clippings of “Mande Burung”, the Man of the Jungle, a creature, half man and half ape, that has been spotted and recorded in local folklore for generations. They may be a hoax.

Scientists are at present conducting DNA tests on the hairs. More importantly, they are taking part in an ancient ritual common to almost every culture on Earth, and one that grows ever more important as the world grows smaller.

The search for the yeti can be dismissed as pseudo-science or wishful thinking, but it is a phenomenon with increasingly profound psychological significance in the modern world. As more species face extinction, natural habitat shrinks and climate-driven anxiety spreads, the innate human desire to find unknown creatures appears to be intensifying.

Cryptozoology - the study of species sighted by explorers or recorded in folklore but unverified by formal science - is booming. In recent years there has been a flood of books, encyclopaedias and guides to cryptids, creatures both fantastical and possible that survive somewhere on the wild, uncharted borders between science and fantasy.

In a thoroughly explored world, when Google Earth can whisk us to the most remote corner of the planet via a computer screen, cryptozoology still offers mystery, discovery and the unknown. If the internet promises the whole of knowledge, our fascination with unknown beasts provides a strange counterbalance: the human need to know that we do not know everything.

Ancient maps often depicted a dragon, unicorn or some other mythical beast on the edge of the known world- the remarkable rise of cryptozoology shows how desperate modern society has become to put the dragon back on our maps.

Communities have always defined the frontiers of their civilisation by dangerous, unknown beasts: the Loch Ness Monster; Mamlambo, the river monster of South Africa; the Aye-Aye in Paraguay, a sort of vicious tree-dwelling sheep and not to be confused with the real Aye-aye from Madagascar; the chupacabra or “goat-sucker” in Central America; and many more.

The latest Encyclopaedia of Cryptozoology lists some 1,600 different creatures that have evaded formal discovery. What is extraordinary about them is not their variety, but their remarkable similarity across time and geography.

The hairy almost-human is ubiquitous - Native Americans told of man-beasts living in the forests, Nepalese sherpas described “Metoh-Kangmi, “dirty men in the snow” which, after mistranslation, became abominable snowmen; China has its own version, the Yeren or wild men.

In medieval times, bestiaries of fantastic monsters represented the dangerous unknown, creatures both imaginary and real. They also offered oblique moral lessons, such as the phoenix rising from the ashes to promise life after death.

By the beginning of the last century, there were few large areas left to explore, and most species had been shot and stuffed, identified and catalogued. Yet, instead of disappearing, sightings of new animals have multiplied. While some turn out to be valid, most reflect a deeper psychological urge: to discover but also to preserve the unknown.

In part, the flood of contemporary cryptid encounters reflects a collective environmental guilt: as more and more animals are threatened with extinction by Man, so Man seems ever more determined to believe in the existence of new creatures in uncharted spaces.

The joy that greeted last week's announcement that 125,000 hitherto unsuspected lowland gorillas have been “discovered” in Congo is a reflection of the same deep-seated need to believe that, despite the wreckage visited on the planet by Man, there are wild areas beyond our ken where animals, known or unknown, can flourish unmolested in an ecological Eden.

The gorilla itself was not “discovered” by Western science until 1847. Numerous animals once considered mythical have turned out to be real - the coelacanth, a fish believed to be extinct since the Cretaceous Period, was finally found in 1938; Western scientists first identified the saola, an ox living in the forests of Vietnam, in 1992. In 2005, the WWF caused a sensation by announcing that a hidden camera in the Borneo forests had filmed a mysterious animal the size of a cat with red fur and a bushy tail.

We respond in a similar way to stories of untouched Amazonian tribes, and the discovery on the Indonesian island of Flores of the remains of Homo floresiensis, a hitherto unknown “Hobbit” people that apparently survived until relatively recently.

Most stories of lost tribes and newly discovered species turn out to be unproven, or fabricated. But the belief that unknown creatures larger than mere micro-organisms lurk in the deepest jungle and the darkest oceans remains part of our cultural inheritance, immune to scepticism and scientific evidence.

The hairs under Dr Redmond's microscope may not lead us to the yeti, but the yeti will survive: partly out of romance and inherited ancient fears, but largely because, with more than 800 known species facing extinction, the discovery of a single hitherto unknown survivor may help to salve our ecological conscience just a little. Like their medieval predecessors, modern cryptids carry a moral message.

Only this may be predicted with certainty. Scientists and explorers have been hunting, and not quite finding, the yeti and his hairy chums since time began, and they will do so with increasing frequency the faster his possible hiding places disappear.

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