Will our family embrace a 'hobbit' as one of its own?

A diminutive relative's bid to join the human race has begun a fierce debate, says Felipe Fernández-Armesto

When they found her, her teeth were mashed to pulp, her bones rotted and soggy. She was dwarfishly tiny. Her brain was barely as big as a chimpanzee's.

She died 18,000 years ago. But she had the power to subvert anthropological orthodoxy, challenge long-established scientific methods and shake our perceptions of ourselves.

Alongside other members of her species, she had lain - unknown to the world until October when Nature published the results of the excavation - in the soil of the island of Flores in Indonesia.

The discoverers immediately recognised the remains as those of fellow humans and dubbed the newly discovered species Homo floresiensis , ascribing it to the genus to which we belong.

All the journalists emerged from their briefings with the same message: a previously unrecorded kind of human - christened "hobbits" by PR-minded archaeologists - had joined us.

Speculation bubbled over: members of the new "race" might be the archetypes of leprechaun myths; maybe they are not extinct, but await discovery in the "Lost World"-like environment of Flores.

Stand by for reaction. The classification of the new finds in the genus homo will be challenged with partisan fury, which will display impassioned differences about how and where to draw the limits of humankind.

In So You Think You're Human , I tried to sketch a previously untold history: of how the perceived limits of the human community have varied from time to time and between cultures, and how two simultaneous yet mutually conflicting processes have characterised it.

On the one hand, our understanding of what it means to be human has progressively broadened. Groups excluded as bestial or demonic - such as non-whites, and, more recently, pygmies and "Hottentots" - have gained the acceptance they deserve.

In other creatures' cases - such as, in the late 18th and 19th centuries, those of the so-called great apes - doubts have been resolved in favour of their classification as non-human.

Every enlargement of our definition has been frenziedly contested because humankind is a moral community, and every time we embrace a group as human we accord its members moral equality with ourselves.

On the present frontiers, some ethicists militate for our moral community to embrace the unborn and the vegetatively moribund, others for the inclusion of apes and other animals.

A parallel conflict is under way in palaeoanthropology over whether Neanderthals were human in the same sense as our ancestors: the overwhelming evidence that they had rich moral, ritual and intellectual lives is dismissed by academic sceptics, who fight almost as keenly as the "scientific" racists of the 19th century fought to exclude blacks.

The issue is vital because if a species other than Homo sapiens can be recognised as human, there is no logical place at which to draw the boundary of our moral community.

The theory of evolution places us inside the animal continuum. Bertrand Russell quipped that there was no conclusion short of votes for oysters. Homo floresiensis makes the problem acute. If creatures with the brain size of a chimp can be in the genus, why not chimps? And if the species in the genus are all properly called "human", why should "human" rights be confined to only one of those species?

The case is inconclusive. Classification of floresiensis in the genus homo depends on risky reasoning: that the species evolved from the widespread hominid, Homo erectus ; that its diminutive stature is the result of isolation; that the facial and cranial proportions of known specimens count for more than other anatomical features.

Yet even those who deny humanity to the "hobbits" must acknowledge the discovery's impact. It raises questions about the continued usefulness of traditional taxonomy. It intensifies debate about the ontological status of species and genera.

Floresiensis makes untenable the importance of brain size: big brains do not make their possessors qualitatively superior to other creatures.

To judge from adjacent finds, the "hobbits" had technology typical of early palaeolithic Homo sapiens , despite chimp-sized brains in imp-sized bodies.

The fact that the discoverers sensed their kinship with the creatures shows how strongly, in the course of our history, we feel bound to embrace the stranger. How much wider are we willing to extend that embrace?

Felipe Fernández-Armesto is professor of global environmental history at Queen Mary, University of London, and author of So You Think You're Human (Oxford University Press, £8.99).