Some of us like to claim that humans are the only property-owning animal, but even if this were true - for tribes of monkeys defend their turf and dogs fight over bones - it would be a recommendation only from arguable ideological standpoints.Cognition, higher consciousness, even perhaps conscience and soul are attributes we assign to ourselves in our desire for self-differentiation. We suppose that we alone have a notion of transcendence - but, like most of our claims to unique sagacity, this is the result of our inability to communicate with other species. It is like dismissing as dumb the people whose speech you cannot understand.No one has yet taught a chimpanzee much human language. On the other hand, even the most dedicated human students have made only rudimentary progress in talking to gorillas. Experimenters are disappointed when the chimpanzees fail to respond to efforts to teach them sign-terms for abstract concepts.

Gorillas, no doubt, suffer from frustrations of their own with human interlocutors.The very attempt to distinguish ourselves from animals is a delusive form of self-flattery The line has never been satisfactorily drawn. Tribes commonly have no word for "man" that includes members of other tribes They refer to those excluded as "monkeys". In the 18th century, theorists wearied readers with efforts to prove that orang-utans were human. The hero of one of Thomas Love Peacock's satires was an orang-utan who, possessed of every atonal faculty except speech, acquired, with a reputation as "a profound but cautious thinker", a baronetcy and a seat in the House of Commons. Pygmies, Hottentots and Aborigines, meanwhile, were relegated to sub-humanity. Now we prefer to classify humans as animals, linked by evolution in an embracing continuum, and have done with it.

But, by comparison with our fellow creatures, we persist in giving ourselves top ranking.When the astral scrutineers review the evidence and try to identify Earth's top species, they will find some points in our favour. It is, for instance, an objective fact about us humans that we can survive in more environments than almost every other creature - except for the parasites and micro- organisms we carry inside us wherever we go. We will probably pass muster as the species with the best collective memory: as far as we know, our ability to record information makes us best equipped for what we call progress and best placed to exploit vicarious experience - though we may be found wanting if judged by the use we make of their privilege.And, just as historians measure societies relative to one another by their effectiveness in making war, so we shall be seen to advantage in our power to destroy other species. Only a few micro-organisms - whom our cosmic observers may admire for the rapidity and mutability with which they evolve - exceed us in this respect. Most other sources of human pride are hard or impossible to value by objective standards.Our biggest rivals for the scrutineers' esteem will probably not be other animals. The consciousness from which we exempt the microbes may be discounted as ascribed, in a form or by a measurement unknown to us, to other species.We may not have to await the day of the triffids to be judged inferior to plants.

During our recorded history, we have helped to make some plants - especially wheat, maize and rice - among the most rapidly adapted and widely grown species in the planet. We think we have exploited them; but in measurable terms, they have done rather well out of us. From the viewpoint of the astral scrutineers, it will look as if they have cunningly manipulated mankind for their own propagation and distribution.Species like these, with which we live in mutual dependence, may not be strong enough to survive us, but compared with many others - especially plants - we will be seen by the cosmic judges as fragile vessels, exceptionally prone to self-destruction. The conservation movement has made us worry about the durability of the natural world, as if nature could not last without mollycoddling by us Trees, lichens, weeds were here before us. They will be here after we are gone: what objective test could be more conclusive? A still imperfectly domesticated nature is waiting to take revenge.When the Prince of Wales talks to his plants, let us hope that he does so without condescension.