To the untrained eye, deserts look barren, especially during dry periods. However, because of their evolution in relative geographic isolation, most deserts of the world are rich in rare and endemic species, and are hence highly vulnerable to biological extinction and environmental degradation. In spite of their remarkable convergence in adaptation, deserts are different in their origin and their evolutionary history.

Their incredible variation of the world's deserts in rainfall patterns, continentality, temperature regime, and evolutionary history have all contributed not only to their biological uniqueness, but also to their wondrous wealth of life-forms and adaptations, from some of the shortest-lived ephemeral plants, to some of the longest-lived giant cacti; from seed-eating rodents that do not need water to survive and depend on their burrows to regulate their metabolism almost as if the burrow was an extended part of their body, to amazing pollinators like nectar-feeding bats that migrate thousands of miles following the flowering seasons (Davis 1998). This adaptive diversity - what Darwin, strongly influenced by deserts himself, called "forms most beautiful and most wonderful" - is what makes deserts unique.

In the hot deserts we may find giant cacti and trees with mammoth fleshy stems coexisting with some of the toughest hardwoods; ground-creeping succulents side by side with fogharvesting rosettes, incredibly fast-growing annuals together with the hardiest drought-resistant perennials; shrubs of enticing odours with some of the nastiest, spiniest plants ever. Very few parts of the earth contain a richer collection of natural adaptations.

The fragmented evolutionary history of the deserts of the world has been the driving force of their biological rarity, of adaptation to local conditions, and of specialization to isolated environments. After millions of years in isolation, the forces of evolution and fragmentation have yielded unique life-forms in each desert, strangely-shaped desert plants and extraordinary animals. The world's deserts are biological and cultural islands, lands of fantasy and adventure, habitats of surprising, often bizarre growth-forms, and territories of immense natural beauty.