ABSTRACT
Alien species, we are told with good reason, are the biggest threat to biodiversity on the planet after habitat loss and climate change. Earlier ages would not have known what we are talking about; we think very differently about nature as the centuries pass. The modern preference for biodiversity over bio-uniformity, like the privileging of rare or unusual taxa over common ones, is a cultural construct of recent times. It has little to do with science per se, though from the 18th century and the time of Linnaeus, collecting and examining the differences between species was a critical part of science. The dominant attitude towards species even today, moreover, does not consider that biodiversity should override bio-utility. Animals, plants and insects either have a value to people, or they do not, and those that do are held to be more worthwhile than those that do not. Scientists and conservationists who want to be taken seriously by governments must still disguise biodiversity as bio-utility and play up the value of, for instance, tropical habitats as a gene pool of unknown treasures which might come in handy to people one day, or stress that reintroduction of the European beaver into Scotland will benefit the tourist trade. The most important taxa, in this traditional and enduring world view, have clear economic value (e.g. salmon, cows, cabbages, bees), although some have only decorative or amusement value (e.g. goldfinches or monkeys in a cage).
