Wallace’s Realms: the Archipelago of Continents

Abstract

It is one of the first themes of this book that if we are to understand what is likely to happen to ecological balance in the world, we need to examine the past as well as the future. If during the last 100 million years the flora and fauna of the world had been able to develop in such a way that every organism had a good chance of spreading to all parts of the globe that its characteristics could tolerate, so that there was only one species for each kind of ecological situation, the potentialities of future change under the impact of man’s activities would be different. They would be far less, though still considerable, because man has altered habitats as well as moving species around like chessmen. In the kind of world described, where there were no barriers to spread, we should have mostly pan-tropical and pan-temperate species (we do mostly have panarctic ones as it is), bipolar forms, continental species reaching every island, fresh-water species moving freely to all isolated waters, marine animals also girdling the world and reaching northern and southern hemispheres. The rabbit might already have been in Australia, the coypu in East Anglia, the mitten crab in the Elbe, and the giant snail in the Mariana Islands. That is to say, they would if they had evolved successfully in face of rival lines.