2. The Environmental Complexity Thesis 3. On Complexity 4. The ECT as a Component in Many Evolutionary Scenarios

One problem faced in discussions of the evolution of intelligence is the need to get a precise fix on what is to be explained. Terms like "intelligence," "cognition " and "mind " do not have simple and agreed-upon meanings, and the differences between conceptions of intelligence have consequences for evolutionary explanation. I hope the papers in this volume will enable us to make progress on this problem. The present contribution is mostly focused on these basic and foundational issues, although the last section of the paper will look at some specific models and programs of empirical work. Some people have a very demanding picture of what is required for intelligence, thinking that it always involves such sophisticated skills as planning, language-use, and perhaps even some sort of consciousness. To these people, intelligence is to be contrasted with instinct. Perhaps in this rich sense of the term, intelligence is even to be contrasted with the simpler types of learning, such as learning through reinforcement (operant conditioning). From this first point of view, the problem of explaining the evolution o