The main focus of 'A Brief History of Intelligence' is to explore the evolution of the brain and its implications for the future of artificial intelligence. Max Bennett examines how our cognitive abilities have developed over millions of years and how this understanding can be applied to create intelligent machines.

Max Bennett explains that intelligence is fundamentally about predicting the future. He introduces the concept of 'predictive coding,' where our brains actively construct predictions based on past experiences and sensory data. This approach helps in developing AI systems that are proactive and capable of learning from their environment.

The book provides several insights for AI development, including the importance of understanding the brain's predictive mechanisms, the role of constraints in shaping intelligence, and the historical evolution of cognitive abilities. These insights suggest that AI systems should be designed to operate within specific constraints and should be built with increasing levels of complexity and autonomy, inspired by the evolution of natural intelligence.