The human brain is now at risk from itself. Like a terminus, it is an end point of our environmental mistakes but it is also a starting-point both for those mistakes and for correcting them. Millions of people are suffering a decline in intelligence due to pollution, the absence of vital environmental micro-nutrients and a degraded psycho-social environment. The self-threat created by the human brain is new in the history of human evolution, and our brain is the only thing in the ecosystem at risk from its own behaviour. The author identifies a trait in human behaviour - pertinacity - which helps to explain why. Yet this raises deeper questions. Could ecointelligence recognize and curtail the environmentally destructive behaviour of human intelligence? Could adverse environmental change eventually lead to regressive brain evolution? And what does the brain's self-threat mean in relation to human consciousness?