In order to force people to solve problems, God created material life with molecules which are extremely hard and stable. It takes a lot of work to get complex results with molecules. God forces people to solve problems by starting with simple conditions which have to be increased in complexity. The process of going from simple to complex is evolution. All types of evolution occur in human attempts to create more complex conditions of life.
Reason is evolution of reality.
To understand how and why evolution occurs, consider the reasoning process. Reason is creating relationships between realities. Whenever relationships are made, consistent relationships support each other, and inconsistent relationships contradict each other. So the former increase, and the later decrease. The increase in consistent relationships is the evolution of reality.