Final answer:
John Maynard Keynes is the scholar who believed that the economy is constantly changing and developed the school of thought known as Keynesian economics. Keynesian economics emphasizes government intervention to stabilize the economy during economic downturns.
Step-by-step explanation:
The scholar who believed that the economy is constantly changing and evolutionary economics is a school of thought developed from those ideas is John Maynard Keynes. Keynes was a 20th-century British economist who developed Keynesian economics, which emphasizes that government intervention is necessary to stabilize the economy during economic downturns and smooth out market cycles. His ideas were put to the test during the Great Depression and have had a significant impact on economic thinking.