Our ancestors didn't have to exercise per se because they rarely sat down. They moved all day long, and research shows THIS is absolutely key for health. In fact, studies show that engaging in consistent exercise does not counteract the adverse cardiovascular and metabolic effects of prolonged sitting.
So non-exercise movement is now recognized as being a foundational piece for optimal health — even more so than exercising for an hour a few times a week. Ideally, you'd do them both, but if you're currently sedentary, start by sitting less.