Evolution doesn't care if you're grumpy, it only "cares" if you succeeded in reproducing.
Tissues that aren't stressed naturally atrophy to conserve energy, which saves on food, which is adaptive in evolutionary terms. This has the natural implication that those tissues will reach an equilibrium where they are barely stronger than your most basic needs.
If the only stress you experience is getting off the couch to get some food, just doing that will be a little difficult. Larger, sudden stresses will cause injuries because your tissues won't be adapted to handle them.
Exercise ensures that we mentally and physically exceed our normal stress thresholds, so the remaining stresses of life is less stressful by comparison.
Tissues that aren't stressed naturally atrophy to conserve energy, which saves on food, which is adaptive in evolutionary terms. This has the natural implication that those tissues will reach an equilibrium where they are barely stronger than your most basic needs.
If the only stress you experience is getting off the couch to get some food, just doing that will be a little difficult. Larger, sudden stresses will cause injuries because your tissues won't be adapted to handle them.
Exercise ensures that we mentally and physically exceed our normal stress thresholds, so the remaining stresses of life is less stressful by comparison.