Question

Analyze what the consequence might be if the lining of the small intestine were completely smooth instead of having villi.

Answer 1

This would reduce the capacity of the ileum to absorb nutrients from the food we eat. The efficiency of absorption would be much lower that is currently. This, therefore, would cause animals to be much smaller than they currently are because they would need to eat a lot of food  to absorb the same amount of nutrients that would sustain their large bodies. Being big would be a disadvantage in natural selection.

Villi increase the surface area of absorption hence considerably increase the efficiency of nutrient absorption from the food we eat.