Why grow grass?
You may have asked yourself this question at one time or another. It's like a child's question such as: why is the sky blue? We grow grass for one reason: we can mow it and it survives, even thrives. Any other plant, even most other grasses would die after being mowed with any regularity. There are over 10,000 species of grass, yet only about 50 of those are suitable for use in a lawn.
Why can lawn grasses be regularly mown without dying, and still maintain a healthy and attractive appearance? Unlike most plants, lawn grasses grow from the base of the plant, well below the sharpened rotating lawn mower blade. Other plants grow at the tips that don't respond well to being repeatedly cut.
The process of mowing is actually reducing the plants leaves and cutting down its ability to use photosynthesis. Photosynthesis is the process that takes carbon dioxide from the air and turns it into carbohydrates that the plant uses for food. When the plant looses some of this ability, it overcompensates by producing additional leaves. The result: an even thicker, denser lawn.
So, the answer to the question "why grow grass?" is: because it's the one plant that adapts best for the environment we've created for ourselves.
Why is grass able to be cut, and keeps on growing?
The answer is that long before there were lawn mowers, there were herds of wild animals that grazed the prairies of America and Africa. These animals grazed on grass, nibbling at the nutrient rich plants all the way down as close to the ground as they could get. The plants that survived this intense grazing developed a root crown located just out of reach of the grazing animal's teeth. This intense cutting and re-growing developed the ability of the grass to regenerate itself, even after being chewed down almost to the root crown.
So the prairie grasses survived and thrived, and grew into a thick turf that held the soil in place even during long periods of draught. It wasn't until the advent of expansive farming that uprooted this thick turf that we had expansive soil erosion as seen in the midwest during the Great Dust Bowl of the 1930s.
As homeowners looked for a way of covering the area around their homes, to cut down on dirt and mud being continually tracked into the house, it became clear that the one plant ideal for this purpose was the prairie grasses. In time the prairie grasses were modified through selected pollination into the variety of turfgrasses we have today.