Lawns have become part of our world, and surround every house in our suburbs. Even apartment buildings in the city may have a few square feet of lawn in front. Some think our love of lawns might be traceable to our descent from early humans, who learned to walk upright in the savannah plains of Africa. Standing upright was a convenient means of seeing over the grasses, and spotting approaching predators. It also allowed for tracking prey. Having a lawn makes great sense if you are expecting raids from the neighbors – as early man had to expect. But today, when neighborhood raiders are soon locked up, grassy yards seem to be vestigial, like an appendix: serving no purpose, providing no benefit. Of course,…