Likewise, life is a constant struggle between organisms and viruses, each one evolving to counteract the other, so, in effect, they are running to stand still.
Hedgerows also demonstrate this concept. Neat suburban hedges are made of identical plants propagated by cuttings from a garden center. So, a suburban hedge is a row of single species clones. But a hedge in the countryside has a wider variety of species and has survived longer, as proven by Hooper’s Rule: count the number of species in a 30-meter stretch and multiply by 100 to get an estimate of its age. The photo shows the hedge outside the village church in Chiddingstone, Kent, UK. There are five different species in a 30-meter stretch: hawthorn, field maple, yew, oak, and blackthorn. This would imply that the hedge is 500 years old, which tallies well with the local historical records.