My daughter Fran has a mad cockapoo called Amber and she is having a problem with dog fleas. Well that’s Amber not Fran. The treatment Fran’s been using for three or four years doesn’t appear to be working anymore. This set me thinking, because the dog fleas have almost certainly built up a resistance to the over-the-counter chemical that’s been routinely applied to Amber’s neck.
Similar things happen in horticulture and agriculture, because living things evolve through natural selection, as Charles Darwin realised. Chemicals that used to be effective get less effective
