When you get rid of variety entirely, you risk exposing a crop to something it can neither cope with nor evolve to defend itself against.
We have evolved to defend ourselves from a guy with a knife or an animal with big teeth, but we are not wired to make decisions about barely perceptible threats that gradually accelerate over time.
Men have evolved "to defend at the sperm level against their mates' having another lover in the same fertile period -- not many others, but one or two," Alison Jolly, a Princeton primatologist, wrote in her 1999 book "Lucy's Legacy" (Harvard University Press).
If a customer was admiring an Oreocereus celsianus (commonly known as the old man of the mountain), she would learn before leaving the store that it comes from the high Andes, and that its fluffy mop of white hair evolved to defend it from the sun and the snow.
Scientists have long argued that this mechanism originally evolved to defend humans and animals against parasites like certain worms.
It is based on a molecular system that single-celled creatures evolved to defend against invading viruses.
Natural poisons are often enzyme inhibitors that have evolved to defend a plant or animal against predators.
Plants have evolved to defend themselves against biotic stressors such as insects and pathogens.
The immune system has evolved to defend the organism against a variety of pathogens and applies threshold mechanisms for regulation.
It may have initially evolved to defend the genome against invading transposable elements and other genomic parasites [ 7].
Cell death is essential for normal animal development and to destroy pre-cancerous and auto-immune cells, but it has been postulated that apoptosis originally evolved to defend primitive multicellular organisms against intracellular pathogens such as viruses.
