P infestans is only one of the many plant pathogens that changed the world. Back in the 19th century, Britain’s drink of choice was coffee, and its colony Ceylon (now Sri Lanka) was the world’s greatest coffee producer. That all changed with the arrival of the East African coffee rust fungus, which found a ready-made feast among Ceylon’s dense, back-to-back plantations. The British government sent Harry Marshall Ward, another pioneering plant pathologist, to deal with the problem. He issued a now-familiar warning: planting crops in vast monocultures is an invitation for virulent epidemics. No one listened. Within two decades, the fungus had slashed Ceylon’s coffee production by 95 per cent, forcing the industry to relocate to Indonesia and the Americas. The crippled plantations were replaced by tea bushes, and tea displaced coffee as the quintessential British beverage.
If Marshall were around today, he would probably be disappointed that his advice still goes unheeded. We still tie the fortunes of entire regions to single staples. Around 90 per cent of the world’s calories come from just 15 types of crops, most of which are highly inbred monocultures planted over sprawling acreage. These monocultures skew the evolutionary arms race in favour of pathogens, and create the conditions wherein old threats can easily evolve into new virulent strains.
[It appears that monocultures are “unnatural” in the most significant sense… they run counter to evolution. Diversity seems to win every time.]