Top of the list is the mosquito, which WHO reports “causes millions of deaths every year” by spreading the malaria parasite (405,000 deaths in 2018) and many other diseases. It turns out the most dangerous animals to humans are insect pests.
In some parts of the world, these have and still can cause famines. Think of locusts (famously called plagues), rats, potato blight and many others, against which we routinely deploy pesticides. There is, of course, a wider meaning of pestilence – animals, plants and micro-organisms that harm us indirectly by attacking our crops or herds.
It may be useful to distinguish between what the Old and New Testaments call “plague,” by which I mean the infections we pass on to each other (even though many of them, such as COVID-19, originate in other animals) and pathogens and parasites that we don’t spread directly to each other but are spread to us by other animals, (which might be considered “pestilence” – diseases spread by pests). Horsemen 2 and 3: Pathogens and parasites Mosquitoes cause ‘millions of deaths er year,’ according to the WHO. So what happened to Elton’s four ecological horsemen? Why are we not controlled? Is there a fifth horseman that will cause our populations to crash at some point, as lemmings do? The human population has more than tripled in the past 70 years, from 2.5 billion in 1950 to 7.8 billion today. Nonetheless, we are suffering a population explosion, just as lemmings and other species do from time to time. Coli bacterium were to double every 20 minutes – the rate found in optimum conditions – it would take only two days (that is, 2 144 ) for the weight of E.Coli to exceed the weight of the Earth – yes, just two days! Clearly, and happily for us, that does not happen, nor does it happen for all the other species – including us. In one astonishing passage, Carroll tells us that if a single E. In thinking about how animal numbers are regulated to avoid over-population, “Elton suggested that, in general, increases in numbers were held in check by predators, pathogens, parasites and food supply.”Įlton’s four regulators are clearly very effective. In his 2016 book The Serengeti Rules, Sean Carroll discusses the work of pioneering ecologist Charles Elton in the 1920s. The Book of Revelations in the New Testament lists the Four Horsemen of the Apocalypse as conquest, war, famine and death, while in the Old Testament’s Book of Ezekiel they are sword, famine, wild beasts and pestilence or plague.īut whatever we call them, they are remarkably close to what we might call the four horsemen of ecology that regulate population size in nature.
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