Early Modern Times – cicadian rhythms

Early Modern Times - cicadian rhythms

Dear readers,

This spring, billions of cicadas belonging to ‘Brood X’ will emerge in the Eastern United States. Brood X cicadas emerge only once every 17 years. Little known is that one of the first persons to document this 17-year cycle was the 18th-century African-American polymath Benjamin Banneker (1731-1806). Let us consider who Banneker was and how he came to identify this cicadian rhythm.

A 2014 article by Janet Barber and Asamoah Nkwanta discloses how Banneker’s handwritten observations of the cicada were almost lost due to a fire in his cabin following his burial. Fortunately, these were among the documents kept by his friends before the cabin was set afire. Banneker was a native of Maryland, working as a farmer but also an autodidact in mathematics, astronomy, and other sciences. Barber and Nkwanta speculate that his curiosity about the natural world was influenced by his Dogon ancestry. The Dogons are a West African people (located in Mali) named after the ‘dog star’, Sirius, and distinguished by ‘their philosophy of theology and cosmology which is supported by a sophisticated numerical system’. Banneker achieved a measure of fame for his inventions, mathematical puzzles, land surveying of Washington DC, and letter to Thomas Jefferson–US Founding Father and slave owner–arguing against the prevailing view of Blacks as intellectually or morally inferior human beings. Although Jefferson never gave up his slaves despite his ‘enlightened’ principles, he had to concede that given Banneker’s accomplishments in science, the latter was Dogon good.

At the age of 17, Banneker noticed a sudden emergence of what he thought were locusts. He observed these insects dancing and singing their characteristic drone, and then dying 4-6 weeks after mating. Banneker was struck by their reappearance when he was 34, then age 51 and 68. As he put it, ‘So that if I may venture So to express it, their periodical return is Seventeen years, but they, like the Comets, make but a short stay with us–‘. The males thus made a buzz, a sort of invitation to females to go cicadancing. After mating, the female would then lay their eggs in tree branches, which after falling down would deposit the nymphs underground. After 17 years, then, the nymphs would grow to adulthood and emerge above ground to become cicadaddies and -mummies before dying.

As a mathematician, then, Banneker wondered why these cicadas went through a 17-year cycle (other periodic cicadas return in 13 as well as 17 years). This would continue to puzzle naturalists and mathematicians after Banneker. 13 and 17 are prime numbers, i.e., divisible only by 1 and themselves. Among the various explanations of why such cicadas would go through a prime number cycle, two hypotheses seem plausible: prime periodicities thwart cycles of parasites and other predators; prime periodicities avoid hybridization and mixing with other periodic cicada broods. Either way, given the current interest in edible insects as high-protein replacements for meat-eating, one could imagine an entymological steakhouse featuring a signature dish composed of cicada broods freed from their underground sojourn every 13 or 17 years: a slow-roasted prime lib.

Till next time,

Simon Kow

Director, Early Modern Cicadaredevil Studies Program

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