Cicadas vs. Darwin

The Cicada Challenge to Darwinian Evolution

Evolution News & Views They'll create quite a commotion next month, but they're mostly a harmless nuisance or a wonder of nature, depending on your outlook. They're the northeast brood of Magicicada, the so-called 17-year locusts. Smithsonian Magazine tells about them:

Residents in the Northeast U.S. waiting for warm temperatures may get a surprise along with their May flowers: When the soil reaches 64 degrees Fahrenheit, they'll also get a visit from billions and billions of cicadas.

This latest brood is composed of several species including Magicicada septendecim, M. cassini and M. septendecula, and is expected to take over West Virginia, Virginia, Maryland, New York, Ohio, Pennsylvania and a tiny spot on Long Island. 

In an event that only happens once every 17 years for this brood, the creatures will soon dig their way out of the soil, shed their exoskeletons and emerge en masse. The swarm will spend two to six weeks mating and singing their grating, sing-song call before dying and blanketing the ground with their crispy brown corpses. [Emphasis added.]

Here's a natural wonder worth thinking about. There are 14 identified species of periodic cicadas in the United States. A southern brood on a 13-year cycle came up in 2011 (see Live Science). Both 13 and 17 are prime numbers. Evolutionists have long touted their adaptive story about why this is. Smithsonian says:

Researchers have theorized that the insects spend such a lengthy time underground in an effort to outlive parasites that may harm them, Eoin O'Carroll wrote for The Christian Science Monitor in 2013. Other researchers speculate that the 13 and 17-year life cycles, both prime numbers, are an evolutionary adaptation and a mathematical trick that keeps cicadas from emerging during peak population periods for their predators. 

"A cicada that emerges every 17 years and has a predator with a five-year life cycle will only face a peak predator population once every 85 years," writes Patrick di Justo in The New Yorker, "giving them an enormous advantage over less well-adapted cicadas."

Live Science adds that the sheer numbers provide an advantage, too: no predator could possibly devour so many of them. But it's the prime number quirk that attracts evolutionists' attention:

The key factor is that both numbers are prime; they can't be divided evenly by any smaller numbers (except one). It is no mere coincidence that cicadas have evolved indivisible life cycles. As explained by the entomologist Stephen Jay Gould, prime cycles have a major evolutionary advantage over cycles that are multiples of smaller numbers of years, and for a simple reason: They make cicadas more elusive.

"Many potential predators have 2-5 year life cycles. Such cycles are not set by the availability of cicadas (for they peak too often in years of non-emergence), but cicadas might be eagerly harvested when the cycles coincide," Gould wrote in his best-seller "Ever Since Darwin" (Norton 1977). "Consider a predator with a life-cycle of five years: if cicadas emerged every 15 years, each bloom would be hit by the predator. By cycling at a large prime number, cicadas minimize the number of coincidences (every 5×17, or 85 years, in this case)."

In summary: "Thirteen- and 17-year cycles cannot be tracked by any smaller number."

We could leave it at that, and agree that evolutionary theory is wonderful the way it explains things. Yet think again. Don't the two explanations work against each other? If predation is a problem, why the billions at once? With so many, they could come up every year and do just fine. Why wait? And if selection pressure helps the cicadas, can't it help the predators the same way? Where are the 17-year predators? Besides, you wonder what the predators are eating outside the two-to-six week window the cicadas are active. 

Like the peppered moths and the Galápagos finches, the evolutionary story of cicadas offers a certain intuitive satisfaction, until you start asking questions. Worse, it distracts from the really interesting aspects that really need explaining. To wit:

• The remarkable timekeeping ability of the nymphs to silently count 13 or 17 years.
• The trigger that makes all of them emerge simultaneously. The temperature gauge needs to coordinate with the clock, otherwise they would emerge every year.
• The "incomplete metamorphosis" they undergo (i.e., unlike butterflies shown in the film Metamorphosis, cicadas do not have a chrysalis or pupa stage; the nymphs grow directly into adulthood). Even so, the larvae have to transition from one body plan into another that has completely new structures, like wings, eyes, antennae and reproductive organs. 

Other amazing facts about cicadas tend to get drowned out in the rush to explain the evolution of prime numbers. For instance, cicadas have amazing wing surfaces that burst bacteria. Three years ago, Nature News described nanoscopic pillars on the wings that pop bacterial membranes, shredding them to pieces (see videos in the article). It was such a clever method for disinfection, scientists envisioned creating similar materials that "could one day be applied to public surfaces that commonly harbour disease, such as bus railings." 

PhysOrg mentioned other advantages: "In marked contrast to the biochemical mechanisms of antibiotics, which are subject to acquired resistance, physical mechanisms are non-specific, and cannot be reversed or altered, tackling bacterial cells as a whole." This kind of "anti-microbial physics" could be designed to simultaneously nourish human cells, supporting "a variety of biomedical implants, anti-fouling surfaces or biosensors."

Obviously, any creature capable of powered flight deserves our admiration for impeccable design. Add to that all the other systems required for complex animal life: (e.g., reproductive, digestive, respiratory) and traits characteristic of insects (e.g., articulated legs, compound eyes, antennae) and we see a whole package of systems that challenge blind processes of natural selection.