Recognizing the Complexity of Biological Cascades

This image shows water cascading over a waterfall. Just as the water that falls is hard to reverse, actions in biology can trigger reactions that are difficult to change.

When water cascades over a fall, is difficult to predict where each drop will land. Some might evaporate into the air. Some might splash over to the shore. Some will fall in the river. Unpredictability is a feature of all natural cascades, including those that occur in biology.


What do pollution, obesity, livestock production, and the COVID-19 pandemic have in common?  According to the cornerstones model of healthy food systems, each of these factors plays into the security and sustainability of the food webs we rely on to maintain food security, health, and prosperity.  Other factors are involved of course, but for simplicity in today’s discussion, I will simply use these four factors and illustrate the potential for surprising ways that each factor may influence our food systems.  The most unexpected outcomes often result from biological cascades.

Cascades are series of reactions that are triggered by a single effect.   Cascades can affect natural systems in complex manners that can be nearly impossible to anticipate, regulate, or reverse.

Absurd children’s song illustrates unpredictable outcomes of biological cascades

The ludicrous ways that biological systems can create cascades of interactions always reminds me of the once-popular (and undoubtedly silly) children’s song about the old woman who swallowed a fly.  In an attempt to rid herself of the fly, she swallows a spider to catch the fly.  Because the spider was wiggling and jiggling inside her, she swallows a bird to catch the spider… The song continues, describing an increasingly nonsensical cascade of larger animals that the woman swallows to capture the first, finally ending when she swallows a horse.  You see, she dies – of course.  The absurdity of these lyrics appeals to the imaginative humor of preschool children.  As preschoolers, we hear the song and giggle— a few of kids snicker, and one or two may mourn for the animals that got eaten.  But regardless of the reaction, the song and its imagery stick with us long after we’ve outgrown children’s songs.

This memorable albeit bizarre image of the old woman who swallowed the fly is useful for illustrating the unpredictable outcomes of biological cascades.  Afterall, while I’m not fond of swallowing flys, and I hope to never swallow one, I would not expect swallowing a fly to kill me.  In the past, I would not have expected to get fat because there are too many greenhouse gasses in the atmosphere.

Biological cascades make many outcomes unpredictable

Because biological cascades result in many possible outcomes from a single event, cause-and-effect are difficult to forecast.

For example, we all know it’s not healthy to carry excess weight.  How many of you have been told at one time or another to just eat less to lose weight?  It sounds simple enough, right? Consume fewer calories than you burn.

Yet according to the US Centers for Disease Control, 42.4% of adults in the US are obese [1].  This statistic alone indicates that for at least 42% of us, losing weight is harder than it looks!

The fact is, our health (which makes up one cornerstone of our food system) is influenced not only by direct factors like body weight, but also by indirect outcomes of biological cascades.  For example when an obese person chooses to eat less, his/her body may respond by slowing down his/her metabolic rate.  Hormone and neurotransmitter levels may change. In addition to hunger pangs, the person may experience mood swings and attention deficits that impact their performance. Cravings may occur, and the dieter’s best effort to avoid food may trigger feelings of depression, fatigue, diminished energy, and more.  Combine these feelings with the need to function effectively at home and on the job, and even the strongest resolve may falter.

Pollution creates complex biological cascades.

    Air pollution ranks high among the most serious kinds of environmental destruction simply because air, for all practical purposes, is impossible to contain.  Problems initiated in one country, or even in one factory quickly spread worldwide because air is everywhere, and air is constantly in motion.  But can we connect air pollution to food webs, livestock production, the obesity crisis, and COVID-19?

CO2 as air pollution.  Connections between highly toxic pollutants and our food quality are relatively obvious and direct, because just as all living things require food to make energy, they also require air and water. But what happens when excess quantities of very mildly toxic substances, like CO2, accumulate in the atmosphere?

CO2 comes from burning fossil fuels, but it also comes from living cells as they metabolize energy, and it is clearly not as toxic as, say, lead or arsenic.  You release CO2a greenhouse gas-every time you exhale.

In fact, when I hear the argument that we should stop raising cattle because they emit greenhouse gasses, I worry that this line of reasoning is more toxic than the CO2 or methane it aims to reduce.  Afterall, every living creature on the planet releases greenhouse gasses.  Do we really believe that removing life from earth is the best way to fix the climate?

See, the real problem when we talk about CO2, or even methane, as greenhouse gas is not that they are present in the atmosphere.  Rather, as with all toxins, they become a concern when they are  present in excess.

At high concentrations, greenhouse gasses trap too much heat in the atmosphere.  Excess trapped heat changes our precipitation patterns, alters the runoff patterns that we rely on for water, and even changes the dates at which our soils reach planting temperatures.  Storms and droughts become more extreme. Damage from larger events becomes more difficult to repair.

Changing temperatures can also contribute to phenological mismatches between the maturity dates of pest species and the maturity dates of the insects like ladybugs that control pests.  Losses in the natural synchrony between pests and predators can reduce crop yields by increasing pest damage.  It can also lead farmers to apply more pesticides, leaving more traces of toxic residue on the fruits and vegetables you serve for dinner.

Now, most people won’t attribute increased pesticide use to excess carbon emission and global warming. Since a multitude of other factors could also cause a farmer to use more pesticide, cause and effect just becomes too difficult to prove.  However discussing the pathways by which air pollution could contribute to more pesticide use should help to illustrate just how interconnected these food webs really are, and why it is so important to think carefully about how much  pollution we are really willing to tolerate.

CO2 as a plant growth stimulant.  But if predicting the outcomes of excess greenhouse gasses in the atmosphere isn’t complicated enough already, consider the fact that excess CO2 concentrations can also have beneficial effects on plant growth.   Because plants use CO2 for photosynthesis, increased CO2 levels can increase the rates at which crops mature.   As the plants grow, they consume atmospheric CO2 , creating what might seem like a win-win situation.  More food, less pollution.  On the surface, this sounds like a big plus.   Why not plant some corn so we can stop global warming?

But like so many factors that interact with food webs, what happens on the ground is more complex, thanks to good old biological cascades that influence how plants grow.  One of these is the cascade of reactions involved in photosynthesis itself.   That’s right, photosynthesis-that set of chemical reactions that helps plants grow and pulls COout of the atmosphere.

See, there are different kinds of plants, and different kinds of photosynthesis.  C3 plants like the noxious weed, Canadian thistle (Cirsium arvense) benefit more from excess CO2 than C4 plants like corn.

So while growing plants to sequester carbon is still a great idea, you need to remember that C3 weeds like Canadian thistle (Cirsium arvense), are going to wage a stronger war against your corn than the same weeds would have fought in a world with less CO2. 

When there are more weeds, farmers may use more pesticides (herbicides in particular) to eliminate them.   Did you know that one of the most widely used herbicide ingredients, atrazine, is classified as an obesogen?  That’s right,  atrazine residues in your corn flakes can make you fat.

 Livestock production in a changing climate

When we look at how higher temperatures caused by greenhouse gasses that pollute the atmosphere might influence livestock production the answers are again complex.   For example, a livestock operation in Canada might see their cattle thrive with warmer winters and earlier springs.  They might lose fewer calves.  Of course, they might also see more variable weather with more violent storms [3].

Meanwhile, an operation in Mexico might see increases, not only in flies, ticks, mosquitos, and the diseases these vectors carry, but also an increase in droughts or hurricanes that impact their grazing lands [3]. To cope,  ranchers may turn to – here we go again – pesticides, and these pesticides will leave more residues in our meat and dairy products.

The good news is that ranchers who understand how to use biological cascades to their benefit can exchange pesticide use for a suite of holistic practices that effectivly at reduce pests.   Now I don’t want to detour too much into the discussion of holistic management here, but two ideas that I already see livestock producers implementing include:

1-Integration of wildlife with grazing operations.  Creating wildlife habitat attracts small animals like songbirds that eat flies and other pests.  Habitat for wildlife can also include game habitat.  Revenues generated by hunting permits can cover supplement ranch income, and diversified livestock and wildlife are less susceptible to pests and disease than, say, a monoculture of cattle [4].

2-Sale of “grass fed” stock raised with regenerative grazing practices.  Rotational grazing is a regenerative practice.  Properly implemented, it can build soil health while producing more nutritionally sound livestock that fetch a higher market price. Many consumers today prefer the nutrient density and omega fatty acid balance of grass-fed beef.

And while we are on the subject of consumer food preferences, let’s move back to the subject of obesity.

Obesity as an environmental illness

Once considered a sign of insufficient will power, most health professionals today recognize obesity as a disease that results from toxic cascades.  Often, this illness can be initiated by the use of pharmaceuticals like antibiotics that alter the human microbiome.  It can also be triggered (or confounded) by exposure to agrochemicals and air pollution.  Once obese, victims are prone to many other kinds of chronic disease.

Globally, obesity is now recognized as a disease.  In the US, the Centers for Disease control classify obesity as an epidemic.   It is also widely recognized as a risk factor for heart disease, cancer, and diabetes.

In recent years, obesity has also been described as an environmental illness, and a symptom of socioeconomic disparity.

Scientists are also recognizing pollution in our environment and nutrient deficiencies in our food as drivers of the obesity epidemic.   Modern studies are associating indoor air pollutants such as nitrogen dioxide with obesity [5] [6].   Nitrogen dioxide is emitted by gas, wood, or fossil-fuel burning appliances and also by second-hand-smoke from cigarettes.

Scientists are also finding evidence that the pesticides associated with crop and livestock production leave residues in our food that contribute to obesity [7] [8].  Even pesticides that are no longer used in the US, like DDT, which was outlawed in the US in the 1970’s, still permeate our food webs.

Numerous chemicals that pollute modern ecosystems are now described as obesogens [7] .  Obesogens act by disrupting lipid metabolism within our cells.

Connections between food webs and COVID-19?

We’ve shown how pollution impacts agriculture, how agriculture impacts pollution, and how both factors can contribute to obesity or related health problems. But you may still be asking what does any of this have to do with the COVID-19 pandemic? To connect the dots for you let me present a biological cascade that begins with industrial growth.

Air pollution that includes greenhouse gasses not only influences our agricultural production through changing weather patterns, changing phenologies, and changing patterns of pests and disease, but they also lead to increased use of agrochemicals-including obesogens, carcinogens, teratogens (chemicals that cause birth defects), or other ecotoxins.  These toxins don’t just affect humans.  They also lead to changes in the health and habitat of wildlife like bats.  And as farms and natural wildlife habitats are compromised by climate change and the presence of ecotoxins, so is the nutrient cycling that contributes to the quality of our food.  A carrot farmed from a polluted or otherwise disturbed environment simply will not contain the same level of nutrients as a carrot grown on healthy soil.  This is true even if the two carrots look the same.

Reduced food quality contributes to human health problems by weakening our immune system.   Since our food quality is  diminished-not only by the agricultural factors discussed above-but also by the unwieldy processing and distribution systems that stand between the farm and the dinner table; people, livestock, and wildlife around the world have become vulnerable to disease.   In the US, 6 in 10 adults are chronically ill [9].  This means that in the nation with the most expensive health care system, most adults are sick all the time.

An ecosystem dominated by ecotoxins, greenhouse gasses, and chronic disease is a system that is ripe for viral invasion.   COVID-19 is simply one more link in the chain of events that are cascading through our damaged food webs.   We may slow the progression of COVID-19 with better vaccines and medications, but until we restore the food webs that create an environment where pandemics can thrive, we will remain vulnerable.

This is why some of the most valuable insights we can bring to the table must include insights that help us look beyond the immediate prevention and treatment of COVID-19 and consider ways to prevent the decline of human and environmental health.  Some of the fastest, easiest ways to accomplish this involve utilizing biological cascades in ways that promote multiple benefits to human, environmental, and even economic health.

The Good News: Biological cascades Can Drive Restoration

The good news in all this is that just as our destructive efforts like pollution and bad diets cascade through the ecosystem damaging unexpected targets, restorative efforts can effectively catalyze cascades of restoration.  When you commit to restoring your health in an ecologically sound fashion or building healthy environments around you, you will feel better and you will grow better food.  In addition, you will trigger cascades of benefits that may range from having more time with your loved ones, or more songbirds in your garden, to even having more money in your pocket.  Afterall, it is much cheaper it is to eat whole foods grown without pesticides, exercise, reduce stress in your life, and replace your household chemicals with eco-friendly options than it is to pay for open-heart surgery, stroke rehab.

Essential oils offer powerful alternatives for household cleaners

One simple action that can drive a cascade of multiple benefits involves reducing your use of synthetic chemicals in your home. Let’s face it, we all want a clean home.  But standard household cleaners can have mildly toxic effects that irritate skin and breathing passages. When you replace conventional household cleaners with formulas that contain essential oils and other natural products, you can ignite a cascade of benefits that extend beyond cleaning.

You can replace household all-purpose cleaners with a spray bottle containing 50% white vinegar (the kind you might use for cooking) and 50% water.  Adding 20 drops per liter of essential oils known for antibacterial properties like eucalyptus, orange, or lemon  will give you a great blend for cleaning refrigerators and countertops (careful with granite-the vinegar may be too acidic).  However, the oils you use for cleaning can also bring a suite of physiological and pest-fighting benefits.

Each of these oils contains hundreds of natural volatile compounds that serve multiple purposes.  For example, lemon oil contains limonene and citral (in addition to many other compounds).  A 2007 study in Stress and Health demonstrated that limonene and citral relieve both physical and psychological stress.  These same compounds are also found in orange oil.

Batish et. al (2008) reported that eucalyptus oil fights bacteria, fungi, insects, and mites, while Katz et. al. reported in the Journal of American Dermatology that lemon eucalyptus oil is increasingly popular as an insect repellant due to its efficacy and low toxicity. In 2009, Bioresource Technology concluded that that eucalyptus oils and others have potential as insect repellents.

If mixing your own cleaners doesn’t fit your schedule, you can look for products by Nature Direct or similar companies to provide effective cleaning naturally.

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[1] Centers for Disease Control and Prevention, “Prevalence of Obesity and Severe Obesity Among Adults: United States, 2017–2018-Data Briefs – Number 360 – February 2020,” February 2020. [Online]. Available: [Accessed 25 May 2021].eat
[2] S. Ornes, “Core Concept: How does climate change influence extreme weather? Impact attribution research seeks answers,” Proceedings of the National Academy of Sciences of the United States of America, pp. 8232-8235, 2018.
[3] C. Godde, D. Mason-D’Croz, D. Mayberry, P. Thornton and M. Herrero, “Impacts of climate change on the livestock food supply chain; a review of the evidence,” Global Food Security, p. 100488, 2021.
[4] A. Radke, “The beautiful relationship between cattle & wildlife,” 31 May 2019. [Online]. Available:
[5] A. Ruopeng, J. Mengmeng, H. Yan and C. Guan, “Impact of ambient air pollution on obesity: a systematic review,” Epidemiology and Population Health, p. 1112–1126 , 2018.
[6] C. L. Davis, M. Tingen, J. Jia, F. Shrman, C. Williams, K. Bhavsar, N. Wood, J. Kobleur and J. Waller, “Passive smoke exposure and its effects on cognition, sleep, and health outcomes in overweight and obese children.,” Childhood Obesity, pp. 119-125, 2016.
[7] W. Holtcamp, “Obesogens: an environmental link to obesity,” Environmental Health Perspectives, 2012.
[8] M. K. N. C. P. &. C. B. Merrill, “Association between maternal exposure to the pesticide dichlorodiphenyltrichloroethane (DDT) and risk of obesity in middle age,” International Journal of Obesity, vol. 44, pp. 1-10, 2020.
[9] Centers for Disease Control and Prevention, “CDC,” [Online]. Available: [Accessed 18 5 2021].
[10] “Dust bowl,” 5 8 2020. [Online]. Available: [Accessed 17 5 2021].
[11] “Controlling the global obesity epidemic,” n.d.. [Online]. Available: [Accessed 5 17 2021].


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