The Systems Thinker - Center for Family Consultation's blog

Searching for Nature’s Rules

Authored by Stephanie Ferrara, M. S. W.

“When we ponder the workings of the human body or of the life of the Serengeti National Park, the details would seem overwhelming, the parts too numerous, and their interactions too complex. The power of a small number of rules…is their ability to reduce complex phenomena to a simpler logic of life.” (10) With this thought, Sean B. Carroll introduces his book, The Serengeti Rules:  The Quest to Discover How Life Works and Why It Matters. 

Carroll demonstrates the power of systems thinking in examining how complex living systems are regulated by the functioning and interaction of their parts.  At a molecular level, rules regulate the numbers and kinds of molecules in the body.  At an ecological level, rules regulate the numbers and kinds of animals and plants in a given area.

Carroll takes the reader through the history of the science of physiology and genetics to show how the systems within our bodies are regulated.  Along with explaining the science, Carroll gives us the human story of what drove these pioneers to question status quo thinking, explore new ideas, and devise creative experiments.  We meet the people who have made the breakthroughs, and suffered the setbacks, that have brought us to the level of knowledge we have now for understanding and treating disease.

Carroll then turns to the science of ecology to show how populations of plants and animals are also regulated through complex interaction.  This part of the book was the basis for the PBS Nature program, also entitled “The Serengeti Rules.”  Extraordinary nature photography takes us into the environments with the scientists: the oceans, the forests, and the Serengeti.  We see scientists doing their experiments and we share the excitement of their discoveries.

Ecologists had assumed that the plants and vegetation at the bottom of the food chain set the limits on populations of the herbivores and predators at the top.  Experiments involving removal of the predator species from tidal pools, rivers, and oceans challenged this assumption.  With the predators gone, scientists saw an explosion in the herbivore and plant populations.  The system was regulated from the top down!  This led to the concept of the “keystone species.”  Just as the stone at the apex of an arch is necessary for the stability of the structure, so also are these apex predators at the top of the food web critical to the diversity of an ecosystem.  Dislodge them, and the community falls apart.  Remove the keystone and a set of tropic cascades is set in motion that changes the number of species, and their populations throughout the ecosystem.

From these stunning discoveries, it was possible to draw important conclusions or “rules.”  One rule is that not all species are equal.  Some exert effects on the stability and diversity of their communities that are disproportionate to their numbers or biomass. Keystones are important because of the magnitude of their influence, not their rung on the food chain.  Another rule is that not all predators are keystones and not all keystones are predators.  Some members of food webs have greater top-down effects that ripple through communities and indirectly affect species at lower tropic levels.

The Serengeti National Park, established in Tanzania in 1951, is a vast ecosystem of almost 10,000 square miles, home to one of the last remaining concentrations of large mammals. Observing this vast land from helicopters, scientists were able to count the thousands of animals living there and study the rise and fall of different species.  Anthony Sinclair traced the wildebeests, noting that their numbers dropped when a cattle virus, the rinderpest, infected them, but rebounded after the virus was eliminated. Over the next several years, their numbers grew to an astounding 1.4 million.  Park officials, worried that the wildebeest would overgraze, proposed culling their numbers.  Sinclair made a courageous bet that the population would reset naturally when they reached a certain number. The wildebeest proved him right, leveling out of their own accord at 1.4 million.

This led to another Serengeti Rule:  species compete for common resources, and this competition for space, food, or habitat can regulate the numbers of competing species.  The wildebeest had direct and indirect effect on grasses, fire, trees, predators, giraffes, insects, and other grazers.  They are a keystone species with disproportionate impacts on the structure and regulation of the system.  Sinclair states:  “Without the wildebeest, there would be no Serengeti.”  (144)

Carroll notes that the Serengeti rules apply to ecosystems everywhere.  This science has been applied to the resurrection of Gorongoza National Park in Mozambique, and to the Yellowstone Wolf Restoration project, which Carroll calls “the American Serengeti.”  These remarkable achievements led him to define the ultimate Serengeti rule:  Nature is resilient.

This book and documentary combined are a great way to learn about the underlying rules that regulate nature.  Reading and viewing with Bowen theory in mind, one cannot help but wonder about the possible human analogs.  Are there rules that regulate human families and societies?  Are there individuals and groups that function as “keystones” in human systems?  Do humans hold a keystone position in relation to the life of the earth?   The documentary ends with these words from forest ecologist, John Terborgh:  “Humans are hyper-keystones in the sense that they are all-controlling.  Progress in the last twenty years has shown that an upgraded planet is within reach. There are rules.  We can harness them to heal our damaged earth.  We now recognize that we have a powerful ally in nature itself.”

Carroll, Sean B.  (2016)  The Serengeti Rules:  The Quest to Discover How Life Works and Why It Matters. Princeton, New Jersey:  Princeton University Press.

PBS Nature Documentary.  The Serengeti Rules.  (2019)

Note:  Kira Cassidy, Research Associate at the Yellowstone Wolf Restoration Project will be the guest scientist at the Center for Family Consultation Midwest Symposium on May 6 & 7, 2022.

Stephanie Ferrera




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