Human health and ecosystems: a relationship of  interdependency

The current pandemic reminds us that human and ecosystems healths are closely linked. For decades, scientists, especially in the medical field, thought that it would one day be possible to control all living things on Earth, specifically microorganisms. Scientific ecology, which is the science of life and in ecosystems, teaches us that it is impossible, and that this hygienist idea is dangerous. Indeed, on our planet, life is characterized by the existence of millions of species of different orders (plants, animals, etc.) and in particular viruses and microbes. The “microbes” are even at the origin of respiration and photosynthesis, and play an essential role in the nutrition of plants, herbivores and even humans, as described by symbiosis specialist Marc-André Selosse in his last work. It is therefore futile to want to eradicate or even control viruses and microbes, and the absurd attempts to sterilize beaches in Spain and people in the United States during the pandemic have resulted in disasters.

History sheds interesting light on the link between the emergence of pandemics and the disruption of ecosystems. Indeed, many microorganisms live in the organisms of animals, often rodents or other mammals, for which they are less lethal than for humans. By getting closed to these species, described by us as “wild” human societies creates pandemics. In the case of COVID-19, even if we do not know the precise origin of this pandemic (pangolin or bat), it is undoubtedly has its origin in the disturbance of species or ecosystems previously distant from us.

An old story

A recent book1, dealing with relations, much older than what public opinion thinks, between China and us, contains a chapter on the Black Death (14th century), which singularly sheds light on the current situation. Let us retain two interesting facts from it:

  • Scientists and historians of the time already knew that great calamities followed periods of ecosystem disturbance.At the time, these disturbances were due to damages caused by the Mongol hordes, whose horses turned everything in their path, but also to long-term phenomena, such as groundhog hunting.Since the research of Alexandre Yersin in the twentieth century, we know with certainty that rodents such as gerbils and marmots are the first hosts of plague, which fleas then transmited to the rats that infested cities.

  • Recent research shows that the plague probably originated in Central Asia (Kyrgyzstan or Tajikistan), from where it was brought by the Mongols to the Black Sea, where Genoese merchants (therefore Italians), certainly brought it back to Europe. From that time on, the globalization of trade was therefore not without danger. This does not mean that international trade only had negative effects.

Accelerated erosion of biodiversity

Though not recent, the disturbance, and even the destruction of ecosystems, and more generally of biodiversity, is today taking on a particularly worrying scale. Most species have a limited lifespan on Earth, so the disappearance of species is a normal phenomenon, on a geological time scale. The current rate of disappearance of animal or plant species, estimated by scientists to be 1,000 to 10,000 times faster than the usual rate, should alarm us. Beyond these figures, we can observe the simplification of the landscapes, the drastic reduction in the populations of birds, reptiles and especially insects.

The simplification of our diet is a notable illustration and consequence of this, with around fifteen plants now representing most of the human diet. The following diagram, already old, illustrates one aspect of the loss of food diversity in 80 years (compare the upper part and the lower part), as a decline in the varieties of common cultivated species. Almost 4 decades later, the movement towards food standardization has only accelerated.

Perte de biodiversité alimentaire

What approach to emerging diseases?

Serious as it is, COVID-19 is undoubtedly only the latest in a series of more or less severe pandemics that awaits Humanity if it continues to disrupt ecosystems. Let us not forget also that many other emerging diseases are the consequences of our mode of economic development, and of the environmental disruptions it generates. Modern medicine had wiped out many infectious diseases of the past, but while waiting for the next pandemic, the incidence of so-called “civilization diseases” such as cancer or cardiovascular disease has increased in recent decades. In France, around 2,790 people die of cancer every month, that is more than 16,400 people in the first half of 2020. A good proportion of these deaths are due to ambient pollution, generated by synthetic molecules released into the air, in water and in food.

The analysis above shows the interest of a holistic approach to human health. Since we must forget the idea that our species could master such a widespread and important category of living things – microorganisms – it is import to adapt human activity to the reality of life on our planet. Attempts to do the opposite are doomed to failure. This is why slogans such as “integrating biodiversity into the actions of companies” encounter serious limits. Biodiversity cannot be integrated into any human action. The logic of the living is a predicament which human action must take into account.

There are proposals for new ways to integrate human action in the great cycles of life, whether on a planetary scale or at the scale of local ecosystems. This opens up many avenues to a happy life, within planetary boundaries, as this diagram borrowed from Oxfam illustrates.

From this perspective, the One Health approach is promising. This concept,  introduced in the early 2000s, summarizes in a few words the idea that human health and animal health are interdependent and linked to the health of ecosystems. It should be broadened and mainstreamed, for Humanity to thrive more harmoniously on Earth.

1 Great state: China and the world, by Timothy Brook, 2019. I advise everyone to read this book, the interest of which goes far beyond the issue of pandemics.


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