How long has religion set humanity back?

Killer, companion, trailblazer : How viruses shape human history

Viruses make history. Experience it as if it were live. But it has always been like that.

Up until the last century, more people died from epidemics than from the consequences of armed wars. When smallpox broke out on a large scale in Prussia for the last time in 1870, four times more people succumbed to the epidemic in one year than in the simultaneous war against France.

And the "mother of all pandemics", the Spanish flu that broke out in 1918, killed at least two, more likely three percent of the world population at that time, around 40 or 50 million people, possibly even up to 100 million.

Infectious diseases have long been the deadliest threat

That would be more than in the First and Second World Wars combined, with 17 and 60 million deaths respectively. In any case, it was the greatest disaster of the century in terms of casualty numbers.

It is only recently that "improved hygiene and increased firepower of weapons have made it possible for people to kill more people than microbes can," says microbiologist David Clark.

Up until then, infectious diseases were the deadliest threat. They shortened life, brought immeasurable suffering, - like plague and cholera - depopulated entire regions and set back their economic development by centuries. There is no doubt that epidemics caused by viruses and bacteria have shaped the entire history of mankind.

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It probably began with the Incarnation itself, and great catastrophes have already been demonstrated in the high cultures of Mesopotamia and Central America. And yes, they also let the Roman Empire go under, at that time the most densely populated and most closely interconnected society in the world.

Microorganisms as part of the history of our environment

But they also promoted the Renaissance, produced Western democracies and science, as Clark describes in detail in his book "Germs, Genes and Civilization".

Geography professor, physician and evolutionary scientist Jared Diamond is also convinced that infectious diseases are not only the greatest killers in history.

The microorganisms that cause them have had a decisive influence on the course of the most recent stages of human evolution; they are therefore part of the history of our environment, argues Diamond in his bestseller “Guns, Germs and Steel”, published in German under the title “Arm und Reich. The fates of human societies ”.

Diseases caused by viruses and bacteria are not only part of human life, but are age-old companions of the development of all higher life, "nothing more than an expression of evolution, in the course of which pathogens adapt to new hosts and carriers through natural selection", so Diamond.

The gods also brought epidemics into the world

Epidemics previously unknown to man were not only responsible for decisive crises in human history. They also brought the great gods into the world. With faith, an unparalleled cultural achievement was brought into position against the scourges of humanity.

Religion and morality in the modern sense emerged primarily as a cultural protection system, as a kind of disaster control, claims the anthropologist Carel van Schaik in his "Diary of Mankind - What the Bible Reveals About Our Evolution", which he wrote together with Kai Michel.

A lot of germs have always been there

According to this, epidemics were not only the gods' midwives, but also their most powerful propagandists. Each new epidemic has long appeared to people as evidence of unearthly activity. One reason why the gods must have become angry could always be found in retrospect - a consequence that was often in the interests of the rulers.

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A lot of different germs have always been there. Epidemic diseases, from which we all still suffer today, at least in part, mainly as children, only came into the world around 10,000 years ago with the transition to agriculture and animal husbandry.

Because hunters and gatherers were still largely lacking epidemics, as they were far less numerous and close together for a long time. And nothing hampers the spread of a germ as well as distance between possible hosts. This can currently be seen in the effects that the prescribed “social distancing” is now apparently producing.

In addition, there was another, decisive factor: Since the beginning of the sedentary lifestyle, not only have more and more people lived close together. They also lived close and close to their cattle.

60 percent of diseases are transmitted by animals

Viruses then spread from his first farm animals such as cattle, pigs and chickens to humans, which have since caused diseases such as measles, smallpox, rubella, mumps and whooping cough, but also typhoid, tuberculosis and influenza in us.

After all, around 60 percent of all our diseases are transmitted by animals. And three quarters of all newly emerging infectious diseases jump from animals to humans. To this day, they mostly come from farm animals such as pigs, chickens or cattle, with which many people live together in a confined space, especially in poorer countries.

The first Europeans brought pathogens into the New World - with catastrophic results

In the growing civilizations of the Old World, the pathogens spread with the increasing trade connections. After a natural immunization had built up gradually - over long periods of time, but with countless victims - the first Europeans carried many of these virus-caused epidemics to the New World with globalization after Columbus’s discovery in 1492.

The people there lacked that immunization. 90 percent of the indigenous population succumbed to the infectious diseases. With an estimated 100 million deaths, it is probably the largest bloodletting in human history.

Historians today are convinced that it was only through the Eurasian pathogens - and not the firepower of their initially primitive rifles - that initially a small group of conquistadors and hardly any more European immigrants succeeded in making the once large population of Central, Southern and Eastern Europe To displace North America.

The "Pox Americana" claimed more victims than the battles of many wars

The “Pox Americana”, for example, the smallpox of the New World, would have claimed more lives than the battles of the many wars in America, the Swiss historian Aram Mattioli is convinced. And his Hamburg colleague Jürgen Zimmer recently stated: "The settler societies of North and South America literally emerged in the aisle that bacteria and viruses had cut."

Viruses triggered a demographic catastrophe in the New World, which made it possible for Europe to achieve the colonial dominance that is still manifested today in the divide between the global north and south. It was these ominous souvenirs that Europeans had in their luggage and that made history: those pathogens that had developed over the millennia of close coexistence between the Eurasians and their pets and to which they were more or less accustomed.

Malaria, cholera and yellow fever prevented colonization by the Europeans for a long time

Conversely, infectious diseases such as malaria, cholera and yellow fever in the tropical regions, especially Asia and Africa, have long prevented their colonization by Europeans. Now other epidemics, often referred to as “new epidemics”, are coming back to us from there.

Many of the deadliest diseases - from smallpox, AIDS or Ebola to the flu - were and are caused by tiny pathogens. Viruses come in a myriad of different varieties, even if virologists cannot even begin to say exactly how many there are worldwide.

We live in peaceful coexistence with most microorganisms

Only a fraction, perhaps around 1500, are known to be pathogens. On the other hand, we live in peaceful coexistence with most of the microorganisms that abound all over the world. In fact, they are useful to us and we need them from birth. For example, our digestion only works thanks to a rich microbiome in our intestines, in which the various bacteria are in turn kept in check by viruses.

The food chains in the oceans and soils, for example, also depend on the interaction of bacteria and their viruses, known as “bacteriophages”. The latter, in turn, can also help people when they use phage therapy to combat multi-resistant hospital germs against which antibiotics are no longer effective.

Viruses were among the most "creative" driving forces in evolution

Lately we have even known that viruses evidently belonged to the “most creative” driving forces in the course of evolution. Because a not inconsiderable part of our genome originally comes from viruses. Perhaps, some experts speculate, it is more than half of our DNA.

Once introduced, the virus gene sequences were incorporated into the genetic material of our animal ancestors long ago. What was disadvantageous fell victim to Darwin’s "natural selection".

However, a few of the new gene combinations will have been beneficial, for example because they provided protection against potential pathogens. Viruses are also likely to have become drivers of evolution because they exchange and transfer the genetic material of organisms with one another. They acted like gene ferries and thus enabled genetic innovations.

Viruses are primitive parasites and not even real living beings. They consist of little more than genetic material, which is surrounded by a protein shell. They are like pirates who hijack other cells - be they bacteria or those of multicellular organisms such as humans.

In order to reproduce, the genetic material of the virus enslaves the host cell's cell apparatus, which it then uses for its own purposes, ultimately destroying it.

The killer qualities are also the Achilles' heel of viruses

In spite of all the killer qualities, the latter is also the Achilles' heel of the viruses: they are not viable outside of their hosts, but rather a preserve that can be resuscitated for a certain period of time. You always need a suitable carrier. Because only its cell machinery enables them to have innumerable copies of themselves made and thus to ensure their distribution.

In this way, however, evolution ultimately forces even the deadliest viruses to cooperate with their hosts. The pathogen must destroy the host's cells, otherwise it cannot spread. Destroying all of his hosts in a short period of time is rather a disadvantage for him.

An always fatal virus is dead in the long run

Because the dead do not cough or sneeze, and they are not otherwise good carriers of germs. And even if the time before the host is destroyed is still enough to reach enough new hosts, an always fatal virus is itself at an end in the long term, because it loses all hosts through this overexploitation. The virus then won an evolutionary battle convincingly, but lost the long-term evolutionary race.

It is true that some microbes turn out to be true killers at first. But very few remain. Even initially lethal viruses lose their virulence at some point or die out. Our relationship with pathogens is also based on coevolution, in which viruses have lost their lethality through adaptation, but henceforth use us permanently as hosts.

Random mutation, natural selection: a model for evolution par excellence

Thanks to this everlasting game of random mutation and natural selection, viruses have become the ultimate model for evolution.

A decade before the molecular structure of the genetic material was even elucidated, Max Delbrück and Salvador Luria discovered in 1943 in a later Nobel Prize-winning experiment with bacteria and phages that mutations occur spontaneously. Such genetic changes occur by chance.

Viruses are also constantly changing their genetic information faster than bacteria. They exchange genetic material with one another and, at the same time, learn new things when several variants mix in one host. Thanks to such mutations, pathogens that initially only attack one animal as a host can also develop the ability to penetrate human cells by chance. And if a person happens to be available, they do so and can turn an animal epidemic into a pandemic.

A virus that leaps from animals only needs a few mutations for this. With the usual influenza viruses, it is often only four to five that cause new waves of flu. In the case of the Sars virus in 2003, there were only two mutations that made the difference between the pathogen that infects animals and humans. And in the case of the Spanish flu, the crucial molecule, as was later found out, only differed in a single amino acid.

The coronavirus is ten times less likely to mutate than the flu

In the case of bird flu in 1997, a point mutation was sufficient for the H5N1 virus, which led to the replacement of a single amino acid in a protein in order to make the virus dangerous for humans. The current coronavirus is about ten times less likely to mutate and has so far changed much more slowly than flu viruses, for example.

Fortunately, because we humans, with our world population, which will soon have grown to eight billion and are closely connected, offer a virulent pathogen a huge reservoir in which it is all the more likely to mutate in the event of millions of infections.

Humans and microbes may share a long common evolutionary past, and at least some of the once-scourges of mankind may have lost much of their horrors.

Virus-induced epidemics will not leave us in peace in the future either

However, epidemics caused by viruses will not leave us in peace in the future either. They live in us and from us. But at least we can make that harder for them.

This can be achieved, for example, by being well prepared for the next time. This time it wasn't us: Not only because we hadn't stored any masks, but above all because a few years later, despite the Sars warning from 2003 and the Mers outbreaks, we almost stopped research on novel coronaviruses.

[The author: Matthias Glaubrecht is an evolutionary biologist, professor for animal biodiversity at the University of Hamburg and founding director of the Center for Natural History there. His book “The End of Evolution. Man and the destruction of species ".]

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