Every year, we hear in the news that a flu epidemic has broken out. Some of us go to be vaccinated preventively. Many of us have never had the flu in our lives. From the news we sometimes hear terms like bird flu, swine flu, H5N1. But if we are not directly affected, we will usually lose interest in the topic soon. But why does the flu even exist? Is it with humans from the dawn of their existence, or does it have a beginning in the human population?
Influenza is an infectious disease caused by the influenza virus. The symptoms can be mild to severe and generally do not mean a more serious complication for an otherwise healthy person. We often confuse it with the common cold or the so-called intestinal flu. However, it is a different disease. In the human population, influenza is spread by droplets when coughing or whistling directly or indirectly through contact with a contaminated surface and subsequent contact with, for example, the mouth, nose or eyes. The basic prevention against the flu is thorough and frequent hand washing, annual vaccinations and wearing a mouthguard, especially for sick people and people who care for them. About one billion people become infected with the flu each year and claim hundreds of thousands of victims worldwide.
The history of man on planet Earth dates back several million years. For all that time, however, most of today's common diseases either did not exist (flu, measles, smallpox, common cold), or occurred only very rarely (heart attack, cancer, diabetes). Many viral diseases began to appear in the human population about 10,000 years ago, during the so-called first agrarian revolution. The reason was the domestication of animals and their close coexistence with humans. By domesticating cattle, humanity gained measles, domestication of camels gave us smallpox, domestication of pigs gave us whooping cough, domestication of horses gave us common cold, domestication of ducks gave us influenza, and so on. It is known that cultures that have not adopted domestication, such as the American Indians, have not suffered from any animal-borne diseases. 
But how is it possible that originally an animal virus passes on to humans and becomes a human virus? The reason is a change in animal lives. The virus in its natural environment may not cause disease. Naturally, the virus doesn't even want to kill its host, because then it will die with the host. However, if the virus kills the host, the disease will not normally spread. Close coexistence with humans, especially large-scale farms, in which thousands or even millions of animals are sealed in a small place, represent perfect conditions for the spread of the virus. As for the flu, the original virus, living in the digestive tract of ducks, has been transmitted from duck to duck through excrements in water for millions of years. The virus prospered without having to cause disease in ducks. However, when the ducks moved into human habitation and the virus did not have a natural environment to transmit, it could either mutate or die with the duck. It was random mutations that caused transmission to humans and settled in the airways instead of the digestive tract. The virus is more easily transmitted to other humans by coughing and wheezing, which is why the flu affects the lungs. But in order to cough, one must be sick. The more animals live together and the closer to humans, the more the mutation in the virus grows and the more likely it is to be transmitted to humans.
Infectious diseases have been on the rise for the last 40 years. The World Health Organization has identified increased demand for animal protein as the main cause. Increasing globalization, people's living standards and growing populations are having an impact on increasing meat consumption. Live animals are transported between continents on overcrowded ships, which increases the risk of new and more dangerous diseases.
The cause of influenza in the human population and other infectious diseases is therefore the close life of humans with animals. As this will not change in the near future, we have to keep in mind the words of the World Health Organization: "The question is not whether we will have another pandemic, the question is only when."