Author: Zhao Xumao (Young Researcher, Lanzhou University)
People's feelings about wild animals are always somewhat contradictory - on the one hand, they feel that they are weak, helpless, and in need of human protection, at the same time, people also recognize the important role of wild animals in the earth's ecosystem, and the protection has gradually strengthened in recent years; on the other hand, they feel a little afraid, after all, whether it is atypical pneumonia or the new crown pneumonia that has raged in recent years, the original host of the virus is wild animals. But what many people don't know is that wild animals are actually guarding humans, which is a barrier against viruses invading humans.
Wild animals are the "Pandora's Box" of viruses?
As long as contact with wild animals is reduced, the probability of cross-species transmission of the virus is not large.
The history of human evolution is a history of dealing with epidemics, especially in the past hundred years, the number of people who have died due to viruses is far greater than the number of people who have died due to war. The flu virus that raged during World War I infected 1 billion people and killed more than 20 million people. In the spring of 2003, an outbreak of sarsmonic pneumonia (SARS) occurred. According to data released by the World Health Organization in August 2003, the SARS epidemic affected 32 countries and regions, with a total of 8,422 cumulative cases and 919 deaths worldwide. The Zika virus outbreak in 2014 infected more than a million people in Brazil and caused thousands of cases of neonatal microcephaly. Since the beginning of the 21st century, the coronavirus alone has caused three global plagues: one is the SARS virus; the other is the Middle East Respiratory Syndrome virus; and the third is the new crown virus, and their spread and spread are closely related to the viruses carried by wild animals.
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According to statistics, 60% of human infectious diseases originate from animals, and 50% of animal infectious diseases can be transmitted to humans. Since 1970, more than 75% of emerging and re-emerging infectious diseases have been zoonotic. Taking the coronavirus family as an example, scientists have found more than 500 species in nearly 200 species of bats. Bats are also the original reservoirs for many viruses, such as Ebola, Marburg, rabies, Hendra, Nipah and so on.
So, are these wild animals the "Pandora's Box" of viruses?
To answer this question, we should first understand why viruses in wild animals spread in human society.
Studies in recent years have shown that the root cause is mainly increased human-wildlife contact, leading to close contact between viruses and humans in wild animals, increasing the risk of mutation and transmission in humans. For example, the global trade in illegal and legal wildlife is estimated at $300 billion a year, meaning that tens of thousands of wildlife flows into human society each year. Human activities have seriously damaged the habitat of wild animals and are also one of the important reasons for the increase in zoonotic diseases. In the Amazon basin, for example, forest cover will fall by 4 percent and the incidence of malaria will increase by 50 percent.
As long as this "magic box" is not opened, humans are safe. To some extent, the cross-species spread of these viruses is not the "fault" of wild animals, but the root cause lies in humans.
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We often talk about protecting wild animals, and in the eyes of many people: they are weak, helpless, pitiful, and need human protection. In fact, the reason why we want to protect wild animals is because wild animals are also protecting us humans. Since the new crown pneumonia epidemic, human beings have begun to rethink the relationship with wild animals, from the perspective of epidemic transmission, only by truly finding an intermediate host for the virus can it be possible to completely cut off the transmission chain of the epidemic. Similarly, only by truly realizing the relationship between humans and wildlife can we prevent similar tragedies from happening.
Can wild animals only be protected or exploited?
Wildlife has also long played an important role in protecting human health.
Now we can't have more contact with wild animals, and when science and technology develop in the future, the level of vaccines and treatment is further improved, can we? The answer is no. For a long time, our understanding of wild animals has remained in the protection or utilization, ignoring the important role of wild animals in protecting human health. The author will only briefly introduce from the following three aspects:
First, wildlife can control the spread of disease through biological interactions with the environment.
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Elephants and rhinos in Tanzania's Taragili National Park are heavily poached. But people were surprised to find that with the decline of elephants and rhinos, there have also been a large number of deaths of cattle and sheep and other livestock raised by people near the reserve. Experts have found that the large number of domestic animal deaths is caused by the tsetse fly living in the bush, and its bites cause the animal to become sick – in the natural state, elephants and rhinos have the habit of trampling on the bush, which will control the number of shrubs to some extent. Due to the heavy poaching of elephants and rhinos, the number of shrubs has increased significantly, providing good environmental conditions for the reproduction of tsetse flies, resulting in the death of livestock from severe infestations from infectious diseases.
Outbreaks of Lyme disease have also been linked to a decline in wildlife. The researchers found that human deforestation destroyed the habitat of wild animals, causing the number of top predators in the forest such as wolves, foxes, and owls to decline, resulting in an increase in the number of white-footed rats, an important host of Lyme disease, which in turn increased the possibility of Lyme disease spreading to humans through ticks.
Second, wild animals can reduce the spread of zoonotic diseases through a "dilution effect."
There is the "dilution effect hypothesis" in ecology: the higher the species diversity, the lower the risk of human contracting diseases. That is to say, the richer the diversity of species, the more stable the ecosystem, and the stability and security of the ecosystem is related to the health of human beings themselves.
While the number of local pathogens with high biodiversity is also high, a high number of individual pathogens does not mean that the risk is high – the process of disease transmission is highly dependent on the frequency of exposure, and biodiversity can reduce the likelihood of exposure through host competition and regulatory functions. In other words, where species diversity is high, exposure to viruses is reduced, reducing the chance of outbreaks of zoonotic diseases. In addition, studies have shown that as human activities intensify, not only does species diversity decrease, but so does the community structure of species change. In layman's terms, it is easier to coexist with species that carry zoonotic diseases in places where humans are more intensive, such as hedgehogs and rodents in cities, which increases the probability of virus transmission.
Third, wildlife is an important part of protecting ecosystem stability.
Wildlife is an important part of biodiversity and plays an indispensable role in ecosystems. You know, viruses existed on earth before humans, and one of the important reasons why humans have not been infected by many viruses is that wild animals have erected a barrier between viruses and humans.
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At the same time, biodiversity also indirectly affects human health through management with the environment. The "old friend hypothesis" has been proposed, arguing that the human immune system and the microbes that live in the human digestive system have co-evolved, so these microorganisms are part of the human immune system. The microorganisms in the human body will be affected by environmental microorganisms, living in an environment with high biodiversity and stable ecosystems, and the microorganisms in the environment can supplement the diversity of microorganisms in the human body and help the human body better adapt to new foods and environments.
In real life, under the influence of human activities, wild animals are facing huge changes in populations, habitats and so on. What effect these changes will have on humanity is still unknown. Take, for example, the Amazon rainforest. Palm trees are one of the main tree species in tropical rainforests, and after a long period of co-evolution, tall palm trees bear huge fruits, attracting the spread of some large-billed (beaked) birds and completing forest renewal. However, with the intensification of human hunting, the population of large-billed birds has declined rapidly, thus affecting the spread of palm tree seeds, and those tall, large-fruit palm trees are facing extinction, and palm trees with small fruits instead rely on the spread of small-billed birds, which are favored by natural selection. This result affects the community structure of the entire rainforest. We know that tropical rainforests are the lungs of the earth, and the impact on the earth's ecological environment has a whole-body effect. How will such a change affect the planet? Perhaps, only history can give us the answer.
It doesn't matter if one or two animals go extinct?
The loss of one organism directly or indirectly leads to the loss of 10 to 30 other organisms.
Today's rate of species extinction is 100 to 1,000 times higher than before humans dominated the earth. The biggest harm of humans to wild animals is the destruction of their habitats - at present, 2/3 of the world's wildlife habitats have been disturbed and destroyed by humans, making a large number of wild animals at risk of extinction.
There are 932 species of threatened vertebrates in China, which already accounts for 21.4% of all animals; six large animals living in China, including three species of rhinoceros, Przewalski's wild horses, high-nosed antelopes, and Xinjiang tigers, have all become extinct in the past hundred years or so and disappeared from the earth forever.
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After the reform and opening up, the mainland has stepped up the protection of wild animals. Since the Eighteenth National Congress of the Communist Party of China, the new concept of ecological civilization has been deeply rooted in the hearts of the people, from legislation to the establishment of protected areas to the construction of national parks, etc., the protection of wildlife on the mainland has leapt to a new level.
Some people may feel that the extinction of tens of millions of species on the earth is harmless. This kind of thinking is really very wrong. The famous ecologist Mr. Edward Wilson once said a very classic phrase, which roughly means: humans need ants, but ants do not need humans. Although inconspicuous, ants are one of the most important decomposers on Earth, playing an important role in the material and energy cycles on Earth. As an important part of the base of the ecosystem pyramid, the extinction of ants may lead to the collapse of the Earth's ecosystem.
Each organism lives in a certain ecosystem and interacts with other biological species. The loss of one organism will directly or indirectly lead to the loss of 10 to 30 other organisms, and the loss of 10 to 30 organisms will lead to the loss of hundreds, thousands or even tens of thousands of organisms.
This will also have irreversible effects on human health – the decline or extinction of certain organisms will inevitably affect the ecosystems in which they live. If the ecosystem is severely damaged, the virus in the wild animal needs to find a new host, and the probability of human infection will be greatly increased.
For wildlife conservation, "no buying, no killing" is not enough. We should have a higher pursuit: the harmonious coexistence of people, animals and plants, microorganisms. We all live together on the planet, blended in ecological diversity and interdependent.
As mentioned earlier, viruses existed on Earth before humans, and they both threaten humans and co-evolve with entire ecosystems. Extinction of viruses is unrealistic. To some extent, wild animals are an ecological great wall for human beings to resist viruses, and only by maintaining biodiversity and ensuring ecological security can we ensure human health!
Guangming Daily (2022.05.12. 16th edition)
Source: Guangming Network - Guangming Daily