A world filled with elephants
1500, under the rule of King Manuel I, the Portuguese Empire was in full swing. Since 1434 crossed Cape Bohado, the Portuguese have been advancing steadily along the west coast of Africa.
1498, Degama crossed the Cape of Good Hope and arrived in India; 1500, Pedro lvares Cabral arrived in Brazil. It was in this year that the king sent an expedition back to gambia river in West Africa to explore the "dark center". However, only one member of the expedition finally returned safely, and the others were left in Africa by the epidemic.
John de Barros, a historian of later generations, wrote: "God sent an angel, wielding the sword of fire with deadly fever, to prevent us from entering the clear spring in this garden, from which the golden river flowed into the ocean we conquered many times."
Hundreds of years later, this deadly fever, malaria, still made European adventurers afraid to go deep into the interior of the "dark continent" until Europeans extracted quinine, a specific drug for treating malaria from the American Cincinnata tree. Even in the19th century, David Livingston, the greatest African explorer, and his wife died of malaria.
Even in 1900, a quarter of the inland areas of Africa were still unexplored. Dean Swift once described the dilemma when people drew this dark continent: "On the map of Africa, geographers fill in the blanks with wild animals. Therefore, for hilly areas that are not suitable for living, fill elephants to replace the lack of towns. "
During this period, deadly infectious diseases brought by Europeans, such as smallpox, measles, typhus, influenza and diphtheria, swept across the American continent, wiped out most native American Indians and helped Europeans conquer America completely.
Guns, Bacteria and Steel, jared diamond's masterpiece, provides a convincing explanation for why American Indians can't escape the fate of being conquered by infectious diseases. The fate of Africa and other tropical countries is linked to malaria, the most terrible infectious disease in human history.
Why did European colonists conquer America thousands of miles away instead of Africa at hand? Why are they all aborigines? Today, India's total population is only 48 million, while Africa has a population of 10 billion. Why does modern Africa still fall into the trap of poverty? Why does India seem rich but poor, and the caste system has lasted for thousands of years? The answers to these questions may go back to ancient times, with malaria as the protagonist.
Evolutionary arms race
As most people know, malaria is a parasitic infectious disease caused by single-celled Plasmodium, which is spread by Anopheles mosquitoes. But what few people know is that the four kinds of plasmodium that can infect people, namely Plasmodium vivax, Plasmodium falciparum, Plasmodium vivax and Plasmodium ovale, have completely different characteristics, evolutionary history and geographical distribution. On the scale of thousands of years, these protozoa have launched a fierce evolutionary arms race with human beings.
Plasmodium vivax malaria accounts for more than 80% in India, the Middle East, Central and South America and the Caribbean, and does not exceed 10% in Africa. Plasmodium originated in Africa. Why was vivax malaria driven out of his hometown?
We know that Plasmodium vivax has been raging in Africa for at least100000 years. In this long process, Africans have evolved a weapon against Plasmodium vivax-Tamiflu antigen is negative: more than 90% areas in West and Central Africa lack Tamiflu antigen, which is a protein on the surface of red blood cells, blocking the path of Plasmodium vivax entering red blood cells. Thanks to this powerful weapon, most Africans are basically immune to vivax malaria.
Unfortunately, Tamiflu negative antigen may have solidified for less than 70,000 years through evolutionary mechanism, so Homo sapiens who walked out of Africa 70,000 years ago did not carry this gene, and modern Indians and Americans could not resist the invasion of Plasmodium vivax.
Plasmodium falciparum is the most terrible of the four kinds of malaria, which is famous for its acute onset and high mortality. More than 80% of malaria in Africa is falciparum malaria. The appearance of falciparum malaria may be only a few thousand years. Humans around the world have evolved a variety of weapons to fight falciparum malaria: thalassemia in the Mediterranean, sickle cell anemia and G6PD deficiency in Africa, and polycythemia in Melanesia.
Although these weapons are powerful in the fight against falciparum malaria, they often kill 1,000 enemies and damage 800. For example, if a person inherits two sickle cell genes from his parents, he often cannot live to adulthood; People who inherit only one gene on one side have no abnormal symptoms, but the mortality rate drops by 90% after being infected with falciparum malaria.
However, the other side of the battle-plasmodium evolved faster. In the last few decades of the 20th century, plasmodium became resistant to chloroquine, artemisinin and other specific drugs.
The evolutionary arms race between mankind and Plasmodium falciparum tells us the fact that human evolution has never stopped. The late paleontologist stephen gould once thought: "In the past 40,000 to 50,000 years, human beings have not changed their biological characteristics. We have created all cultures and civilizations with the same body and brain. "
We know Gould was wrong: the evolutionary history of thalassemia, G6PD deficiency and sickle cell anemia is only a few thousand to ten thousand years. Africans, Europeans and Americans have different bodies, and it is this difference that makes the United States and Africa have completely different histories.
Melancholy tropics
Malaria is mainly a tropical disease. Without the tropics, the life cycle of plasmodium becomes longer or even stops breeding, and the activity ability of Anopheles mosquitoes also drops sharply. However, in tropical areas such as Africa, South Asia, Southeast Asia, Central America and the Caribbean, malaria not only affects the living conditions and ecological environment of human beings, but also completely changes the socio-economic operation of tropical countries.
Sub-Saharan Africa is the only "stable transmission area" of malaria. As a result of repeated infections, a large number of children died before the age of 4-5 (at the beginning of the 20th century, half of East African children died before the age of 4, most of which were due to malaria), and the survivors could get some protective immunity, so the risk of death when they were infected with malaria again was greatly reduced.
Malaria is also easy to infect pregnant women, leading to birth defects such as high abortion rate and low birth weight. What is particularly frightening is that malaria and AIDS are deadly combinations. People infected with HIV are more susceptible to malaria, and women infected with malaria are at higher risk of transmitting HIV to their newborns.
In addition, in many African countries, more than 30% people carry sickle cell gene, and at least one of their offspring will die of disease.
The seeds of bad luck in Africa have been planted. Due to the lack of domesticated mammals, Africans did not raise all kinds of livestock like people in Eurasia when they began to enter the settled agricultural society from hunting and gathering society four or five thousand years ago.
Africans cut down trees to build villages, and the population and density began to expand. At the same time, a large number of ponds and stagnant water have been created in the tropical rain forest, turning the settlement into a paradise for Anopheles mosquitoes.
Anopheles mosquitoes that adapt to this living environment only feed on human blood because there are no other animals to choose from. Under the action of natural selection, an Anopheles gambiae with a strong preference for human blood was produced. Anopheles gambiae consumes human blood 80- 100% of the time, while Anopheles on other continents often consume less than 20%. This is the most important reason why the malaria infection rate in Africa far exceeds that in other regions.
The biggest challenge faced by Africans living in areas with stable malaria transmission is the extremely high child mortality rate, which has lasted for thousands of years and may have an impact on both physiological and cultural systems.
For example, sub-Saharan Africans have a higher probability of fraternal twins than other ethnic groups: the probability of having twins in Yoruba, West Africa is 4.5%, which is four times the world average; Under the same conditions, African women's pregnancy time is one week shorter than that of European women, premature babies have a greater chance of survival and menarche is earlier.
Indian patient
India is a different story. Plasmodium vivax malaria, which is rampant in India, exists in an unstable way and is more deadly to adults. Because there are not enough frequent infections to maintain protective immunity, people are threatened by malaria for life. At the same time, Indians lack the protection of Tamiflu antigen negative gene, which makes vivax malaria and falciparum malaria become dangerous killers together.
1947, 75 million of the 330 million Indians were infected with malaria; In India in the first half of the 20th century, more people died from malaria than from other causes combined. In order to avoid malaria, one of the favorite drinks of British colonists in India was gin and tonic water, which later became the darling of bars.
It may not be accidental that Buddhism appeared in India, thinking about life and death and paying attention to the afterlife. Volume 5 of the first Shurangama Sutra: "From the beginning, we were born with all kinds of ignorance. Although we know more about Shangen, we still have malaria every other day. " The Japanese abuse of cold and heat is uncertain, and Buddhist scriptures use this as a metaphor for the birth and death of ignorance.
With the prevalence of malaria and other tropical diseases, a lot of energy is consumed by these microorganisms, and it is difficult for rulers to recruit enough soldiers and public works workers to maintain a unified empire. The political and military fragility of the Indian empire may be related to this. Critics often compare tropical India and temperate China on the same level, which is far from the truth.
In addition, India's caste system may be related to tropical diseases such as malaria. The study of Indian genome shows that the caste system of intermarriage within caste has been strictly implemented for thousands of years.
A reasonable guess is that foreign invaders (such as Aryans who invaded India about 3000 years ago) were attacked by tropical infectious diseases such as malaria when they entered tropical India. The caste system and the taboo of cross-caste contact have become firewalls, reflecting the invaders' fear of keeping a safe distance from infectious diseases.
An indelible curse
Today, the flow of people and trade between areas with stable malaria transmission and other areas are still very difficult, and foreign investors are terrified. 198, mining giant BHP Billiton invested1400 million USD to build an electrolytic aluminum plant in Mozambique. In two years, there were 7,000 malaria cases, and 13 foreign employees died.
Malaria inhibits trade and foreign investment in epidemic areas, and economic development naturally becomes a luxury. The map of malaria epidemic areas in the world is actually a map of poor countries in the world.
The average income of two northern temperate countries and three southern temperate countries in America is five times that of tropical countries 17 sandwiched between them; The five richest countries in Africa are also located in the north and south temperate regions of Africa. There are almost no developed countries in the tropics, and malaria is hard to escape.
Malaria not only inhibits the communication between epidemic areas and the outside world, but also inhibits the vitality of local people.
Because there is a great chance that children born in Africa will not live to adulthood, African children tend to pay more attention to quantity than quality. However, in a society with a high fertility rate, women have to spend almost all their time on having children and lose their job opportunities.
Today, malaria is still an important factor affecting the fertility rate. As can be seen from the figure below, the area with fertility rate over 4 almost coincides with the stable malaria transmission area.
For the survivors, repeated malaria infection in childhood has damaged the development of brain and body organs, and the learning time of school-age children has also been affected, making it difficult to effectively form the human capital of the whole society. People suffering from malaria are generally depressed, lack initiative and focus on short-term interests.
In the past 200 years, the progress of epidemiology has eliminated most deadly infectious diseases and pushed the remaining few to the brink. But malaria, the oldest infectious disease, is still the last fortress standing in front of mankind.
In 20 12, there were still 200 million cases of malaria infection, and 600,000 people died of malaria. Although the infection rate and mortality rate in most countries have been controlled, the stable malaria transmission area in sub-Saharan Africa has not been broken and the situation has not been greatly improved.
In fact, with the help of DDT and chloroquine, a specific drug for malaria treatment, by the 1960s, more than a dozen countries had eliminated malaria, and the number of cases in India, a major malaria country, had dropped to 654.38 million+people. It seems that victory is just around the corner. 1962, rachel carson published the best-selling book Silent Spring, which pointed out the toxicity of DDT and predicted the drug resistance of Anopheles.
Since then, DDT has been banned in the United States, and drug-resistant Anopheles and Plasmodium have appeared separately, and have been reintroduced to Africa from Southeast Asia. At present, a completely effective malaria vaccine has not yet appeared, and it is also a difficult problem to completely control Anopheles in tropical areas. This infectious disease since ancient times is destined to accompany its host for a long time.