When the first humans started moving out of Africa some 350,000 years ago, they looked for dry areas — the savannah grasslands, the deserts of southwest Asia. Because tropical regions, while bountiful with food and water, were also home to malaria-carrying mosquitoes. So, why prehistoric humans entered India — where it was wet, warm and humid — about 70,000 years ago has puzzled scientists. But a new study offers an answer.
The malarial parasite in prehistoric India is likely to have been the more benign variant. “Nor should we forget that India’s own medical system was able to take up the fight against diseases thousands of years ago, while in other malaria-affected areas of the world, a similarly effective, Ayurveda-like medicine system did not exist,” Dr Attila J Trájer, lead author of the study published in ‘Quaternary International’, told TOI.
The study, by scientists from the Sustainability Solutions Research Lab at the University of Pannonia and funded by the Hungarian government, examined why ancient humans preferred dry and arid areas. They studied 449 archaeological sites, 94 of which are in India, to understand what determined the settlement and migration patterns out of Africa. “It seems mosquito-borne diseases, like malaria, could have a strong effect on the population dynamic of ancient humans,” Trájer said.
Malaria-carrying mosquitoes are believed to have appeared between 28.4 and 23 million years ago, long before humans. “It is almost certain that the common ancestor of humans and primates already had at least one malaria parasite,” said Trájer. “As in the present times, it is plausible that malaria caused high mortality among children under 5 year and pregnant women.” Which means malaria parasites evolved with humans and apes, and biological factors were just as important as climate in charting the course of humans across the face of the planet.
The movement towards South Asia, about 60,000 to 70,000 years ago, consequently, was an aberration. “At this moment, two parasites — Plasmodium falciparum and Plasmodium vivax — cause 40-60% of the malaria cases in India. In the past, before the Neolithic Revolution (about 12,000 years ago), the more benign vivax malaria may have been the dominant form in Indian peninsula. The more severe falciparum may have been absent from the subcontinent,” he said.
A genetic marker for long-term falciparum malaria impact, for instance, was found in Indian Ocean coastal areas of what is now Iran (Strait of Hormuz) and Pakistan (Kathiawar Peninsula), it was absent in western India. “It means that in the last thousand years, (falciparum, the more deadly) malaria was not endemic in this area, … the most important natural strait between southwest and southeast Asia,” the study said. The other, Plasmodium vivax, may even have evolved in south Asia “and only returned to Africa in historical times,” Trájer added.
When it did evolve, India gradually developed a form of medicinal system to stave off such diseases. “Then, climatic conditions naturally changed over time and trading, and the technological and cultural development of mankind also affected the geographical malaria risk patterns.”