A genetic study on mosquitoes from northeastern India and Southeast Asia has traced the evolution of human-biting preferences in certain species to around 1.8 million years ago.
Scientists have found that the malaria-transmitting Anopheles species developed a taste for humans around 2 million years ago, a period overlapping with the arrival of Homo erectus, an extinct ancestral hominin species, into southeast Asia 1.8 million years ago.
The preference for feeding on human blood appears to have evolved across the Malay peninsula, Sumatra, Java and Borneo long before modern humans arrived there 76,000 to 63,000 years ago — and before these malaria-carrying mosquitoes’ ancestors developed the trait in Africa an estimated 509,000 to 61,000 years ago.
“Human blood-feeding in Anopheles species emerged far earlier than previously anticipated,” Upasana Singh, a biologist and postdoctoral researcher at Vanderbilt University in the US who led the study, told The Telegraph. “And it developed independent of the arrival of anatomically modern humans.”
Singh said this contrasted sharply with other disease-spreading mosquitoes, including Aedes aegypti and Culex pipiens which shifted feeding preferences to humans only within the past 10,000 years alongside the demographic expansion of modern humans.
Earlier research had shown that mosquitoes originated more than 200 million years ago and fed on vertebrates for tens ofmillions of years. But among the 3,500 known species of mosquitoes, only a small fraction show a preference for human blood.
In their study, Singh and her colleagues from the University of Manchester in the UK and the Indian Council of Medical Research sequenced the DNA of 38 mosquitoes from 11 Anopheles species, including Anopheles baimaii, a malaria carrier across northeastern India and Southeast Asia.
The researchers used the DNA sequences, computer models and estimates of DNA mutation rates to reconstruct an evolutionary family tree of the Anopheles genus.
Their study, published in the journal Scientific Reports on Thursday, suggests that the ancestors of the Anopheles group werefeeding on monkeys and gibbons in the Malay peninsula, Borneo, Sumatra and Java before the arrival of Homo erectus there.
The mosquitoes’ shift away from feeding on tree-dwelling monkeys to feeding on humans, the study suggests, involved a two-stage process.
First, an increased abundance of ground-dwelling species between 3.5 million and 2.6 million years ago triggered an evolutionary response in mosquitoes to seek ground-dwelling hosts. Then, evolutionary changes leading to a preference for human body odour occurred after Homo erectus arrived in the region 1.8 million years ago.
Scientists have known from evidence based on prehistoric stone tools that Homo erectus lived in southeast Asia around 1.8 million years ago.
“Beyond providing corroborating evidence for early hominin habitation in these regions, our data suggest something more significant: these (hominin) populations had achieved substantial densities,” Singh said.
“The size of these ancestral populations was substantial enough to exert selective pressure on mosquitoes to drive the evolution of human-feeding preferences.”
Mosquito-borne diseases remain a major public health burden, with an estimated 249 million cases and over 608,000 deaths worldwide from malaria alone. Mosquitoes also spread through their bites multiple viruses, including dengue, chikungunya, Japanese encephalitis and West Nile fever, among others.
But the timing and circumstances under which preferential feeding on humans — known as anthropophily — emerged in the Anopheles had remained under debate.