How the mosquito got a taste of human blood

Around 1.8 million years ago, a certain mosquito in Sundaland, Southeast Asia, smelt the blood of a hominin, Homo erectus. After the first taste, this mosquito species became so attracted to human blood that it evolved its anatomy for the exclusive new diet. 

A paper in Scientific Reports (bit.ly/Mosquito-Blood) suggests that anthropophily (preference for humans as hosts) in mosquitoes evolved just once, soon after the arrival of hominins in Sundaland, and that this ancestral species gave rise to multiple anthropophilic descendant species. It was earlier thought that anthropophily developed several times during evolution, and much later. The ancestral species most likely fed on monkey blood before it took to hominins.

"Only a small number of mosquito species prefer to feed on humans, and those are the ones responsible for spreading most mosquito-borne diseases," says lead researcher Upasana Shyamsunder Singh, who was earlier with The University of Manchester, U.K., and is now a postdoctoral scholar at Vanderbilt, U.S. " I was keen to understand when this relationship began."

She collected mosquito samples from Northeast India, adding them to an earlier database of her PhD supervisor, Catherine Walton, comprising samples from Southeast Asia. The database had both mosquito species which fed on monkey blood and those that sucked human blood. The DNA of 40 individuals from 11 species was sequenced. Molecular dating and ancestral-state reconstruction indicated the evolutionary history of the Leucosphyrus group of the Anopheles mosquito, tracing it to a single ancestral species. Singh points out that mosquitoes did not opt for human blood because they found it tastier. "Female mosquitoes need blood mainly to obtain proteins for egg production," she says.

The paper says that 1.8 million years ago, increased aridity, particularly during glacial periods, likely formed a north-south corridor of seasonal forests and grasslands that facilitated early hominin migration through parts of Southeast Asia into Java. A possible reason for the evolution is that hominins became more abundant in the Sundaland region and were more accessible " which may have created an evolutionary pressure on these mosquitoes to adapt to a new host ", she says.

The study also provides indirect, non-archaeological evidence for the arrival of H. erectus in Southeast Asia. The timing of their arrival in the region remains contentious, with estimates ranging from 1.3-1.8 million years ago, though this study now provides a clearer date.