Thousands of years ago some mosquitoes made "a really good evolutionary move": They developed a taste for humans. A new study digs into the genes that led to this evolutionary shift, which had many mosquitoes give up on furry forest animals—and it relied on guinea pigs and pantyhose to reach its conclusion. As Rockefeller University explains, school researchers studied two types of mosquitoes in Rabai, Kenya, whose disparate behavior was first observed in the 1960s. Aedes aegypti formosus (black mosquitoes) favor forest creatures, while the brown-bodied Aedes aegypti aegypti prefer humans. The researchers headed to Rabai five years ago, collected mosquito larvae, and confirmed those preferences were still the case after breeding them in the lab.
They then began a process of cross-breeding and sorting that ultimately allowed them to identify an odor-receptor gene, Or4, that was much more highly expressed in human-preferring mosquitoes. To suss out which odor Or4 was homing in on, the researchers had human volunteers and guinea pigs don pantyhose for 24 hours. A machine then sorted out each individual chemical, and one called sulcatone was present only in the stockings worn by humans. But the researchers note that sulcatone alone can't explain the preference; they added sulcatone to guinea pig odor and the brown-bodied mosquitoes showed no increased preference for the odor. Still, the researchers write in Nature that "our results provide a rare example of a gene contributing to behavioral evolution." (Meet the parasite that feasts on mosquitoes' blood.)