Apparently, mosquitoes didn’t always love the taste of human blood: it was a clever evolutionary adaptation, American researchers have found. To arrive at their conclusion, they dressed people and guinea pigs up...in pantyhose.
Our bodies exude a specific chemical vapor known as sulcatone – that’s what the little pests came to know and love.
"They've acquired a love for human body odor, and that's a key step in specializing on us," Professor Leslie Vosshall of Rockefeller University in New York explains.
The study by Vosshall and her team was published in the journal Nature.
More specifically, thousands of years ago an evolutionary split emerged between mosquitoes feeding exclusively on furry forest beasts and those who like humans as well. It’s all down to the 14 genes that scientists now say are linked explicitly to a love of human blood.
One specific evolutionary mechanism that came out of the genetic adaptations is OR4 – a receptor, which “we found recognizes a compound present at high levels in human odor,” researchers say.
The study is remarkable in that its results “provide a rare example of a gene contributing to behavioral evolution and provide insight into how disease-vectoring mosquitoes came to specialize on humans.”
Apparently the mosquitoes picked up the trait several thousand years ago. They figured that a whiff of sulcotane must mean human settlements nearby. That equaled food and water.
“It was a really good evolutionary move. We provide the ideal lifestyle for mosquitoes. We always have water around for them to breed in, we are hairless and we live in large groups,” she added.
Pantyhose & guinea pigs
To arrive at their conclusions, the scientists asked volunteers to wear pantyhose for 24 hours. They then placed the worn garments in a special machine designed to separate the chemicals that make up our body odor from one another.
That’s how they arrived at sulcatone. The chemical didn’t show up in pantyhose worn by guinea pigs (yes – guinea pigs. In pantyhose.)
Sulcatone was found to give our body odor the trait that makes it specifically human. But scientists emphasize that there are other, unstudied mechanisms or traits that separate us from animals as well.
Despite sulcatone being the operative chemical here, it was found that adding it to the odor of a guinea pig did nothing to boost the mosquitoes’ thirst for guinea pig blood.
The team believes that to become truly comfortable around humans – let alone see them as a source of food - thousands of years needed to pass.
"There's a whole suite of things that mosquitoes have to change about their lifestyle to live around humans," Vosshall explains. "This paper provides the first genetic insight into what happened thousands of years ago when some mosquitoes made this switch."