Most people carry an intact version of TAAR5, and easily recognize the fishy fragrance as mildly repulsive — an ability that might have evolved to help our ancestors avoid spoiled food. But a small number of the Icelanders in the study carried at least one “broken” copy of the gene that appeared to render them insensitive to the scent. When asked to describe it, some even mistook it for a sugary dessert, ketchup or something floral.
“They were really not even in the right ballpark,” Dr. Gísladóttir said.
A blunted sense for bad-smelling fish might sound maladaptive. But TMA doesn’t always spell trouble, especially in Iceland, where fish features prominently on many menus. The country is famous for nose-tickling dishes like rotten shark and fermented skate, which serve up about as much odor as you may imagine.
That might be why the TAAR5 mutation appears in more than 2 percent of Icelanders, but a much smaller proportion of people in Sweden, Southern Europe and Africa, the researchers found.
“If they hadn’t looked at this population, they might not have found the variant,” said Bettina Malnic, an olfaction expert at the University of São Paulo in Brazil who was not involved in the study.
Paule Joseph, an expert in sensory science at the National Institutes of Health, noted that these genetic changes could affect, or be affected by, dietary patterns. “It would be good to see a similar study in another population and more diverse group of individuals,” Dr. Joseph said.
Dr. Stefánsson said it’s a shame he doesn’t carry the rare mutation, considering how much cod liver oil he had to swallow as a child at the behest of his mother. Still, he eventually figured out a way to escape the chore.
“I told my mother, ‘I’m not going to have another spoon unless you do it yourself,’” he recalled. “I never took cod liver oil again.”