(CNN)When humans first began settling in the Galapagos Islands nearly two centuries ago, they brought house cats.
Is fear hereditary? Darwin's frightened Galapagos finches suggest the answer is yes
Those cats hunted finches, scaring the small birds who were unused to the predator. A decade ago, the cat population was largely removed but the finches still act as if they are in danger, puzzling scientists.
"It suggests the behavior could be hereditary, but it could also be other things such as learning or cultural transmission of behavior," said Kiyoko Gotanda, a zoologist at the University of Cambridge.
The finches' fearful responses, which scientists call anti-predator behavior, now pose a threat to their survival, according to a Gotanda's study, which was published Wednesday in the Journal of Animal Ecology.
Humans settled on the Galapagos archipelago, famed for its rich biodiversity that inspired Charles Darwin's theory of evolution, in the early 19th century. Apart from cats, settlers also introduced invasive species like rats, dogs, and pigs -- which spelled trouble for small native island animals.
These animals, including birds and reptiles, displayed little anti-predator behavior back then because they had never seen these new predators before -- they were only used to local predators like owls.
When Darwin visited the islands, which lie 621 miles (1,000 kilometers) from Ecuador, in 1835, he famously got close enough to throw his hat over the birds because they were so unused to humans they didn't see him as a potential threat.
But this "evolutionary naivete" also meant the finches were easily hunted and targeted by the new predators, raising concerns for the biodiversity of the islands, said the study.
The finches eventually did develop anti-predator behavior, learning to fly away when a potential threat approached. And the threat was also lessened over the years -- conservation efforts have seen invasive predators cleared and eradicated from four of the archipelago's 19 islands.