This time difference, according to the researchers, suggests that the feared objects "popped out" from the display and were detected more automatically.
In a related experiment, the researchers found that people who had indicated on a questionnaire that they were afraid of snakes or spiders identified the fear-inducing images even faster than they identified the objects that did not evoke fear. This quicker response by people with a phobia about snakes and spiders is an emotional reaction that enables them to better avoid the objects they fear, the researchers said.
"Evolution has equipped mammals with a readiness to easily associate fear to recurrent threats in their evolution," said Öhman. "Thus, given that fear is activated when a snake is around, they condition fear to the snake much easier than to other stimuli that are around."
Evolution of Perception
LeDoux said that while the research is sound, it's difficult to make any conclusions about the evolution of perception with utmost confidence because there is no fossil record.
Richard McNally, an associate professor of psychology at Harvard University in Cambridge, Massachusetts, agreed. "The biggest challenge that we face in considering these theories of evolution is we cannot recover the evolutionary historythere is no fossil record," he said. "People seem to have different thresholds for saying what is a plausible account of evolution."
McNally questions, for example, whether mammals really have evolutionary cause to be afraid of spiders. Only 0.1 percent of the 35,000 different kinds of spiders in the world are poisonous, he noted.
Öman acknowledged that more research is needed to bear out the findings of the new study, but he contends that a fear of snakes, at least, seems to be shaped by evolutionary influences.
"Snakes have provided a recurrent threat throughout mammalian evolution," he said, adding that "individuals who have been good at identifying and recruiting defense responses to snakes have left more offspring than individuals with less efficient defense systems."
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