- Tom Swan, who managed Ned Lamont’s 2006 Senate campaign.

- Bob Fertik of Democrats.com, who you used to see at every liberal event pushing for the impeachment of former President George W. Bush.

- Paul Hogarth of BeyondChron.

- Todd Beeton of MyDD.com.

- John Arovosis of AmericaBlog.com.

So some of the people you’d expect to join this, but not really a landslide of anti-Specter sentiment. I can think of dozens of prominent progressives who have not joined this particular cause.

Intrigued, I called the study’s head researcher, Douglas Oxley of the University of Nebraska, to see if he agreed with this conclusion.

“In some ways [the study has] been misinterpreted,” said Oxley. He said that his study didn’t find a link between DNA and political leanings. “We could have things happen to us in the womb or later in life that could cause” physiological and ideological differences.

The study, released yesterday, tested the physiological responses of 46 participants to various threatening images, like bloody faces. It found that people who self-identified as “in favor of socially protective policies” responded much more strongly to the stimuli than people who held more liberal views on such issues as welfare, abortion, immigration, gay rights and school prayer.

The researchers concluded that people of different ideological persuasions have divergent physiological reactions, and that people with socially conservative views tend to be more shocked by potentially threatening stimuli.

“Some people have said that we’re calling conservatives ‘frightened’ or something along those lines,” Oxley said. “And we’re not. All we’re suggesting is that there’s a physiological difference between people who hold one set of political beliefs and people who hold another set of political beliefs.”

The study had its limitations — the sample size was small and all of the subjects were white Nebraskans — but it’s still a small step toward a greater understanding our ever-increasing ideological divide, even if the answer doesn’t lie in our genes.