According to Pew, more Republicans deny evolution than they did five years ago:
David A. Graham ponders the cause of the problem:
One possibility is that respondents who identified as Republican and believed in evolution in 2009 are no longer identifying as Republicans. Fewer scientists, for example, are reportedly identifying with the GOP, and the overall trend is for fewer Americans to call themselves Republicans. But both Gallup and separate polling from Pew found approximately the same party ID in 2009 and 2013. Another is that the rise of “intelligent design” education has helped to swing younger Americans against evolution. Yet the age breakdown remains similar in 2009 and 2013, with respondents ages 18 to 29 most likely to believe in evolution.
What does that leave? Maybe the gap represents an emotional response by Republicans to being out of power. Among others, Chris Mooney has argued that beliefs on politically contentious topics are often more rooted in opposition to perceived attacks than anything else—an instance of “motivated reasoning.” Given that Democrats have controlled the White House and Senate since 2009, this could be backlash to the political climate, though it will be hard to tell until Republicans control Washington again.
Zack Beauchamp weighs in:
A wealth of research into political psychology shows that people’s partisan affiliations affect their beliefs on basic facts.
Republicans are overwhelmingly more likely to think the economy is doing well when Republicans hold the Presidency, and ditto with Democrats when their guy holds the White House. A recent experiment found that even basic math is contaminated by politics; people are much more likely to correctly solve basic math problems when, in context, solving them correctly helps rather than hurts their party.
In the evolution context, this suggests a feedback effect at work among Republicans. As the GOP becomes more associated with the creationist cause as a consequence of demographic shifts, Republicans start to feel more like being skeptical of evolution is their “team” position. So even Republicans who are demographically more likely to accept the basic science of evolution start to reject it, because that belief best harmonizes their beliefs with the perceived interest of their political party.
Allahpundit notes that “Gallup detected movement away from the creationist position among Republicans over roughly the same span that Pew was detecting movement towards it.” But he acknowledges that Pew’s numbers might be correct:
[M]aybe this is a simpler partisan impulse, where contempt for the political worldview as personified by the president bleeds over into some people’s judgments about perennial cultural disputes too. Wouldn’t surprise me to find support for evolution among Democrats rising a few points once the next Republican president takes office. It’s a defensive impulse against a political opponent who’s taken power, whether that impulse is really justified or not.