@Wilso,
People are entitled to their opinions, however wrong it may be.
As collective individuals, republicans are no less smarter than collective individuals who are democratic.
A considerable dominant constituent of the Republican base are Fundamentalists. Fundamentalism being a political philosophy that believes religious leaders should be given political power by virtue of their standing as authorities on religion. As it is known that some aspects of the US political system are not “democratic." As an example, only engineers who are licensed can produce plans and blue prints in order for a city planning department or commission to be recognized. More importantly, engineers and associations of engineers are afforded a certain quasi-official status, such as testifying in court before legislative bodies, or even in the popular press as experts. Reports from such organizations carry much weight in the popular arena, as well as with elected and appointed officials. Fundamentalism is about giving that same un-democratic power to religious leaders based on their religious expertise. Creationism is likely an extension of that political agenda, to create a “science” in which religious leaders would be “experts."
In hopes of winning Fundamentalist votes, the Republican Party has been willing to embrace the Fundamentalist movement. As such, they are at least willing tolerate, if not, actively embrace, creationism and other related anti-science ideas. They do this not from personal or even collective conviction but political calculation. Supporting creationism means votes in elections.
In that manner, the Republican Party embraces the Anti-Global Warming movement. This position is take in order to create a carbon fuel industry which as a pretty clear vested interest in this movement which is obviously non-scientific (or at least anti-climatology). However, the Republican Party has made these movement for its own for cynical political reasons, not simply because they are “stupid," as you believe they are.