Does Prejudice Overthrow Empathy?

According to a recently published study, children with low intelligence are more likely to hold prejudiced attitudes as adults.

I will have to read the actual study in order to capture the important details, which Pappas does not identify in her article.  As much as I am inclined to chuckle at this article, and smugly snort "Why yes, only stupid people could be prejudiced," the article goes so far to say that people with low intelligence would also be more likely to be politically conservative.

So here are my questions:

1. How is "intelligence" being defined and assessed by the researchers?

2. If people with Down's Syndrome or other developmental disabilities are also identified as people with "low intelligence", would people with Down's Syndrome or other developmental disabilities also be more likely to prejudiced or politically conservative?

3. Would Adolf Hitler be considered someone of low intelligence, considering that he was a white supremacist who believed in military dictatorship?

4.  Does being "liberal" make you more likely to be of "high intelligence" and/or less likely to be prejudiced?

5. Is there an assessment tool that defines and measures empathy?  Non-human animals are capable of empathy; non-human mammals will nurse baby animals outside of their species, and non-human animals raised with other species will get along with those different species (including humans).  Do humans operate differently than animals in this regard?

Please feel free to comment and discuss.