A genetic predisposition to note the negative.

Another interesting example of viewing the world through gene-colored glasses...Todd et al. note an interesting behavioral correlation involving a gene variant, carried by ~50% of Caucasians, of subtype B of the α2-adrenergic receptor: people with the variant are more likely to take note of negative events. They use the "attentional blink" paradigm to reach this conclusion:

The attentional blink...is a phenomenon in which participants are typically unable to identify a target stimulus when it is presented less than approximately 500 ms after a previous target in a rapid stream of stimuli. One interpretation of this blink is that it reflects a failure of attentional filters to consolidate the second target into working memory when it appears too quickly after the first, which results in impaired perceptual awareness. When the second target has emotional significance, there is a reduced attentional blink, or an emotional sparing. This emotional sparing, or reduction of the attentional blink for emotional stimuli relative to neutral stimuli, can be seen as the relative tuning of selective attention to affective stimuli.

Here is their abstract (which contains the fairly common error of using "are responsible for" instead of the more correct "correlate with"):

Emotionally enhanced memory and susceptibility to intrusive memories after trauma have been linked to a deletion variant (i.e., a form of a gene in which certain amino acids are missing) of ADRA2B, the gene encoding subtype B of the α2-adrenergic receptor, which influences norepinephrine activity. We examined in 207 participants whether variations in this gene are responsible for individual differences in affective influences on initial encoding that alter perceptual awareness. We examined the attentional blink, an attentional impairment during rapid serial visual presentation, for negatively arousing, positively arousing, and neutral target words. Overall, the attentional blink was reduced for emotional targets for ADRA2B-deletion carriers and noncarriers alike, which reveals emotional sparing (i.e., reduction of the attentional impairment for words that are emotionally significant). However, deletion carriers demonstrated a further, more pronounced emotional sparing for negative targets. This finding demonstrates a contribution of genetics to individual differences in the emotional subjectivity of perception, which in turn may be linked to biases in later memory.