Boys tend to be callous and display unemotional traits because of difference in brain structure, finds a research. Callous-unemotional traits are characterized by a lack of empathy, a disregard for others' feelings and shallow or deficient affect, such as a lack of remorse or guilt. These traits have been linked to deficits in development of the conscience and of empathy.

The findings showed that in typically-developing boys, the volume of the anterior insula or gray matter volume -- a brain region implicated in recognising emotions in others and empathy -- is larger in those with higher levels of callous-unemotional traits. The volume explained 19 per cent of the variance in callous-unemotional traits seen only in, but not in girls with the same personality traits.