Why do some people not have them?
(please read part1 for context)
Emotions are evolutionarily valuable if the outward signs are difficult to mask; a fake smile is controlled by the cerebral cortex, and looks different to the natural smile created by the limbic system. However, if the proportion of players that can convincingly fake emotions is at a low frequency, then the majority do not change their life tactics and the rare ability to be a great deceiver gives enough evolutionary advantage to keep those genes in the population.
This explains why Antisocial Personality Disorder is to be expected at low frequency in any population – with the frequency affected by the type of society. I would guess that a society with low mobility and a high cost of being found out (dishonour=shunned forever) would have a lower incidence of sociopathy, but I am unaware of any research to bear this out either way.
Sociopaths may feel the limbic emotions, but not the ones generated in the neocortex (probably related to the smaller amygdala and reduced grey matter in the prefrontal cortex found in the brains of sociopaths). However, they are very capable of reading the emotions of others (in contrast to autistic spectrum traits, which also include lack of complex emotions such as empathy).
There is some evidence that children below the age of 5 or 6 do not have a fully developed neocortex and so are often seen to exhibit sociopathic traits that demonstrate lack of empathy, violence, and emotional manipulation. For example, young children will often look distraught and in tears but when given their toy back will immediately turn it off and appear happy again. In this case, is the child really experiencing the emotion, or are they just simulating it to manipulate their way to what they want?
Of course, as always, the truth is a mixture of many things – a genetic component is proved, and the preponderance towards males being sociopathic is some evidence of a link with autism. This sex divide may be due to genes on the Y chromosome, or possibly due to gene interaction with testosterone.
Nurture can play a role through someone being desensitised to emotions as a defence mechanism from an abusive upbringing. Nurture and environment could also play a role by activating genes.
All the above should be taken as opinion – there is some research material available on sociopaths, but it mostly deals with the incarcerated violent ones as test subjects and so presents a very skewed view of the phenomenon.
click here for Part3
click here for Part3