Does parenting influence personality?

According to a number of studies it is very small or even negligible. The latest book I read, The Blank Slate by Steven Pinker, makes reference to studies on the influence of genes and environment on personality. They yield estimates of about 40% of genetic influence and a modest 7% of shared environmental influence. Of the remaining variance, half is due to nonshared environmental influences and half to measurement error.

Personality was measured with five main determinants: extraversion, neuroticism, conscientiousness, agreeableness and openness. Genetic influence on personality was measured in several ways. One was to take the correlation between identical twins who were separated at birth and reared apart. They share all their genes and none of their environment, so any correlation between them must be an effect of the genes. Another way was to compare identical twins reared together, who share all their genes and most of their environment, with fraternal twins reared together, who share half their genes and most of their environment. Genetic influence was then estimated as twice the difference between the correlation for identical twins and that for fraternal twins. The influence on personality of the shared home environment (effects of parenting) was estimated as twice the fraternal twins correlation minus the identical twins correlation.

Other techniques compared biological siblings, who share half their genes and most of their environment, with adoptive siblings, who share none of their genes and most of their environment. The conclusion was always the same, much to the surprise of the researchers themselves, that genes account for 40% to 50% of one's personality whereas that of the shared home environment is negligible. The remaining 50% is argued to be due to nonshared environment and chance.

Based on these studies, contrary to widespread belief, systematic differences in treatment within the family does not explain personality differences. These findings then imply that each individual chooses from a range of stimuli and events largely on the basis of his or her genotype to create a set of experiences; meaning that people's genes help to create their own environment. This view of human development amplifies the effects the genotype has on the phenotype. Therefore, a violent individual isn't violent because his parents abused him, but rather because they are themselves violent (they transmitted to him their "violent" genes).

Link to Steven Pinker's The Blank Slate.

Reference of one of the mentioned studies:
Bouchard, T.J., Jr. 1994. Genes, environment, and personality. Science, 264, 1700-1701.