Most scientists now accept that the nature/nurture debate is not a case of either/or but of genes and environment working together in a complex pattern to influence people's mental health. Researchers from the University of Iowa looked into one example of this examining how genes and attachment work together to influence how good young children are at self-control. They studied 89 children testing them to see whether they had a variation in a gene called 5-HTTLPR, measuring the quality of their relationship with their mothers at 15 months and how good they were at self-control at 25,38 and 52 months. They found that among children who carried a certain variant of the gene insecure attachment to their mothers at 15 months led to poorer ability to control their emotions later. However, those children who had secure attachment to their mothers at 15 months did not have problems with self-control later even if they carried the variation in the 5-HTTLPR gene.
Kochanska, Grazyna, Philibert, Robert A. and Barry, Robin A. - Interplay of genes and early mother-child relationship in the development of self-regulation from toddler to preschool age The Journal of Child Psychology and Psychiatry November 2009, 50(11), 1331-1338