ABSTRACT
Theories dating back millennia attribute different personality types to physiological differences, to significant life events or to both. Formal psychological theories linked physiology and personality characteristics through theories of body type or embryological development or brain functioning. Other personality development theories focus on life events. The author goes to talk first about theories which root personality in physiology, and then about the formative role of certain life events. Both formal and informal ideas about personality and physiology have difficulties around the diagnosis of personality and the diagnosis of physiological differences and life events, none of which is straightforward. The author discusses one important regulatory system that is fine-tuned by early experience earlier, the hypothalamic pituitary adrenocortical (HPA) axis. If the HPA axis becomes over-reactive or under-reactive, there is an increased risk of physical and mental disorders. The author notes the importance for infants of managing stress reduction and emotion regulation.
