Personality是the combination of characteristics or qualities that form an individual’s distinctive character，即个性；例如︰John has a very strong personality.(约翰的个性很强。)Mary has a sunny personality.(玛莉是个乐观开朗的人。 )
Personality也解lively, engaging qualities，气质；例如︰She has loads of personality.(她是个富有独特气质的人。)一个人的个性、性格也叫character，the mental and moral qualities distinctive to an individual，个人的独特心理与道德特质。
已故美国心理学家Gordon Allport是研究personality的先驱。他这样形容personality︰”Personality is and does something … It is what lies behind specific(特定的、具体的) acts and within the individual.”
Personality决定一个人待人处世的态度，故常说“性格决定命运”，但决定性格的又是什么？是先天的遗传，还是后天的培养、环境和经验的影响？这些都是从科学角度问的问题。而有些心理学前辈就认为和生理有关。 Christian Jarrett在”The hidden side to your personality”一文中写道：
Some of the founding fathers(创建人) of the psychology of personality wondered about this very question. Writing in 1961, the US psychologist Gordon Allport said he had faith that “sometime in the distant future, well-proved facts concerning personality will be found to interlock(相扣) with well-proved facts of human biology.”
近年有研究就发现︰
Looking inside our body gives greater clues. And a trickle(细流) of recent findings has recently turned into a torrent(急流), as studies are now revealing how personality is linked with many aspects of our biology, from our hormones(荷尔蒙) and our immune system(免疫系统) to the microbes(微生物) in our gut.
荷尔蒙和细菌
首先是cortisol，a type of steroid hormone which will be released when humans face stress or have low blood glucose，人类的一种肾上腺素荷尔蒙，当人承受压力或血糖过低时它就会分泌。有研究发现：
The higher that participants scored on the trait of conscientiousness (which is associated with self-discipline, orderliness and ambition), the lower the levels of cortisol in their hair.
Conscientiousness是责任心、有良心、认真、尽责。 Conscientiousness关乎自律、条理，志向。 “This study therefore provides early evidence that highly conscientious people are also less likely to be stressed.” Conscientiousness高的人不太容易觉得受压、焦虑。在基本心理上，他们是”less sensitive(敏感的) to stress”，故亦较健康和长寿。
另有研究发现︰”a small but significant(重要的) association between higher scores on neuroticism(神经过敏症) and levels of Gammaproteobacteria”。 Grammoproteobacteria是肠脏中的有害细菌。研究发现这些细菌与neuroticism的性格有关联。
People who score highly on this trait (neuroticism) are prone to(容易) anger, hostility(敌意), low moods and worry. They are also more at risk of poor physical health.
说不定不久的将来，我们随了靠观察和问卷外，也可以用验血、量度心跳率或荷尔蒙和肠道细菌来找出一个人的性格。 Daniel Nettle的Personality: What Makes You the Way You Are，解构性格之谜。
