Each one of us has some risk for becoming depressed. For some the chance might be remote, while for others it can be almost inevitable.

　　我们每个人都有一定程度的抑郁风险。对于有些人来说，机会很小；对于另一些人来说几乎不可避免。

　　We all have our own vulnerabilities for depression, based on our life experiences, health conditions, substance use, and genetic predisposition. A person's risk for becoming depressed at some point in his or her life ranges from low to high, based upon the interaction of all of these factors.

　　对于抑郁，我们都有各自的薄弱点，这些可能和人生经历、健康情况、物质滥用和遗传易感性有关。在这些因素的共同作用下，一个人一生中的抑郁风险有高有低。

　　A good general way to think of the factors that lead to depression is with the two-hit hypothesis. This model suggests that people become depressed when the effects of their genetic composition—which itself puts them somewhere on a scale of low-to-high likelihood of eventually developing depression—combine with stressful life experiences.

　　采取“两步假设法”可以从宏观上了解这些因素是怎样导致抑郁的。这个模式认为，在基因组成（其本身也对产生抑郁影响有高低之分）和充满压力的生活的共同作用下，人们就抑郁了。

　　Even those individuals with a low genetic tendency for depression can become depressed when they experience extreme stress. On the other hand, people with strong genetic predispositions may become depressed without experiencing much stress. Naturally, the people with both high stress and strong genetic predispositions are the most likely to have a depressive disorder.

　　即便一个人抑郁的遗传倾向程度低，但是处于极度压力下的时候，这人也会抑郁；同样，抑郁的遗传倾向程度高的那些人，即使没处于压力环境中，也可能抑郁。自然地，那些高压力、高(遗传)基因易感性的人患抑郁症的可能性最大。

　　While the two-hit hypothesis is useful conceptually, making predictions for particular individuals is still a challenge. For example, because of their psychological characteristics, people respond to stress in different ways. Plus, the genetics of depression is not as simple as something like eye color.

　　虽然这“两步假设法”理论上行得通，可是要预测特定个体，依然是一个挑战。例如，心理特征不同的人对压力的反应不同。另外，抑郁的基因可不像决定眼睛颜色的基因那么简单。