learned 用作形容词时除表示“有学问的，博学的”和“学术性的”外，还有一个意思是，就是表示“通过后天学习得来的”“通过学习（或经验）获得的”。你的句子意思是：
Obviously, it’s a learned response—people aren't born that way. 很显然，那是后天习得的反应——人们并非生来如此。
又如：
Speaking a language is a learned behavior. 说语言是后天的习得。
These eating patterns are a learned behavior. 这些进食模式是习得性行为。
Your anxiety is a learned reaction, and it is nurtured and sustained by the events of your everyday life.  人的焦虑是后天反应，由日常生活中的事件催生和维系。