Anxiety is an adaptive human experience that may occur at all ages and serves to
help draw attention to, avoid or cope with immanent threat and danger. Given its
evolutionary importance, it has strong genetic and biological underpinnings, and
when it serves that adaptive function for the organism, anxiety may be viewed as
useful. However, complex adaptive systems, such as our adaptation to threat or
stress, by definition provide many and often interrelated points of breakdown or
dysregulation, which, if sustained, may lead to psychopathology. Anxiety has
been described as a common currency for psychopathology, indicating that it is a
first line and universal way for us to respond to stress and threat. It is more
or less prominent in patients diagnosed with practically all psychiatric or
neurodegenerative disorders. This has lead to the inclusion of anxiety as a
cross-cutting symptom measure in the development of DSM-5 (APA, 2013). Given
that they are rooted in a complex adaptive system that has many potential points
of impact to develop pathology, it is not surprising that anxiety disorders are
extremely heterogeneous. This heterogeneity of anxiety disorders pertains to
symptomatology, etiology and outcomes, and poses great challenges to both
research and clinical practice.