Conclusion So what causes depression? Well, after thousands of years of theorizing, and tons of modern research, the short answer is: we still don’t really know. Depression is complex. While it’s tempting to point to one specific cause, the reality is that depression is the result of several factors intermixing in ways that are nearly impossible to untangle. Because the causes of depression are so complex and varied, we may in fact never be able to precisely pin down its origins, especially on an individual, case-by-case basis. Whether the evolutionary theory of depression turns out to be accurate or not, the actions it prescribes to cure it are decidedly some of the most effective for leashing the black dog: living more like our forebearers by eating healthy, exercising, reducing stress, getting out in nature, belonging to an intimate community, etc.