Some problems with the speculation, known to anyone who has read about or dealt with depression:
* Difficulty concentrating is one of the symptoms of depression. You can't think.
* Depression typically begins for no apparent reason in the person's life circumstances. It's often seasonal, triggered by things like changes in the length of the day.
* Depression doesn't lift when you've solved a problem. It lifts for no apparent reason, too.
* Depression is often fatal.
A better speculation: depression is a disorder of the circadian rhythms.
Reading over a few of the abstracts, the consensus appears to be that depression can be caused by defects in circadian rhythm, but that the relationship isn't necessary, and may not be sufficient. If I were you, I'd ease off on using "amateurish speculation" as an epithet in this situation.
Difficulty concentrating is a tricky symptom. Depressed people may have difficulty concentrating on what they want to think about, but they may ruminate obsessively on unpleasant topics. That fits nicely with the article's speculation that depression is "nature’s way of telling you that you’ve got complex social problems that the mind is intent on solving."
Some problems with the speculation, known to anyone who has read about or dealt with depression:
* Difficulty concentrating is one of the symptoms of depression. You can't think.
* Depression typically begins for no apparent reason in the person's life circumstances. It's often seasonal, triggered by things like changes in the length of the day.
* Depression doesn't lift when you've solved a problem. It lifts for no apparent reason, too.
* Depression is often fatal.
A better speculation: depression is a disorder of the circadian rhythms.