evolution: good and bad, at the same time

Through my life in NUS, it is admittedly the first time I see two vehement camps in Evolutionary Biology.

Evolutionary Psychologists seek to answer this question to every phenomenon:
-How is this maladaptation a consequence of the long evolutionary history of mankind?

Human Behavioral Ecologists seek to answer another kind of question:
- How is this trait beneficial in its own way to have survived in the gene pool?

I was talking to a Psychology student, trying to explain to her why the wearing of high heels increases fitness. To that, she frowned and responded: "Just because depression is on the rise, do you say that depression has massive advantages and is therefore not eradicated from the population?"

I frowned. I was stumped.

"Well," she continued, "The reason why depression is on the rise is because of change in environmental circumstances. Stress, which had not been present in the past, has overwhelmed and activated the once-silent genes of depression present in a certain percentage of the population."

Sounds convincing. So I went to my evolution class after that having this idea in mind - not everything should be argued as "fit". My classmates were presenting on Non-suicidal self-injury, or in layman terms, self-mutilation. I frowned. Such a morbid topic.

"These people who engage in NSSI are fit."

My jaw dropped. If depression isn't "fit", this is definitely a maladaptive trait!! It must have arisen because in the past there were less stress, more social activities (think tribal), less boredom, greater need to roam and hunt. I raised my hand but my professor missed it. He responded to one of the similar questions in the class, "This trait is fit relative to other depressed sufferers."

My god. He succeeded. He was still consistent with his argument on fitness, in that every single trait has its own fitness!!

How can this be? Two sides to a coin, and both sides never meet. Evolutionary psychologists treat everything as an "exception", hence they are studying such phenomena. Human behavioral ecologists treat everything as the "norm", and seek to explain why such phenomena exists, by normalizing them.

From a commenter:
Evolutionary psychology does seek to explain the phenomena in terms of its evolutionary adaptiveness. Hence, they also claim that maladaptive traits/disorders are actually adaptive in some sense. Thus, are really talking about the same thing, rather than 2 sides of the same coin.
And as for your Psychology friend, it just sounds like she doesn't buy the Evolutionary perspective, and she is right that it is unlikely to explain maladaptive traits. Still, the evolutionary prespective is very useful in explaining many phenomena, but it cannot explain everything too (although it tries..and seemingly fails). In that sense, that is when other frameworks/perspectives should be used, like the environmental demands, etc..