Why did humans evolve to be traumatizable? Why did humans evolve to be traumatizable, instead of being more resilient and treating trauma in a detached manner? Don't symptoms of trauma reduce a person's biological fitness? Is PTSD an adaptation, and if so, what is it an adaptation for? After all, the stress reaction and emotional imprinting appears to be designed rather than an accident.
There are a lot of assumptions you are making here. &quot;Being traumatizable&quot; isn't really a trait. We evolved a brain in a certain way, with an amygdala and hippocampus that work a certain way. Those components have been critical in our ability to form knowledge + interact socially with one another. Instances of malfunction in the face of trauma/PTSD are a side-effect of an imperfect biological system, BUT that doesn't render the whole system useless/detrimental in the evolutionary sense.
Secondly, you're assuming it does reduce biological fitness. I'm sure it makes it harder in indirect ways, but ultimately, PTSD symptoms actively mess with very few people's ability to have sex and pass on genes. PTSD does seem to have a strong, albeit complex genetic component. For as long as people with PTSD are reproducing (and most of them are) then there will be a genetic predisposition for developing PTSD in the gene pool.
Third, how is it designed? I am confused by this one. People have a tendency to wrongly assume that almost every trait is an adaptive trait. Maybe in this case it is and we just haven't found what the beneficial feature is BUT, it is highly more likely and logical that a) as stated above, it's just a by-product of another highly adaptive trait aka, our particular brain structure and function. They come in a 2-for-1 deal and as much as PTSD sucks or might reduce biological fitness, those are completely offset by the benefits and increase in fitness due to our brain circuitry.
OR b) it's a neutral variation that doesn't significantly increase or decrease our fitness, therefore is maintained in the population because it has no reason to be selected out. Another reminder that our own negative human experience of suffering through PTSD doesn't inherently mean much in the eyes of evolution, as long as we can reproduce.