But I also agree with Conor that Nesse has come up with nice evolutionary explanations for the adaptiveness of depression and similarly maladaptive seeming traits. Why we Get Sick is a great book.

If you’re going to be thinking about potentially maladaptive traits from an evolutionary perspective I recommend the following stuff as a brief introduction:

http://www-personal.umich.edu/~nesse/Articles/Nesse-EvolMed-SciAmer-1998.pdf

http://www.youtube.com/watch?v=pcnCJqDa1us

If it interests you further I have Nesse and Williams’ book on Darwinian medicine that offers some ways in which to look at potentially crappy things, e.g., antisocial behavior from an evolutionary perspective (although behavior etc is given a relatively small amount of space in the book).

Caspi et al. (2002): The effect of childhood maltreatment (ages 3-11) on antisocial behavior (mid-20s) stronger for men with inhibited promoter for MAOA activity.

Caspi et al. (2003): Given the presence of stressful life events between ages 21 and 26, individuals carrying at least one “s” allele of the 5-HTT gene show steeper increases in depression and greater likelihood of onset of depression than individuals carrying no “s” alleles.

Okay, this is cool. Regarding a couple of Conor’s points, they are both good examples of continuous, rather than dichotomous, genetic switches, and the first one is a nice example in which behavior is shaped largely in a critical period of childhood.

I think they largely point to unconscious processes driving personality development. The explanation for the 2002 paper is that individuals with low MAOA activity are less able to withstand the neural system damage & stress that results from childhood maltreatment, and thus are more likely to become antisocial. The explanation for the 2003 paper is that possessing an “s” allele on the 5-HTT gene increases an individual’s overall reactivity to stressors (acute or prolonged), and thus these folks have a propensity to be more stressed out and become depressed.

I can’t think of a good post-hoc explanation for why either of these findings would represent a conscious personality development strategy. Maybe maltreated children intentionally become antisocial to fight back against their crummy, dangerous home environments? Maybe naturally stressed & reactive people act more depressed to elicit sympathy and support from others in times of significant life challenges? Those types of explanations seem to be a stretch; they require us to invert our thinking about what shades of personality are adaptive. Conscientiousness and self-control are adaptive, not impulsivity and antisocial behavior, right? Emotional stability is adaptive, not depression, right?

What do you guys think?

Whereas the examples from the Hagen and Hammerstein paper were more discrete in nature, personality seems to be more of a continuous kind of thing, I think. From what the authors describe, the water flea Daphnia either grows a protective helmet or doesn’t grow a protective helmet based on the presence or absence of a cue in the environment which when present flips a genetic switch. So, I think any argument for a strategic (in the evolutionary sense of the word) view of personality may be more complicated than an argument for the same view in the helmet development of a water flea (surprise surprise!).

I think the following and more would have to be disentangled:

a) whether we are talking about genetic switches, and if we are, how this leads to continuous rather than discrete change,
b) whether there is a sensitive or critical period for certain aspects of personality or whether malleability remains throughout the lifespan (if certain aspects of personality or more or less malleable you might as why, under this strategic framework), and
c) whether strategic dispositional flexibility is encoded a priori into the nervous system as a form of learning.

Maybe I misunderstand but I’m not sure I would attempt to separate conscious processes from more “automatic” or unconscious processes by classifying them as different types of adaptation. In other words, while consciousness and reasoning probably make thinking about adaptation more complex, in my mind conscious processes can reflect the workings of adaptations and unconscious processes can reflect byproducts or noise and vice versa.

One way to view the question you are asking is whether flexible disposition shows evidence of design and within our understanding of how genes shape and maintain nervous systems/behavior, etc.

Re. personality psychology showing greater external validity: not surprising. Off the top of my head, here are two explanations (which are not mutually exclusive). First, correlational studies almost NEVER are published on the basis of single studies reporting ONE correlation. Personality researchers measure and correlate a bunch of stuff, and interpret results by closely examining correlation matrices, not searching for one particular correlation. And, if matrices reveal inconsistencies, few researchers (I hope) go onto report the one significant correlation that emerged. This is quite a contrast to the typical social psych study that includes one DV, and gets written up and published on that basis. It’s much easier to get a false positive when this is the norm, than when you’re looking for, and reporting, several different correlations/effects that are all consistent with a general theme. Second, the emphasis on external validity is one of the (many) philosophical bents that differentiates personality from social researchers, as was found in our 2008 paper (Tracy, Robins, & Sherman, JPSP) on this topic. As we argued there, this difference may be in part due to a difference in what researchers think they’re doing. Personality researchers believe that they are measuring constructs that predict real world behaviors and outcomes. Social researchers do too, but many of them also think that the mental processes they study are themselves important– reaction times tell us something about how the mind works–regardless of whether they predict anything else beyond that in the real world.

It’s hard to see some line of people who were extremely high or low in any of the big five traits reproducing more successfully than those who had all five in a healthy moderation.

For the purposes of blogging, here’s a weird theory as to why high levels of neuroticism could have helped in the evolutionary past. We know from animal research that even highly monogamous species (some birds) cheat on their mates, essentially, females want to make babies with a bird that sings pretty songs but they want to build a nest and care for the babies with often a much duller mate, a mate who is going to be faithful and see the offspring to maturity so they can continue the line. That’s pretty similar to what humans do too. A neurotic male might be highly protective of his mate thus cutting off her opportunity to cheat (and smashing babies that he fears might not be his own, this was big back then no jk), this way he ensures paternal certainty and keeps the pair-bond going until the child reaches sexual maturity. Males low in neuroticism would prolly just raise the cuckold’s baby and chill on a vine somewhere until his line was all but wiped out.

Another weird theory could be that gossiping and perspective taking (I’m assuming people who are highly neurotic do this…) could have lead to more complex thinking and rapid brain development.

Crude example perspective taking ->
“I’m gonna kill that boar aagghhhh” < - Low neuroticism (dies).
"If I sneak up behind the boar, he won't see me" <- High neuroticism (kills boar, shares boar, gets mates).

Crude example gossiping ->
“K, see you later honey!” <- Low N (she’s going to cheat on her mate, have other dude’s baby, his genes get passed, not yours)
“K, see you later honey!”…(to Grog) “Where she going Grog?” <- High N (Grog tells him, he intercepts)

Anyways, I’m prolly wrong but just sayin’

Alec