Behavioral Ecology Blog

“When there are large populations and behavior of a complex structure, it observably turns out that the individuals of a species can have quite varied forms of behavior and that they may serve the interests of a nest or family or tribe in quite varied fashions,” Nash told psychiatrists. “In some varieties of ants there are specialized members of a nest that are ‘warrior ants,’ and these are quite specialized in their function. And with the bees, only the queen and the haploid drones function directly in the genetics of reproduction, and most of the hive are ‘worker bees.’

Now here Nash is correct I treating mental illness as variation- in some weird way, how we perceive the world around us much be under natural selection- and yes- variability does exist *Just ask my wife* About the specialization and caste structure in eusocial hymenoptera- I’m a little less clear about his point… Is he trying to say that those with mental illness serve some special societal role? What might this role be? I’ll stop here in an effort NOT to offend people..

“It is conceivable that the susceptibility of humans to depression or to bipolar disorder may correlate positively specifically with the composition of poetry,” Nash said. He noted that the American poet Robert Lowell was hospitalized at McLean Hospital near Boston at the same time that Nash was admitted for schizophrenia.

It would be interesting to do an analysis to determine the relationship between mental illness and creativity. Does creativity increase with severity of mental illness- this is obviously not a linear relationship (those suffering from severe mental illness are probably too ill to function in ANY capacity…), but is does seem likely that there is some positive relationship- at least in minor to moderate mental illness. The major challenge with undertaking this type of study would be to detect causality- which is of course what Nash is arguing for..

“One thing about diversity in natural species that is well understood by evolutionary biologists is that the natural phenomenon of mutations serves to prepare a species for adaptation to changing conditions or for improved adaptation to an existing level of environmental circumstances,” Nash said. “This is a topic that has been studied in game theory…. If species are considered as players in a game that continually repeats, and if the species are provided with the possibility of change through mutation of their playing behavior,… then the effect is that the players or species can be shown to naturally evolve so as to get better payoffs from the game

Ummm John, I think you are mistaken here, on 2 different levels. 1st, and most basic is the confusion with levels of selection.. While there is much debate between those the individual levels vs. the gene level- species level selection has been soundly rejected in the literature since Williams laid it to rest over 30 years ago (But see D.S. Wilson and a few others for discussion of “multilevel selection”). 2nd the idea that mutation prepares individuals for environmental change has been discredited multiple times. While it is true that more variable species are more likely to possess the specific capacity to adapt, this is a probabilistic argument- nothing else. It is of course possible that species X with 2 “forms” outcompetes species Y with 20 “forms” given a specific environment. You would have predicted the opposite outcome knowing only of the “amount of diversity” each species had.

“So a possible, but perhaps questionable, inference is that humans are notably subject to mental illness because there was a need for diversity in the patterns of human mental functions,” Nash said.

This is a neat idea- after all what differentiates us from out closest relatives is our ability to have abstract thought processes. While this has successfully aides out transformation into what we are today- it is quite likely that it has come at a price-an increased susceptibility for mental illness.. BUT THAT IS NOT ADAPTATION!!! It’s pleiotropy…

Aside from the Nash’s missteps, one must ask the question… IS mental illness adaptive? If not (and if it is selected against, as I suspect it is), WHY does it continue to be so prevalent? So the 1st question is not as easily answered as I would hope- Does mental illness enhance reproductive success relative to “normal people”? Now severe mental illness seems surely selectively negative- but that about mild and moderate mental illness (by the way- the most common)? It’s not so clear… It might be negative, neutral, or positive. Who knows? Are there data that speak to this question? I imagine that any study that tried to answer this question would be severely confounded by the fact that a very large proportion of depressive disorders are treated with medication and/or psychotherapy.

Not much to say for the contrary view- what if mental illness is selectively negative- why is there so much of it??? Certainly Nash’s pleiotropy is at the top of the list here…

Does anybody know more about this? Are there studies that look at selection and mental illness? I’m fascinated….