I don't believe it ever was Bartels intent to put decisive numbers on the causes of emotionality and my closing sentence was more of a taunt than a serious statement. You took the bait, but you're dead right in conveying the risks such generalisations entail.

In Bartels' defence, science is not (always) about that; it's about finding stuff out that are interesting, finding new frontiers. There is little knowledge, apparently, on how the biological component influences our psychological state. Personally, I find that fascinating and would want to know more what's going on there.

I see it like this and I make an analogy to my reaction to REACH, the legislative approach in Brussels to make companies test their chemicals thoroughly before they are put in consumer products. My first response to REACH was, "Oh no, there we go again with the aspartan angst and all the public legends." But thinking about it a little more (and also interacting with others), I came to the conclusion that it was far, far better to know more about all the consequences of chemicals than to not know, and take the hysterical reactions (which I believe would undoubtedly come) for granted. In that respect, I view this research somewhat similar. I'm more inclined to know than to not know.

Consider though. There's growing evidence that the occurrences of asthma (and allergies) are linked to certain foodware, and especially emulgators, flavour extracts etc. But that's not enough to explain it: there must also be a genetic variation that makes some people more susceptible to responding to these foodwares and cause an increased risk in getting asthma. So if this is true (it hasn't been proven), this is a two-pronged problem: genetics and environment. But it will undoubtedly help if the specialists can determine how large the influence is of the genes in this. I think the same can be true for the problem of depression: if you are genetically "weak" in happiness, you would be more susceptible to the environmental/nurture factors. That doesn't eradicate the legitimacy of their unhappiness.

Last point, as I said to whataboutbob as well, I find it interesting that many in this thread immediately lodge onto the downside of the issue, literally. Can we equal a lack of happiness immediately to depression? I doubt that, but I'm not an expert at all...