I'm a bit jaded by science. Yes, there's substantial evidence that life can travel from one planet to another, or at least from Mars to Earth, which strongly suggests that life on Earth came from Mars. What's more, there may be life on Mars still! Yes, but those are just microbes, so... Also, if life on Earth started on Mars, how did life on Mars start? Psychology as a field and a science is almost entirely underwhelming. Virtually every recent finding using MRI machines is deductive at best and maybe even borderline fraudulent, as, really, MRIs just track the infusion of oxygen from one region of the brain to another. They certainly don't answer why or even if a center is functioning in response to a given stimulus, be it religious icon, sexual object or the chance to commit altruism. Ad inifinitum, ad nauseum, so on and so on.
It's really, I suppose, just jadedness from being exposed to so many scientific findings that fail to give a full, satisfactory explanation. So you can imagine how excited I was when I came across a passage in an article on the principles of neuroarchaeology that mentioned how the SLC6A4 gene affects human personality. This particular gene is responsible for encoding the protein that is in turn responsible for transporting the neurotransmitter serotonin from the synapse, where it actively works its hoodoo, back to the neuron from whence it came. This transporter is the vehicle, literally, for the process of reuptake, which is where a neurotransmitter's function is switched to the off position.
There are two types of versions (alleles) of the SLC6A4 gene, a long (L) version and a short (S) version. Research has found that people with the S version of this gene produce fewer of these transport vehicles than people with the L version. Serotonin has the effect of raising our response to stress in part by stimulating the amygdala, which is pretty much the thing that makes you honk your horn and shout expletives in traffic. So people with heightened anxiety suffer because there's a lot more serotonin hanging out in their synapses in much the same way the neighbors suffer from a loud party at all hours of the night. When you have enough cars to get everyone back to their place, the party dies down and the neighbors can get some sleep.
People with the L version tend to respond less acutely to stress, including chronic stress and so it's here that we've just arrived at the genetic basis for the distinction between Type A and Type B personalities. From now on we can call them Type S and Type L instead.
But that's not all the neuroarchaeology article had to share. These same researchers that demonstrated a link between the SLC6A4 gene and high-strungedness and laidbackedness took their findings further in another study. Not only are people divided into these two types of personalities, so too do they give rise to at least two types of societies -- those that prize collectivism, where the good of the group is valued above individual achievement, i.e., Japan or North Korea, and individualist societies, the kind like the United States, where people love rags-to-riches stories of individuals gaining wealth.
It turns out that collectivist societies tend to have higher concentrations of S-allele variants of the SLC6A4 gene, while individualist societies tend to have higher concentrations of the L version of the allele. Part of this is genetic selection, more people with the S allele reproducing together will beget more S allele offspring, but the researchers concluded that collectivist cultures are also the result of S-allele people clustering in groups based on the finding that collectivist cultures display lower prevalence of anxiety than S-allele individuals at large.
Sure, these findings can be used for evil, perpetuating the us-versus-them isolationism humans of all personality types value. But it's a really satisfactory explanation of the very curious fact that nations, like people, tend to exhibit characteristic personalities and that is good enough for now. [youtube=http://www.youtube.com/watch?v=7rncfjgPIK8&w=610]