As is often the case with me, my comment was semi-serious and semi tongue-in-cheek.

For one thing, I've observed that many brain functions, just like functions in the rest of the body, trend toward sort of a pre-set homeostatis level which can be perturbed but which tends to quickly come back to the 'set' point. Many psychotropic drugs quickly build up a "tolerance".

Then again, I see no rigorous definition of "happiness" here, which is rather a glaring lack. Simply asking people whether they're happy may be more a measure of rationalization than a gauge of contentment. (for instance, to reconcile one's self-image with reality; Festinger's "cognitive dissonance" explains a lot).

Physiologically, you can alter your mood by stuff as simple as deep breathing or modest exercise; is that sort of well-being "happiness"? Is the serotonin boost you get from prozac "happiness"? Or is it something more elusive? It's possible to be contented but deeply concerned. It's possible to have "fun" - fleeting perhaps - even while doing something out of desperation or ignoble motive.

When the Hutu's killed the Tutsi's in Rwanda, they vastly enjoyed themselves. They were happy; it's one mode of human collective action. That sort of happiness will be on the upswing, and it may not be dysfunctional from a biological standpoint.

But hey, it's the pursuit of happiness, right?

With apologies to Roger Miller:

Ya can't roller skate in a buffalo herd
Ya can't roller skate in a buffalo herd
Ya can't roller skate in a buffalo herd
But you can be happy if you've a mind to

Ya can't buy coffee if there's nothing in the store

Ya can't feed a billion when the fertilizer's gone

Ya can't click your heels in a Halliburton camp

Ya can't get a backrub from a cannibal mob

etc.

But you can be happy if you learn to appreciate irony, ignore pain and deprivation, and watch the Big Show. Cultivating low expecations and good drugs may help.

There's probably only one kind of happiness, and even it may not be "real".