All of this helps explain why internet use can arguably become addictive in the sense that some chemicals are addictive -- that is, we can develop a dysfunctionally strong devotion to the internet, a devotion that leads us to neglect obligations and responsibilities (such as getting a novel written). After all, the internet, like these chemicals, allows us to trigger our neuronal reward mechanisms with much less work, and much more frequently, than was possible in the environment of our evolution.

For example: In that environment, there was no pornography, much less the vast and instantly accessible supply found on the web. Nor was there the nearly infinite supply of gossip that is available now that we can spend our time trolling Facebook or living vicariously among celebrities and following their lives on TMZ. Nor was a robust round of social esteem always, potentially, just a moment away; it wasn't possible, in a very small and technologically primitive social universe, to at any time of day launch an observation or joke and hope for the prompt affirmation of dozens of retweets or Facebook likes. Nor was there a YouTube that permitted the easy indulgence of various natural human visual appetites -- watching endearing infants or two guys fighting or real-life slapstick or whatever.

In other words: the internet, like a pack of cigarettes or lots of cocaine, lets you just sit in a room and repeatedly trigger reward chemicals that, back in the environment of our evolution, you could trigger only with more work and only less frequently. That's why an internet habit, like a cocaine habit, can reach dysfunctional levels.

The above-listed forms of internet dependence -- porn, Facebook, TMZ, Twitter, YouTube -- are just a few of the possible ingredients of any one case of internet "addiction." And each of these ingredients itself involves God-knows-which neurotransmitters and neuronal receptors and, by extension, God-knows-how-many genes. And all of us have lots and lots of these genes--genes that make us susceptible to internet addiction. Because what the internet does is take lots of things that natural selection designed us to find gratifying and make them much easier to get.

Sure, some of these genes may vary from person to person in ways that make some people particularly susceptible to internet addiction (though environmental influences -- e.g. learning self-discipline -- presumably play a very big role). In fact, it will probably turn out that lots of genes vary in this way -- genes that influence impulsiveness or self-discipline generally, or genes that influence the strength of particular drives, like lust or the urge to gossip. In fact, there will turn out to be so many genes which are so modestly correlated with internet addiction that if journalists write stories every time such a gene is found, or is thought to have been found, they will find that they're not shedding much actual light on the situation.

And if they call these genes "internet addiction genes," that will be kind of misleading (which is why I've put that phrase in quotes in the title of this post). These genes are really just genes for being human. That's why using the internet well is a challenge for us all.