The mystery of addiction — what it is, what causes it and how to end it — threads through most of our lives. Experts estimate that one in 10 Americans is dependent on alcohol and other drugs, and if we concede that behaviors like gambling, overeating and playing video games can be addictive in similar ways, it’s likely that everyone has a relative or friend who’s hooked on some form of fun to a destructive degree. But what exactly is wrong with them? For several decades now, it’s been a commonplace to say that addicts have a disease. However, the very same scientists who once seemed to back up that claim have begun tearing it down.

Once, addictions were viewed as failures of character and morals, and society responded to drunks and junkies with shaming, scolding and calls for more “will power.” This proved spectacularly ineffective, although, truth be told, most addicts do quit without any form of treatment. Nevertheless, many do not, and in the mid-20th century, the recovery movement, centered around the 12-Step method developed by the founders of Alcoholics Anonymous, became a godsend for those unable to quit drinking or drugging on their own. The approach spread to so-called “behavioral addictions,” like gambling or sex, activities that don’t even involve the ingestion of any kind of mind-altering substance.

Much of the potency of AA comes from its acknowledgement that willpower isn’t enough to beat this devil and that blame, rather than whipping the blamed person into shape, is counterproductive. The first Step requires admitting one’s helplessness in the face of addiction, taking recovery out of the arena of simple self-control and into a realm of transcendence. We’re powerless over the addictive substance, and trust in a Higher Power, and the program itself, to provide us with the strength and strategy to quit. But an important principle of the 12 Steps is that addiction is chronic and likely congenital; you can be sober indefinitely, but you will never be cured. You will always remain an addict, even if you never use again.

The flourishing of the 12-Step movement is one of the reasons why we now routinely describe addiction as a “disease.” To have a disease — instead of, say, a dangerous habit — is to be powerless to do anything except apply the prescribed cure. A person with a disease is unfortunate, rather than foolish or weak or degenerate. Something innate in your body, particularly in your brain, has made you exceptionally susceptible to getting hooked. You always have and always will contain a bomb, the important question is how to avoid setting a match to it. Another factor promoting the disease model is that it has ushered addiction under the aegis of the healthcare industry, whether in the form of an illness whose treatment can be charged to an insurance company or as the focus of profit-making rehab centers.

This conception of addiction as a biological phenomenon seemed to be endorsed over the past 20 years as new technologies have allowed neuroscientists to measure the human brain and its activities in ever more telling detail. Sure enough, the brains of addicts are physically different — sometimes strikingly so — from the brains of average people. But neuroscience giveth and now neuroscience taketh away. The recovery movement and rehab industry (two separate things, although the latter often employs the techniques of the former) have always had their critics, but lately some of the most vocal have been the neuroscientists whose findings once lent them credibility.

One of those neuroscientists is Marc Lewis, a psychologist and former addict himself, also the author of a new book “The Biology of Desire: Why Addiction is Not a Disease.” Lewis’s argument is actually fairly simple: The disease theory, and the science sometimes used to support it, fail to take into account the plasticity of the human brain. Of course, “the brain changes with addiction,” he writes. “But the way it changes has to do with learning and development — not disease.” All significant and repeated experiences change the brain; adaptability and habit are the brain’s secret weapons. The changes wrought by addiction are not, however, permanent, and while they are dangerous, they’re not abnormal. Through a combination of a difficult emotional history, bad luck and the ordinary operations of the brain itself, an addict is someone whose brain has been transformed, but also someone who can be pushed further along the road toward healthy development. (Lewis doesn’t like the term “recovery” because it implies a return to the addict’s state before the addiction took hold.)

“The Biology of Desire” is grouped around several case studies, each one illustrating a unique path to dependency. A striving Australian entrepreneur becomes caught up in the “clarity, power and potential” he feels after smoking meth, along with his ability to work long hours while on the drug. A social worker who behaves selflessly in her job and marriage constructs a defiant, selfish, secret life around stealing and swallowing prescription opiates. A shy Irishman who started drinking as a way to relax in social situations slowly comes to see social situations as an occasion to drink and then drinking as a reason to hole up in his apartment for days on end.