Throughout the long history of humanity, one simple fact has persisted: everything changes. This is not a simple fun quirk about being human but an inevitable force, like a glacier carving down a mountain. The question should never be can humans change. It is, when will they change. Many assumptions have come up throughout history over this issue. Idioms like 'you can't teach an old dog new tricks' and 'a leopard can't change it's spots' are founded in egocentric beliefs in the steadfastness of human will or the misplaced idea that fear will prevent change. The idea that humans cannot change who they are is both foolish and wrong. Humans are defined by change.
The entire adolescent stage of life is wrought with change. Some are simple enough. Most are drastic and even painful. In this stage, maturity in the body lead to sexual interest and the want to explore such interests. Some practice heterosexuality explicitly, while others choose homosexuality, while still other choose to experiments with bisexuality. These are experiences that lend change to our identities and we become defined by them in different ways. Culture will dictate the severity of opinion for sexual orientation, but the labels that are inherent within each will stand firm and have their effects. It is simple: when the majority of the community is heterosexual, those who are homosexual will be the subject of scorn and, thus, be defined by their tribulation, changing them. Whether they experience ostricization from friends or family, or find acceptance in a new community friendly toward their life style, they will be changed.
The want for change is constant. Humans want to change who they are. Frequently reidentifying themselves should one persona not fit them accurately enough. This desire drives people to take steps in varying directions. Facing a dead end job with unreasonable hours, while you spouse is home alone concerned with how much time is spent together, one would choose, eventually, to rectify the situation. They will find a new job, and change how they are identified. Many opt for the military route to change themselves. It is this want that includes drug addicts. For those that have hit rock bottom, it is never a struggle as to whether or not they can change. They will change or they will die. That is not to say that upon rehabilitation, they no longer struggle with addiction. It is that they no longer are identified by their addiction to drugs. This is a continuous journey, one that takes a person from who they were to who they are.
Fear is the most peerless inspiration for change. It is not a force for stagnation, like most would assume. Fear of failure, being rejected, death, heights. All impress upon the person the need to change who they are and how they are identified. They will take steps to avoid specific activities where their fears have a possibility of being realized. When I was young, I had a friend that I spent a great deal of time with. She and I were playing at our school and she, being enthralled with gymnastics, decided to show off her aptitude on the bars. Hanging from her knees some ten feet from the ground, she lost her grip and fell on her neck, the impact breaking it. She died shortly after that and I have been afraid of heights ever since. Alone, they don't terrify me so much. With others, however, I am crippled by horror. My friends today know to avoid putting me in situations like this. I am identified with my fear.
People can change who they are. Most of the time, this happens without even knowing it. It is absolute that even the most reserved and mild mannered of people will be pushed to change. Eventually, the want will exceed into the boundary of need and change will happen. There are cautionary tales for those who resist change. These are embodied in stories of botched plastic surgeries and mid life crisises. They warn you not to be so proud and egomaniacal as to think humans cannot change who they are. Change is happening even now, whether they like it or not. And it will continue to happen. Everything changes.