The hands of an elderly member of the Japanese mafia (the "Yakuza"). In addition to the tattoos, note the amputation of the little finger. It is one of the many forms of ritual mutilation practiced in human society. The idea is that the suffering involved proves the will of the sufferer to belong to a specific group.
Translated from Italian and slightly modified from "Effetto Seneca"
Until recently, there existed a criminal organization in Japan whose members went by the name of Yakuza. It was similar to the Italian mafia, so much that it is often called the "Japanese mafia." The Yakuza practiced various forms of ritual mutilation, one was the amputation of the last phalanx of the little finger. Fosco Maraini describes it in his "Meeting with Japan" (1958), telling us that he himself cut his little finger as a protest against the Japanese government during WW2.
Cutting off a phalanx of the little finger is a good example of a ritual mutilation. As an impairment, it is minor, but it is visible, painful, and a test of courage for those who do it. Thus, it is a testimony of belonging to a certain group - in this case the Yakuza. Today, they have almost disappeared in Japan and with them the hands with the amputated little finger. But ritual mutilation in other forms is common in other regions of the world.
In the western part of Eurasia, there are two types of widespread ritual mutilations: male circumcision and infibulation in its various forms of female genital mutilation. For both, there is talk of possible health benefits, but there is no definite evidence for that. They are, rather, evidence of belonging to a social or religious group. As we know, circumcision is mandatory for Jews, it is common, but not mandatory, among Muslims although, it is less common but not rare among Christians. In Europe, about 20% of the males are circumcised, a percentage that rises to about 80% in the United States.
All in all, circumcision does not have great effects on the body of the circumcised, but as far as infibulation is concerned, we are talking about a real mutilation that heavily affects the sexuality of the woman who undergoes the practice. It is condemned by the Christian religion, it is not part of the Jewish tradition, and has been the subject of Islamic Fatwas that prohibit it. In many states, it is explicitly prohibited by law.
Yet, infibulation in its various forms tenaciously resists in certain areas of the world where it is an ancient tradition, especially in Africa. It is difficult for us Westerners to realize why women in these regions do not see it as an imposition, but as a source of pride, a proof of maturity, and of belonging to the society in which they live. In these societies, the non-infibulated woman is considered an outcast, an enemy to be isolated and demonized. It is a perverse mechanism that persists despite many attempts to eradicate the practice.
There are, and were in the past, many other ritual mutilation practices that affect both men and women. It is said that in ancient times the Amazons amputated one of their breasts to shoot better with the bow. It is almost certainly a legend. Even if it were true, it's unlikely it would have improved their ability to skewer enemies with arrows. If the Amazons (assuming they ever existed) did that, it was for the same reason that led the Yakuza to sever a phalanx of their little finger: publicly showing that they belonged to the group.
In China, the binding of girls' feet was practiced until recently. It was a form of mutilation: a real daily torture with consequences that lasted for a lifetime. As adults, these women were unable to walk alone. Fortunately, today it is no longer practiced, but some elderly Chinese women who underwent this practice in their youth are still alive.
In the West, the prevalence of the Christian vision starting from Paul of Tarsus tended to reject any irreversible intervention on the human body. Nonetheless, minor forms of mutilation remained common, such as piercing the earlobes for earrings.
More often than not, in recent times, mutilations were performed with the support of "Science." One example was the removal of children's tonsils, as it was fashionable to do in the 1970s. An operation that probably did not cause much harm, but whose usefulness is at least questionable. It is still performed nowadays.
Much worse is the case of radical mastectomy for the treatment of breast cancer. As Siddhartha Mukherjee describes in his book. "The Emperor of All Maladies" (2010), it was an invasive therapy that in some cases involved "the complete excision of all breast tissue, axillary contents, removal of the latissimus dorsi, major pectoral muscles and minor and internal mammary lymph node dissection". And all this without a real medical reason to justify it. The result was a radical and irreversible mutilation that turned the woman into an invalid for the rest of her life.
In our society, theoretically rational, we might think that we have freed ourselves from these customs that we consider superstitions or at least errors of evaluation of a still imperfect science. But the "suffering-based proof of belonging" mechanism is deeply ingrained in our thinking and tends to pop up in one way or another, with or without medical justifications.
Let's just think about the use of tattoos, considered primitive and barbaric in the West until a few decades ago, today widespread among young people. Getting a tattoo is painful and therefore a test of courage for those who do it. It is also irreversible so that it is proof of definitive belonging to a certain social group. So it is not surprising that it has spread so quickly in a society that gives to the young little or nothing, apart from beatings, real or virtual.
It is impossible to deny that, under a smattering of rationality, our mentality is still that of much older times. And when we are under social stress, obsessive and punitive tendencies come out easily and are impossible to stop. Thankfully, women today don't have to cut their breasts for better accuracy with the bow (for now), and men don't have to slice off their little fingers to show their courage (for now).
But society changes in unpredictable ways and today it would be possible to use new ways to prove that someone willingly underwent some kind of painful ritual in order to belong to a certain group. No need to show actual scars, a digital certificate will be enough. Whether this will actually take place is left to the reader to ponder.