When I was a 16-year-old yeshiva boy studying in Jerusalem, my friends invited me to go with them to “shlug kaparos” on the day before Yom Kippur. Though I grew up Orthodox, in Houston, I was not familiar with the term (which translates loosely as “beat the atonements”), but I was quickly off to the Mahane Yehuda market, where we muttered a quick prayer as a shochet waved a chicken over our heads. He slaughtered the animal and threw it into an overflowing bin destined for the poor. Later that day, fearing that I ruined the ritual by cheaply “sharing” a chicken with others, I did it again, this time in the parking lot outside the Har Menuchot cemetery. (That shochet had run out of live chickens so we used a dead one instead.) As I recited Kol Nidre that evening, murmurs of angst crept into my head: Was that really a holy act? As it turns out, many commentators, both medieval and modern, have called it a grave mistake.Like many rituals, kapparot emerged in the early medieval period as a folk custom that scholars later struggled to understand. They questioned the origins of the practice, which, like tashlikh, might appear as an attempt to magically manipulate one’s fate.Historically, kapparot had several variations. In some locales, a bean sprout was planted in a palm wreath two to three weeks before Rosh Hashanah. On the eve of the New Year, the plant was waved seven times over the head of each child in the home, and then thrown into a river. Elsewhere, the custom was performed before Yom Kippur and not only for children, with various types of animals for different people. The rich preferred horned animals, an allusion to the ram that replaced Isaac on the sacrificial altar.Ultimately, the chicken became the animal of choice, in part because of its cost. Equally significant, one Aramaic term for rooster is gever, which also means “man” in Hebrew. The chicken was thus seen as an appropriate substitute for the condemned penitent, with male and female species used for each gender, and additional birds taken for pregnant women. (In some places the entrails were thrown on top of a person’s house to feed birds, a perceived act of kindness to those creatures).The central moment of kapparot should be the confessional, in which the penitent lays his hands on the chicken, proclaims his guilt, and declares that the bird is to be killed in his stead. While some protested that the ritual too closely resembled Temple rites, others believed that there was no fear of people confusing kapparot with an official sacrifice. Indeed, some highlighted the symbolic parallels to the biblical Yom Kippur ceremony, in which the high priest lays his hands in confession on a goat that was subsequently thrown off a desert cliff.While kapparot enjoyed widespread popularity among scholars and laity alike, especially in Ashkenazic lands, some Sephardic scholars harshly criticized this custom as a foreign ritual akin to many idolatrous practices. Rabbi Shlomo ibn Aderet (d. 1310) successfully protested the version of the ritual in his native Barcelona, which included killing one chicken for each child in the house and then hanging the chicken heads on the doorpost along with garlic.Following ibn Adret’s lead, Rabbi Yosef Karo banned kapparot in his famous code, the Shulchan Aruch. However, his 16th-century Ashkenazic contemporary, Rabbi Moshe Isserles, contended that its antiquity proved its legitimacy. Rabbi Isaac Luria and other famous mystics ascribed redemptive value to the practice, with some later Sephardic decisors legitimizing it if one donated the chicken to charity. While a few authorities still demurred, many endorsed the custom provided that its practitioner engages in introspection and repentance.Why had I never performed this ritual, and why haven’t I done it since? In the fifteenth century, Rabbi Yaakov Moelin suggested that one could “redeem” the chicken with money to be given as charity, since monetary donations would be less embarrassing to the poor. Others added that the killing of so many chickens at once caused errors in ritual slaughter, rendering the food non-kosher. Some decisors suggested using fish or money as an alternative; the latter is what is suggested in most of today’s Yom Kippur prayer books.Perhaps my angst as a 16-year old reflected sympathy for animals—and a reemerging halakhic trend. “On the eve of this holy day,” said the late Rabbi Hayim David HaLevi, “why should we display unnecessary cruelty to these animals and mercilessly kill them before bequesting from God mercy upon us?” The mass killing of animals, he added, contradicts a different medieval custom, almost entirely forgotten today, of refraining from all slaughter before the New Year as an act of increased mercy on God’s creatures. In this spirit, and given increased accusations of mishandling of the chickens, prominent figures like Rabbis Shlomo Aviner and David Stav have urged Jews to err on the side of treating animals kindly and use money instead. Traditionalism should, of course, have its place, but on the eve of Yom Kippur, we shouldn’t turn a request for mercy into an act of cruelty.