Jack London's mother, Flora Wellman, was the fifth and youngest child of Pennsylvania Canal builder Marshall Wellman and his first wife, Eleanor Garrett Jones. Marshall Wellman was descended from Thomas Wellman, an early Puritan settler in the Massachusetts Bay Colony. Flora left Ohio and moved to the Pacific coast when her father remarried after her mother died. In San Francisco, Flora worked as a music teacher and spiritualist, claiming to channel the spirit of a Sauk chief, Black Hawk.
Biographer Clarice Stasz and others believe London's father was astrologer William Chaney. Flora Wellman was living with Chaney in San Francisco when she became pregnant. Whether Wellman and Chaney were legally married is unknown. Most San Francisco civil records were destroyed by the extensive fires that followed the 1906 earthquake; nobody knows what name appeared on her son's birth certificate. Stasz notes that in his memoirs, Chaney refers to London's mother Flora Wellman as having been his "wife"; he also cites an advertisement in which Flora called herself "Florence Wellman Chaney".
According to Flora Wellman's account, as recorded in the San Francisco Chronicle of June 4, 1875, Chaney demanded that she have an abortion. When she refused, he disclaimed responsibility for the child. In desperation, she shot herself. She was not seriously wounded, but she was temporarily deranged. After giving birth, Flora turned the baby over for care to Virginia Prentiss, an African-American woman and former slave. She was a major maternal figure throughout London's life. Late in 1876, Flora Wellman married John London, a partially disabled Civil War veteran, and brought her baby John, later known as Jack, to live with the newly married couple. The family moved around the San Francisco Bay Area before settling in Oakland, where London completed public grade school.
In 1897, when he was 21 and a student at the University of California, Berkeley, London searched for and read the newspaper accounts of his mother's suicide attempt and the name of his biological father. He wrote to William Chaney, then living in Chicago. Chaney responded that he could not be London's father because he was impotent; he casually asserted that London's mother had relations with other men and averred that she had slandered him when she said he insisted on an abortion. Chaney concluded by saying that he was more to be pitied than London. London was devastated by his father's letter; in the months following, he quit school at Berkeley and went to the Klondike during the gold rush boom.