The phrase "my brother's keeper" is a reference to the Biblical story of Cain and Abel from the book of Genesis. It is generally understood to mean being responsible for the welfare of a brother or other sibling or, by extension, for other human beings in general. Cain, who is quoted as having made this statement, claimed not to have this responsibility. The phrase, however, is often used with the suggestion that people do have such a responsibility to care for and watch over their fellow human beings.
Cain and Abel
The story of Cain and Abel appears in the first 16 verses of the fourth chapter of Genesis. The phrase "my brother's keeper" appeared in William Tyndale's 1530 English translation. Tyndale's translation was one of those incorporated into the King James Version of the Bible, which was completed in the early 1600s and has been one of the most widely used versions of the Bible.
Cain and Abel were sons of Adam and Eve. Cain, a farmer, and Abel, a shepherd, each sacrificed the fruits of their labor to God. God looked favorably upon Abel's sacrifice, but not Cain's, and in his anger over the incident, Cain murdered his brother.
God later asked Cain where his brother was, and Cain replied, according to the King James Version, "I know not. Am I my brother's keeper?" God, who knew that Cain had killed Abel, punished the murderer by making him a "fugitive and a vagabond." When Cain complained that anyone who came across him would kill him because of his actions, God declared that vengeance would be taken on anyone who killed Cain, and God marked Cain as a sign that he was not to be harmed.
With his question — "Am I my brother's keeper?" — Cain attempted to hide his misdeed by claiming no responsibility for his brother. Followers of Biblical teachings often interpret this story as a reminder that they are, indeed, responsible for the welfare of other people. Someone who is his brother's keeper looks out for and cares for others, even if they are not actually related to him or her. For example, a person who tries to be a "brother's keeper" might donate his or her time or resources to help others and will place the needs of others before his or her own.