When a family secret comes to light, lives are changed forever in this honest, beautiful, and sometimes painful memoir. When Mark, adopted at birth, set out to find his genetic family as an adult, he found something he never expected—three full-blood siblings, including a persistent sister who would alter the course of his life. He finds himself faced with the emotional task of coming to know his entire birth family, along with the unintended impact it has on his parents and his marriage. This raises age-old questions around the understanding of his own identity and his place in the world—now framed in extraordinarily real and explicit terms: What defines family? Nature or nurture? Life rarely affords such an opportunity for self-examination.

The story focuses on the relationship that develops between Mark and his sister, Rachel, as they discover each other through constant letters and eventual face-to-face meetings. When Rachel learns that Mark and his wife are struggling with having children, a radical idea takes over—could she, a sister he never knew and still barely knows, one who lives on the other side of the country, possibly carry their child? Would they trust her to? Including original correspondence between Rachel, Mark, and their biological mother, Marilyn, Love & Genetics follows the events of a tumultuous year in an astonishing story of love, loss, and the meaning of family.