The Gene

Family History and the Search for Heredity

Family history can make heredity feel immediate and personal. In Siddhartha Mukherjee’s family, mental illness appeared again and again across generations. One uncle, Rajesh, was brilliant and full of energy in his youth, but later developed extreme mood swings that eventually became bipolar disorder. Another uncle, Jagu, lived with schizophrenia and spent much of his life cut off from ordinary independence, trapped by voices, fears, and strange systems of belief.

At first, the family tried to explain these illnesses through trauma and history. The Partition of India had uprooted families, shattered communities, and exposed millions to violence, so it seemed possible that such suffering had damaged the minds of these brothers. That explanation became harder to hold when a younger relative, Moni, developed schizophrenia despite growing up in a far more stable world. The repeated pattern suggested that something more than circumstance was moving through the family line.

That question leads to the gene, the unit of heredity that carries biological instructions across generations. Genes help explain why families share not only faces and body types, but also risks for certain diseases. They do not control a person in a simple, mechanical way, yet they create tendencies and vulnerabilities that can appear again and again. In this sense, heredity is not just a record of resemblance. It is also a record of possibility.

Modern life has been shaped by three powerful ideas: the atom, the byte, and the gene. The atom explains matter, the byte explains digital information, and the gene explains inherited biological information. Once scientists began to understand genes, they could ask sharper questions about health, behavior, and identity. That search would grow from garden experiments to molecular biology, from family stories to global science.

The study of heredity eventually moved from observing patterns to identifying a physical code. DNA was discovered as the molecule that stores genetic information, and its double-helix structure showed how that information could be copied and passed on. Later, scientists learned how to sequence genes, clone them, and connect some of them to diseases such as Huntington’s disease and cystic fibrosis. Those discoveries made it possible to test for inherited risk, but they also created new uncertainty. Knowing what may happen in the future can be as unsettling as not knowing.

Today, genetics no longer stops at explanation. Scientists can now do far more than trace inheritance or read a sequence of DNA. They can sometimes alter genes directly, including in ways that may affect future generations. That shift has turned heredity into one of the deepest scientific and moral questions of modern life.