On October 6, 1942, my mother was born twice in Delhi. Bulu, her identical twin, came first, placid and beautiful. My mother, Tulu, emerged several minutes later, squirming and squalling. The midwife must have known enough about infants to recognize that the beautiful are often the damned: the quiet twin, on the edge of listlessness, was severely undernourished and had to be swaddled in blankets and revived.

The first few days of my aunt’s life were the most tenuous. She could not suckle at the breast, the story runs, and there were no infant bottles to be found in Delhi in the forties, so she was fed through a cotton wick dipped in milk, and then from a cowrie shell shaped like a spoon. When the breast milk began to run dry, at seven months, my mother was quickly weaned so that her sister could have the last remnants.

Tulu and Bulu grew up looking strikingly similar: they had the same freckled skin, almond-shaped face, and high cheekbones, unusual among Bengalis, and a slight downward tilt of the outer edge of the eye, something that Italian painters used to make Madonnas exude a mysterious empathy. They shared an inner language, as so often happens with twins; they had jokes that only the other twin understood. They even smelled the same: when I was four or five and Bulu came to visit us, my mother, in a bait-and-switch trick that amused her endlessly, would send her sister to put me to bed; eventually, searching in the half-light for identity and difference—for the precise map of freckles on her face—I would realize that I had been fooled.

But the differences were striking, too. My mother was boisterous. She had a mercurial temper that rose fast and died suddenly, like a gust of wind in a tunnel. Bulu was physically timid yet intellectually more adventurous. Her mind was more agile, her tongue sharper, her wit more lancing. Tulu was gregarious. She made friends easily. She was impervious to insults. Bulu was reserved, quieter, and more brittle. Tulu liked theatre and dancing. Bulu was a poet, a writer, a dreamer.

Over the years, the sisters drifted apart. Tulu married my father in 1965 (he had moved to Delhi three years earlier). It was an arranged marriage, but also a risky one. My father was a penniless immigrant in a new city, saddled with a domineering mother and a half-mad brother who lived at home. To my mother’s genteel West Bengali relatives, my father’s family was the embodiment of East Bengali hickdom: when his brothers sat down to lunch, they would pile their rice in a mound and punch a volcanic crater in it for gravy, as if marking the insatiable hunger of their village days. By comparison, Bulu’s marriage, also arranged, seemed a vastly safer prospect. In 1967, she married a young lawyer, the eldest son of a well-established clan in Calcutta, and moved to his family’s sprawling, if somewhat decrepit, mansion.

By the time I was born, in 1970, the sisters’ fortunes had started to move in unexpected directions. Calcutta had begun its spiral into hell. Its economy was fraying, its infrastructure crumbling. Internecine political movements broke out frequently, closing streets and businesses for weeks. Between the city’s cycles of violence and apathy, Bulu’s husband kept up the pretense of a job, leaving home every morning with the requisite briefcase and tiffin box, but who needed a lawyer in a city without laws? Eventually, the family sold the mildewing house, with its grand veranda and inner courtyard, and moved into a three-room flat.

My father’s fate mirrored that of his adoptive city. Delhi, the capital, was India’s overnourished child, fattened by subsidies, grants, and the nation’s aspirations to build a mega-metropolis. Our neighborhood, once girded by forests of thornbushes and overrun with wild dogs and goats, was soon transformed into one of the city’s most affluent pockets of real estate. My family vacationed in Europe. We learned to eat with chopsticks, twisted our tongues around the word “croissant,” and swam in hotel pools. When the monsoons hit Calcutta, the mounds of garbage on the streets clogged the drains and turned the city into a vast, infested swamp. A stagnant pond, festering with mosquitoes, collected each year outside Bulu’s house. She called it her own “swimming pool.”

Why are identical twins alike? In the late nineteen-seventies, a team of scientists in Minnesota set out to determine how much these similarities arose from genes, rather than environments—from “nature,” rather than “nurture.” Scouring thousands of adoption records and news clips, the researchers gleaned a rare cohort of fifty-six identical twins who had been separated at birth. Reared in different families and different cities, often in vastly dissimilar circumstances, these twins shared only their genomes. Yet on tests designed to measure personality, attitudes, temperaments, and anxieties, they converged astonishingly. Social and political attitudes were powerfully correlated: liberals clustered with liberals, and orthodoxy was twinned with orthodoxy. The same went for religiosity (or its absence), even for the ability to be transported by an aesthetic experience. Two brothers, separated by geographic and economic continents, might be brought to tears by the same Chopin nocturne, as if responding to some subtle, common chord struck by their genomes.

One pair of twins both suffered crippling migraines, owned dogs that they had named Toy, married women named Linda, and had sons named James Allan (although one spelled the middle name with a single “l”). Another pair—one brought up Jewish, in Trinidad, and the other Catholic, in Nazi Germany, where he joined the Hitler Youth—wore blue shirts with epaulets and four pockets, and shared peculiar obsessive behaviors, such as flushing the toilet before using it. Both had invented fake sneezes to diffuse tense moments. Two sisters—separated long before the development of language—had invented the same word to describe the way they scrunched up their noses: “squidging.” Another pair confessed that they had been haunted by nightmares of being suffocated by various metallic objects—doorknobs, fishhooks, and the like.

“Honey, it’s never too early to apply for summer language programs.” Facebook

Twitter

Email

Shopping

The Minnesota twin study raised questions about the depth and pervasiveness of qualities specified by genes: Where in the genome, exactly, might one find the locus of recurrent nightmares or of fake sneezes? Yet it provoked an equally puzzling converse question: Why are identical twins different? Because, you might answer, fate impinges differently on their bodies. One twin falls down the crumbling stairs of her Calcutta house and breaks her ankle; the other scalds her thigh on a tipped cup of coffee in a European station. Each acquires the wounds, calluses, and memories of chance and fate. But how are these changes recorded, so that they persist over the years? We know that the genome can manufacture identity; the trickier question is how it gives rise to difference.

David Allis, who has been studying the genome’s face for identity and difference for three decades, runs a laboratory at Rockefeller University, in New York. For a scientist who has won virtually all of science’s most important prizes except the Nobel (and that has been predicted for years), Allis is ruthlessly self-effacing—the kind of person who offers to leave his name on a chit at the faculty lunchroom because he has forgotten his wallet in the office. (“We know who you are,” the woman at the cash register says, laughing.)