Summary
Mukherjee’s uncles Rajesh and Jagu and his cousin Moni have all suffered from mental illnesses with genetic origins. Their stories serve to introduce the gene, the “fundamental unit of heredity” that holds the key to the physical and emotional characteristics of each human life.
Need to Know: No understanding of human biology—physiology or behavior—can be complete without first understanding the nature of the gene.
The Walled Garden
The concept of the gene was first formed by Gregor Johan Mendel in 1865. However, theories of how human traits are transmitted date back to Aristotle, who theorized that they were contained in “instructions” within the body that were passed on from generation to generation.
Aristotle’s theories of heredity were surprisingly accurate; but after him, little progress was made in genetics until the 19th century.
“The Mystery of Mysteries”
Charles Darwin’s 1831–1836 voyage to South America and the Pacific to collect animal specimens and fossils of their predecessors led him to believe that new species were created in a struggle for survival. The ones best equipped to adapt to shifting conditions would endure, in a process of “natural selection.”
Need to Know: Darwin’s On the Origin of Species proposed the theory of evolution but did not provide an explanation for how heredity works.
The “Very Wide Blank”
Darwin later sought to explain heredity with the theory of “pangenesis.” He believed that tiny particles called gemmules, contained within the cells of living organisms, passed on their essential traits to their offspring, blending the characteristics of both mother and father. His colleagues dismissed the theory because it did not explain why some traits disappeared and then reappeared in later generations.
Need to Know: Darwin’s failure to explain heredity came about in part because he was a brilliant naturalist, but not adept at carrying out experiments.
“Flowers He Loved”
Gregor Mendel’s research breeding hybrid pea plants led him to conclude that the traits of organisms must be contained in single, indivisible units. Although he did not invent the term, Mendel had identified the fundamental qualities of what we call a gene today.
Need to know: Mendel’s seminal work on heredity was received with silence; his contribution to science was not recognized until long after his death in 1884.
“A Certain Mendel”
The Dutch botanist and geneticist Hugo de Vries, aware of Mendel’s work, observed that plant species spontaneously generated new varieties—ones with longer stems or flowers of different colors. He termed these variants mutants and the process, mutation. Nature, he posited, spontaneously created mutants with specific qualities and the ones best adapted to changing circumstances were able to survive, creating new species.
Need to Know: Hugo de Vries’s discovery of spontaneous mutation extended Darwin’s theory of natural selection.
Eugenics
Darwin’s cousin Francis Galton was an early proponent of eugenics, which advocated the selective breeding of men and women in order to create a superior society. The notion appealed to a British ruling class appalled over the rising power and numbers of the working class, and to sectors in the United States concerned about the effects of massive immigration.
Need to Know: The eugenics movement in the United States and Britain used theories of genetics to justify social experiments that included forced sterilization.
“Three Generations of Imbeciles Is Enough”
During the 1920s, individual states began to pass laws authorizing imprisonment or sterilization of men and women deemed to have genetic criminal tendencies or mental deficiencies. The first legally forced sterilization was performed on Carrie Buck, an impoverished single mother in rural Virginia who, like her own mother, was confined to a penal colony after being diagnosed as a “moron.”
Buck, who did not express any objection to the procedure, was sterilized under a 1924 Virginia law that was later upheld by the US Supreme Court, opening the way for thousands of such forced sterilizations.
Need to know: In the United States, eugenics became, if not the law of the land, a powerful tool for people who sought to protect society from what they regarded as moral and social decay.
“Abhed”
Thomas Morgan, a researcher at Columbia University in New York, conducted extensive experiments on fruit flies and found that genes were linked to one another and to chromosomes. Based upon this notion of “linkage,” a student of Morgan’s, Alfred Sturtevant, constructed the first genetic map.
Need to Know: Thomas Morgan’s graphic description of genes’ location on chromosomes as “beads on a string” illustrated their linkage to one another, and to chromosomes. This was the first genetic map.
Truths and Reconciliations
Theodosius Dobzhansky, a Ukrainian biologist ...