The Master Builder

Starred review from June 5, 2023
“What makes you and me individual human beings is not a unique set of DNA but instead a unique organization of cells and their activities,” according to this revelatory study. Developmental biologist Martinez Arias’s first book for general readers pushes back against the notion that genes are “the architects of our bodies,” pointing to the case of triplets who shared a genetic mutation for a cleft lip that manifested differently in each sibling—the cleft was on the right side for one sibling, the middle for another, and the third had a cleft palate—despite all three having identical DNA. What actually explains how individuals develop are cells, which he contends are “master builders” that use the raw “materials” of DNA to construct organisms and have “the ability to learn, move, and count, to measure space and time.” To illustrate, he describes how during the early stages of embryonic development cells exchange chemical signals to symmetrically distribute eyes, ears, and arms, revealing an ability to organize geometrically that cannot be accounted for by DNA. Martinez Arias’s novel thesis invigorates, and the lucid scientific discussions will hold readers’ attention even through involved examinations of how cells respond to specific proteins. This is the perfect complement to Siddhartha Mukherjee’s The Song of the Cell. Illus.

June 1, 2023
A fascinating argument that what makes a human is "not a unique set of DNA but instead a unique organization of cells and their activities." Books that glorify DNA as the key to life are abundant, but they miss the point, according to this ingenious argument by Martinez Arias, a professor of systems bioengineering. The author emphasizes that every cell in our body contains identical DNA that forms our genes (about 25,000 in humans), which deliver instructions for the amino acids that make up the proteins that form our bodies. As Martinez Arias demonstrates, "DNA cannot send orders to cells to move right or left within your body or to place the heart and the liver on opposite sides of your thorax; nor can it measure the length of your arms or instruct the placement of your eyes symmetrically across the midline of your face." Cells do that. From the perspective of a cell, DNA is a catalog with a vast array of building materials, from which the cell picks and chooses. The end result is a miracle called life, an entity that has no relation to any of its components. Just as a flock of birds or a city can't be predicted from the list of its individual parts, a cell appears when the right combination of DNA does its work in a phenomenon called emergence. No scientist knows for sure, but most theorize on what happened after the first crude cells ("archaea") appeared 4 billion years ago: Feasting on a mixture of nitrogen, hydrogen, sulfur, and carbon, and creating oxygen as a waste product, they swallowed up but did not digest aerobic bacteria. Over several billion years, they learned to turn sunlight into energy, survive in the open, oxygen-filled air, and--in the trillions--work together in the forms of plants and animals. Describing his own and others' research, Martinez Arias makes a convincing case that cells, with assistance from DNA, gave rise to our species and all the others. A rich, detailed exploration of the vitality of cells.

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