A Short History of Nearly Everything | Study Guide

Bill Bryson

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A Short History of Nearly Everything | Part 5, Chapter 26 : Life Itself (The Stuff of Life) | Summary



Bryson points out about 99.9% of the genes of all human beings are the same, and "this is what makes us a species." It is the remaining .1% that makes people individuals. This sets the stage for his discussion of the chemical deoxyribonucleic acid, or DNA.

Inside each human cell is a nucleus, and inside that are long strands of chromosomes—23 derived from the mother and 23 from the father. DNA makes up the chromosomes, or the "instructions necessary to make and maintain you." There are about two yards of DNA packed into every nucleus, and it has four basic components, called nucleotides. The four nucleotides are adenine, thymine, guanine, and cytosine.

DNA was discovered in 1869 by Swiss scientist Johann Friedrich Miescher, who theorized they were the "agents behind heredity." Scientists were willing to believe DNA was associated in some way with heredity, but they couldn't understand its role. Chromosomes were discovered around the 1880s by several scientists. Then in 1904 a young American scientist named Thomas Morgan proved chromosomes "were at the heart of inheritance." His conclusion was based on experiments he conducted with the common fruit fly, tracking the traits they inherited through generations.

Ultimately, the structure of DNA was uncovered by a group of four people "who didn't work as a team ... and were for the most part novices." Their names were Maurice Wilkins, Rosalind Franklin, Francis Crick, and James Watson. Crick and Watson are generally given the credit for the discovery of DNA's structure and, along with Wilkins, received the Nobel Prize for their work in 1962. But, Bryson shows, they would not have made their discovery without Franklin's X-ray crystallographic images of the structure of the DNA molecule. The work involved beaming X-rays through crystals of DNA and capturing their shadows on film. The images showed DNA took the form of a "double helix," with two strands of material that wind around each other like a twisted rope ladder. The "rungs" are made of a type of sugar and are joined by nucleotides that always combine in the same way: guanine with cytosine and thymine with adenine. The order of these paired nucleotides determines an organism's physical characteristics. In 1953 Watson and Crick published "A Structure for Deoxyribose Nucleic Acid" in Nature, accompanied by separate articles by Wilkins and Franklin.

Now scientists turned to understanding the sections of DNA that "control and organize vital functions": genes. These are the segments of DNA that contain the chemical codes that determine an organism's characteristics. DNA replicates as its two strands separate and pair with a matching strand. Normally the replication takes place accurately, but occasionally one of the nucleotides is misplaced. Such errors, called "Snips" by biochemists, account for differences among individuals. The complete set of genetic instructions for an organism is called the genome.

By uncovering the structure of DNA, scientists were able to explain how "we are all so similar." However, while science generally knows what makes up DNA and much of the tissues of the human body, medical and biological science still understand little about how it all works together. Bryson suggests the answer may lie in the proteome, or "library of information that creates proteins." However, this is considerably more complicated than understanding the blueprint for DNA.


Bryson discusses the discovery of DNA largely through the work of four individuals, two of whom are well known—Watson and Crick—and two—Franklin and Wilkins—who are less well known but were integral to the discovery of DNA's structure. Bryson once again emphasizes often the scientists who make a discovery possible are often not given the credit.

The discovery of the structure of DNA was fundamentally important to the advancement of genetics as a science. Genetics has given us numerous medical advances, such the ability to identify a genetic component to certain illnesses. It has advanced the understanding of evolutionary history and has allowed biologists to more fully understand the evolutionary relationships between different species, among numerous other advances. Even so, Bryson makes clear while the understanding of the structure of DNA and the human genome "tells us what we are made of," it says "nothing about how we work." He suggests increasing scientific understanding of chemical processes in the body should come through a deeper understanding of proteins.

Bryson sums up the chapter with a commentary on the inherent mystery still within DNA. While scientists know it is the basis of all living creatures and have unraveled its structure and composition, its complexity is formidable. It will be decades before a full picture of its multiple functions and interrelationships with bodily processes becomes clear.

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