A Short History of Nearly Everything

by

Bill Bryson

A Short History of Nearly Everything: Chapter 26 Summary & Analysis

Summary
Analysis
If a person traces their genealogy back eight generations, they have 250 direct ancestors. That number rises to a million at 25 generations and a billion at 30 generations—that’s more people than existed back then, meaning that we all have common ancestors. Ancestrally, Bryson says, we’re “all family.” In fact, most people share 99.9 percent of their genes. Each of a person’s cells has a nucleus, and each nucleus has 46 chromosomes which contain the instructions necessary to make an individual. Each chromosome is made of a “wonder” chemical called DNA, and each person have a lot of it—up to 20 million kilometers worth of DNA exists inside a human body. DNA has one purpose: to make more DNA. DNA isn’t itself alive, but it is fundamental for life.
Bryson addresses DNA with the aim of instilling amazement in the reader about the building blocks of life. Once again, Bryson uses evocative writing to engage the reader, nesting scientific facts about DNA within imaginative descriptions that help the reader imagine DNA’s complexity, so that they begin to feel a sense of wonder and curiosity about the building blocks of their own bodies. 
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A Swiss scientist named Johan Friedrich Miescher first discovers DNA in 1869, and other scientists discover chromosomes in 1889. Many scientists suspect that either chromosomes or DNA (or both) have something to do with heredity because they live inside every cell, but they know little else about them. In 1904, Thomas Hunt Morgan begins investigating chromosomes by breeding fruit flies, which have only four chromosomes. He’s able to deduce that chromosomes have something to do with how traits are passed on, though even by 1933, some scientists still don’t believe in genes. In 1944, Oswald Avery cross-breeds bacteria, decisively showing that DNA is the active agent in heredity. 
Bryson stresses—as with most other aspects of science—how recent the scientific knowledge of heredity is. Though DNA is first discovered in the 1800s, it takes until 1944 for serious research to take off on a broad scientific scale, meaning that scientists have had less than a century’s worth of research time to gain knowledge about DNA. This alludes to the fact that science still has a long way to go.
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A decade later, four competing scientists in England—named Maurice Wilkins, Rosalind Franklin, Francis Crick, and James Watson—finally crack DNA’s structure. Franklin, who’s a woman, makes the most progress despite facing a lot of prejudice in the 1950s. Franklin isn’t allowed to eat with other faculty and is often treated with a lack of respect, or “formalized disdain that dazzles modern sensibilities (actually any sensibilities).” Franklin is the only one with good results from her experiments, but she hides her images of DNA strands from the others—until Crick and Watson take them in 1953 “without her knowledge or consent.” From Franklin’s images, Crick and Watson learn that DNA is a double helix, and they go on to win the Nobel Prize for this discovery. 
Bryson leverages his discussion of scientists competing to discover DNA’s structure to show, once again, how patriarchy impinges on scientific research by making working conditions unpalatable for female scientists like Franklin, who have to eat separately and are treated as inferiors by their colleagues. Bryon stresses that despite this, Franklin  makes the most progress on the hunt for DNA’s structure, which shows once again that had male scientists in this era not let their sexism deter female colleagues, even more progress would have been made.
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Quotes
DNA’s double helix shape looks like a twisted rope ladder: the rungs (or steps) of the ladder are formed by joining bases—specifically, G with C or A with T. The order in which the letters appear as they progress up the ladder is the human DNA code. When it’s time to make a new DNA molecule, the ladder rips down the middle like a zipper, and each half goes to make a new partnership (or a new rope ladder). This happens in “a matter of seconds, which is quite a feat,” according to Bryson. Most of the time, DNA replicates accurately so that each new ladder is an identical replica of the ladder it ripped away from.
Bryson symbolizes DNA as a rope ladder to help the reader visualize its double helix structure, and he uses the analogy of a zipper to represent the mechanism of DNA’s replication. Once again, Bryson appeals to the reader’s imagination, preferring metaphors over technical, dry, or abstract information, as he thinks this will be more engaging for the non-professional reader. 
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Sometimes, though, a letter gets in the wrong rung on the rope ladder—in technical terms, a “single nucleotide polymorphism” or “Snip” happens—and this can affect the body that the cells eventually turn into. It might mean that the human is worse off (say, they’re more likely to get a disease), or better off (say, they have extra red blood cells). These slight differences play out to affect the likelihood of survival: they’re the mechanism for Darwin’s idea of natural selection. 99.9 percent of one’s DNA is identical to every other human’s, but the 0.1 percent difference is made up by one’s Snips. Everyone’s genome is thus slightly different—but only by a tiny margin.
Bryson continues the metaphor of the rope ladder to explain how evolution happens: when a component is placed in the wrong order (or “rung”) of the ladder, the genetic qualities that the DNA builds will be slightly different. If it’s to the person’s advantage and they survive to reproduce, the new order will be preserved and passed on. Once again, Bryson stresses how human existence is largely a matter of chance—effectively, humans exist because of a very long chain of “Snips” that gradually change the bodies built by DNA.
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Bryson says that all animals are, in a way, “slaves to their genes,” which is why salmon and spiders are prepared to die during mating—the impulse to disperse genes trumps their impulse to survive. Scientists experimenting with cross-breeding species realize that humans share 60 percent of their genes with fruit flies and 90 percent with mice. It’s hard to isolate genes for a specific trait, though, as most inherited traits arise from combinations of genes that are harder to pin down than single genes. The more we learn, the more complicated the picture seems, which is why cracking the human genome seems more like the beginning of something much bigger. So far, we know what genes are, but we don’t really know how they work. 
Bryson highlights—as with other aspects of science—that the more scientists delve into genetic research, the more complex things get, and the more they realize how little they actually know. There are many fundamental things that scientists don’t know about genes beyond what they are and which ones belong to which animals. This means that genetic research, like all other scientific fields, is only at the beginning of its journey.
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Quotes
It turns out that scientists now also need to crack the human “proteome,” a new concept capturing the information that creates proteins, which is far more complicated than the human genome. Despite the complexity of our genes, Bryson thinks it’s a “profound” truth that we are closely related to everything on Earth—even half the chemical functions that happen in bananas also happen in humans, prompting Bryson to conclude that “all life is one.”
Genetic research is so new, in fact, that concepts are still being developed to grasp the fundamental components of heredity (such as “proteome”), meaning that the foundations of this science are still being laid. Bryson also emphasizes how interrelated all living beings are in order to subtly imply that humans should not be so careless with species that share our planet with us.
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