Variation in a pea plant, and in all life, stems from DNA.
Amadeo Bachar

Key Concepts

• The idea that nature “selects” favorable variations in organisms was at the heart of Charles Darwin’s theory of evolution, but how those variations arise was a mystery in Darwin’s time.
• Random changes in DNA can give rise to changes in an organism’s traits, providing a constant source of variation.
• Certain kinds of DNA changes can produce major differences in form and function, providing raw material for the evolution of new species and even new human cultures.

On a shelf in a library in Texas sits a small green volume, originally published 150 years ago and now generally recognized as one of the most important scientific books ever written. Its future success was not at all apparent when this first-edition copy of On the Origin of Species was printed, however. As Charles Darwin finished the proofs of his new work, he drew up a short list of important colleagues who should receive advance copies. He then anxiously awaited the verdicts of the leading thinkers of his time.

England’s most famous living scientist in 1859 scribbled his reactions in notes found throughout that little green volume preserved at the University of Texas at Austin. Marked “from the author” on its frontispiece, it is the advance copy that Darwin sent to Sir John Herschel, one of his scientific heroes, whose own treatise on natural philosophy had first inspired Darwin to become a scientist. In the 1830s Herschel had memorably described the origin of species as a “mystery of mysteries” that might occur by natural processes. Darwin quoted Herschel’s words in the very first paragraph of the book, which laid out the ingenious solution to the “mystery of mysteries” that Darwin was offering to both Herschel and the world.

   
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