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Matters are made worse by the fact that the meaning of the word has changed over time, and remains ambiguous to this day.
    When inventing the wheel, it is best to ensure that it is round before deciding what color to paint it. So, before we can get a handle on the word “evolution” in all its protean and subtle variety, one must first understand how it works, on the most basic nuts-and-bolts level. This is why Darwin started
The Origin of Species
by outlining such a mechanism—and not mentioning the word “evolution” at all. Darwin had very good reasons for not using the word in his masterpiece, as I shall explain a bit further on. Until then one might do a lot worse than follow his example.
    Like many people these days, we in the Gee household keep chickens in our backyard. The hens are of several different breeds. We started with bantams, small birds whose function is more ornamental than anything else. They don’t lay many eggs, perhaps ninety per bird per year. They are, however, long-lived. At the time of writing, one of our first hens, a Pekin bantam, is four years old and still going strong. Our next two hens, Polish bantams, are almost as old, and in rude and squawking health. We also have several standard-sized hens, which lay more and bigger eggs.
    But the prizes for productivity go to those in the flock that started their careers in intensive egg-production facilities. A battery hen canlay as many as three hundred eggs per year, but at a cost—the hens don’t live long. When a battery hen stops laying regularly, she dies of old age. Battery hens have been bred that way, to invest as much energy as possible into producing eggs, at a cost to their own bodily maintenance. Our first four battery rescues died of old age within two years, and we are now on our second quartet.
    All the battery hens have russet feathers and red combs. They look just like the Rhode Island Reds my mother kept when I was a boy. As every backyard farmer knows, Rhode Islands are just about the best hens to keep if you like lots of eggs. These battery birds plainly have Rhode Island in their heritage, but they’ve been turbocharged to ramp up egg production at the cost of virtually everything else. In other words, they have been selected. If farmers depend for their livelihood on selling as many eggs as possible, they will breed future stock from the most productive egg-layers, and make the rest of the hens into cat food. They’d continually breed from the best layers in each generation, until, many generations down the line, they’d have created a new breed of hen that routinely lays many more eggs than any hen in the original flock.
    This idea—the “artificial” selection by stockmen intent on breeding hens that lay more eggs, sheep with fleecier fleece, bulls with beefier beef, and so on—is intuitive, makes sense to anybody—and was how Darwin started the
Origin
.
    What Darwin did next was a master stroke. Once he’d established artificial selection as an obvious and unarguable phenomenon, Darwin used it as an analogy for what goes on in the natural world. In nature the role of farmers is played by the environment. Creatures won’t be “artificially” selected by farmers for this trait or that, but “naturally” selected by the ever-changing environmental conditions in which they live. If the climate turns cold, those elephants that happen to have more body hair will be more likely to survive than those that are less hirsute—long enough to breed and pass on their hairiness to their offspring, while the baldies devote their energies to keeping warm rather than reproducing. If the climate continues cold, the bald elephants will eventually be replaced by woolly mammoths.
    The beautiful thing about natural selection is its simplicity. All it requires to work are four things, three of which are readily apparent with eyes to see. They are heritable variation, the ever-changing environment, superabundance of offspring, and