Technically, Charles Darwin wasn't the first person to stumble upon evolution. Darwin was one in a string of people, one of whom was his own grandfather, who thought there must be a strange reason animals "continue to improve" over time. Decades later, while Darwin was following tortoises in the Galápagos, another man, Alfred Russel Wallace, was conducting his own research in the Malay Islands north of Australia. Wallace reported his findings first—a theory of "evolution"—but Darwin's opus, The Origin of Species, was more comprehensive. It was also marketed better.
Such is the case with evolution. The fittest survive and the weaker find themselves wiped away by time, or worse, death. The central idea of natural selection is advantage, and Darwin had it, which explains why Darwin will forever be synonymous with evolution and Wallace's legacy mostly went the way of the passenger pigeon and the Tasmanian tiger, a footnote in high school science classes.
This is one of the lessons in Evolution: A Visual Record, a book of stunning images by photographer Robert Clark that show evolution at work. Many of the images Clark took on assignment for National Geographic, and they all speak to a larger, central theme. Why do today's species exist while their relatives went defunct? For the same reason that humans became dominant instead of Homo erectus. Clark's book explains this principle with a famous example of giraffes. Giraffes with long necks could better reach food in treetops. Those with short ones disappeared. That's why you've never seen a Climacoceras, a short-necked relative of modern giraffes that lived 15 million years ago in East Africa.
The fact that evolution can be seen is itself remarkable. Darwin cautioned that the process of nature weeding out the weak happened over millennia, not decades. But Darwin may have miscalculated on this point, which isn't really his fault. For all that he studied the past, he couldn't have known that future humans would become exceedingly skilled at evolution, and that human activities—such as selective breeding, of, say, rabbits or peaches—could accelerate the creation of new species, or, at times, bolster weak specimens, enabling them to exist longer than they might have survived on their own.
Anyone wanting to find their own example might start with insects. "Insects are by far the most widespread and abundant example of evolution on Earth," writes Joseph Wallace, a science writer who contributed to Clark's book. Darwin loved insects, especially beetles, although he never could have studied even a small fraction of them in his lifetime. Today's scientists think there could be a million species of insects, or 30 million, or any number in between. Insects may be small compared to a horse or rhinoceros. But everything about them—their size, their color, their diet—reveals some way they adapted better than their relatives.
Or for an easier example, you might look to your dog. Most modern dog breeds like the golden retriever or basset hound have only been around for a few hundred years. Today, every junkyard mutt introduces a new breed. That breed may then evolve into something entirely new—evolution at play in just a few years. In the case of dogs, survival of the fittest usually ends up being survival of the cutest. Why else would Chihuahuas still exist and Bullenbeissers not? How long can French bulldogs, which often require C-sections to deliver puppies, survive on their own?
Nowadays, to study evolution is, in large part, to study extinction. And if humans are the culprit, so is the climate, thanks mostly to humans. Climate change means a less predictable existence for animals like the polar bear, or the quiver tree of South Africa. You can't ask the golden toad or Monteverde harlequin frog how they will adapt because none of them exist, two of the first species that climate change drove to extinction.
And what about humans? Clark's book explains how dark skin, dark eyes, and dark hair developed in the hot, sunny conditions of East Africa, where our species originated. Lighter skin and blond hair came when people moved to cooler, cloudier areas. Considering current behavior, humans thousands of years from now might have bigger eyes to take in more information, and bigger brains to process it. One study predicts that future women will be shorter, stouter, have lower cholesterol, and stay reproductively fertile longer.
That's if extinction doesn't strike us first. Some scientists who study evolution in real time believe we may be in the midst of the world's sixth mass extinction, a slow-motion funnel of death that will leave the planet with a small fraction of its current biodiversity. One reason that no one can forecast how it will end—and who will be left standing—is that, in many ways, our understanding of evolution itself continues to evolve.