Fossils of prehistoric animals show us that life on Earth is always changing. Over time, old species disappear and new ones develop from them, like new relatives appearing in a family tree. These new species appear thanks to a process of gradual change we call evolution.
Evolution is driven by a process called natural selection. Animals and plants produce more offspring than survive to adulthood, all of them slightly different. Nature selects those with the best characteristics, which then pass on these characteristics to the next generation.
The giraffe’s neck
The giraffe’s long neck evolved because natural selection weeded out individuals that couldn’t reach food high in the trees. With each generation, the tallest giraffes got the most food and had the most babies. Over time, the species changed as its neck grew longer.
TAKE A LOOK—A STORY OF FINCHES
The most famous person to collect evidence for the idea of evolution was the English naturalist Charles Darwin. He visited the Galápagos Islands in the 1830s, where he found a range of similar finch species, each with a beak suited to its particular diet. He realized they’d all evolved from a common ancestor that had settled on the islands long ago.
An unpopular theory
People made fun of Darwin for his ideas; he was drawn with the body of a chimpanzee in 1871 when he proposed that humans were related to apes.
One reason Darwin was ridiculed is that the fossil record is much too sparse to show a process of gradual change. However, some key fossils show clear links between related animal groups. One example is Archaeopteryx—a missing link between dinosaurs and birds.
EVOLUTION OF THE ELEPHANT
In a few rare examples, we can see gradual evolution in fossils. The elephant belongs to a group of animals called proboscideans. Over time, proboscideans became larger and developed larger tusks and trunks. But the ancient animals shown here may not be direct ancestors of the elephant—they are merely glimpses of parts of the elephant’s large and hidden family tree.
Darwin realized that animal breeders change their breeds using a process very similar to natural selection. Instead of letting nature choose which animals will breed, breeders make the choice themselves.
Darwin called this artificial selection. All dog breeds were created this way from their wild ancestor, the wolf.