10 Extinct Hominids

A Neanderthal skull (left) is positioned next to the skull of a modern Homo sapiens (right). In between sits the Manot Cave skull, which scientists say proves Homo sapiens migrated out of Africa 65,000 years ago. Nir Alon/ZUMA Press/Corbis

Since at least the time of the ancient Greek philosophers, we have been comparing the human race to the other animals that inhabit this world. We're driven by the same instincts and urges as animals, yet humans are infinitely more complex in emotion and thought. Several breakthroughs in the past two centuries have helped us explain this. And yet, many questions remain.

In the 18th century, Carolus Linnaeus designed a Latin-based naming system for the planet's species and labeled ours Homo sapiens, meaning "wise man." In 1859, Charles Darwin published his theories about natural selection, or how species change by adapting to their environment: Those individuals with successful traits are more likely survive to pass on those traits. After many generations, therefore, the whole species rejects some traits and adopts others.

Such an evolution from chimpanzee to human would take many millennia. Fortunately, archaeologists have uncovered many different kinds of fossils of extinct species that exhibit similarities to both chimps and humans. By examining bone structure, teeth and DNA, researchers can make educated guesses as to these species' mobility, diet, brain size, age — and how we might be related.

Hominids are the group of species that includes humans, chimpanzees, gorillas and orangutans in addition to their immediate ancestors. (Hominins are a subfamily of hominids that includes the genus Homo and its immediate ancestors or relatives). The history of hominids is not a straight line from chimps to humans, but rather a diverse family tree that's still being debated and assembled as we find more fossils. We'll explore the species that came before us, many of which thrived for much longer than Homo sapiens have been around.