Hailed as a find for the ages, a rare skull of a 1.8-million-year-old human relative could provide answers to longstanding questions about the lineage of our species. It also fuels debate over what differentiates one hominin species from another, and could mean that Homo habilis, Homo rudolfensis and other early bipedal hominins may all be members of Homo erectus, rather than distinct species.
Figuring out when modern humans left Africa and migrated throughout the world is a complicated task. For example, some evidence suggests modern humans may have migrated out of Africa and into Asia as early as 120,000 years ago. Further evidence puts modern humans in India and other parts of South Asia prior to the super-eruption of Mount Toba in Sumatra, which took place 74,000 years ago.
When Lucy and other Australopithecines were walking around Ethiopia 3.4 million years ago, they may have encountered another hominin species that still climbed trees and also walked, but with a gait more like an ape than their bipedal neighbors. The tantalizing new discovery of a few fossil foot bones shows that at least one species retained an opposable big toe, one million years after the grasping feature was thought to have disappeared.
What is it, exactly, that distinguishes us from other species? The definition of humankind has perplexed scientists, philosophers and theorists for centuries. DNA composition differentiates species in a technical sense, but that definition is hardly satisfying. Certainly there must be something more ethereal that separates us from “lower” forms of creatures. Over the centuries, several definitions have emerged — from using tools to speaking — but have then been proven insufficient in some heuristic way. So I propose another option: manipulating energy.
Modern humans reached the islands of Southeast Asia by approximately 50,000 years ago, but our ancestors’ journey was not easy. Even during times of low sea level, a voyage to some of these islands would have required crossing open water, leaving many scientists to wonder how humans arrived on the most isolated islands.
The debate over when our ancestors first used stone tools is not over just yet. In August, researchers had reported finding scratch marks on two 3.4-million-year-old animal bones that they said were made by Australopithecus afarensis — the ancestor made famous by Lucy — scraping meat off the bones with sharp-edged stones. If true, that would push tool use back to 800,000 years earlier than previously thought.
How and when did modern humans leave Africa and colonize the rest of the world? Many archaeologists would probably tell you that about 60,000 years ago, Homo sapiens walked up through Egypt, crossed the Sinai Peninsula into the Levant region of the Middle East and then continued on to Eurasia.
Mapping out how one species of early hominin branches to another has always been complicated by the rarity of complete specimens and lack of precise dating methods for fossils more than 50,000 years old. Now researchers studying the braincase, pelvis, hands and feet of a primitive hominin — which lived about the same time early Homo species were evolving — are taking full advantage of a rare, nearly complete assemblage of fossils and a new highly accurate dating method to once again redraw humankind’s ancient lineage.
In the Great Rift Valley in northern Kenya, researchers have discovered a cluster of footprints that look almost exactly like those you or I might leave on a sandy beach. These prints, however, were left by early hominins more than 1.5 million years ago, making them the oldest known evidence of fully modern bipedalism.