Fossil hunters working under the baking sun in a dry bed of the Lake Turkana basin in northern Kenya recently made a remarkable discovery. They found the skull and jawbone of a humanlike creature that lived 3.5 million years ago. The scientists believe the bones might belong to the ancestor of the human race.
The trouble with the discovery is that scientists thought they had already discovered the ancestor of the human race. They thought it was Lucy.
Everyone Loves Lucy
Who’s Lucy? Lucy is a 3.2-million-year-old partial female skeleton that was unearthed in the arid badlands of the northern Afar region of Ethiopia in 1974 by Donald Johanson, now an Arizona State University anthropology professor. Named after the title character in the Beatles song “Lucy in the Sky With Diamonds,” the short-legged Lucy stood about 107 centimeters tall (about 3 feet 6 inches), weighed about 30 kilograms (66 pounds), and was bipedal (walked on two legs). Lucy had long arms for swinging through trees; a chimplike, protruding face; and huge grinding teeth.
No fossil skeleton of Lucy’s age and anatomy had ever been found before. So Johanson created a new scientific category for her species: Australopithecus afarensis, which means “southern ape from the Afar region.”
Our Evolutionary Tree
Lucy became the most famous fossil discovery of the 20th century. Johanson and others concluded that Lucy and her fellow species members were the ancestors of all the hominid species that lived after her, including modern humans (Homo sapiens). Hominids are a family of primates that includes humans and the ancestors of humans. Primates are mammals with forward-pointing eyes and flexible fingers and toes used for gripping objects. Unlike other primates, such as apes and monkeys, hominids are bipedal and developed bigger brains over time. The first hominids appeared on Earth about 3 million to 4 million years ago.
As you can see from the diagram, the hominid family tree branched out in many directions after Lucy. Some of the species in that family tree belonged to a group of hominids called australopithecines. Those hominids walked on two legs but had relatively small brains. Lucy, herself, was an australopithecine.
The ability to walk on two legs left hominids tree to become specially adapted for gripping things, which eventually enabled them to make simple tools. The first toolmaking species of hominid was one of Lucy’s descendants, Homo habilis, which emerged about 2.4 million years ago. H. habilis is considered the first human species. H. habilis eventually gave rise to H. erectus, which was followed by H. heidelbergensis and finally, H. sapiens–us!
That’s how scientists drew the human family tree until last spring. Then in March came startling news from Meave Leakey, head of paleontology at the National Museums of Kenya. Leakey reported finding a brand-new skeleton in the hominid family closet. Unearthed near Kenya’s Lake Turkana, this humanlike creature lived at the same time Lucy did and could just as easily be our ancestor.
The 3.5-million-year-old skull and partial jawbone look like nothing ever seen before. Instead of an ape face like Lucy’s, the new fossil find features a large, flat face with a less protruding jaw, more pronounced cheekbones, and surprisingly small teeth and molars. It’s the oldest known complete cranium of any member of the human family.
Because no long bones or ribs were found with the skull, Leakey and her colleagues don’t actually know the hominid’s sex–it could have been a Lucy or a Linus–or how well it walked on two legs. What they do know is that although it had a small, chimpanzee-sized brain case like Lucy’s, its face was astonishingly humanlike.
Because the skull looked so different from Lucy’s, Leakey concluded that this long-lost relative needed a totally different scientific category. She named it Kenyanthropus platyops, meaning “flat-faced man of Kenya.”
Because tooth size and face shape relate to the way a species chews its food, scientists surmise that K. platyops ate fruits, berries, insects such as grubs, and maybe even small animals. Big-toothed Lucy, on the other hand, most likely grazed on chewy roots and grasses. The two species probably did not compete for food when they shared the once-lush woodlands and meadows of eastern Africa 3 million to 4 million years ago.
Which Is It?
So the human family tree turns out to have had at least two main branches, only one of which could have led to us, Homo sapiens. But which one? “Anthropologists will have to decide which of these [two] forms of early human actually lies in our ancestral tree,” said Frank Brown, a University of Utah geologist and member of Leakey’s team. “It cannot be both.”
Or it could be neither. Modern humans have been searching for their prehistoric roots for only a short time. Maybe our real ancestor is still lying on a dusty African plain, waiting to be discovered by a future scientist–perhaps by you!