Fossils of early humans and their relatives show how our ancestors changed over millions of years. Large numbers can be written in words or in standard form, so 4.4 million years is 4.4 × 106 years.
Ardi is a fossil of Ardipithecus ramidus that lived about 4.4 million years ago in Ethiopia. Her skeleton shows she could walk upright on two legs, but she also had a grasping big toe, so she could still climb trees. Her brain was small, about the size of a chimpanzee's.
Lucy is a fossil of Australopithecus afarensis from about 3.2 million years ago, also found in Ethiopia. Her hip and leg bones show she walked upright more efficiently than Ardi, but her brain was still small. Lucy is 1.2 million years younger than Ardi.
Richard Leakey's team found fossils in Kenya from about 1.6 million years ago, including a nearly complete skeleton known as Turkana Boy, of the species Homo erectus. It had long legs, a body shaped much like ours and a larger brain than Lucy's. Together the fossils show a trend: walking upright evolved before large brains, and later species looked more like modern humans.