Human evolution hasn’t occurred in a simple easy-to-trace straight line. In fact, it’s more of a messy, zigzag affair. It illustrates how evolution isn’t just about adaptation to changing environments or for survival. Natural selection can also be experimental, even wildly experimental.
Several species of bipedal primates evolved, then about 2.4 million years ago, Homo habilis appeared with a larger brain and the ability to make and use tools. In addition, the cast of a fossilized brain of Homo habilis reveals growth in the left lobe area of the brain that modern scientists call Broca’s area—an area associated with the ability to speak.
Natural selection capitalized on this exploratory path. Among the thousands of flaked stone tools discovered with Homo habilis are those that may have been used for butchering animals and scraping off segments for food, but there is no evidence of the use of fire for cooking their meat. Nor were hunting tools discovered. Therefore, scientists conclude that Homo habilis must have been a scavenger.
Less than 500,000 years later, however, another species of Homo would appear in the fossil records with a much larger brain and the ability to make fire: Homo erectus. The two species co-existed in Africa from 1.9 mya (million years ago) to about 1.4 mya.
The 4′ tall Homo habilis walked erect but more bent over than Homo erectus who at 5’10” average height would have towered over its predecessor. Homo erectus looked less apelike and had shorter arms, longer legs, and a flatter face than Homo habilis. Moreover, in addition to its larger brain and its ability to make fire, Homo erectus was our first ancestor to travel and live outside of Africa. In fact, the fossil discoveries were first uncovered in Java, Indonesia, and the new species was nicknamed Java Man. Today fossil evidence of Homo erectus extends across Africa, Europe, the Near and Far East making this new species the first world traveler in our direct lineage.
To complicate matters, two other contemporary species of Homo appear to have also lived in Africa at the same time: Homo ergaster and Homo rudolfensis. The exact relationship between the four co-existing species of our Homo genus is a topic that remains hotly debated among paleoanthropologists. As of now, it is unclear if Homo erectus evolved from Homo habilis or from another species, perhaps one that is currently unknown. But digs are ongoing, and new discoveries always seem to hover on the horizon. (to be continued in the next post)