For nearly 40 years, scientists have suspected that a linear family tree — one in which Homo sapiens evolved directly from Homo erectus with no time of overlap — doesn’t properly represent our origins. However, a skull found in 1972 that was very different from typical specimens suggested early humans weren’t always alone, perhaps accompanied by a species with a relatively large brain and long flat face. Back then, scientists could merely speculate that this skull belonged to a completely separate species, entitled Homo rudolfensis. After all, there was only one fossil found, hardly enough to make a claim for a separate species. Now, with the discovery of three new human fossils that are between 1.78 and 1.95 million years old that also seem to belong to Homo rudofensis, scientists can safely posit that there were at least two contemporary Homo species, in addition to our progenitor Homo erectus, living in East Africa as early as two million years ago.
Our earliest human ancestor is thought to be Homo erectus, a species that dates back 1.8 million years ago. However, 50 years ago, scientists discovered an older, more primitive species of human called Homo habilis that possibly co-existed with Homo erectus. With the discovery of these new fossils, uncovered near Lake Turkana in Kenya by Meave Leakey and Louise Leakey, a mother-and-daughter team of paleoanthropologists, scientists are beginning to believe that Homo rudolfensis and Homo habilis were around when Homo erectus was walking the earth, complicating the simplistic family tree that is a staple of high school biology textbooks.
“Humans seem to have been evolving in different ways in different regions,” said Professor Chris Stringer of the Natural History Museum in London. “It was almost as if nature was developing different human prototypes with different attributes, only one of which, an ancestor of our species, was ultimately successful in evolutionary terms.”
However, as is the case with science, these conclusions aren’t without problems: Stringer notes that the Homo rudolfensis skulls “might still be just large specimen[s] of Homo habilis.” According to Bernard Wood of George Washington University, in order to confidently categorize current and future fossils “more work needs to be done using the faces and lower jaws of modern humans and great apes to check how different the shapes and the palate can be among individuals in living species.” In other words, if there is significant variation in the skulls of modern human beings, it’s possible that these fossils actually belong to the same species, a species that happens to sport various skull shapes and sizes.
Regardless of the direction that these fossils take modern science, Dr. Leakey believes that findings like these demonstrate the veracity and wonder of human evolution: “It leads to amazing adaptions and amazing species and we are one of them,” she said.