A 2.8-million-year-old lower jawbone uncovered recently in Afar, Ethiopia may be the earliest record of ancient humans ever discovered. A graduate student from Arizona State University (ASU) first discovered the jawbone back in 2013. Now, two new papers published online in the journal Science report the research team’s findings. The fossil predates what scientists had considered to be the origin of humankind by around 500,000 years. The evidence found, combined with digital reconstructions of previous fossils of early human species, may change what scientists understand about the history of man considerably.
All archaic human species are believed to derive from a single, common ancestor more than two million years old, Homo erectus. These “humans” were around for more than nine times as long as modern-day humans have been. Homo erectus are the oldest known species to have the more human-like body proportions and expanded brain cavities. However, the lower jawbone from the Ledi-Geraru research site in northeastern Ethiopia pushes the origin of humankind back by half a million years before Homo erectus.
Analysis of the fossil, led by William Kimbel director at the Institute of Human Origins and lead author Brian Villmoare of the University of Nevada, Las Vegas, showed higher features such as symmetrical premolars, slim molars and an evenly proportioned jaw. However, features like the sloping chin of this latest fossil may link it to more primitive species like the smaller-brained, more apelike, 3 million-year-old Australopithecus afarensis – exemplified by the famous skeleton of “Lucy”. More of the specimen is currently required in order to classify it to a species of Homo, however. The researchers acknowledge that the jawbone resembles that of Lucy’s, and may even have originated from it. As such, experts consider the fossil to be of the species that led to modern humans. “It’s an excellent case of a transitional fossil in a critical time period in human evolution,” said Kimbel.
Researchers have apparently had a challenging time piecing together mankind’s ancient evolutionary journey due to partial fossil records. The chain dates back 5-7 million years, culminating at a common ancestor that humans share with chimps and bonobos. William Kimbel, director of ASU’s Institute of Human Origins, said in a news release, “The importance of the specimen is that it adds a data point to a period of time in our ancestry in which we have very little information. This is a little piece of the puzzle that opens the door to new types of questions and field investigations that we can go after to try to find additional evidence to fill in this poorly known time period.”
In another paper also recently published in Science, the team suggest that around 2.8 millions years go, climate change might have transformed forests in Afar into grasslands. In response to such a profound change to a habitat, a species may either go extinct or adapt to the new environment (in other words, evolve). Villmoare believes that other species more suited to the new environment influenced these ancient human ancestors to develop larger brains and more agile bodies in order to survive.
This jawbone uncovers the mysterious era where the human genus appeared. It links the modern human to its ancestors, helping researchers pinpoint when the evolutionary transition may have occurred. Genomic studies of the jawbone using next-generation sequencing tools might show just how different modern humans are to this fossil species and help identify defining changes that took place once humans separated from their common ancestor – in essence exploring what is exclusively “human”.
What might the world look like if modern-day humans existed alongside ancient species of human today?