Optical Illusions: The Challenge of Tracing Human Origins
If tracing this lineage from our earliest ancestor seems inconsistent or spotty, that’s because it is. We have a makeshift model of human history that had been cobbled together by geneticists, archaeologists, anthropologists and biologists. Finding common ground and an overall consensus among these different disciplines makes finding the truth even harder. Looking back at human history is an optical illusion; new archaeological discoveries are always challenging what we already know, and constant revisions are being made.
In 2013, a major find would cause further controversy within the already complex grouping of hominids. In Dmanisi, Georgia, an archaeological dig was under way. After finding a series of four similar-looking skills during the dig, the fifth one looked irregular. This skull had a small braincase, large teeth and a powerful jaw, but judging by the skull’s shape and structure, it must have been attached to a long-limbed, human-like body, not a short-limbed, muscular body like Australopithecus. An apelike skull attached to a human body are features that never co-existed prior to this discovery. This has led scientists to believe that the Homo Subspecies of Ergaster, Erectus, Rudolfensis, Habilis and so forth, may have actually been one species that simply looked different - much like the varying appearances of different races we encounter today. This find has been known as “Skull 5”, and has already caused a debate about how the homo species should be classified. This finding will spawn a debate until a newer find is unearthed and new data is presented. These revisions will continue until we either run out of fossils or more advanced technology allows us to shed light on this ongoing mystery.
The Dmanisi early Homo cranium, ‘Skull 5’. Photo courtesy of Georgian National Museum
The scientific dating of species that have been found is volatile by nature. Lucy, the Australopithecus specimen went through several date revisions since she was found. Anthropologist Susan Martinez outlines the numerous times Lucy has been re-dated to fit with contemporary theories. In the 1950’s following Lucy’s discovery, she was estimated to be at least 500,000 years old. This number changed in the 1970’s to at least a million years old. After new discoveries in Ethiopia, that number jumped to two million. The wide estimates between these broad and sweeping figures are known as scatter in archaeological terms. A species known as Petralona Man is said to have existed between 70,000 to 700,000 years ago. Another known as Morocco Man was first estimated to be 40,000 years old, until further tests actually placed him at 125,000 years old. The prevalence of scatter across these finds makes it no wonder why our lineage is so difficult to trace. How is it that these figures come to be so slippery and hard to pin on a timeline?
The skeletal remains of ‘Lucy’ (Australopithecus). Image source: Wikipedia
The techniques used to calculate the date of a fossil aren’t perfect and are subject to error. A technique known as radiocarbon dating works by measuring how levels of carbon have dropped in a bone fragment or artifact over time. Exposure from the sun on a piece of bone, for example, accumulates nitrogen in the bone fragment. This nitrogen turns into carbon-14, which acts as a measuring guide for how old an object is. Over time, carbon-14 levels decrease – these levels serve as a yardstick for the age of the object. This technique is most accurate up to a period of 60,000 years – anything longer and results are often unreliable. The level of carbon decay may have varied across different time periods in the past. Some species may have had less exposure to sun, or climate change may have influenced the amount of carbon in the atmosphere. The higher the fossil is in the surface of the Earth, the more likely it comes into contact with weather, animals and other agents. Even exposure to coal can contaminate the carbon levels in a finding, yielding highly different results. A finding in France known as the Fontechevade Man has been estimated to be between 40,000 to 800,000 years old just based on readings of nitrogen levels alone. Scientists have even resorted to using different levels of dating to counterbalance the levels of scatter that may occur from carbon dating.
One technique known as faunal dating looks at the animal remains of species that may have existed millions of years ago. Traces of these species can let us know how old an object is, but can yield confusing results. Susan Martinez offers a good example: We have estimated Trilobytes (an ancient crab-like species) to have existed at least 550 million years ago – the Cambrian era. But any finding with traces of Trilobytes is said to be from the Cambrian era. How do we know Trilobytes are 550 million years old? Because Trilobytes existed 550 million years ago. This argument goes in circles and explains why a technique like faunal dating is unreliable in reading human fossils we encounter. We use fossils to date rocks, or rocks to date fossils – we are left with only relative dates of which species lived when. These are problems that arise when trying to date these fossil finds. Each new find re-writes history, which is written again, further confusing our already obscure and complicated origins.