Man’s unrelenting quest to chart out the precise pattern of his ancestry got a lightning jolt of excitement this month. Fossil hunters have dated a tranche of jaw, tooth and skulls (in picture), unearthed at different periods since the 1960s, from a cave in Jebel Irhoud, Morocco. These have been proffered as proof of the oldest known humans. The pair of research papers reported in Nature suggests that science may have grossly underestimated the age of humanity. Until last month, the consensus was that humans were about 2,00,000 years old. This discovery pushes the history of human evolution back to at least 3,00,000 years.
There are multiple reasons why this is significant. One, it shows the extremely inventive methods that archaeologists and paleo-anthropologists tap to date human history. Here they used electron spin resonance dating that tells you how long a sample — in this case the enamel from the teeth — had been exposed to the radiation from the surrounding sediment in which it was buried. The age was computed by measuring the atoms with unpaired electrons (free radicals) which were created by the ambient radiation. The other technique employed was thermo-luminescence. Accompanying the bones were flints that were probably used to make fire. When heated, electrons are released from those rocks and over time solar radiation replenishes those electrons. In a lab, such stones are heated again and — based on the number of electrons — scientists can figure out how long ago those stones were first fired.
In 2010, scientists extracted DNA from Neanderthal bones and were able to sequence the entire genome of that species, which is considered our most mysterious cousin. From this we know that 2-4% of DNA in Europeans and Asians is of Neanderthal provenance and that there was a far deeper connect between the two species than was previously assumed.
Discovery in western Africa
Another aspect of the Jebel Irhoud find was the location: Morocco. In the last four decades, fossil finds in the East African Rift Valley, such as the bipedal ape Lucy, human precursors Homo habilis and Homo erectus , had veered scientific opinion to the east of Africa being the ‘cradle of mankind’. However South Africa, with recent discoveries of pre-humans such as Homo naledi and million-year-old ancestors of hominids, such as Australopithecus sediba , has persistently laid claim to be the cradle of mankind. Now with Morocco, there’s an entirely new west side story that has cropped up.
Archaeologists have usually sought to mark out the descent of man through traits such as bipedalism, tool making, brain volume and existence of social structure in ancestral species. However, many of these traits are now seen to be far more widely distributed in the animal kingdom in beings that are not even remotely linked to the human lineage.
The acuity of electron-spin measurements, thermoluminescence and DNA extraction methods will only blunt the sharp distinctions that Homo sapiens sapiens has created to distinguish itself from its siblings. Humanity, it is increasingly clear, is easier to define than humans.
