WITH dire warnings about environmental destruction, looming food shortages and international strife, it often feels humanity is on the brink of dying out.
But an extensive new genetic study now suggests that humans may already have had a brush with extinction during the Stone Age, 70,000 years ago.
The number of early humans may have shrunk as low as 2,000 before numbers began to expand again in the early Stone Age, according to an analysis released today.
It claims genetic evidence suggests that catastrophic environmental conditions occurred which pushed early man to the same status as the dodo. Today, more than 6.6 billion people inhabit the globe.
Previous studies using mitochondrial DNA (mtDNA) – which is passed down through mothers – have traced modern humans to a single "mitochondrial Eve", who lived in Africa about 200,000 years ago.
The migration of humans out of Africa to populate the rest of the world appears to have begun about 60,000 years ago, but little has been known about humans between "Eve" and that dispersal.
The new study, published in the American Journal of Human Genetics, looks at the mitochondrial DNA of the Khoi and San people in South Africa which appear to have diverged from other people between 90,000 and 150,000 years ago, making them a unique source of DNA evidence.
The Khoi people dominated the subcontinent for millennia before the appearance of groups, and still exist today as a distinct tribe. They are considered to be a people which has preserved the original human lifestyle along with genetics.
The San, also known as Bushmen, have a similarly ancient lineage, with archeological evidence that they had an advanced early culture stretching back as far as 20,000 years ago.
The researchers, led by Doron Behar of Rambam Medical Centre in Haifa, Israel and Saharon Rosset of IBM TJ Watson Research Centre in New York, and Tel Aviv University concluded humans separated into small populations prior to the Stone Age, when they came back together and began to increase in numbers and spread to other areas.
Eastern Africa experienced a series of severe droughts between 135,000 and 90,000 years ago and the researchers said this climate shift may have contributed to the population changes, dividing into small, isolated groups which developed independently of one another.
As they assert in their report: "The study of extant genetic variation in African populations with complete mtDNA sequences provides an insight into past Homo sapiens demographics, suggesting that small groups of early humans remained in geographic and genetic isolation until migrations during the late Stone Age."
They add: "Though the archeological record from this period is too poor to reliably identify reasons for the split(s), recent studies show that the sporadic settlements of Homo sapiens in north-west Africa, the Near East, Chad, and southern Africa may have been caused by stressful climatic fluctuations known to have occurred throughout the mid-Stone Age."
Meave Leakey, a palaeontologist and adviser on the Genographic Project, launched in 2005 to study anthropology using genetics, said: "Who would have thought that as recently as 70,000 years ago, extremes of climate had reduced our population to such small numbers that we were on the very edge of extinction."
GREAT LEAP FORWARD FOR HUMANITY
THE year 68,000BC saw the beginning of a European Ice Age – known technically as the Wurm Glaciation – which meant humans endured a long cold snap.
By then, Neanderthals had spread out over much of Europe and western Asia, and it was about this time that Aboriginal tribes are thought to have started arriving in Australia, with other tribes appearing in South America.
Two Neanderthal skulls from France dated to this time revealed man had a hypoglossal canal the size of modern humans, which indicates they were most likely to be capable of speech. This period saw a great leap forward in human development, marked by the use of the first stone tools, and jewellery. It seems humans had also begun to paint and it is thought they were using symbols to communicate.