June 29, 2010 Leave a comment
Fossil and genetic evidence suggest that anatomically modern humans (Homo sapiens) evolved in Africa around 200,000 years ago. Further evidence strongly suggests a bottleneck effect in early human populations. It seems that our earliest ancestors were challenged continually to find their ecological niche, the stress from which effectively reduced or limited population growth. Given the current evidence, there many have been as few as 2,000 individuals at one time. By today’s standards, we would have been considered an endangered species. Clearly, ecology had an overwhelming effect on the evolution and behavior of our earliest ancestors.
Our ancestors subsisted on a diet of meat—hunted or scavenged—and gathering edible vegetation. The land requirements for a hunter gatherer culture are heavily dependent on the surrounding ecosystem. Hence, in an ecosystem that challenged its very existence, our early ancestors sustained themselves by moving frequently, which continually pushed them to adapt quickly to new environments, learn new survival skills, and to be flexible.
Balancing Ecological Production and Human Consumption
Around 90,000 years ago, give or take 10,000 years, our ancestors began migrating out of Africa. The Recent African Origin (RAO) is the prevailing model supported by several scientific disciplines, such as paleoanthropology and archeogenetics . This model does not preclude earlier migrations out of Africa by other human groups, but so far there is no evidence that earlier migratory groups survived to the present day.
Of course, our ancestors were searching for a more beneficial ecosystem, not discovering another continent. Their focus was on survival, but migrating to new surroundings posed additional challenges: deciphering which vegetation was edible or poisonous, finding materials for hunting, food preparation—even shelter, and understanding the behaviors of newly discovered animals. Obviously our ancestors took on those challenges, whether or not they had the option of weighing them against the familiar challenges of their previous surroundings.
There is ample physical and biological evidence that our ancestors met the challenges of a life outside Africa. In fact, the human population began to increase steadily and spread slowly throughout Asia and Europe. At an almost indiscernible average rate of one mile per decade, our ancestors continually widened the range in which they searched for food and other necessities, which suggests that humanity finally found its niche in their ecosystem.
Over the long term, the rate of one mile per decade was enough for our ancestors to reach the Eastern edges of Asia and western shores Europe in less than 45,000 years. Despite recent evidence of multiple genetic bottlenecks along the migratory paths, our ancestors demonstrated their flexibility and control over the skills and behaviors born under adverse conditions in Africa to sustain human populations through a wide variety of ecosystems in Asia and Europe. In other words, the balance between ecological productivity and human consumption was maintained through this period of continual migration.
A Shift in the Balance
Through a combination of circumstance and increasing ingenuity, human migration continued across significant bodies of water and reached what are essentially closed ecosystems—Papua New Guinea and Australia.
(to be continued)