Monday, November 5, 2012

In the November/December 2012 issue of Orion magazine, there is a wonderfully informative and delightfully engaging article by Charles C. MannState of the Species, in which he discusses the history and fate of Homo sapiens as a biological species. Please do read the entire article. Below I am going to present an outline of the salient features, frequently relying on the words of the author. Consider them as abridged excerpts.

Homo sapiens emerged on Earth around 200,000 years ago. Those humans were anatomically modern, but not behaviorally modern: they possessed no language, no clothing, no art, no religion and had the simplest of tools. Those early humans had so little capacity for innovation that for the first 100,000 years of their existence, we find no evidence of any significant cultural and social change. Furthermore, humans were confined geographically to a small area in East Africa (and possibly another area in South Africa).

Then, mysteriously, 50,000 years later humans were drawing cave art, using specialized tool, had clothing, religious worship and rituals, and were communicating via language. How did this sudden transformation come about in what is geologically a finger snap?

We are not really sure what happened. It is possible that favorable genetic mutations swept throughout the species that led to an increase of mental capacities and abstract thinking. It may have come about by interbreeding with Neanderthals. It may simply be a result of the invention of language. 

It may also have been related to a significant geological event that happened 75,000 years ago: a huge volcano exploded on the island of Sumatra, creating Lake Toba, the world’s biggest crater lake, and ejected the equivalent of as much as 3,000 cubic kilometers of rock. Dust hid the sun for as much as a decade, plunging the earth into a years-long winter accompanied by widespread drought. This predictably threatened the survival of countless species, including Homo sapiens: the number of humans shrank dramatically, perhaps to a few thousand people. This bottleneck is evident from the remarkable genetic uniformity of humans. This bottleneck may also have helped alter the genetic composition of Homo sapiens, because in small populations favorable mutations can spread very rapidly, and uncommon variants can become dominant.

How it happened is unclear, but around the time of Toba behaviorally modern humans emerged and spread out into the world; human footprints appeared in Australia within as few as 10,000 years.

What does the growth curve of a typical species look like? Take a species of bacteria. It's population would be kept in check and steady by the size of its habitat, by the limited food supply and by competing organisms. However, put a small population in a petri dish and the behavior radically changes. There is no competition, and the food supply and habitat appear to be endless. At first it grows slowly, then it hits an inflection point, and there is a frenzy of exponential growth. The petri dish is swamped. The rapid growth continues until it hits the second inflection point - the edge of the petri dish. As the food supply is exhausted and waste materials accumulate, the bacteria begin to die and ultimately the population falls to zero.

From a biological perspective, Homo sapiens look like one of these briefly fortunate species: for the modern humans the post-Toba world presented itself like a petri-dish. Around 10,000 years ago with the invention of agriculture, we hit our first inflection point. There has no been stopping us since then. In just the past two hundred years, human population has exploded from 1 to 7 billion. In 2000, the chemist Paul Crutzen gave a name to our time: the “Anthropocene,” the era in which Homo sapiens became a force operating on a planetary scale.

Like a typical biological specie, it can be expected that our 
"growth will continue at a delirious speed until we hit the second inflection point. At that time we will have exhausted the resources of the global petri dish, or effectively made the atmosphere toxic with our carbon-dioxide waste, or both. After that, human life will be, briefly, a Hobbesian nightmare, the living overwhelmed by the dead. When the king falls, so do his minions; it is possible that our fall might also take down most mammals and many plants. Possibly sooner, quite likely later, in this scenario, the earth will again be a choir of bacteria, fungi, and insects, as it has been through most of its history."
Is a different outcome possible? It may be. Unlike other species, we are characterized by remarkable behavioral plasticity; we have the ability to change our behavior, not just on an individual level, but also on a social one. This behavioral plasticity has conferred to us great powers of adaptation, instrumental to our biological expansion. Can we as a species constrain our own growth before we hit the second inflection point? To do so would be biologically unprecedented. Is our behavior plastic enough to take on such a challenge? The possibility exists, but that itself is no predictor of the outcome. Time will tell whether Homo sapiens will end up any different from bacteria in a petri-dish.



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