For hundreds of thousands of years proto-humans had been making and controlling fires---presumably for warmth, protection from wild animals and for cooking. Archeological evidence reveals the presence of fire pits for at least the past 800,000 years but cannot tell us exactly when our pre-human ancestors first controlled fires.

Harvard University biological anthropologist Richard Wrangham presents a compelling hypothesis that Homo erectus began cooking food 1.8 million years ago (“Catching Fire: How Cooking Made Us Human,” Basic Books).

1.8 million years ago Homo-erectus had evolved larger skulls (bigger brains), smaller pelvises and rib cages (smaller abdomens) and especially smaller teeth (softer foods). These evolutionary changes were directly due to and/or involved with the cooking of foods, says Wrangham. He points out that at no other time in our history did our teeth, skull and pelvis change size so drastically. Wrangham calls this an “indisputable” “signal” in the fossil record because cooking concentrates and softens wild foods, thus requiring smaller dentition and stomachs---also freeing proto-humans from the endless chore of chewing and digesting large masses of coarse wild foods. This allowed those bigger, higher-energy-consuming brains to focus on the development of tools, culture and more complex social structures. [NOVA will present programs about Homo erectus---PBS Ch. 7 - Tuesdays Nov 3, 10 and 17 - “Becoming human - Unearthing our earliest ancestors”]

While the controlled use of fire had a profound effect on human prehistory, the effects of this early use of fire on the global climate were probably negligible. There just weren’t enough humans to make a difference.

We do know, however, that for perhaps 40,000 years Australian Aborigines had been setting seasonal wildfires to clear vast tracts of land to remove old growth and encourage new growth of plants and grasses for grazing animals and to drive wild game. We also know that American Indians have done the same. In the recent Ken Burns film on America’s National Parks, he recounts the return visit to Yosemite Valley of the last surviving member of the Indian tribe that used to live there but was kicked out by the Whites who “discovered“ the valley. The elderly Indian lady remarked that the valley floor looked different---more brushy and overgrown than she had known it. She said her people used to set fires each spring to clear the undergrowth. Such practices encouraged the growth of some plants, trees and animals and discouraged others.

THE RISE OF AGRICULTURE -

For uncounted millenniums small bands of proto-humans and humans wandered from one “Eden” to another---moving on when the area became stripped of wildlife, wild foods, herbs, trees and fresh water. When the “Eden“ became fouled by their own wastes and depleted by overuse they departed---moving on to “greener pastures.”

Agriculture of sorts had already been practiced long before it became more fully developed at the time of the early city states around ten-thousand years ago. These earlier agricultural practices included protecting already-growing wild food plants from the depredations of animals and insects and the husbanding of wild plants by weeding.

The development of true agriculture---organized farming with digging sticks, plowing and the planting of seeds---totally changed humanity. Life became more efficient---easier in one sense. But organized agriculture certainly introduced a terrible drudgery into the lives of newly “civilized” people---leading to the development of those social classes who did the dirty work and those who lorded it over them. There was also a great estrangement from nature itself---nature and the wild was now seen as the enemy instead of the source of life. These problems haunt humanity to this day.

The rise of agriculture is well-documented---it changed everything. The world-wide development of agriculture made city-states possible. Agriculture allowed large groups to settle in fixed places---and also gave rise to total warfare by providing stores of food, fixed sites for weapon-making to equip armies of soldiers specializing in military matters and thus able to make war against each other and to overpower the more “primitive“ hunter-gatherers by using an agricultural base to support extended campaigns. This is how the true “subsistence” cultures were eliminated or driven into the more inhospitable regions of the planet.

For the purpose of this piece, organized agriculture led to a way of life that featured overpopulation, concentrations of human waste and pollution which caused sprawling effects upon the surroundings, the land areas, the streams, lakes, oceans and the atmosphere---the environment. These environmental effects were by-products of activities that have allowed us to “specialize” and develop “civilizations.”

The scientific key to differentiating human-caused environmental and climate changes from “natural cycles” is to document where and when natural causes no longer explain altered weather cycles---but where and when the increased concentrations of human-caused greenhouse substances do correlate with changes in climate patterns. William E. Ruddiman used this technique to address the subject of the earliest human-caused climate change (March 2005 Scientific American, “How did humans first alter global climate?”).

By comparing ice core samples from 8000 years ago with samples from the previous 400,000 years Ruddiman concluded that human farming with it’s attendant overpopulation, land-clearing, deforestation and slash and burn agriculture was already adding unnatural amounts of climate-changing CO2 to the atmosphere. This additional CO2 constituted an even greater increase in the natural and usual cycles of CO2 that had occurred during all the previous 400,000 years in those periods following the retreat of glaciers.

In other words, 8000 years ago---soon after humans first plunged into agriculture---abnormal increases in concentrations of greenhouses gases could no longer be explained by natural cycles of increases that usually occurred after an ice age.

The concentration of greenhouse gases increased again 3000 years later and included larger amounts of methane. Methane occurs naturally but is also a by-product of agricultural and domesticated animal-raising civilizations and an even more potent greenhouse gas than CO2. Methane levels that had gone through regular cycles for 400,000 years in every post-glacial period were now showing increases that could not be explained by natural causes.

In fact, Ruddiman’s hypothesis is that human agriculture-induced global warming actually prevented the natural cycle of an expected ice age from occurring---long before the modern industrial age caused greenhouse gases to rise even more precipitously. [Note: There are many other greenhouse gases---one is the now-banned “propellant” in pressurized spray cans that, even in small amounts, caused the ozone layer to become depleted.]

THE “LOST CIVILIZATIONS” -

For centuries humans have wondered about the “lost civilizations”---their ruins tantalize our imaginations. With the development of satellite imagery pointing the way to specific causes, there is now every evidence to show that the great early civilizations---from the fertile crescent of biblical fame to Cambodia’s magnificent Ankgor Wat complex of canals and temples to the South American Maya, Inca and Aztec civilizations---all went into decline after the stripping of surrounding forests literally changed the climate and the water resources and soils were depleted by overpopulation. These early, failed civilizations overused the resource base. [Note: Today, the rich nations and the rich inhabitants create far more pollution than the poor countries and poor inhabitants---who do create far more children. The poor do devastate the environment by cutting forests for firewood, etc. but the rich countries over-utilize the resources of the poor countries and contribute most of the greenhouse gases by far.]

Satellite surveys at various wavelengths have discovered that the great early "jungle” civilizations extended far beyond the perimeters of the more durable, surviving stone ruins we still see today. Great civilizations came and vanished and jungles and blowing sands simply covered the extent to which they had once been spread out.

Limestone was extensively burned in order to make plaster for temple and other walls; trees were cut for fuel and building; the land was cleared for farming; and streams were diverted for irrigation. There is no doubt that local climate was changed by the city states with their intensive agricultural base---to the ultimate detriment of sustainable farming.

Clearing large areas of forests had an effect on local climate (as it does today)---usually involving a decline of rainfall but with sudden floods that cause erosion, depletion of soils, resultant agricultural failure and the abandonment of the high population centers of the city-states. These ruins of civilizations are found from the Orient to the Middle East to South America and the US Southwest. Their declines were often accompanied by periods of particularly destructive warfare to gain control of dwindling resources. [read Jared Diamond’s "Collapse: How Societies Choose to Fail or Succeed." Also his great book, “Guns, Germs and Steel,“ which explains how natural circumstances of geography---not innate superiority---allowed Europeans to rapidly conquer less “advanced“ civilizations.]

The decline of the great civilizations of the past is now far less of a mystery---they were brought down by ecological damage caused by humans themselves. We weren’t driven out of Eden---we wrecked the environment and were forced to leave.

Next time (perhaps with other subjects in between): Part Two - It ain’t happenin’ and we didn’t have nothin’ to do with it.