CPSP218G Fall Semester: Earth, Life & Time Colloquium

Humanity's Impact on the Natural World:

There's Nothing New Under the Sun...
Thomas R. Holtz, Jr.

The "Noble Savage" Myth: A myth known since at least Classical times is that technologically inferior peoples lived morally and ethically superior lives to those of civilized men. (At least this beats the alternative myth of the "Savage Savage": untrustworthy, lacking in morality, etc.) One modern manifestation of this myth is that while Western Industrial society and its technology are clearly detrimental to the environment, non-industrial peoples "live at one with Nature." Sadly, the paleontological, archaeological, and historical record shows differently.

The Pleistocene Megafaunal Extinction: Unlike all previous mass extinctions, the loss of species during the last 60 ka has been almost exclusively limted to terrestrial mammals and birds, and among these to large-bodied animals (except on islands: more about that below). As humans spread from continent to contient, the large-bodied mammals and birds (and in Australia, reptiles) disappeared. This resulted in a major overhaul of the biodiversity of the terrestrial realm. For example, take a look at this chart:

The species listed in red are the ones that disappeared with human arrival in the New World.

The herbivores may have been hunted directly for meat. The carnivores are likley a different story.

(North American carnivores present at the time of human arrival)

Few human cultures regularly hunt carnivores for meat (although they may for protection and as prestige items). Instead, they were probably driven to extinction as their food source (the large herbivores) became rarer and rarer.

Africa, and to a lesser degree Eurasia, had fewer extinctions at this time. The animals of this region had co-evolved with humanity's ancestors, and so had developed techniques and strategies to live in a world with people.

Some of these Eurasian animals arrived in North America at the same time as humans. These include the moose (Alces alces), the elk (Cervus elaphus), the brown bear (Ursus arctos), and the timber wolf (Canis lupus). Thus, four of the "Big 5" of America's wildlife are actually no more native to North America than are people.

The fifth, Bison bison, evolved from earlier North American bison species. One of the responses of the American bison was to adopt huge herds as a defensive strategy. This strategy works very well in an environment with the newly arrived sophisticated pack hunters: timber wolves and humans. In the 19th Century, however, advanced hunting technology (rifles) and distribution technology (carts, wagons, and trains) allowed for the massive slaughter of bison:

(Note: the vast amount of bone generated by these hunts actually went to be used as fertilizer.) Bison range crashed, until the species was nearly extinct in the wild:

Thankfully, efforts of environmentalists, the U.S. government, and private landowners came together to save this species. However, a similar story had a less happy ending for the passenger pigeon (Ectopistes migratorius):

Once the most common bird in North America, a combination of deforestation (for farming) and hunting (from small parties to industrial-scale projects for the canning industry) drove the species to extinction in the wild in the 19th century. Martha (seen above) was the last living member of this species, who died on September 1, 1914 in the Cincinnati Zoo.

Island Extinctions: During the last few thousand years, humans spread from the continents to more distant islands: Madagascar, New Zealand, and the vast reaches of the Pacific. Again, destruction followed in humanity's wake. Some of these were again large-bodied animals: various lemurs (including gorilla-sized Megaladapis) and the giant flightless elephant bird of Madagascar; the diverse flightless moas of New Zealand; some species of giant tortoise in the Galápagos; etc.) Surviving island animals are often very naive with regards to predators such as humans, making them easy pickings.

However, in contrast to the terrestrial extinctions, much of the small wildlife of the islands were wiped out as well. While some of this may have been directly from human activity, much of it was likely from invasive species. For example, Rattus exulans, the Polynesian rat, hitched along for the ride with the Polynesians, and so made their way to islands in which rodents were previously unknown. The eggs of native birds became their tasty treats... (So the idea that invasive species are only a recent problem is incorrect; we've brought our domestic animals and plants, as well as unintentional passengers, along with us as we spread around the world.)

Fire: Humans use fire for many things. For the majority of our history, it was the only source for heating homes/camps and for cooking food. Fire has also been used to modify the landscape: eventually for "slash-and-burn" agriculture (where the fire burns down fields, removing problem trees and fertilizing the soil), but even in hunting-gathering societies. This includes practices of setting fields afire to flush out small game and to manage the mix of wildlife present in order to hunt. But it tends to promote the following problem, namely...

Deforestation: Human uses trees for shelter (as is and as wooden planks, logs, etc.); fuel; building material; food; and much more. But living trees also provide us with local climate regulation, in terms of shade, albedo (the reflectivity of the trees), and by transpiration (release of water into the atmosphere). In fact, in many environments trees are a major source of atmospheric water, and their loss greatly affects the weather patterns.

An example: one contributing factor to the 9-10th century decline of the Classic Maya in southern Mexico and northern Central America was deforestation. Maya buildings were typically decorated with plaster, which was itself made by cooking limestone. But it takes a strong fire to cook limestone, so the forests around the major Maya cities disappeared. With them went much of their agriculture, as the weather patterns changed. This led to major social upheavals, and a collapse of the traditional Maya city states.

(Additionally, trees are a major source of oxygen in our atmosphere, and an effective carbon sink over the scale of a few decades).

Ending Thoughts: Humans have always modified the world around us. In the end, what agricultural-and even more, industrial-societies do differently is the scope, scale and speed of the damage they wreak on the world around them. But, we have our scientific knowledge and insights from past events which allow us to now better forecast and plan for changes we would produce, and so reduce their effects.

Last modified: 6 October 2008