The reason I became concerned about human population is that I wanted to work for peace. Long ago, I believed (and still do) that overpopulation is likely to lead to armed conflict.
Scarce resources are the most common cause of armed conflict. People are hungry and their neighbors have food, so a raid is initiated to steal their sustenance. Another scenario involves a growing group whose land area is limited. They look envyingly to the other side of their border with rich land and few people; invading a neighboring territory is a common cause of war. The Nazis used Lebensraum (living space) as an excuse to invade adjacent lands, thus catalyzing World War II. Recently, we fought the Iraqi war over another valuable resource petroleum.
Religion is also a common cause of war even though most religions claim that they want peace. We are afraid of Muslims overrunning our beliefs. We have forgotten, however, many followers of Mohammed still remember how the Christians tried to exterminate Islam during the Crusades.
We know that a graph of the human population was almost flat for many centuries before the last couple hundred years. Why was there so little growth for so long, followed by such an amazing acceleration?
Many reasons are given for the past slow increase in population. High infant mortality, poor hygiene, infectious diseases and meager food supply all contributed. These factors all changed with the industrial revolution.
There is another cause, however, that we dont usually consider as a reason for slow population growth. Several books give us a clue. The Great Big Book of Horrible Things by Matthew White lists the worlds largest mass killings. The Roman gladiators (responsible for more than 3 million deaths) and the Crusades (another 3 million) are listed. The imperialism of Genghis Kahn destroyed 40 million people, the Atlantic slave trade 16 million and the conquest of the Americas 15 million. Overall, about a half-billion people died from the hundred cruel calamities described in this book.
Two books put forth a theory that may be a more significant past cause of mortality. War Before Civilization: The Myth of the Peaceful Savage, by Lawrence Keeley, and Constant Battles: Why We Fight, by Steven Le Blanc and Katherine Register, both posit that our ancestors killed each other in significant numbers. They look at archaeological evidence from around the world, especially right here in the Southwest.
In the past, there were small bands of people living all over the world. Recent evidence suggests that these societies were more violent than previous archaeologists ever acknowledged. Overall, these authors estimate that 10 to 15 percent of people in prehistoric societies died from conflict.
Disease and starvation werent bad enough. It seems that homicide and warfare are important reasons human population grew slowly for millennia. Past people destroyed their neighbors to steal their resources. In some cultures, there is even evidence of cannibalism; not only did they kill, but also ate their neighbors flesh.
War is a terrible way to limit population growth. Unfortunately, battles and cruelty with extensive loss of life seem to have been the way of life in our dark past.
We are living in a period of relative peace, according to Better Angels of Our Nature. A reviewer of this book summarizes its thesis: Our era is less violent, less cruel and more peaceful than any previous period of human existence. What may not be self-evident (few of us have the long view of history needed) is that the world has actually become less violent.
This book goes further than just to claim that we are living in an era with decreased armed combat. The author, Steven Pinker, is a Harvard psychologist who believes that we have slowly changed our mores to accept less violence in our personal lives less spanking of children and less persecution of people for their beliefs, ethnicity, color or sexual orientation. With this current long peace has come longevity and more people.
Apparently, small raids and horrible things kept our population small, and the long peace is one cause our numbers have increased so rapidly. Relative peace has allowed our population to outgrow the carrying capacity of our planet by 50 percent. I share a concern with a Pentagon document from 2003: As famine, disease, and weather-related disasters strike due to ... climate change, many countries needs will exceed their carrying capacity ... which is likely to lead to offensive aggression in order to reclaim balance.
Richard Grossman practices gynecology in Durango. Reach him at firstname.lastname@example.org. © Richard Grossman MD, 2012