Sometimes, we start out by healing a wound and end up by healing a heart.

No, not those facts of life, but these:

In October world population will reach 7 billion. That's 35 times as many as lived in Christ's time. And 5 billion of that total have been added since the birth of today's 80 year-olds.

In Genesis God commanded: "Be fruitful, and multiply, and replenish the earth, and subdue it." We have surely become fruitful multipliers.

By 1800 we numbered about one billion, up 800,000 in 1800 years, an average gain of 450,000 per year. But we discovered bacteria, learned how to control many diseases, extend life, and mitigate the risks of childbirth, adding an average of 62 million people per year in the last 80 years, and over 80 million per year today, concentrated in less-developed, poorer nations of Asia and Africa.

We applied science to agriculture, forestalling (for the moment) Thomas Malthus' prediction that geometric increases in population would leads to mass starvation. We have also done much to "subdue" the earth, but we are failing in the charge to "replenish" it.

So where does that leave us? Since Biblical times the planet is not much different physically, except for manmade changes. It is still the same size, with the same surface ratio of land to water. But we have depleted many of its resources and damaged its restorative ecosystems.

Forest cover is down by 40% since the end of the ice age. The amount of carbon dioxide (CO2, a major greenhouse gas) in the atmosphere has gone from 280 parts per million (ppm) to 387 ppm, causing the planet to warm, ice-caps to recede, and sea level to rise.

Fresh water supplies are stressed in many places, as glaciers melt and aquifers are pumped beyond rainfall recharge rates. Topsoil erodes much faster than it can be recreated. Fertilizer run-off is causing lifeless "dead zones" in the oceans. Material-intensive lifestyles now consume far more energy and materials per capita than in 1800, and that load is increasing exponentially as developing countries follow the pattern we in America enjoy and to which we feel entitled.

The waste products of this economic extravagance threaten our climate, our oceans and their fisheries, our fresh water, and the health of the ecosystems on which all life (even ours) depends.

Some see the problem as a choice between economic prosperity and the environment, and favor the economy. Purple (whose work experiences include industry, environmental organizations, the military, academia and government) believes that is a false choice. It seems to him self-evident that a successful economy requires an environmentally stable and socially just planet. Failure to attain that balance ensures strife: failed economies, mass migrations, wars over resources, and eventually environmental collapse and a major die-off of people. This dreadful outcome is not without precedent; over millennia several civilizations have failed in this way, though none (yet) on a global scale.

What can we do? Corrective actions are available, but many entail near-in costs to obtain future benefits. Some, such as family planning to slow population growth, contradict deeply held ideological or religious beliefs. Others, such as CO2 emissions reduction, will call for lifestyle changes. Our political system will be challenged. But, as President John Adams observed: "Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passions, they cannot alter the state of facts and evidence."

His great-grandson Henry added some cautionary words in "Education of Henry Adams": "Knowledge of human nature is the beginning and end of political education," followed a few pages later by: "Practical politics consists in ignoring facts."

Current debates among Republican Presidential hopefuls confirm these words. So, we voters must wake up, heed the warning of "7 billion people," and demand that our government act to prevent America and our civilization from entering a long and dangerous downhill slide. Given human nature, it won't be easy.