Environmentalists protest tar sands oil in South Portland. They promote charging for plastic bags at the grocery store. They change their light bulbs and drive their hybrid cars. And yet the environmental movement is strangely silent on the single biggest issue causing all of our environmental ills: overpopulation. Not a word of protest. Not a peep.

People will protest the wearing of fur, promote veganism, decry GMOs in their food and insist on free-range eggs. But do they wonder if there are too many vegans (or farmers or holistic healers or whoever)? Apparently not. We decide when there are too many deer, too many mice, too much milfoil. But I guess there are never too many people.

When we tsk, tsk at the populations of Africa, India or China, is it because we smugly believe that we are seeding the Earth with our own superiorly enlightened offspring? Why does it not occur to anyone that we are the problem? All of us. And our children. And their children.

I remember in college we did the classic drosophila exercise. We plugged a test tube with a porous sponge after introducing some fruit flies and a growing medium (probably fruit). Then we started counting. Day by day, the population increased exponentially as we graphed the results. As the population neared its peak, what had been a clean, clear test tube started to get kind of scuzzy. Fruit fly excrement and dead fruit flies piled up as resources dwindled and the population crashed. Of course, our graphs described the classic bell curve.

Well, I feel like we have entered the scuzzy phase of our own human Malthusian exercise. We have managed to modify our climate – and not for the better. We are awash in our own waste, chemical and otherwise. (Think not? Remember this the next time a beach is closed because of E. coli bacteria). We are responsible not only for depleting but also actually changing the balance of life in the oceans. It is looking like we are going down in history as the cause of the Sixth Mass Extinction Event. I don’t even want to mention hermaphroditic frogs.

These are changes of global significance. I dare say the test tube we call Earth, our only test tube, is beyond scuzzy.

What madman is responsible for this sick, twisted experiment? What kind of lunatic, knowing the consequences (or worse still, not knowing) would continue down this path of self-destruction? Who would be so irresponsible as to throw away the future of the only place they can call home and leave that shattered place for their children?

Every last one of us.

Even hybrid cars and solar panels require fossil fuels for their manufacture. Even organic farms require land to be cleared for agriculture. Ordered your “Save the Whales” shirt through Amazon? That will be delivered by truck and may have been shipped by boat through a whale feeding area. Have you ever looked down on the United States from 30,000 feet? Man’s footprint is everywhere. We just take up too much space. Why do you think piping plovers are having so much trouble?

So consider this: What would it be like to dial back the population from its current 7 billion (and counting) to the population of the Earth around 1800 – about 1 billion people – but we get to keep our modern technology? It certainly could not have seemed very crowded back then (although our Native American neighbors might have something to say about that). And I cannot think of a single environmental problem that would not be helped by a drastic reduction in the Earth’s human population.

So let’s start the discussion (again) that Paul Ehrlich began back in 1968 with “The Population Bomb.” But let’s renew it with the hindsight and insight we have gained since then.

Instead of basing the capacity of the Earth on the number of people we can feed, let’s base it on the number of organisms it can optimally support. Sure, continue to do all that feel-good stuff like shopping at the farmers market. But unless population growth is reversed, it won’t matter how many light bulbs you change. The end result will be the same.

We’ve been unwilling or unable to curtail our use of fossil fuels and our depletion of natural resources. Maybe it would be easier to curtail our own fecundity. If we don’t, our failure could be spectacular.