Once you start diving into this issue of environmentalism or sustainability, or maybe just turning the occasional ear towards it, you will get hit with this one issue that seems to be at the forefront: overpopulation. There is too many people, man! That's what they have said for awhile now. It seems obvious, too. I know I have witnessed growing population with my own eyes in my own lifetime. Aside from issues like poverty and hunger that may or may not be directly related to "over"population, it's an unarguable statement: earth is only so big. It's a foregone conclusion that a species' numbers cannot continue to increase indefinitely on a finite world. I have found that it's easiest to make it as simple as possible, so, here we go.
Nature tends to have a way of keeping balance, and those that say humans are not natural or above nature are wrong. Sorry, you are wrong. Thinking something like that just shows me you don't understand nature. Population increases comes from a higher birth rate than death rate. More new people than people dying makes more people. We have a natural inclination to make more people. Babies are cute and we love them. We can't get enough of the act of making babies, no need to go into detail there. Also, we don't want people to die, it makes us mourn. Death sucks, generally. Nature WANTS us to make a larger population. That dont make sense, does it. Well it goes deeper.
Nature has checks to balance our drive to populate. A guy in history, Thomas Malthus, if I remember correctly, earmarked the top three natural causes of depopulation to accelerate the death rate to keep people from overrunning an ecosystem. They were disease, war, and starvation. More people makes more filth, which makes more disease. More people makes more conflict, which makes more war. More people makes less food, which makes more starvation. So emphasis on health, conflict resolution (tolerance), and food production have been issues for millenia. We seem to be getting better at dealing with these issues. We seem to be.
So, lets run thru some simple answers. Get off the planet. Well, we hit the same problems, just look at what happens in biodomes. Nature's a bitch! Kill people- we seem to be good at that as a race, but who wants to live in a world like that. I always want to tell the people who say something like that, "Okay, you first." Limit births- good luck with that. Also, if we go too far with limiting births, what do we lose? What if Mother Teresa, Martin Luther King, or Einstein had been aborted or their parents decided to not overpopulate the world. I know- balance. If you understand evolution, you will understand that the greater variety there is, the better chance you have for an advancement in the gene pool. Diversity is strength, that is a sustainable attitude to internalize. It will benefit you now and be of benefit generations to come.
Before I go on to far and make this all too complex, there is a simple answer to start from. We have to stabilize, find balance. Sustainable answers look a little different than what we've seen before, just a little. Have children, but not too many. The ones we have must be allowed to reach their potentials so they can maximize their benefit to the rest of us. We must accept death, and celebrate the contribution that person left us with. Let there be death, but let no death be in vain. No person is an island, and everyone we influence is really our key to immortality. And in that we come back to sustainability.
War, illness, and starvation (scarcity) all hamper, in their own ways, the realization of full potentials. These problems are not simple, but we can start from a simple place.
Diversity is strength. Compassion promotes diversity.