Just take the thing! Just take the fucking picture! - Prince Philip, Duke of Edinburgh

I do believe ... that human population pressure--the sheer number of people on this planet--is the single most important cause of the degradation of the natural environment, of the progressive extinction of wild species of plants and animals, and of the destabilization of the world's climatic and atmospheric systems.
The simple fact is that the human population of the world is consuming natural renewable resources faster than it can regenerate, and the process of exploitation is causing even further damage. If this is already happening with a population of 4 billion, I ask you to imagine what things will be like when the population reaches six and then 10 billion.... All this has been made possible by the industrial revolution and the scientific explosion and it is spread around the world by the new economic religion of development.

Why then be concerned about the conservation of wildlife when for all practical purposes we would be much better off if humans and their domestic animals and pets were the only living creatures on the face of the earth? There is no obvious and demolishing answer to this rather doubtful logic although in practice the destruction of all wild animals would certainly bring devastating changes to our existence on this planet as we know it today...The trouble is that everything in nature is completely interdependent. Tinker with one part of it and the repercussions ripple out in all directions... Wildlife — and that includes everything from microbes to blue whales and from a fungus to a redwood tree — has been so much part of life on the earth that we are inclined to take its continued existence for granted...Yet the wildlife of the world is disappearing, not because of a malicious and deliberate policy of slaughter and extermination, but simply because of a general and widespread ignorance and neglect.

We talk about over- and underdeveloped countries; I think a more exact division might be between underdeveloped and overpopulated. The more people there are, the more industry and more waste and the more sewage there is, and therefore the more pollution.