Heinz Haber (1913–1990), German physicist, astronomer and science journalist in an interview shortly before his death:
"He (note: Aldous Huxley) said a sentence that I think of at least once a week: "The problem of overpopulation, unresolved, will make all our other problems unsolvable. All the annoyances that beset us, the pollution, the ozone hole You can attribute energy deprivation to overpopulation." According to my considerations and calculations, our 'spaceship earth' can carry about a billion people. A larger number of people are beginning to pollute our earth. Two billion can still be endured, four billion are terrible, today we are five, will there will soon be six and ten billion people on earth. That can only be a catastrophe."

Note from the petition initiator: Heinz Haber calculated the number of around 500 million people who would be ideal for the earth. He published this number in his book "Our Blue Planet: Story of the Earth's Evolution".