"In most parts of the world people live longer and healthier lives than they did a century ago. Longer life spans,along with declining birthrates, mean that there are growing numbers of ‘old’ people in many developed countries in relation to the younger working population expected to support them in their old age. But much analysis of this issue has overlooked two inconvenient truths [young people also grow old and raising average world fertility would lead to even faster population growth]." (Quoted from paper)