The Vice-President of the Conservation Foundation in Washington, DC and renowned ecologist Sir Frank Fraser Darling explores the concept of Man's responsibility for his natural environment in his Reith series entitled 'Wilderness and Plenty'. In his fourth lecture entitled 'Global Changes - Actual and Possible', Sir Frank Fraser Darling explores the problem of overpopulation and its likely effect on the natural world. He considers the population problem in relation to other environmental factors such as increasing levels of carbon dioxide in the atmosphere, increased reliance on technology and the reduction in all natural environmental buffers. He ponders whether rises in prosperity and population might just signal the decline of the habitable world.