Living within constraints Constraints on the expansion of the global food supply In early times people were hunters or predators; they had to survive by killing other species. Although predators are supposed to be the strongest in the food chain, people were vulnerable because they had to depend on the same species below them. Even our senses were not as developed; hearing, smell, sight were and still are not as good as those below us. We cannot kill with our teeth or nails, as some alligators might do. So after 4 ice ages, there were only 25,000 people left. That's when they realized they had to change their loss strategies and invented subsistence farming. People have domesticated animals, plants, and going by today's population numbers, we are doing very well. The world's population has grown slowly for much of the historical past; it was only after 1900 that growth accelerated. The 1992 population was 5.5 billion. Today the world population increases by approximately 1.7% per year, corresponding to a doubling period in 40 years. By the early 1960s, most nations were self-sufficient in food; now only a few are. Except for some parts of Africa, production has outpaced population growth worldwide. Per capita production has now slowed and appears to be declining. In line with recent studies, we estimate that with a global population of 5.5 billion, food production is adequate to feed 7 billion people with a vegetarian diet, with ideal distribution and no grains fed. livestock. Yet perhaps around two billion people live in poverty today, and more than a billion in “absolute poverty” live with hunger. Inadequate food distribution is a major contributing factor to the current situation. Less than half of the world's land surface is suitable for agriculture, including grazing. Almost all the productive land in the world, flat and rich in water, is already exploited. Most undeveloped land is too steep, too wet, too dry or too cold for agriculture. Water shortage: Pressures resulting from population growth have put a strain on water resources in many areas of the world. Around the world, 214 river or lake basins, home to 40% of the world's population, now compete for water. If we improved water conservation, we would increase yields of rain-fed and irrigated crops. A major difficulty arises simply from how quickly food supplies would have to be expanded to keep pace with or exceed population growth rates in those countries experiencing high growth rates..