In the undergrad course I teach "Environment and Society" one of the important environmental issues we take in class is human population growth. And no one can take stock of the issue without bumping into Thomas Robert Malthus and his theory on population.
Malthus was an Anglican country parson who wrote one of the most influential works in science "An Essay on the Principle of Population". This essay influenced Darwin and Wallace at a time they were formulating their evolutionary theory.
Malthus being a parish priest was able to create his theory from christening, marriage and funeral records. What better place to be a demographer!
Malthus' essay has three important concepts. Some environmental science textbooks call these as "prophecies" while some call it "predictions". For the sake of scientific objectivity, I prefer the latter term.
The predictions are
1) Population will increase exponentially as long as their is enough food (Malthus initially modelled growth in a geometric progression)
2) Humans like to have sex
3) Eventually populations will exceed the capacity of the earth to produce food and population will crash. (Malthus suggested that food production follows an arithmetic progression)
The first has been observed in the lab and our good ol'e ecology textbooks have the classic examples. The second needs no science to prove! The third remains a hypothesis but in lab cultures this can be observed.
Advances in agriculture and medicine have proven the third prediction as unfounded until quite recently (yesterday!). Now the blurbs have screaming headlines of "food crisis" at a global scale and some scientists have suggested we revisit Malthus' ideas.
Malthus may have the last laugh. Our paradigm of technology being able to forestall the third prediction is based on an assumption of the unlimited resources our planet can provide. But Malthus presciently recognized that this isn't true.
Mathusian theory has its critics. Karl Marx and Friedrich Engels were the most notable of them all. Marx argued that what Malthus saw as the poor's tendency to reproduce beyond their means is a dynamic of the capitalist system.
Marx and Engels may have the second-to-the last laugh since Malthus has been proven wrong on one account. Human population growth rates have slowed down in the last 50 years and this should have made food security more certain. But it isn't. Instead we see an increase in the use of natural resources. The only explanation for the phenomenon is the global capitalist system. In no time of human history has more than 2 billion people (India and China) becoming capitalist. This is definitelty placing a strain on the planet's carrying capacity.
Malthus and Marx have seen the two sides of the same coin. A new paradigm has to be set in coming to grips with world food insecurity which is a sign of the global environmental catastrophe Jared Diamond has written and warned us about.