At the time of Smith countries liked to grow in population. Smith said that the most decisive mark of the growing prosperity of a nation is a growing population. Between 1776 and 2000 somehow pseudo scientists and economists brought about the idea of overpopulation, starting maybe with Malthus in 1810. What a pity.
A large population, just like a large company, can produce far more per capita (better division of labor) than a smaller country. Countries like China and India have been trying to control their population for decades (by encouraging birth control or other more drastic measures) to the tremendous LOSS of these nations. Let people decide how many kids they want to have and they can afford to bring up-governments shouldnt violate individual and family liberty by telling them how many kids they can have or by encouraging birth control (based on overpopulation paranoia by pseudo scientists). One more objective measure of overpopulation would be density rather than simply the population of a nation. The Netherlands has been one of the richest countries of Europe for hundreds of years, and it is one of the most densely populated as well. In the last decades we have seen the spectacular rise of Taiwan, Hong Kong and South Korea, countries with very high density of people. Japan has been a very rich nation for several centuries at least, at par with the UK, The Netherlands and Switzerland. A higher density of people INCREASES their productivity-witness how people live so well in a big city within the same country in comparison to smaller towns or farms. Efficiency of exchange of produce and productivity goes up with proximity. Most humans live in cities for a reason. There's plenty of land left-even if you drive around in Taiwan or Japan you see that most of the country is largely unpopulated. People prefer to live in buildings and cities, and are not being "cramped" into a city as some land lover anti-city people claim.
Northern Europe and now some other countries of Europe are encouraging population growth, which is a good thing for the world. No matter where we live, a thriving nation can always buy things from us, whatever we produce, and it is great to see the number of humans on the planet increasing. The Chileans can sell them more Copper and the US more Starbucks Coffee Franchises to such a nation.
I do not have numbers from Malthus' times, but it should be clear that despite all his warnings, we have continued to increase in numbers, and in general live better than a few hundred years ago (measure by wealth, by average age, lower children deaths). In 1770 approx, the English speaking North America was about 4 Million in population, UK was 8 Million, and France was 24 Million. Look at where we have come today! The United States is 300 Million people, the UK and France are 60 Million.
Governments and environmental groups should stop buying into the false theories of alarmists of overpopulation. We have many more inhabitants than before, and probably will keep on growing-we shouldnt be whining about something which should be celebrated.