Chapter 1 of Smith’s famous text argued that specialization is key to economic growth. He explained how making each man a master of his particular trade makes production faster and leads to further innovation; a cycle of rapid growth then ensues. This growth spreads more wealth over more people, narrowing the gap between princes and peasants. Malthus, in his First Essay on Population, debunked Godwin’s argument that a more egalitarian society and economics will end poverty. Malthus mainly argued that population inevitably reaches an equilibrium with subsistence because population naturally tends to increase but subsistence is definite.
These two philosophers’ arguments are more closely related than they seem at face value. Malthus argued that population is limited by what the earth has to offer. Smith proposed a way to make production much more efficient–specialization. Increased specialization, makes production of materials, all of which are either directly or indirectly from the earth, more efficient. Therefore the more efficient production becomes, the more people the rather can support. The only true limitation on the human population is technology, which is forever developing at an increasing rate. Thus population capacity can never be accurately predicted. The factors which we see at limitations to the population capacity now are mainly space, food, water, and clean air. However, what if science brings up the ability to turn all waste from resources into new resources? Then space would become the final limitation. What if we then develop a way to live at higher elevations or beneath the sea? Questions like these seem unreasonable at the present day, but who could have predicted that nuclear energy would possible one thousand years ago?
I think another limitation to population capacity is disease. In Malthus’s time especially, the life expectancy of the average human was not stunning, and peasants were even worse off. With time, technology reveals cures for the diseases plaguing the planet and thereby increases human capacity, but new diseases always seem to surface. I think Malthus would view disease as a natural check on human population which inevitably brings equilibrium back into focus.
Malthus’s essay strictly refers to the limitations of earth in that the rate of population growth and the rate of the subsistence that the population needs to survive are moving at very different paces. In response to your question, asking if it is avoidable to over-capacitate earth by finding other places to live, the esteemed astrophysicist and cosmologist Stephen Hawking has explicitly stated that if mankind intends to survive we must find a way to leave earth and move to outer space within a century. It is true that we could have not predicted the technological advances from Malthus’s time to now; however, I think that it is evident that our species leaving earth within a century is extremely advanced. In which case Malthus may be correct in his predictions after all.