According to the UN, some time next week the world's population will reach seven billion. Many will see this as a bad thing. But I think we should be cheering for joy. Seven billion mouths to feed also means seven billion brains – and it's brainpower that is the key to human flourishing.
The worriers take the Malthusian view of population. Thomas Malthus famously predicted that population growth would create a relentlessly poorer world, as population growth was geometric (2, 4, 8, 16, 32...) whereas technological advancement is only arithmetic (2, 3, 4, 5, 6...). Population would grow faster than farming technology could support it. What Malthus didn't realize was that technology and wealth are linked to population: the more people there are, the more brains there are. The more brains, the more ideas. And ideas are infinitely reproducable. Unlike economic goods, my posession of an idea doesn't deprive anybody else of possessing that idea as well.
Thus, one brilliant idea can improve an infinite number of lives. The most important of the last fifty years from a Malthusian point of view was Norman Borlaug, father of the "green revolution" that brought high-yield, disease-resistant strains of wheat to the poorest countries in the world. But there are plenty of others – two recently deceased ideas-generators are Steve Jobs and Dennis Ritchie (inventor of the C programming language). The ideas they came up with would be just as useful in a population of seven million as seven billion. The same goes for artists: a piece of music is just as beautiful listened to by seven people as seven billion.
But won't these extra people, born disproportionately to the world's poorest families, just hold others back? Another potential Steve Jobs is fine in California, you might say, but not Calcutta. Alas, more babies really are a burden to poor families. But, crucially, this isn't the cause of their poverty – there are plenty of poor countries that have very low birth rates, like Russia. The cause of poverty in the developing world isn't lots of babies, but bad government. The most famous example of famine in the last few decades was the Ethiopian catastrophe during the 1980s; a direct consequence of a war against the people by Ethiopia's communist government. Other, even more dreadful famines of the 20th Century – such as the Ukrainian Holodomor of the 1930s and the Great Chinese Famine of 1958–61 – were caused by incompetent or wicked states, not a natural lack of food.
Poverty today has similar roots: it's very hard to find a poor country with a good government. Where there is poverty and famine today, it's a consequence of bad government, not a Malthusian food shortage. And this also presents an opportunity for tremendous improvements in the lives of all humans: if, somehow, those bad governments can be improved, a billion brains are waiting to be unlocked. Having lots of people isn't an obstacle to more human flourishing. On the contrary: it's the best way we can achieve it.