Malthus was famously wrong. He wrote a whole manifesto about how England (population then: 9 million) couldn’t possibly support a growing population (today it’s 66 million). Whenever the country generated enough surplus food to prevent famine, people would have more kids, use more marginal land, and be right back at the risk of famine again.
This theory was perfectly logical: food production fluctuates unpredictably, and people have short memories. Food supply has been a meaningful economic constraint until surprisingly recently. In the 1840s, for example, the British railway bubble was partially catalyzed by a few years of good harvests, which had the country in an optimistic mood. More recently than that, South Korea needed food aid to prevent famine in the early 1960s.
Malthus missed out on two countervailing forces: first, he underestimated the potential growth of crop yields. In 1800, wheat yields per acre rose 40% in the UK. Today, they’re about 6x the 1800 level.
He also misunderstood the long-term trend in birthrates. When infant mortality is high, parents tend to have as many kids as they can feed; when that constraint relaxes, there’s a shift towards a model of investing more in each child and having fewer of them.
So, Malthus missed the mark, in both directions. The optimists triumphed!
But they didn’t triumph due to some natural law. Malthus had a fairly accurate description of the world. At the time that he was writing, crop yields were rising, and fertility was rising, too; fertility peaked a decade after his Essay on the Principle of Population. But in the two centuries preceding his book, average crop yields per acre predicted average fertility with an r-squared of .65, i.e. about two thirds of the variance in fertility could be accounted for by crop yields:
It’s easy to argue against Malthus right now, but the facts were on his side at the time.