Thanos’s Plan
Now that you understand something about the Malthusian model, watch the following clips. This is two scenes from the Marvel movies where Thanos explains why he is hunting the Infinity Stones and why he wants to use them to wipe out half the population of the universe.
Take a moment to think about what Thanos gets right, and what he gets wrong, about finite resources, population, and living standards. Does it sound like he understands the implications of a Malthusian model? He helps illustrate some things which can seem paradoxical about the Malthusian setting, and which tend to trip lots of people up.
Thanos asserts that the universes resources are finite. In a physical sense, he has to be correct about that. We can have a different discussion about whether that ultimately matters, but let’s take that as given. That’s like the fixed $X$ in the Malthusian model. Thanos doesn’t say it out loud, but presumably he also thinks that production in the universe is constant returns to scale (like a Cobb-Douglas) with respect to $X$ and people. This means that if we add people, total output goes up but per capita output goes down. This is what he’s referring to with “going to bed hungry” and all that. With fixed resources, holding everything else constant, increasing population lowers living standards. So far so good for Thanos.
Where does he start to mix things up? He says that population will keep growing and lowering living standards if “left unchecked”. But that requires a very particular assumption about population growth and living standards. Thanos is assuming that population growth rates are insensitive to living standards. In other words, as living standards fall he’s presuming that we keep having kids and that population continues to rise. Except that if living standards get low enough we can see (at least on Earth) that mortality goes up and population growth rates fall if living standards fall. That’s the key Malthusian assumption he misses. The universe was not going to exhaust the resources in some kind of population boom unless aliens somehow live longer the worse their nutrition.
Thanos also completely ignores the impact of productivity growth on raising the effective amount of resources the universe have. He’d have been better of doubling R&D than halving population, for sure from an ethical perspective.
The following things can both be true in a world of finite resources and Malthusian population growth.
- Living standards would go up if the population fell for some reason.
- Living standards won’t fall continually even if population grows.
People sometimes assume that (1) means (2) is false. That isn’t the case.
The Historical “Snap”
We actually saw a version of Thanos’ plan happen on Earth. When the Black Death tore through Europe in the fourteenth century, it killed somewhere between 30 and 50 percent of the population. This major decline in the number of people meant that those remaining had access to a greater stock of resources per capita. As a consequence, living standards increased dramatically. Greg Clark in A Farewell to Alms reports real wages in England doubling between 1350 and 1450, while in Italy wages grew two-and-a-half times larger in the same period. These increased living standards, however, did not last. By the 1500s real wages across Europe were back to pre-Black Death levels.
The return of living standards to their pre-Black Death levels was coincident with the recovery of population to its previous size, consistent with the Malthusian model. Italy’s population was 10 million in the year 1300, prior to the Black Death. After falling to 7 million in 1400, by 1500 it was back to 10 million. In England, population dropped from 3.75 million to 2.5 million during the Black Death, and then by 1500 was back to 3.75 million. All those numbers are from Atlas of World Population History by Colin McEvedy and Richard Jones, but take those with a grain of salt as they are rough estimates.
So point 1 from above holds. If you wipe out a big chunk of the population, then yes living standards for the survivors do go up because there are more fixed resources per person. But the Malthusian population dynamics kick in and eventually living standards go down again as population grows. This is also something that Thanos go wrong. Snapping away one half of the population today doesn’t ensure anything about the future. But note that while living standards fell again as population increased after the Black Death, living standards did not drop to zero and Europe did not become some barren hellscape. In fact one can trace some of the origins of sustained economic growth and modern demographics to the period right after the Black Death. Thanos’ model of the universe is too simplistic, and he was never going to accomplish his end goal.
You can see how this works in the app for the Malthus model. This link will take you directly to the app on its own page, or the app is embedded here to play with.
Use this and see what happens when you use the sliders to shift the initial population, $L_0$, down, as if there was a big pandemic. Go through the tabs and note how this makes GDP per capita jump up, but then the growth rate of GDP per capita becomes negative after that as the economy recovers back to steady state. Also note that population falls, but eventually goes right back to the same path it would always have been on.