Ubbelohde notes with emphasis and reason that periods of international conflict often coincide with significant progress in science and engineering. This should not surprise us. Progress in these fields is very costly, and implies a significant, short-run opportunity cost to the securing of reproduction for the wider population. It will therefore find a limit, an equilibrium well below the theoretical maximum for progress. Put another way, in peacetime science and engineering will not progress as fast as it could, because the population prefers to consume the wealth rather than assigning that resource to science. In times of war, the presence of deadly external threat alters that balance and means that it becomes reasonable and probably worthwhile to assign more resources to science and technology, in other words to reduce security of reproduction a little in the short run in order to increase it in the longer run.