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This is creepily similar to the plot of Kurt Vonnegut's novel Galapagos, published in 1985 (Homo floresiensis was discovered in 2003). In the novel, all of humanity dies out due to an epidemic, except for a small band of humans who get stranded on the Galapagos islands (reference to Darwin's voyage). Over the following millennia these humans evolve into aquatic mammals with much smaller brains.
What's the critical population size for the effect to occur? Does it imply that SF "generation ships" are doomed? How about isolated arcologies?
The canonical example is, I think, the aborigines of Tasmania after they were cut off from the mainland. Over the 8000 years of isolation, the ~10,000 Tasmanians lost most of their technology - fishing, the ability to make fire or bone tools, etc.
One would hope literacy would help a lot, but then again, a generation ship needs astoundingly more expertise than a hunter-gatherer tribal society.
The story, as I read when visiting relevant sites in Tasmania (and confirmed on wikipedia) is one of "necessity is the mother of invention" in reverse - Tasmania being a veritable paradise compared to most of the mainland. Fishing traps for scaled fish were not especially important given the effort they required compared to eating shellfish and seals while environmental changes and increasing tribal territory sizes made hunting land animals even easier. They also never lost fire.
This example isn't especially strong evidence that technology loss is caused by a 10k population size.
And why didn't Malthusian limits encourage them to maintain their technology? (I also didn't say they lost fire, but the ability to make it.)
After 1830 or so there is a PC reluctance to mention certain facts about the Tasmanian aboriginals that people previous to that time found glaringly obvious.
I was actually reading about Tasmanian aboriginals of that time last night. In particular I had been reminded that Melbourne was actually founded by Batman, which just seems kind of badass. Knowing that said Batman acquired some of the resources needed to found Melbourne (then "Batmania") by being rewarded for capturing a notorious bushranger made it seem even more badass. It was somewhat less rewarding to discover that Batman got most of his wealth and prominence from hunting down and massacring Tasmanian Aboriginals in the Black War, which was going on at the very time that you mention (1830).
The above leads me to devalue rather heavily that which was being said about the Tasmanian aboriginals at the time. People who are in the process of killing another group of people in order to take their land aren't the kind of people you go to for unbiased opinions about their victims.
What facts? That they were all bumbling idiots? That's just racism. You got that wherever European explorers went, and was demonstrably wrong in every case I've ever come across.
In the case of a generation ship, you can just use selective breeding to keep people intelligent.
Presuming you can maintain a social structure for that many generations. Since you also need to maintain the ship, staying intelligent falls out as a subgoal of staying alive.
As I understand it, it's not that a small population directly causes intelligence loss, but that intelligence is less of a selective advantage in an isolated population with no big fierce predators, and the costs of growing a huge brain become unfavourable. Perhaps body size also comes into it: isolated populations on a small island are known to evolve towards smaller bodies, and smaller bodies generally go with smaller brains.
What is required of a successful generation ship to maintain and improve intelligence is to design it in such a way that intelligence remains a selective advantage. The simplest method in the context of speculative future technology would be controlled breeding, but that is not so easily applied to the generation ship that is this planet.
The article argues that small population does directly cause intelligence loss - or rather, that it breaks anything that depend on too many parts of the the genome to be too precisely balanced. But why would you let genetic drift and natural selection operate on a generation ship at all? That's a recipe for disaster; it's nearly impossible to predict what results would come out of it. It'd be much better to bring along frozen embryos (or something equivalent).