"The results of earlier research, indicating rats housed in a quasinatural colony drank significantly less sucrose-morphine than rats isolated in standard laboratory cages, could not be replicated"
In my opinion this tells a lot.
BTW: There are other researchers that replicated similar results on similar experiments too:
So is better to see all the experiments to avoid bias.
And your other linked experiment isn't at all similar and doesn't have similar results. It's not even about opiate addiction.
Btw, Bruce Alexander is still alive and it wouldn't be that hard for him to find the funding to replicate his experiment, with better controls, if he wanted to.
> The results of earlier research, indicating rats housed in a quasinatural colony drank significantly less sucrose-morphine than rats isolated in standard laboratory cages, could not be replicated, as the consumption of sucrose-morphine by the isolated animals in the present two studies was reduced. [emphasis added]
Without that last bit, the reader is left with the impression that all rats were highly addicted regardless of their environment, but the results were the opposite. All rats were less addicted than expected, regardless of their environment. Again, you're correct that the updated studies refute the original, but I feel like that distinction is important in a discussion that centers around addiction more than just the Rat Park experiment.
Additionally, the abstract notes that the latest studies may have been biased by a strain of rats that is less prone to addiction that those used by the Rat Park study. You noted in another reply that this indicates genetics play more of a role in addiction than environment, but this also calls into question any inferences about human addiction that are based on rat studies which do not include an analysis of the specimens' genetic predisposition toward addiction.
Finally, research that supports the result of the Rat Park does exist . Studies have found isolated mice are less resistant to addiction compared to those living in stimulating and social environments . Another study found that rats isolated in key parts of their development are more prone to alcohol and amphetamine addiction in adulthood . Based on the latter example, the effects of environment on addiction may be more nuanced that the Rat Park experiment would suggest.