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They did so even in the presence of a tempting chocolate treat, foregoing the lever that would release the food in favour of the one that would save the drowning rat.
The rats therefore engage in helpful “prosocial behaviour” even if there was no apparent reward. Saving a distressed rat was valuable to them.
Past experience played a role too. If the saviour rat had had a similar near-death experience, it was much quicker to help.
But when there was nobody to save, or the distressed rat was replaced with an inanimate object, the rats no longer pressed the lever.
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