Congruence bias

Biological Parallel

Squirrels learning 'oak acorns are nutritious' repeatedly sample oaks throughout autumn (confirming tests), rarely sampling potentially poisonous buckeyes (disconfirming tests). Congruence bias—testing only positive examples—reflects asymmetric learning costs: confirming safe foods builds robust recognition patterns; testing toxic alternatives risks death. In stable environments, verifying that working strategies still work mattered more than exploring dangerous alternatives. Falsification is Popper's ideal, but positive testing was ancestral pragmatism when errors could be fatal.