[2] The parallel individuation system has been attested in human adults, non-human animals,[2] such as fish[3] and human infants, although performance of infants is dependent on their age and task.
[4] The evidence for parallel individuation system comes from a number of experiments on adults, infants and non-human animals.
For example, adults perform error-free when they enumerate elements for numerosities from one to four, after which their error rate rises.
[4] Parallel individuation system in animals was demonstrated in an experiment in which guppies were tested on their preference of social groups of different size, under the assumption that they have a preference for bigger-size groups.
[3] However, not all studies find confirmation of this system and for example New Zealand robins showed no difference in their understanding of small (1 to 4) and larger (above 4) amounts.