title: Evidence for two numerical systems that are similar in humans and guppies.
abstract: BACKGROUND
  Humans and non-human animals share an approximate non-verbal system for representing and comparing numerosities that has no upper limit and for which accuracy is dependent on the numerical ratio. Current evidence indicates that the mechanism for keeping track of individual objects can also be used for numerical purposes; if so, its accuracy will be independent of numerical ratio, but its capacity is limited to the number of items that can be tracked, about four. There is, however, growing controversy as to whether two separate number systems are present in other vertebrate species.
  
  
  RESULTS
  In this study, we compared the ability of undergraduate students and guppies to discriminate the same numerical ratios, both within and beyond the small number range. In both students and fish the performance was ratio-independent for the numbers 1-4, while it steadily increased with numerical distance when larger numbers were presented.
  
  
  CONCLUSIONS
  Our results suggest that two distinct systems underlie quantity discrimination in both humans and fish, implying that the building blocks of uniquely human mathematical abilities may be evolutionarily ancient, dating back to before the divergence of bony fish and tetrapod lineages.
authors.affiliation: Department of General Psychology, University of Padova, Padova, Italy. christian.agrillo@unipd.it
authors.forename: Christian
authors.initials: C
authors.lastname: Agrillo
authors.forename: Laura
authors.initials: L
authors.lastname: Piffer
authors.forename: Angelo
authors.initials: A
authors.lastname: Bisazza
authors.forename: Brian
authors.initials: B
authors.lastname: Butterworth
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D005075:Biological Evolution; D003071:Cognition; D004193:Discrimination Learning; D005260:Female; D006801:Humans; D008297:Male; D055641:Mathematical Concepts; D011036:Poecilia; D013334:Students; D055815:Young Adult