Collecting entails substantial costs in terms of effort, money, time and space needed to find, obtain and store desirable items. Still, the non-utilitarian nature of collectibles suggests that a simple economic justification of this behaviour is unlikely. Moreover, the apparent sex difference, with collectors being almost exclusively men, indicates a possible reproductive motive. However, presently available theories have failed to identify these motives and predict its patterns leaving collecting behaviour unexplained. This paper employs recent developments in the fields of evolutionary psychology and theoretical biology in order to construct a plausible theory which accounts for collecting behaviour. In particular, it is argued that collecting has evolved to facilitate reliable communication between males with respect to their unobserved resource acquisition capacity. Based on this theoretical framework three hypotheses are derived: the desirability of a collectible item is positively related to its rarity, aesthetic pleasingness, and size. Evidence based on eBay auction sales of fossilised dinosaur eggs provides support for all three hypotheses.