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The seeds of various plants were used as weights because their mass reputedly varies so little. Carob (Ceratonia siliqua), which has given its name to the carat, is particularly famous in this regard. But are carob seeds unusually constant in weight and, if not, how did the myth arise? The variability of seeds sampled from a collection of carob trees (CV=23%) was close to the average of 63 species reviewed from the literature (CV=25%). However, in a perception experiment observers could discriminate differences in carob seed weight of around 5% by eye demonstrating the potential for humans to greatly reduce natural variation. Interestingly, the variability of pre-metrication carat weight standards is also around 5% suggesting that human rather than natural selection gave rise to the carob myth.

Original publication

DOI

10.1098/rsbl.2006.0476

Type

Journal article

Journal

Biol Lett

Publication Date

22/09/2006

Volume

2

Pages

397 - 400

Keywords

Fabaceae, Genetic Variation, Models, Biological, Plant Physiological Phenomena, Seeds, Species Specificity, Trees