[Taxacom] Pop article on taxonomy's decline

Richard Zander Richard.Zander at mobot.org
Sun Jan 30 13:23:00 CST 2011

The average is misleading. I've seen a publication a while back demonstrating that the number of species per genus in botany is a distributional curve, with lots of monotypic or bitypic genera and a few huge genera with lots of species, and a spectrum of genera with various numbers of species. I doubt that the human ability to sort by 7's is relevant. (Sevens? Five is the limit for me.)

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Richard H. Zander 
Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299 USA 
Web sites: http://www.mobot.org/plantscience/resbot/ and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Modern Evolutionary Systematics Web site: http://www.mobot.org/plantscience/resbot/21EvSy.htm

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Thomas Pape
Sent: Sunday, January 30, 2011 5:44 AM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Pop article on taxonomy's decline

>>> So, either the vascular plants are much more speciose per genus than other organisms, or my average of 8 is a gross underestimate [...] it would be interesting to see some figures for other groups, particularly major insect groups ...

The issue of 'how many species per genus' is perhaps more a psychological or cognitive issue in so far as genera are man-made constructs. Eight is (today) the number of bits in a byte. Eight is the lucky number in many cultures. Even more compelling, perhaps, is that the human mind on average has the capacity to operate simultaneously with seven words, concepts, sounds or the like (***Miller 1956). So, perhaps the human mind has an innate urge to break up genera when they exceed that number?
When Roger Crosskey (1980) edited the Afrotropical Diptera catalogue, he made this interesting observation on the number of species per genus:
Afrotropical:	8.12 (16,318 spp. in 2,009 genera)
Oriental:		8.51 (15,694 spp. in 1,876 genera)
Nearctic:		8.18 (16,130 spp. in 1,971 genera)
However, if calculated from what we currently have in Systema Dipterorum (www.diptera.org), the figure is slightly above 13 species/genus.
/Thomas Pape, Natural History Museum of Denmark
***Miller, G.A. (1956) The magical number seven, plus or minus two. Psychological Review 63: 81-87.

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