One origin? (viral evolution)

Thomas Lammers lammers at VAXA.CIS.UWOSH.EDU
Mon Jul 23 12:39:07 CDT 2001

At 01:10 PM 7/23/01 -0400, Eric Dunbar wrote:

>Please excuse this rather basic question by a taxonomy neophyte. What
>exactly is the difference between/def'n of a clade and a grade?

A clade is a group containing all descendents from a given common
ancestor.  The  tetrapods are a clade as they include all descendents from
whoever it was that first crawled up out of the water in the devonian.

A grade is a group that omits one or more descendents of a given cvommon
ancestor.  Reptiles are a grade because they do not include the Birds,
which are descended from the same ancestor.

Thomas G. Lammers, Ph.D.

Assistant Professor and Curator of the Herbarium (OSH)
Department of Biology and Microbiology
University of Wisconsin Oshkosh
Oshkosh, Wisconsin 54901-8640 USA

e-mail:       lammers at
phone:      920-424-1002
fax:           920-424-1101

Plant systematics; classification, nomenclature, evolution, and
biogeography of the Campanulaceae s. lat.

"Today's mighty oak is yesterday's nut that stood his ground."
                                                 -- Anonymous

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