[Taxacom] Chicken or the egg? (was: Clade age)

Kenneth Kinman kennethkinman at webtv.net
Tue Nov 15 21:59:38 CST 2011

Hi Richard and Curtis,          
        Well, I'm no going to take sides on this one, because it is
often sort of like which came first (the chicken or the egg).  Often
species are based initially on one (holotype) or a few other specimens
(some still are).  If you initially have only a single specimen (such as
many spider species), the physical attributes only deal with one sex
(which can have surprisingly very different morphology vis-a-vis the
other sex), and thus both membership and attributes are extremely

        When membership is so limited, attributes that the set (species)
"must have" are so incomplete that only other specimens of the same sex
can be admitted into the set based on those attributes.  Only the
observation of successful mating and reproduction can later expand the
membership to members of the opposite sex (which then also expands
membership based on the expanded list of attributes).       

     So if membership is based on a single holotype, reliance on
attributes can often initially fail.  On the other hand, membership and
attributes can be the opposite extreme (too many members with the same
known attributes), lumping together cryptic species where both
membership and attributes then need to be split.  So, I disagree that
attributes automatically determine membership, even though they often do
so, especially as sampling increases.  When a species is newly
discovered, neither membership nor attributes can be assumed to be
anywhere near complete, and thus it is common in such cases than neither
can be assumed to take precedence.                 

Richard Jensen wrote:            
        The attributes determine membership, not vice-versa.  We cannot
recognize a set unless we specify the attributes that members of that
set must have (i.e., have defined the set). Once we have defined the
set, we can then ask if any particular entity belongs to that set.  But
we can't assign membership until the set is defined. 

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