Dan said: > You argue from infintesmals...since one cannot exactly define the > dividing line, it doesn't exist. But, in reality of course, the > cluster in gene space that defines humans is a number of SD away > from the cluster than defines the closest apes.
This may well be so, and yet for any pair of species A and B there are paths in gene space that have the property that one end of the path is in the cluster for species A, the other end of the path is in cluster B, and every point along the path gives the genome of a viable organism (given a suitable environment in which morphogenesis can occur). (This is true because any pair of species have a common ancestor if one looks far enough back in time, so one can head from species A towards a genome from the ancestral species C, and from there towards species B.) Given this, if one wishes to define species membership as a binary predicate, then one will necessarily be able to produce viable organisms that span the boundary between the "member of species A" region and the "not member of species A" region, and furthermore to do so in such gradual steps that the distribution of individuals look essentially continuous in any variable one wishes to measure. The "fact" that species are distinct entities today is caused purely because there are no extant intermediate forms between them. This is not a necessary state of things, and indeed there are cases of populations with large geographical ranges that have the property that pairs of individuals (of different sex!) found close together can all (or almost all) breed with each other, but pairs containing one from each end of the range cannot. If modern humans and some other hominid type were such a population today then I think the inadequacy of our current scheme for including or excluding animals from humanity would be manifest. The rest of your email is also interesting, but I will have to think about it with the hope that I'll be able to formulate some coherent thoughts before the discussion moves on. Rich _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
