摘要：A fundamental question in biology, and more specifically in palaeontology, is ‘how much variation is there within a biological species?’ To answer that question, it is necessary to define a species, notably in a way that can be applied in palaeontological contexts. Recognising that boundaries between taxa may not always be clear, an appeal has been made for a probabilistic definition of a species 1-3 , based on pairwise comparisons of specimens and morphometric analyses using least squares linear regression analysis associated with a general equation of the form y=mc+c, where x and y are linear dimensions of a skeletal element such as a cranium 4 . The degree of scatter around the regression equation (associated with morphology) is quantifiable using the log of the standard error of the m co-efficient (log sem). Here it is shown how this morphometric approach can be applied to cranial specimens attributed to two extant species of Pan, and to extinct Plio-Pleistocene hominins in a temporal sequence, indicating the lack of clear boundaries between species, thereby challenging the prevailing concept of alpha taxonomy 5 which assumes discrete entities. An appeal is made for an alternative concept, namely sigma taxonomy.
关键词：biological species constant;species variation;conspecificity;morphometrics;taxonomy
