166
J. HESLOP-HARRISON
named as species, and the grouping of these units in a category system
derived in all essentials from that of Linnaeus. However these activities
may be embroidered - for example, by the attribution of lofty motives
concerned with phylogeny - it is demonstrably true that they form the
major part of taxonomic research.
Now it is a peculiarity of Linnaean-style classification that its requirements do themselves generate a “species concept” - one which has
come to be accepted almost universally and usually unquestioningly by
practising taxonomists (Heslop-Harrison, 1962, 1963). The properties
required of a variational unit suitable for recognition as a named species
are that its constituent individuals should show overall resemblance, in
that any one should have more characteristics in common with any
other than would either with an individual of another group; that i t
shows distinction from other groups of the same kind ; and that it should
have some degree of persistence in time. These are essentially the properties of the morphological species of Mayr (1942) and others.
Two of the practical consequences of attempting to apply universally
a species concept of this general type are, firstly, that units of very
varied biological character are defined as species in different groups in
consequence of the diversity of genetic systems prevailing among plants,
and, secondly, that in some groups where discrete variational units
cannot be distinguished the taste of individual taxonomists becomes
the sole determinant of what shall be ranked as species, so that
chronic disagreement about nomenclatural treatments is practically
inevitable.
In sexually reproducing, outbreeding groups, however, Linnaeanstyle taxonomy has met with reasonable success, and it has become
apparent that this has been so because of the existence in these groups
of variational units which do, in the main, conform satisfactorily in their
properties with those required of the taxonomic species. These units
constitute the biological species of Mayr (1942). Mayr’s definition of
biological species is as follows : “Species are groups of actually or potentially inter-breeding populations which are reproductively isolated from
other such groups.” As he has himself pointed out, this kind of definition
contains criteria of two kinds : that concerned with reproductive isolation, and that of collectivity - “species are groups, etc.” Partly in
consequence of this duality, no basis is available for the objective
definition of the biological species any more than existed for the Linnaean species : indeed it may be argued that the reasoning of Mayr and
others simply provides the theoretical endorsement for the application
of Linnaean style classificatory methods in sexual groups (HeslopHarrison, 1955,1963).
There are several uncertainties arising from Turesson’s definitions and
J. HESLOP-HARRISON
named as species, and the grouping of these units in a category system
derived in all essentials from that of Linnaeus. However these activities
may be embroidered - for example, by the attribution of lofty motives
concerned with phylogeny - it is demonstrably true that they form the
major part of taxonomic research.
Now it is a peculiarity of Linnaean-style classification that its requirements do themselves generate a “species concept” - one which has
come to be accepted almost universally and usually unquestioningly by
practising taxonomists (Heslop-Harrison, 1962, 1963). The properties
required of a variational unit suitable for recognition as a named species
are that its constituent individuals should show overall resemblance, in
that any one should have more characteristics in common with any
other than would either with an individual of another group; that i t
shows distinction from other groups of the same kind ; and that it should
have some degree of persistence in time. These are essentially the properties of the morphological species of Mayr (1942) and others.
Two of the practical consequences of attempting to apply universally
a species concept of this general type are, firstly, that units of very
varied biological character are defined as species in different groups in
consequence of the diversity of genetic systems prevailing among plants,
and, secondly, that in some groups where discrete variational units
cannot be distinguished the taste of individual taxonomists becomes
the sole determinant of what shall be ranked as species, so that
chronic disagreement about nomenclatural treatments is practically
inevitable.
In sexually reproducing, outbreeding groups, however, Linnaeanstyle taxonomy has met with reasonable success, and it has become
apparent that this has been so because of the existence in these groups
of variational units which do, in the main, conform satisfactorily in their
properties with those required of the taxonomic species. These units
constitute the biological species of Mayr (1942). Mayr’s definition of
biological species is as follows : “Species are groups of actually or potentially inter-breeding populations which are reproductively isolated from
other such groups.” As he has himself pointed out, this kind of definition
contains criteria of two kinds : that concerned with reproductive isolation, and that of collectivity - “species are groups, etc.” Partly in
consequence of this duality, no basis is available for the objective
definition of the biological species any more than existed for the Linnaean species : indeed it may be argued that the reasoning of Mayr and
others simply provides the theoretical endorsement for the application
of Linnaean style classificatory methods in sexual groups (HeslopHarrison, 1955,1963).
There are several uncertainties arising from Turesson’s definitions and