Species

214 Species

After Dobzhansky, the Beginnings of the Modern Debate

At the time of the modern synthesis, announced in Julian Huxley’s book by that

title in 1942,^22 there was little dispute amongst those involved that species were real

enough, but there was a wide range of opinion about what that meant. Darlington,

for example, explicitly appealed to Ray’s dictum (in Latin) that to sort living beings

into species we need no more than “distincta propagatio ex semine,”^23 but that

[t]here are many kinds of species and many kinds of discontinuities between species.^24

He noted that

We feel we ought to have a ‘species concept.’ In fact there can be no species concept

based on the species of descriptive convenience that will not ensnare its own author

so soon as he steps outside the group from which he made the concept. The only valid

principles are those that we can derive, not from fixed classes but from changing pro-

cesses. To do this we must go beyond the species to find out what it is made of. We

must proceed (by collaboration) to examine its chromosomal structure and system of

reproduction in relation to its range of variation and ecological character. From them

we can determine what is the genetic species of Ray, the unit of reproduction, a unit

which cannot be used for summary diagnosis, but which can be used for discovering

and relating the processes of variation and the principles of evolution.^25

In contrast, Julian Huxley in his introduction to The New Systematics argues
that Dobzhansky’s 1937 definition “goes far beyond the facts.”^26 Huxley notes the
constancy of cross-fertilization among plants in particular, and says that therefore
“Dobzhansky’s definition is untrue, or, if true, taxonomic practice must be so re-cast
as to rob the term species of its previous meaning.”^27 H. J. Muller’s contribution to
that volume agrees—there is no fixed rank dividing species from varieties or races,
although

... divergence goes on very differently, and much more freely, between those which

can and do cross, and it is therefore justifiable and useful, even though difficult, to

make the species distinction, if it is made in such a way as to correspond so far as

possible with this stage of separation. At the same time it must be recognized that the

species are in flux, and that an adequate understanding of their relationships can be

arrived at only on the basis of an understanding of the relationships between the minor

groups and even between the individuals, supplemented by the study of the differences

found through observations on the systematics of the larger groups.^28

(^22) Huxley 1942.
(^23) Darlington 1940, 137.
(^24) Op. cit., 158.
(^25) Op. cit., 159.
(^26) Huxley 1940, 16ff.
(^27) Huxley 1940, 17.
(^28) Muller 1940, 258.