HOW THINGS BEGAN

New Zealand Listener, Volume 22, Issue 553, 27 January 1950, Page 5

HOW THINGS BEGAN

Sir,-In your issue of January 6, "A.A.N." (referring to the evidence for evolution) reminds-me of "the rule of logic that it is invalid to argue from the particular to the general." All that this means is that the theory of evolution is not strictly proved, in the sense in which, say, a theorem Of geometry is proved from the axioms; and this much I readily grant him, Let me remind him in his turn that the same may be said of every generalisation whatever that natural scientists make-not one of them, even the most assured, is strictly demonstrable from the data on which it is based,-and all are liable to correction in the light of further discovery. When "4.A.N." thus indicates that he is- willing to abandon the whole of natural science rather than. accept the theory of evolution, I can only regard this as a tribute to the strength of the theory. "A.A.N." also in effect . endorses Father Duggan’s demand that I give a specific case in which biologists are doubtful as to how to. mark : off. the border between major. groupings. I offer them both Peripatus, the difficulty about which is to place it in its proper phylum (i.e., the division coming immediately after that into plant and animal kingdoms-certainly a "major" one). Peripatus was originally classified along with earthworms,. leeches, etc., in the phylum Annelida; in most modern text-books it is placed along with centipedes, insects, crayfish, etc., in the phylum often in defiance of the general. account. given by the same writers of what an Arthropod is. Thus Parker and MHalswell, who classify Peripatus as an Arthropod, tell us that "Arthropods are characterised by the universal absence of cilia’; -but Peripatus has cilia. They also tell us that Arthropods have segmented limbs (and in fact "jointed-legged" is ‘the literal meaning of their name); but Peripatus has not. Certainly no biologist-now classifies Peripatus as an Annelid; but some authorities prefer to treat the smaller group of Onychophora to which it belongs as a separate phylum: There is no doubt now as to what the characteristics of the Onychophora are, but there is still dorbt as to whether their known. differences from centipedes, etc., would or would not be usefully employed as marking off a distinct "major group." Yet Father Duggan would have us believe that all biologists not only "accept the existence of such groups as fishes, arthropods, birds, without question" (italics mine), but also "have no doubt about which of these’ groups a given organism is to be assigned to" (Evolution and Philosophy, pp. 186-7).

ARTHUR N.

PRIOR

(Christchurch).