74 SECTIONAL ADDRESSES. 



Let us be clear as to the meaning of these terms. Variation is 

 said to be determinate, or, as Darwin called it, ' definite,' when all the 

 offspring vary in the same direction. Such definite variation may be 

 determined by a change in the composition of the germ, due perhaps 

 to some external influence acting on all the parents ; or it may express 

 the direct action of an exteiTial influence on the growing offspring. The 

 essential feature is that all the changes are of the same kind, though 

 they may differ in degree. For instance, all may consist in some addi- 

 tion, as a thickening of skeletal structures, an outgrowth of spines or 

 horns ; or all may consist in some loss, as the smaller size of outer 

 digits, the diminution of tubercles, or the disappearance of feathers. 

 A succession of such determinate variations for several generations pro- 

 duces seriation ; and when the seriation is in a plus direction it is called 

 progressive (anabatic, anagenetic), when in a minus direction, retro- 

 gressive (catabatic, catagenetic). When successive additions appear 

 Ia.te in the life-cycle, each one as it were pushing its predecessors back 

 to earlier stages, then we use Cope's phrase — acceleration of develop- 

 ment. "When subtraction occurs in the same way, there is retardation 

 of development. Now it is clear that if a single individual or genera- 

 tion produces offspring with, say, plus variations differing in degree, 

 then the new generation will display seriation. Instances of this are 

 well known. You may draw from them what inferences you please, 

 but you cannot actually prove that there is progression. Breeding- 

 experiments under natm'al conditions for a long series of years would 

 be required for such proof. Here, again, the palaeontologist can point 

 to the records of the process throughout centuries or millennia, and 

 can show that there has been undoubted progression and retrogression. 

 I do not mean to assert that the examples of progressive and retrogres- 

 sive series found among fossils are necessarily due to the seriation of 

 determinate variations ; but the instances of detenninate variation known 

 among the creatures now living show the palaeontologist a method that 

 may have helped to produce his series. Once more the observations of 

 neontologist and palaeontologist are mutually complementary. 



Predetermination. 



So much for determination : now for Predetermination. This is a 

 far more difficult problem, discussed when the fallen angels 



' reasoned high 

 Of providence, foreknowledge, will, and fate. 

 Fixed fate, free will, foreknowledge absolute. 

 And found no end in wandering mazes lost. ' 



— and it is likely to be discussed so long as a reasoning mind persists. 

 For all that, it is a problem on which many palaeontologists seem to 

 have made up their minds. They agree (perhaps unwittingly) with 

 Aristotle * that ' Nature produces those things which, being con- 



* ^v<Tei yap [ylvovrai] 3<ra otto nvos eV outois iipxv^ <rvvix^s icivov/xiva acpiKye^rat 

 fXs ri T€\os. Phyg, II., 199b, 15, ed. Bekker. 



