192 



NATURE 



[October 7, 1920 



Fossils and Life.* 



By F. A. Bather, M.A., D.Sc, F.R.S. 



II. 



THE argument for orthogenesis based on a race- 

 history that marches to inevitable destruction, 

 heedless of environmental factors, has always seemed 

 to me incontrovertible, and so long as my knowledge 

 of paleontology was derived mainly from books I 

 accepted this premise as well-founded. But more 

 intensive study generally shows that characters at 

 first regarded as indifferent or detrimental may have 

 been adapted to some factor in the environment or 

 some peculiar mode of life. 



Prof. Duerden's studies of the ostrich lead him to 

 the opinion that retrogressive changes in that bird 

 are destined to continue, and " we may look forward," 

 he says, "to the sad spectacle of a wingless, legless, 

 and featherless ostrich if extinction does not super- 

 vene." Were this so, we might at least console our- 

 selves with the thought that the process is a very 

 slow one, for Dr. Andrews talis me that the feet and 

 other known bones of a Pliocene ostrich are scarcely 

 distinguishable from those of the present species. But, 

 after careful examination of Prof. Duerden's argu- 

 ments, I see no ground for supposing that the changes 

 are other than adaptive. Similar changes occur in 

 other birds of other stocks when subjected to the 

 requisite conditions, as the flightless birds of diverse 

 origin found on ocean islands, the flightless and 

 running rails, geese, and other races of New Zealand, 

 and the Pleistocene Genyornis of the dried Lake Calla- 

 bonna, which, as desert conditions came on, began 

 to show a reduction of the inner toe. Among 

 mammals the legs and feet have been modified in the 

 same way in at least three distinct orders or sub- 

 orders during different periods and in widely separated 

 regions. [The instances w'ere given.] 



In all these cases the correlation of foot-structure 

 with mode of life (as also indicated by the teeth) is 

 such that adaptation by selection has always been 

 regarded as the sole effective cause. 



Mv colleague, Dr. \V. D. Lang, has recently pub- 

 lished a most thoughtful paper on this subject. His 

 profound studies on certain lineages of Cretaceous 

 Polyzoa have led him to believe that the habit of 

 secreting calcium carbonate, when once adopted, per- 

 sists in an increasing degree. Thus in lineage after 

 lineage the habit "has led to a brilliant, but com- 

 paratively brief, career of skeleton-building, and has 

 doomed the organism finally to evolve but the archi- 

 tecture of its tomb." These creatures, like all others 

 which secrete calcium cak-bonate, are simply suffering 

 from a gouty diathesis, to which each race will 

 eventually succumb. Meanwhile, the organism does 

 its best to dispose of the secretion; if usefully,, so 

 much the better, but, at any rate, where it will be 

 least in the wav. Some primitive Polyzoa, we are 

 told, often sealed themselves up; others escaped this 

 self-immurement by turning the excess into spines, 

 which in yet other forms^ fused into a front wall. 

 But the most successful architects were overwhelmed 

 at last by superabundance of building material. 



While svmpathetic to Dr. Lang's diagnosis of the 

 disease, still I think he goes too far in postulating an 

 "insistent tendency." He speaks of living matter as 

 if it were the over-pumped inner tube of a bicycle 



• Opening address of the Pre«idcnt of Section C (Geoloey), delivered at 

 the Cardiff Meeting of the British Association on August 14. Greatly 

 abridged. Only the larger excisiont are indicated by asterisks. Continued 

 from p. 164. 



NO. 2658, VOL. 106] 



tyre, " tense with potentiality, curbed by inhibitions " 

 [of the cover], and "■ periodically breaking out as 

 inhibitions are removed " [by broken glass]. A race 

 acquires the lime habit or the drink habit, and, casting 

 off all restraint, rushes with accelerated velocity down 

 the easy slope to perdition. 



A melancholy picture ! But is it true ? The facts 

 in the case of the Cretaceous Polyzoa are not dis- 

 puted, but they can be interpreted as a reaction of 

 the organism to the continued abundance of lime-salts 

 in the sea-water. If a race became choked off with 

 lime, this perhaps was because it could not keep pace 

 with its environment. Instead of " irresistible momen- 

 tum " from within we may speak of irresistible pres- 

 sure from without. Dr. Lang has told us " that in 

 their evolution the individual characters in a lineage 

 are largely independent of one another." It is this in- 

 dependence, manifested in differing trends and differ- 

 ing rates of change, that originates genera and species. 

 Did the evolution follow some inner impulse, along 

 lines "predetermined and limited by innate causes," 

 one would expect greater similarity, if not identity, of 

 pattern and of tetnpo. 



Many are the races which, seeking only ornament, 

 have (sav our historians) perished like Tarpeia be- 

 neath the weight of a less welcome gift : oysters, 

 ammonites, hippurites, crinoids, and corals. But I 

 see no reason to suppose that these creatures were ill- 

 adapted to their environment — until the situation 

 changed. This is but a special case of increase in 

 size. In creatures of the land probably, and in 

 creatures of the water certainly, size depends on the 

 amount of food, including all body- and skeleton- 

 building constituents. When food is plentiful larger 

 animals have an advantage over smaller. Thus by 

 natural selection the race increases in size until a 

 balance is reached. Then a fall in the food-supply 

 handicaps the larger creatures, which may become 

 extinct. So simple an explanation renders it quite un- 

 necessary to regard size as in itself indicating the old 

 age of the race. 



Among the structures that have been most frequently 

 assigned to some blind growth-force are spines or 

 horns, and when they assume a grotesque form or, 

 disproportionate size they are dismissed as evidences 

 of senility. Let us take the case of certain spinv trilo- 

 bjtes. Strange though these little monsters may be, I 

 cannot, in view of their considerable abundance, be- 

 lieve that their specialisation was of no use. Such 

 spines have their first origin in the tubercles which 

 form so common an ornament in Crustacea and 9ther 

 Arthropods, and which serve to stiffen the carapace. 

 A verv slight projection of any of these tubercles 

 further acts as a protection against such soft-bodied 

 enemies as jelly-fish. Longer outgrowths enlarge the 

 body of the tribolite in such a way as to prevent it 

 being easily swallowed. When, as is. often the case, 

 the spines 'stretch over such organs as the eyes, their 

 protective function is obvious. This becomes still 

 more clear when we consider the relation of these 

 spines to the body when rolled up, for then they are 

 seen to form an encircling or enveloping chei'aux-de- 

 jnse. But, besides this, the spines in many cases 

 serve as balancers; thev throw the centre of gravity 

 back from the weighty head, and thus enable the 

 creature to rise into a" swimming posture. Further, 

 by their friction thev help to keep the animal sus- 

 l>cnded in still water with a comparatively slight 

 motion of its numerous oar-like limbs. Regarded in 



