Page Six 



EVOLUTION 



January, 1928 



The final decision as to all facts and theories of Organic 

 Evolution must rest finally with experts in Biology. 

 But all branches of science as well as all humanistic 

 studies are already affected and vitalized by it. For 

 it has become plain that no array of knowledge and no 

 line of thought can fail to consider it, and to be in- 

 fluenced by its methods. For behind every phenomenon 

 lies a cause and a history, and to know anything well de- 



mands a study of causes and effect and of the details 

 of how it came about. Nothing static exists and to 

 know a thing only as it is is to miss a large part of 

 real understanding. By force of its necessary effective- 

 ness in the pursuit of wisdom, the "method of Darwin" 

 comes each year to occupy a larger and larger part in 

 all phases of human thought. 



The Origin of Land Vertebrates 



By Maynard Shipley 



THE geological record shows that there was a very long 

 period of time — millions of years — during which 

 there was not a land animal on earth, excepting spiders, 

 scorpions, centipedes, millipedes, molluscs, crustaceans, 

 worms, and insects. In other words, backboned animals 

 (Vertebrates) inhabited the waters only. (But even the 

 earliest fish possessed, not a true backbone, but only a 

 cartilaginous rod, which later became a truly bony ver- 

 tebral column.) During an enormous period of the 

 earth's history, then, there were no animals on the earth 

 which possessed lungs, or limbs of bone and flesh. 



The earliest fossil remains of vertebrate land animals 

 belong to the period known as the Devonian, the sedi- 

 ments of which were deposited not later than some 

 twenty million years ago. These earliest land forms 

 would, naturally, belong to the Amphibia; for, if evolu- 

 tion is a fact, they would necessarily be derived from 

 some group of fishes. 



How Lungs Evolved 



In order that a land vertebrate should evolve from a 

 fish, the earliest terrestrial inhabitant would have to de- 

 velop four limbs for land locomotion, and lungs to sup- 

 ply the body with oxygen. Its eggs might continue to 

 be laid in the water — as is the case with the frogs of 

 today. The earliest land vertebrate would naturally be 

 amphibious, living part of the time in the water and 

 part of the time on land. But lungs and limbs do not 

 arise by magic. The lungs of the earliest Amphibians, 

 as also their limbs, were unquestionably derived from 

 some pre-existing organs. Every organ in the body of 

 any animal has some genetic relationship to some older 

 structure in some lower form. Whence, then, lungs? 



We should surmise, even know, on the evolutionary 

 theory, that there existed in early Devonian time — in the 

 closing epoch of which occurs the oldest known foot- 

 print of a land vertebrate (viz., Thinopus antiquus) — 

 a group of swamp-inhabiting fishes which supplemented 

 their gill-breathing by air-breathing. And the Devonian 

 strata afford abundant proofs of the correctness of this 

 very logical inference. It can be shown just how the 

 lungs of the Amphibia were derived directly from the 

 air-bladder (or "swimming-bladder") of a gill-and-lung- 

 breathing fish of the early Devonian period. 



The fact that there is, in most Fishes, a connection-tube 

 between the air-bladder, the oesophagus (or pharynx), 

 and the mouth, through which air is inhaled and ex- 

 haled, leads, in certain cases, to very important results — 



apart from the ordinary function of the swimming- 

 bladder as an organ used to facilitate rising and sinking 

 in the water. The inhalation of air served to feed the 

 arteries of the walls of the swimming-bladder with oxy- 

 gen, this organ, in certain groups, serving as a substitute 

 for the gills in times when stagnant water was poisoned 

 with an excess of carbonic acid, arising from decaying 

 vegetable or animal matter in more or less putrid pools. 

 It was observed by Semon, in Australia, that the lung- 

 fish Neoceratodus fosteri was able to survive in a par- 

 tially dried-up water-hole so foul that it was full of 

 dead fish of the ordinary kinds — fish wholly dependent 

 upon gill-breathing. Another genus of lung-fish, of 

 which three species are found in Africa, is able to 

 breathe air still more largely by means of the air-bladder 

 — the sole breathing organ during the dry season. 



In both Protopterus of Africa and Lepidosiren of 

 South America, the swimming-bladder is bilobed, or 

 double, and the walls are developed into pockets, or sac- 

 culi, exactly like the lungs of land vertebrates. The en- 

 tire arrangement of the pulmonary veins and arteries, and 

 of the vascular system in general, is very similar to that 

 of the Amphibia, including the structure of the heart. 

 Even the brain of the African Dipneans resembles that 

 of the Amphibia. The larva of these fish is very much 

 like the tadpole of the frog. Fossil remains of two dis- 

 tinct groups of lung-breathers are abundant in Devonian 

 strata — sediments laid down at a time when the earth's 

 crust was characterized by successive elevations and de- 

 pressions of land surfaces. 



Origin of Legs and Arms 



As to the origin of limbs, we must look for their be- 

 ginnings in the fins of the early Devonian fishes. For- 

 tunately, we have a striking fossil example of a fin in the 

 process of being transformed into a forelimb. Examin- 

 ation of a Devonian fossil fish known as Sauripterus 

 laylori reveals a central hand-like lobe-fin of cartilagin- 

 ous rods surrounded by a fringe of paddle-like dermal 

 rays. The dropping of this fringe — a modification of 

 the skin — would leave a cartilaginous arm and hand-like 

 structure, already divided into a humerus, radius, ulna, 

 wrist, and several fingers. The shoulder-girdle of this 

 transition type of fish is homologous with that of an 

 Amphibian, part for part — clavicle, supraclavicle, sca- 

 pula, coracoid. 



Here, then, we furnish the anti-evolutionist with con- 

 crete "links" which are not "missing"! 



