Page sis 



EAOLUTION 



June, 1930 



plants are so wonderfully well fitted to the places 

 they occupy in nature? Consider the fitness of 

 fishes, reptiles, birds and mammals for life in water ; 

 of birds for flying, of moles for burrowing, of deer 

 for running; the fitness of all the organs of the body 

 for their particular functions, of the eye for seeing, 

 the ear for hearing, the nerves for conducting, the 

 muscles for contracting. Indeed there is scarcely 

 a structui-e or function of any living thing wliich 

 does not show such fitness or adaptation, and the 

 problem of the origin of such adaptations is today, 

 as it has alwaA's been, the greatest problem of evolu- 

 tion. 



There are two principal scientific hypotheses 

 which attempt to explain these adaptations, known 

 by the name of their chief proponents as Lamarck- 

 ism and Darwinism. Lamarckism assumes that such 

 adaptations are first acquired by mature organisms 

 and then by some inconceivable process these ac- 

 quired adaptations are transferred to the chromo- 

 somes and genes so as to become hereditary and 

 reappear in succeeding generations. Many attempts 

 have been made to find conclusive evidence of such 

 inheritance of acquired adaptations, but so far 

 without success. The Lamarckian doctrine is at 

 variance with the best-established principles of 

 genetics. 



Darwinism, on the other hand, accepts the evi- 

 dence of genetics that mutations occur in all poss- 

 ible directions and it undertakes to account for the 

 fitness of organisms b_y the early death and elimin- 

 ation of tlie unfit. We know that many genes and 

 combinations of genes are lethal and cause the 

 early death of germ cells or of the organisms into 

 which they develojD. In nature injurious mutations 

 are quickly eliminated, but at present we have no 

 sufficient evidence that natural selection, or Darwin- 

 ism, does explain all the marvellous adaptations of 

 the living world. If to the natural elimination of 

 unfit germ-cells or persons we add the intra-per- 

 sonal elimination of unfit reactions, we can explain a 

 whole class of acquired fitness, but in so doing we in- 

 troduce a quasi-psychic factor, as Darwin did in his 

 hypothesis of sexual selection, and as man}' others 

 have done from Aristotle down to the present time 

 under the terms of "perfecting principle," "indwel- 

 ling soul," " entelechy," etc. Such attempts to ex- 

 plain fitness by an appeal to psychism are specula- 

 tions, not even working hypotheses, for no one has 

 vet found a way of experimentally testing them. 

 Multifarious variation and selective elimination are 

 the best explanations of the origin of fitness that 

 have ever yet been proposed. 



How Did Plants Begin? 



By G. L. WITTROCK 



OBSERVING life in all its forms, we wonder as to 

 its origin. We see animals and plants of all 

 sorts, from one-celled individuals to very com- 

 plex organisms containing billions of cells. Natur- 

 ally we look for origins among the simpler, one- 

 celled forms. Then we note that the animals feed 

 on the plants, and that plants depend but incident- 

 ally upon the animals. This unbalanced relation 

 at once suggests that the plants may liave preceded 

 the animals in evolution. But when we study the 

 one-celled forms of both, we find ourselves confused, 

 they are so much alike. It looks as though they 

 originated together from a common beginning, and 

 then diverged very early along two boldly distinct 

 lines. 



For plants and animals are alike in fundamental 

 structures and functions. They are both built up of 

 living cells composed of protoplasm, and perform 

 the same life functions, respiring, feeding, growing 

 and reproducing. But they have also taken to 

 variant ways of life that have set distinctive marks 

 upon each group. 



The typical plant produces its own foodstuffs 

 out of inorganic matter by a process using sun- 

 light energy and called "photosynthesis," for wliicli 

 the green coloring matter "chlorophyll" is necessary. 

 There are exceptions, such as the degenerate plants 



Indian Pipe and the fungi that have lost this power 

 of primary food production which their ancestors 

 must have possessed. But the typical plant draws 

 its nourishment from the soil in which it is rooted, 

 and spreads a green surface of body or leaves to 

 absorb sunlight and carbon dioxide, all of which, 

 together with water drawn through the roots, build 

 up into foodstuffs packed with energy. 



TJie animal takes those plant foods ready made. 

 It has no power to produce its own foods and lives 

 by consuming plants, either directly or by eating 

 other animals that have eaten plants. That way 

 of living demands movement, from one plant food 

 supply to another, movement to capture or to 

 escape other animals. Fundamental clianges in 

 structure result. The plants develop firm cell walls, 

 usually of cellulose, mechanically rigid so the plant 

 may stand erect in its fixed habitat. The cell walls 

 of animal tissues, on the other hand, largely dis- 

 appear, leaving the cells elastic for motion. The • 

 animals thus gain freedom of movement by becoming 

 dependent on the plants. But tlie price is cheap, 

 for movement brings contacts and problems, de- 

 mands sensitivity and adjustivc reactions, the be- 

 ginnings of mind and eventual mastery of the world. 



The chart shows the life C3'cle of plants complete. 



