HEREDITY, AND THE ORIGIN OF SPECIES.'^ 



[With 1 plate.] 



By Daniel Trembly MacDougal, 

 Director Departincnt of Botanical Research, Carnegie Institution of Washington. 



The surface of the earth is inhabited to-day by hundreds of thou- 

 sands of forms of life, which upon analysis are found to be separable 

 into groups or species, with well-marked and characteristic attributes, 

 which may be transmitted from generation to generation. The strata 

 beneath the surface are found to contain the remains of thousands of 

 other forms now extinct, but which show certain general relation- 

 ships to the existing organisms. If we piece together the actual 

 records and take the backward bearing of our information, we arrive 

 at a period sometime wdthin the last six hundred thousand centuries, 

 when living matter was more indeterminate in the forms which it 

 assumed, and was, perhaps, quite unlike any protoplasm w^e meet at 

 the present time. 



From this primitive substance series of organisms have been pro- 

 duced, Avhich, in the successive stages of the earth's history, show 

 an increasing complexity as the present epoch is approached, and 

 which embrace more numerous forms with the advance of time. 



In this upward movement, this evolution from the simple to the 

 complex, in the production of many from few, it is not to be taken 

 for granted that protoplasm has been a perfect automaton, and that 

 it has nothing but successes scored to its credit in the ever-changing 

 conditions it has met since its beginning. On the contrary, the suc- 

 cession of its forms is a most devious one, and by no means easily 

 traced. Phylogenetic systems are made up chiefly of allowable sup- 

 positions, and it is altogether probable that we do not know more 

 than a fraction of the course of the zigzag, halting, and at times 

 receding steps follow^ed by living matter in its development into 

 existing types. 



Thus the mosses are seen to have reached the ultimate development 

 allowable by their morphological character, and hence are incapable 



°- Lectui'e delivered before the Barnard Botanical Club, Columbia University, 

 December 18, 15^05. Froni The Monist for January, 1906. Reprinted by permis- 

 sion of the Open Court Publishing Company, with corrections by the author. 



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