EVOLUTION, HEREDITY, EUGENICS 525 



C. Darwin. — Variations assumed. Variations of use are perpetuated 

 by inheritance. The Jit survive and propagate. Each cell of the body 

 sends off minute gemmules which enter the germ cells and transmit changes 

 that have taken place in the individual. (This really admits the inher- 

 itance of acquired characters.) 



Weismann. — Variations are due to permutations and combinations of 

 the germplasm. Germinal selection takes place in the union of the germ 

 cells. Germplasm has an unbroken continuity with an extremely complex 

 organization. Body cells are not inherited. 



Mendel. — New species are due to new combinations of chromatin. 

 Dominance and recessiveness are always to be considered. 



Tie Fries. — New species are due to sudden mutations or "sports." 

 Mutations are sudden variations that breed true. De Vries says, a 

 mutant is "a change of wide amplitude which tends to be stable because 

 it involves acquisition of a new unit by the germplasm, but which is 

 necessarily stable only when the individual possessing it mates with a 

 similar individual." It has been suggested that mutations may occur 

 through the addition or subtraction of single characters. 



Evidences for Evolution. Paleontology. — In studying the strata 

 of the earth's crust we find that there is a gradual progression from 

 types with primitive organization to the highly developed. Many- 

 groups of animals and plants reached the climax of specialization 

 at relatively early geologic periods and became extinct. 



The evolution of vertebrate classes is more satisfactorily shown 

 than that of any other group, probably because they represent the 

 latest phylum to evolve and most of their history coincides with the 

 period within which fossils are known, while most of the inverte- 

 brate phyla had already undergone more than half of their evolution 

 at the time when the earliest fossil remains were deposited. 



Fossils Classified. Class i. — Actual remains of recently extinct 

 animals and plants. («) In Arctic ice — the mammoth, {h) Insects 

 preserved in resin-amber, (f) MolJusk shells, teeth of sharks, pieces 

 of buried logs and bones of animals buried in asphalt lakes and peat 

 bogs have been found in well-preserved condition. 



Class 2. Petrified fossils., seen best in plants. Class j. Casts 

 and impressions. These are the impresses of soft-bodied animals 

 left in mud which later solidified. The celebrated Pompeian dog 

 is a striking example. The most remarkable are found in the oily 

 shales of British Columbia. Even soft invertebrates are found in 

 casts. 



