408 GENERAL BIOLOGY 



boring islands there are animals resembling those on the coast of the 

 continent both in structure and habit, yet sufficiently different to be 

 called new species. 

 7. Natural Selection. 



This is an attempted explanation of why present-day forms are what 

 they are, by showing that food is never equal to the possible rate of in- 

 crease in living forms. Such lack of food causes a struggle for existence 

 through which struggle the weakest (the ones being least adaptive), go 

 down, while the stronger (those best able to adapt themselves to their 

 environment), survive. 



Natural selection describes the causes which have prevented surviv- 

 ing forms .from becoming extinct. 



OPPOSING ARGUMENTS 



The arguments which are usually brought forth to oppose these evi- 

 dences for evolution are as follows : 



1 . Paleontology. 



(a) The different kinds of plants and animals found in various 

 geological strata can only demonstrate that similar organisms were either 

 larger or smaller than others, or varied in ways which can be accounted 

 for by a difference in the temperature and food supply of different ages. 

 Examples of this are the horse and mammoth. Then, too, paleontologists 

 insist that their finds can only be explained by assuming that acquired 

 characteristics are inherited, although experimental evidence seems to 

 point against this being true. 



(b) The so-called increasing complexity on the part of so-called 

 "younger" fossils as compared with so-called "older" ones, may always 

 be explained by assuming that Mendelian recessive characteristics have 

 again come forth, and that consequently the so-called "new forms" are 

 really a return of old ones. 



(c) Recent fossils are like modern forms because the climatic 

 changes and the food supply have not varied much during the interval 

 between our own time and the time when the prototypes of these recent 

 fossils lived, and that examples of so-called older forms (those which lie 

 above the recent forms) can be considered evidence for this statement. 



(d) Those who insist on experimental evidence which is always 

 under the control of the experimenter, say that fossil-remains furnish us 

 only with "descriptions" of what is found. It is a "dead** account. It 

 can never give us an explanation. Explanation and interpretation can 

 only come through our logic. Paleontological evidence is therefore all 

 logical and not experimental. A strictly scientific explanation from the 

 experimentalist's point of view must also present experimental evidence. 

 This has not been, and cannot be, done in paleontology. 



