446 AN INTRODUCTION TO ZOOLOGY 



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the lifetime of the individual and handed on to the young, "the 

 inheritance of acquired characters,'' a point to which we shall return 

 later. No satisfactory evidence has been obtained to show that 

 such inheritance occurs at any rate in the crude form in which it 

 has just beenstated, and this doctrine and all it implies, usually spoken 

 of as Lamarckism, is not generally held to-day. It shows a clear 

 recognition of certain important underlying principles however. 

 The first is the idea of modification or mutation of species, the second 

 is the fact that structural characteristics are handed on from parent 

 to offspring, and thirdly that animals are on the whole well suited 

 for the life they lead. 



Here we meet for the first time with a definite recognition of and 

 expression of the idea of Organic Evolution, which has since been much 

 extended, and in its modern form states that the various members 

 of the animal and vegetable kingdoms, as we know them to-day, have 

 not existed for all time, but are the result of a long continuous 

 series of changes. These slow changes have been in progress since 

 an early period of the earth's history, and are still going on and will 

 continue until organisms cease to exist. They have resulted in the 

 production of higher and higher forms of life, or, to put it in another 

 way, the forms we see to-day have been evolved or developed from 

 lower forms, and these from still lower ones, and so on. There 

 has been a gradual progress from the simple to the more and more 

 complex and specialised. This change in the case of certain domestic 

 animals and plants is an observed and observable phenomenon 

 even in the course of a man's lifetime. We now grow in our gardens 

 many kinds of plants that were unknown to our forebears, and, we 

 all know, new " varieties," as they are termed, are added year by 

 year. Not only does this apply to flowers such as roses, etc., but 

 to our crops like wheat, fruit and potatoes, and also to animals. 

 Still it has been questioned in the past and is sometimes questioned 

 to-day by people with little biological knowledge, whether such a 

 conception of change is generally applicable to animals and plants 

 in the state of nature. The answer is undoubtedly yes, but before 

 going on to consider the theories which attempt to explain it, we shall 

 do well to stop for a while and examine the evidences for the occur- 

 rence of organic evolution. These may be dealt with conveniently 

 under four heads : Anatomical, Embryological, Geographical and 

 Palseontological evidence. 



Anatomical Evidence. 



We have had in this course many concrete examples of 

 facts relating to evolution, so that it is only necessary to call attention 

 to the general plan of the evidence. We find that animals, and 



