An Introduction to a Biology 



is like its parent. And this you can't tell me. I want to know 

 about normal heredity ; you give me nothing but information 

 about abnormal. I ask for bread, and you give me what is 

 to me a stone ; interesting and curious, but still a stone." 



I should answer objections of this kind by asking, " But 

 why abnormal ? " Why should we regard the disintegration 

 of biological units as more " abnormal " than that of chemical 

 ones ? It is only by experiment with " abnormal " pheno- 

 mena that the chemist has progressed. If he had stuck as 

 rigidly to the observation of " normal " water as those who 

 bring this objection against the hybridiser would have him 

 do, he would know as little about the chemistry of water 

 as the biologist did about heredity before he began to 

 experiment with it. 



But this answer, though it sounds plausible enough at 

 first hearing, can only be thoroughly satisfactory to those 

 who urge this objection if we can show them that the appear- 

 ance of abnormality is merely due to the fact that we are 

 dealing with normal units in an " abnormal " condition (the 

 result of disturbance by cross-breeding), and if we can show 

 them that we really are not dealing with an abnormal 

 hereditary phenomenon. 



Now what are we to understand by abnormal ? The 

 most definite formulation of what is meant by abnormality 

 in heredity is that of Dr. Archdall Reid. According to him, 

 alternative inheritance has been evolved as a means of 

 keeping the sexes separate, or, to put it in a teleological 

 way, of ensuring that an individual shall be either a male 

 or a female. When the alternative mode of inheritance 

 first became differentiated it was only sex which was in- 

 herited in this way. But just as sex, so to speak, sometimes 

 makes a mistake, and trespasses on forms of heredity which 

 do not belong to it, and blends in inheritance, with the result 

 that a hermaphrodite is produced, so sometimes not-sexual 

 characters, albinism for example, trespass on the mode of 

 inheritance reserved for sex and are inherited alternatively. 



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