20 JOHANNSEN 



characters are conjoined in them. The ment of the hybrids, finds therefore its 



hybrids form eight various kinds of foundation and explanation in the prin- 



egg and pollen cells— ^BC, ABc, AbC, ciple enunciated, that the hybrids pro- 



Abc, aBC, aBc, abC, abc—iLnd each duce egg cells and pollen cells which 



pollen form unites itself again on the in equal numbers represent all constant 



average once with each form of egg forms which result from the combina- 



cell. tions of the characters brought to- 



The law of combination of different gether in fertilisation, 

 characters, which governs the develop- 



Heredity in Populations and Pure Lines 



A Contribution to the Solution of the Outstanding Questions in Selection 



W. JOHANNSEN 



Translated from Ueber Erblichkeit in Fopula- 

 tionen und in reinen Linien, published by Gus- 

 tav Fischer, Jena, 1903. 



/ have translated here only the final swfrmary and discussion fro?n 

 Johannsen's lo?]g paper on pure lines, which was written in German. 

 This thorough and meticidous ifjvestigation of the true significa?7ce of 

 selection was a bombshell to evolutio?iary thought. The efficacy of 

 selection in the production of fiew species had beeji one of the main- 

 stays of Darwin's theory of evolution. Johajmsen's studies deinon- 

 strated conclusively that selectiofj coidd not extend the limits of 

 previously established variability. This fact became important iii 

 arguments against Darwinism, and led to a period when selection was 

 discredited as evolutionarily sig?iifica?Jt. The mutatiojj theory became 

 the new basis for expla?iation of evolutionary pheno7nena. 



As has often happened in biology, the final solution of the problem 

 involved a reconciliatio?i of the two viewpoints. Mutation (as a 

 source of varia?its) and selection (as a method of elimination of some 

 but not all variants) provide the modern basis for explanation of the 

 process of evolution. We owe to Joha?msen our modern viewpoint of 

 selectio?i as a primarily passive process, which eliminates but does 

 not produce variations. 



Although Johamisen uses the German word "Typus" throughout 

 his paper with reference to his pure lines, 1 have substituted his own 

 term, ''■genotype'' inve?ited at a later date. To Johannsen goes the 

 credit as well for inventing the word ''gene.''' It shoidd be ?ioted that 

 he wrestles with the various 7james that had bee?! proposed for the 

 hereditary particles in this paper, on p. 26, but does not at this time 

 suggest the term gene. 



