4 PROBLEMS OF GENETICS 



centuries names were applied in the loosest fashion, and in giving 

 a name to an animal or a plant the naturalists of those times had 

 no ulterior intention. Names were bestowed on those creatures 

 about which the writer proposed to speak. When Gesner or Aldro- 

 vandi refer to all the kinds of horses, unicorns, dogs, mermaids, 

 etc., which they had seen or read of, giving to each a descriptive 

 name, they do not mean to "elevate" each named kind to "spe- 

 cific rank"; and if anyone had asked them what they meant by 

 a species, it is practically certain that they would have had not 

 the slightest idea what the question might imply, or any suspicion 

 that it raised a fundamental problem of nature. 



Spontaneous generation being a matter of daily observation, 

 then unquestioned, and supernatural events of all kinds being 

 commonly reported by many witnesses, transmutation of species 

 had no inherent improbability. Matthioli, 2 for instance, did not 

 expect to be charged with heresy when he declared Stirpium 

 mutatio to be of ordinary occurrence. After giving instances 

 of induced modifications he wrote, "Tantum enim in plantis 

 naturae germanitas potest, ut non solum saepe praedictos 

 praestet effectus, sed etiam ut alteram in alteram stirpem facile 

 vertat, ut cassiam in cinnamomum, sisymbrium in mentham, 

 triticum in lolium, hordeum in avenam, et ocymum in serpyllum." 



I do not know who first emphasized the need for a clear 

 understanding of the sense in which the term species is to be 

 applied. In the second half of the seventeenth century Ray 

 shows some degree of concern on this matter. In the intro- 

 duction to the Historia Plantarum, 1686, he discusses some 

 of the difficulties and lays down the principle that varieties 

 which can be produced from the seed of the same plant are to 

 be regarded as belonging to one species, being, I believe, the 

 first to suggest this definition. That new species can come into 

 existence he denies as inconsistent with Genesis 2, in which it is 

 declared that God finished the work of Creation in six days. 

 Nevertheless he does not wholly discredit the possibility of a 

 "transmutation" of species, such that one species may as an 

 exceptional occurrence give rise by seed to another and nearly 



2 Matthioli Opera, Ed. 1598, p. 8, originally published 1565. 



