128 THE ORIGIN OF SPECIES 



analogous variation, in the enlarged stems, or as commonly called 

 roots, of the Swedish turnip and ruta-baga, plants which several 

 botanists rank as varieties produced by cultivation from a com- 

 mon parent: if this be not so, the case will then be one of analogous 

 variation in two so-called distinct species; and to these a third 

 may be added, namely, the common turnip. According to the 

 ordinary view of each species having been independently created, 

 we should have to attribute this similarity in the enlarged stems 

 of these three plants, not to the vera causa of community qfjde- 

 scent, and consequent tendency to vary in a like manner, but to 

 three separate yet closely related acts of creation. Many similar 

 cases of analogous variation have been observed by Naudin in 

 the great gourd family, and by various authors in our cereals. 

 Similar cases occurring with insects under natural conditions have 

 lately been discussed with much ability by Mr. Walsh, who has 

 grouped them under his law of equal variability. 



With pigeons, however, we have another case, namely, the oc- 

 casional appearance in all the breeds, of slaty-blue birds with two 

 black bars on the wings, white loins, a bar at the end of the tail, 

 with the outer feathers externally edged near their basis with 

 white. As all these marks are characteristic of the parent rock- 

 pigeon, I presume that no one will doubt that this is a case of 

 reversion, and not of a new yet analogous variation appearing in 

 the several breeds. We may, I think, confidently come to this con- 

 clusion, because, as we have seen, these colored marks are emi- 

 nently liable to appear in the crossed offspring of two distinct and 

 differently colored breeds ; and in this case there is nothing in the 

 external conditions of life to cause the reappearance of the slaty- 

 blue, with the several marks, beyond the influence of the mere 

 act of crossing on the laws of inheritance. 



No doubt it is a very surprising fact that characters should re- 

 appear after having been lost for many, probably for hundreds of 

 generations. But when a breed has been crossed only once by 

 some other breed, the offspring occasionally show for many gen- 

 erations a tendency to revert in character to the foreign breed — 

 some say, for a dozen or even a score of generations. After twelve 

 generations, the proportion of blood, to use a common expression, 

 from one ancestor, is only one in 2048; and yet, as we see, it is 

 generally believed that a tendency to reversion is retained by 

 this remnant of foreign blood. In a breed which has not been 

 crossed, but in which bof r , parents have lost some character which 

 their progenitor possessed, the tendency, whether strong or weak, 

 to reproduce the lost character might, as was formerly remarked, 



