Interpretation of Facts 165 



that this is pure chance, there being approximately half as many carriers 

 of either color in each sperm of the male as there is in each egg of the 

 female. Therefore, there is just as much likelihood at any given time 

 of a sperm carrying blackness meeting with an egg carrying whiteness 

 as of one carrying whiteness meeting one carrying blackness and vice 

 versa. But it must not be forgotten that not only the half-breeds, but 

 also the pure bloods of the dominant type will all probably look alike 

 as to color. This appearance of the same color in the half-breeds, which 

 appeared in the dominant pure-blood, is the thing which confused men 

 for many years, and it was only after Abbott Mendel gave us his explana- 

 tion that we have been able to understand why this is so. 



Mendelism has also added some interesting biological speculations 

 to the earlier ideas of naturalists. 



If we define species as meaning all those particular plants and ani- 

 mals which can interbreed and in turn give birth to fertile offspring, it 

 can be seen immediately that we cannot have any new species at all. 

 For, if the offspring of such plants or animals can give birth in turn 

 to other offspring, they belong to the same species as do their parents, 

 and, if they differ in appearance from their parents, they can only be 

 called variations of the parent species. If they do not interbreed, or, if 

 after interbreeding, they give birth to non-fertile offspring (such as the 

 mule, which is the non-fertile offspring of a mare and a jack), then, of 

 course, there can be no further offspring, and we can have no further 

 species. 



Mendelism has added a very important and interesting fact to such 

 theorizing. For example, in the dominant type of offspring of pure-bred 

 parents, there are always pure sperm and eggs which carry recessive 

 characteristics, so that it follows, that at any time in the future, if by 

 chance such pure egg and sperm meet, a totally different type of plant 

 or animal may be produced. But this may be merely the coming forth 

 of a plant or animal similar to some ancestral form, which was the result 

 of two germ-cells meeting that carried the recessive trait. Therefore, 

 although these recessive germ-cells were always present in all ancestors, 

 they were covered up in so far as external characteristics are concerned 

 by the dominant characteristics. A new species, such as this which 

 comes forth suddenly, is called a "sport" in nature, and the theory that 

 all new forms come forth in this way is called the mutation theory. 

 But, as these so-called new forms may be explained as being recessives, 

 again coming forth after lying dormant for ages, there may be here no 

 new species at all. 



