

TYPE AND VARIABILITY 435 



still in spite of vigorous selection ; whether in his selection he 

 is operating with or against nature ; whether the type is becom- 

 ing a little more " fixed " or whether the tendency is more and 

 more to scatter ; whether the mean or general average of excel- 

 lence is approaching or receding from the desired type ; whether, 

 as time passes, variability is lessened or increased ; whether, as 

 the result of selection, new values are coming in at the upper 

 end. In short, by these calculations he may know whether he is 

 making real progress, or is only dabbling in the whirl of vari- 

 ability that is inevitable with all living things, without influ- 

 encing at all the trend of the race. It is needless to say that 

 much of this latter sort of ineffective breeding is going on all 

 about us everywhere. The statistical method is the only known 

 method of securing accurate knowledge of type and variability ; 

 for type is not simply what we desire, but it is what we actually 

 get, and any breeder is working in the dark who does not know 

 the real nature of the whole population of the race he breeds. 



SECTION III PRACTICAL HINTS ON THE TAKING AND 

 GROUPING OF MEASUREMENTS 



It is highly improbable that, in measuring any part of an 

 organism, a perfectly accurate measure is obtained. It may be 

 very easy to measure the length of an object accurately to i inch, 

 or to o.i inch, or even to o.oi inch, if the ruler is sufficiently 

 accurate ; but finally, in trying to measure to as high a degree 

 of accuracy as possible, we come to a point where our ruler 

 fails us. Again, the object measured may be of such a nature 

 that it is futile to try to take measurements beyond a certain 

 degree of accuracy. For instance, it would be useless to try to 

 measure the length of an ear of corn to o.oi inch. Similarly, in 

 weighing substances, it is possible with a good balance to take 

 measurements to ounces or to tenths of milligrams if extreme 

 accuracy were demanded ; but finally, in striving after accuracy, 

 the balance fails us, and we must grant that it is highly improb* 

 able that the weight which we record is perfectly accurate. 



While we thus see that we cannot attain absolute accuracy in 

 any measurements, yet thremmatology is no exceptional field in 



