98 REPORT OF THE CONFERENCE ON GENETICS. 
DOES HYBRIDISATION INCREASE FLUCTUATING 
VARIABILITY ? 
By Proressor W. JOoHANNSEN, University of Copenhagen. 
THE problem of heredity is the subject of very diligent study at the 
present time. ‘Two different methods of investigation have been followed 
by workers, viz. the statistical method and the experimental method, 
but the results of these two methods do not always seem to agree. And 
yet in reality agreement must be found. 
Pure statistics in this matter provide a dangerous and uncertain 
method, not only because the special data are very seldom controllable, 
but especially because (granting their inherent correctness) a scientific 
biological analysis of such data cannot be made: it remains quite 
uncertain whether the numbers in question contain a multitude, or 
a few, or only one single ‘“ sort’’ of organisms—‘ biotypes’’ as I have 
called them (1).* 
In many organisms heredity can only be investigated by the 
statistical method, as for example in the human race, where experi- 
ments are impossible, and in many of the larger animals, such as 
horses, &c. In all such cases the research is limited to the indications of 
genealogical tables, stud-books, &c. But such materials are not at all 
qualified to form a basis for an exact inquiry in heredity. For this purpose 
data are required which can be controlled, and which are sufficiently 
specialised to enable them to be separated into different groups from 
various points of view and in such ways that a true biological analysis 
may be made in each special case. 
The imposing display of mathematical knowledge and refinement 
with which the “ Biometrical School” has dazzled our eyes really 
proves ineffectual for the true understanding of the physiological laws 
of heredity, when the mathematical treatment is not based upon an 
accomplished sorting of the special facts and a biological setting-out of 
the premises which are to be treated. The most prominent biometrician, 
Professor Karl Pearson, has in all his work in this biological domain 
proceeded as if his motto were: “ There are no premises ; all is treat- 
ment!’’ Indeed this very expression was once flung out against me 
in a private discussion with a biometrician. Neglect of premises—in 
a degree quite inconceivable to the experimenting biologists—is the 
Achilles-heel of biometry, and the whole Biometrical School is therefore 
standing on very unsafe ground as to the biological value of its results 
in heredity. 
What mistakes and absurdities the neglect of the premises has 
introduced into the literature of heredity must be known by all who 
have taken notice of Mr. Bateson’s criticisms on “ Homotyposis”’ (2), 
or—not to go further into polemics—who have seen the recent 
* The numbers refer to the list of literature at the end of the paper. 
