1899] THE NUCLEOLUS LN HEREDLTY 241 



germ-plasm is brought about by the extrusion of nucleoli, while the 

 deficiency of chromatin, so often remarked in the 'nuclei of mature 

 specialised cells, as compared with the large size of their nucleoli, 

 would be a natural consequence of a reduction in the number of 

 active, and an increase in the number of dormant, idioblasts, which 

 might be expected to accompany specialisation if, as seems probable 

 from the phenomena of vegetative regeneration, every mature cell 

 must contain all the hereditary substance required for the develop- 

 ment of an individual. 



Inheritance of Longevity. 



Wallace, Weismann, and others have suggested that the normal 

 length of life of organisms, which differs so much in different species, 

 has been determined by natural selection. A creature lives as long 

 as is good for the species. This was a general suggestion — prompted 

 partly by the strange irregularity and apparent capriciousness of the 

 length of life in different animals — and the preliminary question was 

 not raised, " Is longevity a heritable character ? " This is obviously 

 a very important question, since natural selection could not determine 

 or fix the fit duration of life unless that character were inherited. 

 We are indebted to Miss Mary Beeton and Professor Karl Pearson for 

 a contribution towards the required answer. In a paper entitled 

 " A first study of the inheritance of longevity, and the selective death- 

 rate in man," read before the Ptoyal Society of London on 15th June, 

 the authors show that directly and collaterally duration of life is certainly 

 inherited in the male line in man. They believe this to be the first 

 quantitative measure of the inheritance of life's duration. Further 

 data for the inheritance of this character in the female line, and for 

 the study of the inheritance of " brachybioty," or short-livedness as 

 distinguished from longevity, are being collected. The inquiry should 

 be interesting to actuaries as well as to biologists. 



The second part of the paper is not less important. " In the 

 presidential address at the Oxford meeting of the British Association 

 we were told that no one had seen natural selection at work. In a 

 criticism then published by one of us, it was suggested that every 

 one who had examined a mortality table had seen natural selection at 

 work. . . . All individuals die, but some, better suited by their con- 

 stitution and characters to their environment than others, survive 

 longer, and so are able, or better able, to reproduce themselves, and 

 to protect for a longer time their offspring. To assert that natural 

 selection does not exist, is to assert that the whole death-rate is non- 

 selective, or is not a function of the constitution and characters of 

 the individual. Looked at from this standpoint the existence of 

 natural selection really becomes a truism. All that remains when we 



