PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 6 MAY 15, 1920 Number 5 
CALCULATING ANCESTRAL INFLUENCE IN MAN 
a mathematical mejasure of the demonstrated facts of bi-sexuaiy 
heredity 
By Harry H. Laughlin 
Eugenics Record Office, Carnegie Institution of Washington 
Communicated by C. B. Davenport. Read before the Academy, November 10, 1919 
By ancestral influence is meant the contribution of definite hereditary, 
mental, physical and moral qualities, by a given ancestor to a given de- 
scendant. Pedigree-studies have set forth in man, as in many other or- 
ganisms, rules of inheritance of many specific traits or quahties. Cy to- 
logical investigations have shown how chromosomes duplicate, segregate 
and recombine (sometimes crossing-over and showing other special phe- 
nomena) in the course of gametogenesis and fertilization. 
In bi-sexual species of plants or animals, the germ-plasm is not indefi- 
nitely dilutable or divisible as many genealogists have assumed, but its 
dilutability and divisibility are limited by the number of chromosome- 
characteristics of the gametes of the particular species. In the human 
zygote two gametes each with 12 chromosomes unite. This means that, 
barring crossing-over, mutation and other special phenomena, normally the 
human germ-plasm, and consequently all hereditary human qualities, 
that is, the "blood," is divisible only into 24 unequal units correspond- 
ing to the 24 zygotic chromosomes. 
Note — There is still disagreement among cytologists concerning the number of 
chromosomes in man. 
Wieman, H. L., "The Chromosomes of Human Spermatocytes," Amer. J. Anat., 
21, No. 1, January, 1917. This paper concludes that in man the zygotic or diploid num- 
ber of chromosomes is 24, of which 2 are the xy idiochromosomes. 
von Winiwarter, H., "Etudes sur la spermatogenese humaine," ylrc/i, Biol., 27, 1912. 
This paper concludes that the zygotic number of chromosomes in the human male is 
47, in the human female, 48. 
See also Stevens, Guyer, Montgomery and Evans. 
When this problem is settled beyond peradventure, the correct number can be used 
in the accompanying formulas which are here stated in general terms. 
It is well demonstrated that the chromosomes are composed of genes 
or the determiners of natural inheritance. Bach chromosome is a gene- 
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