Heredity, race, and society.

  • Leslie Clarence Dunn
Date:
1947
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Heredity, race, and society. Source: Wellcome Collection.

    56/148 page 54
    Drosophila have been observed to vary in different in dividuals. The appraisal of the total number of genes in that insect has been arrived at by very different indi rect methods which we need not discuss here. We have seen that hereditary differences between brothers and sisters can easily be accounted for if the parents are hybrid for several genes. Brothers, sisters, and relatives in general tend, however, to show family resemblances; the differences between non-relatives are on the whole greater than between relatives. If man has no fewer genes than a Drosophila fly, a human sex cell must carry several thousand genes. Let us assume that only about three hundred of these genes are each represented by at least two alternative conditions such as A and a, dominant and recessive. This is almost certainly an underestimate, but for the purposes of the argument we are going to make, an underestimate, is preferable to an overestimate. Three hundred gene differences are capable of producing a fantastic number of combinations—more than there are electrons and protons in the Universe. Although we can not as yet make an exact count of human genes, we can be very sure that all the gene combinations which exist in all the humans living in the world constitute just a negli gibly small fraction of gene combinations that could be formed. Each Man Is Unique We can not tell whether the innumerable missing gene combinations would make men better or worse than those which happen to exist. All we can tell is that mankind is capable of producing an almost in finitely greater collection of types than that which exists at present or existed in the past. The chance that any two human beings, now living or having lived, have identical sets of genes is practically zero, identical twins always excepted. The hereditary endowment which each of us has is strictly his own, not present in anybody else s unprecedented in the past, and almost certainly
    digitised image 1
    digitised image 2
    digitised image 3