Genetic Analysis 257However, most traits of plants and animals display patterns of continuous varia-
tion. Did Mendel and the geneticists that followed him, inadvertently picked for
their hybridization experiments those traits the factors of which segregate of each
other, independently of the segregation of other factors, whereas the inheritance
patterns of the continuously varying traits do not follow the Mendelian pattern of
inheritance? The hybridization experiments of Nilsson-Ehle with oats and wheat
varieties which differed in the color of their seeds indicated that what looked like a
continuous “normal” curve of color-intensity distribution in the progeny of hybrids
could actually be considered a binomial distribution ascribable to several discrete
genes each of which endows similar phenotypes (colorversusno-color). The color
intensity of the seeds was dependent on the number of color-alleles of all genes
involved. The continuous distribution patterns was ascribed to “environmental”
effects that blurred to some extent the color determined by the number of alleles
[Nilsson-Ehle, 1909].
It was, however, East who emphasized theuniversality of themethodof ge-
netic analysis, when he pointed out that as such it must be capable to handle
quantitatively-varying characters as much as is did qualitatively-different traits:
As I understand it is a concept pure and simple. One crosses various
animals and plants and records the results. With the duplication of
the experiments under comparatively constant environments these re-
sults recur in sufficient definiteness to justify the use of a notation in
which theoretical genes located in the germ cells replace actual somatic
characters found by experiments... Mendelism is therefore just such
a conceptual notation as is used in algebra or in chemistry... [East,
1912, 633]
Since qualitative characters were the ones that could be divided into
definite categories they were the ones attacked.... If Mendel’s law
is to be worth anything as a generality, therefore it must describe the
inheritance of these characters... [East, 1912, 637]By the end of the first decade of the twentieth century the foundations of the
science of genetics were well established. It exhibited not just a reductionist
methodology for the analysis of heredity, but had explicit reductionist concep-
tual connotations, if not of organismic individuation as types, then at least of
genes as the atoms of traits. Johannsen’s conceptual differentiation of the phe-
notype and genotype allowed the study of the mechanics of heredity as well as
the study of the developmental pathway from gene to trait. However, it must be
admitted that although Johannsen emphasized that the phenotype was the inte-
gration of both genotype and the environment, his distinction of terms facilitated a
more literal statement of Galton’s NatureversusNurture, which often established
a dichotomy, rather than dialectic of the two. With the introduction of R. A.
Fisher’s Analysis of Variance, this biased juxtaposition of NatureversusNurture,
or of genotypeversusenvironment, in which “interaction” was relegated to an an-
noying but unavoidable residuum, got a quantitative formulation.Genocentricity