258 Raphael Falk
or biased emphasis on the genetic component of characteristics became often a
biological conception rather than an analytical tool.
The conceptual distinction between the potential for a trait — the genotype,
and the trait proper — the phenotype, induced at least one scientist to over-
come his reservations from the embryological preformationism that was inherent
in the formal notion of genetic theory [Morgan, 1910a]. Thomas Hunt Morgan had
been involved in the study of the causes of sex determination at the cellular level
[Gilbert, 1978]. He saw in Johannsen’s conception of disparate hereditary factors
and traits a “developmental” way out of the de Vriesian notion of hereditary pre-
formationism, allowing him to maintain an organismic approach to development
while accepting a particulate theory of inheritance [Falk, 2003, 89]. For a while he
valiantly attempted to uphold the unity of the contribution of hereditary factors
to traits and the developmental processes in which the factors were involved. He
tried to maintain a many-to-many perspective of factors and traits, but the need to
refer (and identify) the factors through their phenotypes as “markers” demanded
simplifications. So for example, Morgan tried to retain a genetic nomenclature
that contained developmental notions. However, the more genes were discovered
that were involved in a given characteristic, the more complex the nomenclature
become. Eventually, he noted that the nomenclature oriented toward multiple
developmental steps was “not sufficiently elastic to allow the introduction of new
terms in the series” [Morgan, 1913a, 12]. Reluctantly, Morgan had to adopt the
terminology that indicated an etiological relationship between genes and traits
[Falk and Schwartz, 1993].
In compliance with Mendel’s notion of uncovering the laws of heredity, irrespec-
tive of the specific trait involved, this terminology had far reaching consequences.
In theirThe Mechanism of Mendelian HeredityMorgan and his students asserted
that they “use cause here in the sense which science always used this expression,
namely, to mean that a particular systems differs from another system only in
one special factor” [Morganet al., 1915, 209]. Thus, by ignoring the detailed
mechanical-causal notion ofEntwicklungsmechanikof connections between causes
and effects, Morgan and his students reduced causation to patterns conjunction.
“The fact that correlations can be traced between theend productsof ontogeny in
successive generations... is enough to declare that you have found the causes of
these products” [Amundson, 2005]. This differential concept of the gene [Schwartz,
2000], which reduced the relationship tochangesin genes andchangesin traits,
“has cut ontogenetic development out of the explanatory picture” [Amundson,
2005]. Morgan, Sturtevant, Bridges, Muller and many others, reduced the prob-
lems of development to the study of specific, differential factors of the ontogenetic
reaction in a complex organic system, or to “genes for” specific traits [Falk, 1997].
3 THE CHROMOSOMAL THEORY OF HEREDITYAlready in 1896, in hisThe Cell in Development and InheritanceE. B. Wilson
[1896] developed the theory of the cell as the fundamental unit of living organisms