A Critique of Pure (Genetic) Information

32 Chapter 1
hypothesis, cellular differentiation and organismal development are regulated
by the uneven distribution of idioplasm at each stage of cell division.
In this view only germ cells contain the full complement of Anlagen.
The Anlagen then becomes differentially partitioned into daughter cells
during somatic cell division. Ultimately each cell only receives those
Anlagen required for its terminal state of differentiation. Roux had
claimed experimental confirmation of his theory when, using a hot sterilized
needle, he ablated one of the blastomeres of the two-cell-stage frog
embryo. The remaining blastomere continuted to develop, albeit abnormally,
resulting in something like half an embryo. According to the
mosaic theory, the remaining blastomere would contain only that idioplasm
capable of producing half an organism (Allen 1975).
Hans Driesch, working in Naples in the 1880s and 1890s, attempted
to reproduce these findings, using an agitational method for separating
the two blastomeres of the sea urchin. Contrary to Roux’s findings, the
remaining blastomere was fully capable of producing a normal, albeit
smaller, sea urchin larvae (Allen 1975). Driesch countered Roux’s mosaic
model with his theory of the developing organism as a “harmonious
equi-potential system.” According to this theory, cells retain the full
potential of the organism, gaining their developmental specificity not
through directives from within but rather externally and relationally with
respect to their position in the developing organism and the influence of
environment. Driesch, in effect, proposed a nascent developmental field
theory. Although Roux was disinclined to concede the point, it became
generally accepted that his results were due to the residual effects of the
ablated cell matter and that Driesch’s results were truly indicative of the
absence of mosaic nuclear division.
By 1910 Morgan could state unhesitatingly:
We have every evidence that in embryonic development the responsive action of
the cytoplasm is the real seat of the changes going on at this time, while the chromosomes
remain apparently constant throughout the process (Morgan 1910).
Had the mosaic model been successful, as suggested above, many problems
would have been avoided. The idioplasm, presumably located in
the nucleus, would have been seen to “represent” the organism as a
whole and to provide the mechanism for controlling development. The
process of heredity and the process of development would have been sub-