424 THE STRUCTURE OF EVOLUTIONARY THEORY
Darwin's theory into something quite different. He abandoned Darwin's key notion
of the migration of gemmules across cell boundaries—thus removing the rationale
for Lamarckian inheritance. In de Vries' revised concept, the hypothesized
hereditary particles behaved so differently that they required a different name;
thus, still honoring Darwin, de Vries rechristened the gemmules as "pangenes."
In de Vries' concept of Intracellular Pangenesis (the title of his 1889 book),
the nucleus of each cell contains all particles (pangenes) needed to construct an
organism. But only some pangenes are expressed in each cell, thus explaining the
differential morphogenesis of parts. Expressed pangenes migrate out of the nucleus
into the cytoplasm, where they orchestrate the appropriate embryology. In no case
can pangenes move between cells. De Vries wrote: "The hypothesis that all living
protoplasm is built up of pangenes, I call intracellular pangenesis. In the nucleus
every kind of pangene of the given individual is represented; the remaining
protoplasm in every cell contains chiefly only those that ought to become active in
it" (1889, in 1910 translation, p. 215).
This remarkably prescient theory comes as close to the secret of heredity as
anyone had managed in the speculative tradition before the elucidation of genes
and chromosomes. Whiggish historians nearly always regard Intracellular
Pangenesis as de Vries' greatest book. In abstract concept, his nuclear pangenes
differ little from the particles of heredity that would soon be recognized and named
as genes, especially since de Vries viewed his pangenes as a minimal set of basic
instructions, not naively as a collection of items for specifying each overt
phenotypic part. His notion of active and latent pangenes recalls dominant and
recessive alleles—and one might justly argue that de Vries had therefore been
"preadapted" to appreciate Mendel. Fortune, as Pasteur famously said, favors the
prepared mind. Moreover, the notion that all instructions reside in the nucleus
(with passage to the cytoplasm, at appropriate times and places, for transmission of
local messages) bears remarkable isomorphism with our modern mechanism of
DNA, RNA, and the differentiation of cells.
Two further aspects of Intracellular Pangenesis play important roles in this
story. First, de Vries' theory became the source of our modern term "gene"— for
Johannsen explicitly derived the shortened name directly from de Vries' "pangene."
Moreover, since de Vries' "pangene" honored Darwin's name for his speculative
particle of heredity, Darwin himself becomes the ultimate source (via de Vries) for
this basic biological term. Few evolutionary biologists recognize this curious
terminological odyssey, making Darwin himself the ultimate, if indirect, source of
our modern term "gene."
Second, we note in de Vries' treatment of Darwin a microcosm of the strange
and almost painfully ambivalent fealty that tied him emotionally (and verbally) to
Darwin even while he devised a contradictory theory—the source of Seward's
anger, as described in my opening remarks. De Vries' theory, despite its personal
source in Darwin's pangenesis, became a fundamentally different intellectual
entity. In Darwin's pangenesis, gemmules move from