316 Margaret Morrison
“hybrid” and “pure type”.
During the period 1889-1900 de Vries was also promoting the idea that hered-
itary qualities were independent units and argued that the species, as the unit of
heredity transmission, should be replaced by unit characters. With the rediscov-
ery of Mendel’s work in 1900 came several reconceptualizations of it, including
disagreements between de Vries and Correns about the extent to which the law of
segregation was applicable. The various details of how Mendel’s work gradually
gave rise to what Bateson termed the science of “genetics” in 1905 are too numer-
ous to document here. However, the main difference centred on the idea that each
hereditary character had a corresponding structure in each individual. In Mendel’s
work there was no such notion; that is to say, no theory that inherited charac-
ters were determined by a finite number of units present in two copies in each
individual, with each one being able to take two alternative forms (alleles). The
identification of the cytological structure of the nucleus with the structure of the
Mendelian crosses was established in 1902 by Walter Sutton (1877-1916) and along
with it came the reinterpretation of Mendel’s schema in terms of physical division
and combination. This became evident by the replacement of Mendel’s original
representation of characters as A, Aa and a, which indicated the appearance of a
trait, with AA, Aa and aa, indicating the germ structure.
In 1902 while the Mendelians were developing and extending the theory of
inheritance Pearson engaged in a debate with Bateson about themethodological
superiority of biometry over Mendelism. Their disagreement about the status of
Mendelism had passed beyond the confines of biology and instead focussed on
the correct techniques for assessing claims about evolutionary development. To
some extent this is not surprising given what we have seen above — Pearson’s
insistence that the problem of evolution is a problem of statistics. But at this
point in the story there seems to be a more powerful strategy emerging. Recall
that Pearson used statistical techniques to argue against Galton’s claim about
discontinuous evolution by showing that it involved a misinterpretation of the
notion of regression. In his debate with Bateson, Pearson refused to accept any
biological arguments or evidence not grounded in biometrical techniques; in other
words, biology, based on experiment (other than the collection of sample data)
had in some sense ceased to become a source of scientific knowledge for Pearson.
In fact, he [1902] went so far as to claim that one could not even have a coherent
notion of discontinuous variation without the employment of biometric methods.
And, because biometric methods gave the kinds of phenotypic relations that could
be observed in nature, the burden of proof was on the Mendelians to show that
a different distribution of variation was the correct one. But, it wasn’t simply
that Biometry supported the status quo. Many of the phenomena that Bateson
claimed could not be biologically detected, such as differentiation between like
organs and between brothers, Pearson claimedcould be detected (where it had
any sensible influence) by biometric methods. Moreover, there wasno other way
of differentiating any kind of variation from normal variation. Without dealing
with the vital statistics of large populations it would be impossible to make any