Philosophy of Biology

The Development of Population Genetics 315

from one position of organic stability to another. Proponents of saltation, par-
ticularly Galton, claimed that evolution could never progress by small continuous
changes of the sort characterised by Darwinism because there would be continual
regression to the mean. These different views about the nature of heredity and
evolutionary progress are, quite clearly, biological hypotheses that can be distin-
guished from the issue of statistical data analysis introduced by Galton and further
developed by Pearson and Weldon. The latter is concerned with devising methods
for predicting how traits will be distributed in future generations, something that
needn’t be associated with any specific biological theory of heredity.

2 STATISTICAL DARWINISM VS. MENDELIAN FACTORS

This distancing between biology and statistics is further evident in the work of
Weldon, Pearson’s colleague and collaborator. Although Weldon’s approach ini-
tially emphasised morphological studies he was a strong proponent of the use of
statistical methods, and claimed that the problem of animal evolution was essen-
tially a statistical problem. Pearson was aware that such analysis required a more
advanced theory of statistics than was currently available, something he went on to
develop in a series of papers written over the next decade. It was this application
of statistical tools designed to measure variability and correlation and the ways
in which these influenced various kinds of selection that defined the new science
of biometry. In that sense then the biometrician’s goal was to develop a purely
statistical theory of evolution devoid of the physiological aspects of heredity that
interested Galton. Like true empiricists the biometrists rejected causal notions
and instead spoke of “coefficients” that would empirically measure heredity based
on such factors as environment, homogomy and natural selection itself. Pearson’s
goal was to redefine the problem of selection as a problem about heredity which
he could then treat from within the theory of correlation. In the hands of Pearson
heredity was nothing other than a correlation coefficient — its true measure was
the numerical correlation between some characteristic or organ as it occurs respec-
tively in parent and offspring. It was similar to a force whose underling causal
mechanism was deemed irrelevant.
Even before the rediscovery of Mendel’s work in 1900, Bateson, who became
the spokesman for Mendelism in Britain, publishedMaterials for the Study of
Variation[1894]. The book was a sustained attack on the Darwinian emphasis on
continuity and its reliance on adaptation as the sole agent responsible for directing
evolution. Bateson argued that evolution should be investigated by uncovering the
process by which new characters were produced by variation. Through his studies
on hybridization he attempted to show how varieties could be distinguished by
the behaviour of unit characters. Although he was unaware of Mendelian ratios
at the time, his later 1902 book, Mendel’s Principles of Heredity, contained a
translation of Mendel’s paper and a strong defense of his laws. In that same year
he also introduced the term “allelomorph” to define the alternative characters in
segregating pairs and used the terms “heterozygote” and “homozygote” to replace