The Development of Population Genetics 311data. From 1865 onwards his main focus was study of heredity. Galton’s work is
especially important because he was the first to apply statistical methods to the
study of heredity which in turn led to the growth of biometry, a methodology that
would eventually be used by Fisher in developing the mathematical foundations
of population genetics.
1 EARLY DAYS: THE LAW OF ANCESTRAL HEREDITYIn order to appreciate Galton’s contributions we need to know a few details about
the historical context in which he was working. In theOrigin of Species[1859]
Darwin claimed that species became adapted to their environment through natural
selection acting on heritable variation. One of the fundamental difficulties with the
Darwinian theory of evolution was that it lacked any developed notion of heredity
that could serve as the basis for the operation of selection. Instead the Darwinians
simply assumed that the characteristics of the offspring resulted from a blending of
the characteristics of the parents. Evolution by natural selection was a continuous
and gradual process. But this gave rise to further difficulties: It was unable to
account for “sports” (large variations that occurred in single instances); it could
not explain the increase or decrease in a species’ store of variations, and it provided
no way of determining whether particular characteristics in an individual were due
to heredity or the environment. In other words, the laws governing evolution could
not be given until those governing variation were also known. This was part of
the problem Galton attempted to tackle, and to that extent it was continuous
with the problem that occupied the later Mendelians. Unfortunately a solution to
the problems of heredity transmission yielded a further problem for Darwinism.
The notion of discontinuous variation which was crucial to Galton’s theory of
heredity, and later, Mendelism, was in direct opposition to the continuous variation
that seemed crucial to Darwinism. So, could one reconcile an explanation of the
mechanisms of heredity that was seemingly at odds with fundamental aspects of
evolution by natural selection? It was that issue that later gave rise to population
genetics and the synthesis of Darwinain selection with Mendelian genetics.
Galton’s first paper entitled “Hereditary Talent and Character” [1865] attempted
to show that mental and moral characters of humans are the product of the com-
bined action of natural selection and heredity. The paper outlined a general con-
cept of heredity that involved the continuity of the “germ line” and the need to
explain both resemblance and variability within families and races in general, ideas
that Galton went on to develop in subsequent work over the next thirty five years.
The paper also provided an exposition of what became known as the law of ances-
tral heredity which he understood as supporting his hypothesis of discontinuous
evolution. Based on no obvious data except lists of able men who had able relatives,
the law stated that: “The share a man retains in the constitution of his remote
descendants is inconceivably small. The father transmits, on average, one-half of
his nature, the grandfather one-fourth, the great-grandfather one-eight; the share