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Fisher, R. A. (1890–1962) British Mathematician, Geneticist
Sir R. A. Fisher paved the way for the acceptance of
natural selection as the mechanism of evolution and helped
to make the modern synthesis possible.
Born February 17, 1890, Ronald Aylmer Fisher was a
mathematical prodigy. He was accustomed to solitude, both
because of his upbringing and because he was extremely
nearsighted. Because his doctor had forbidden him to read by
electric light, he had to receive his mathematics tutoring at
Harrow School without the aid of pencil, paper, and blackboard.
He developed the ability to work out complex mathematical
solutions in his head.
He began to attend Cambridge University in 1909, the
centennial of Darwin’s birth and the fiftieth anniversary
of the publication of his most famous work (see Darwin,
Charles; origin of species [book]). Despite the ceremonies
that attended the anniversary, Darwin’s theories did not
meet with widespread acceptance at that time. Nevertheless,
young Fisher was strongly influenced by them.
Fisher was even more strongly influenced by the recent
rediscovery of Mendelian genetics, which were being
investigated by William Bateson, geneticist at Cambridge.
Both from his studies of Mendelian inheritance patterns, and
from his association with the statistician Karl Pearson, Fisher
became well-grounded in the study of statistics. His 1927 book
Statistical Methods for Research Workers was a landmark in
the history of scientific research methods, and he eventually
became one of the giants of statistical theory. He developed
the variance ratio, one of the most widely used statistical
parameters in the world today. This ratio in effect expressed
the variation in a sample that could be explained relative to
the proportion that could not be explained. He developed a
probability table that showed how likely the results were to
be significant, depending on the sample size and the number
of categories. For example, a variance ratio of 3 (three times
as much variation explained as unexplained) might be credible
for a large sample size but not for a small one. As a result of
F
Fisher’s table, scientists no longer need to say that “the results
appear to not be due to chance” but can say something like
“the probability that the results occurred by chance are less
than one percent.” Modern scientific research, and its application
in fields as diverse as space travel, industrial quality control,
and the control of diseases, would scarcely be possible
without the statistical tools pioneered by Fisher. The variance
ratio is called the F ratio, after Fisher.
Fisher was one of the founding fathers of population
genetics (see also Haldane, J. B. S.; Wright, Sewall).
Fisher demonstrated mathematically how Mendelian genetics,
which had previously been considered anti-Darwinian,
fit together with Darwinian natural selection, as proclaimed
in the title of his 1930 book The Genetical Theory of Natural
Selection. The concept of “fitness,” which had previously
been vague, was given a precise mathematical definition. His
equations made some oversimplifications—for example, he
assumed that each gene had an independent effect on the phenotype,
rather than interacting with other genes—but were
more advanced than anything that had gone before. His equations
also showed that even the smallest fitness advantages,
over enough time, allowed natural selection to produce big
effects. At the same time he demonstrated that it was small
mutations, not large ones, that caused evolutionary change in
populations.
Fisher’s interest in genetics spilled over into a passion
for eugenics, especially from his association with Charles
Darwin’s son, Major Leonard Darwin. Fisher came to believe
that natural selection was weakened as a result of the comforts
of civilization, that the genes of Englishmen were
becoming weaker, which he believed was the reason that
the British Empire was in decline. One of the founders of
eugenics was Darwin’s cousin (see Galton, Francis), who
was also an expert in statistics, which made it appeal even
more to Fisher. Fisher noted with alarm that the upper class
in British society had fewer offspring than the lower classes.
He put his eugenic theories (with himself at the top, despite