The 100 Most Influential Scientists of All Time (23 page)

Although he made contributions to many fields of knowledge, eugenics remained Galton's fundamental interest, and he devoted the latter part of his life chiefly to propagating the idea of improving the physical and mental makeup of the human species by selective parenthood. Galton, a cousin of Charles Darwin, was among the first to recognize the implications for mankind of Darwin's theory of evolution. He saw that it invalidated much of contemporary theology and that it also opened possibilities for planned human betterment. Galton coined the word eugenics to denote scientific endeavours to increase the proportion of persons with better than average genetic endowment through selective mating of marriage partners. In his
Hereditary Genius
(1869), in which he used the word genius to denote “an ability that was exceptionally
high and at the same time inborn,” his main argument was that mental and physical features are equally inherited—a proposition that was not accepted at the time.

It is surprising that when Darwin first read this book, he wrote to the author: “You have made a convert of an opponent in one sense for I have always maintained that, excepting fools, men did not differ much in intellect, only in zeal and hard work.” This book doubtless helped Darwin to extend his evolution theory to man. Galton, unmentioned in
Origin of Species
(1859), is several times quoted in Darwin's
Descent of Man
(1871). Galton's conviction that mental traits are no less inherited than are physical characteristics was strong enough to shape his personal religious philosophy. “We cannot doubt,” he wrote, “the existence of a great power ready to hand and capable of being directed with vast benefit as soon as we have learned to understand and apply it.”

Galton's
Inquiries into Human Faculty
(1883) consists of some 40 articles varying in length from 2 to 30 pages, which are mostly based on scientific papers written between 1869 and 1883. The book can in a sense be regarded as a summary of the author's views on the faculties of man. On all his topics, Galton has something original and interesting to say, and he says it with clarity, brevity, distinction, and modesty. Under the terms of his will, a eugenics chair was established at the University of London.

In the 20th century Galton's name has been mainly associated with eugenics. Insofar as eugenics takes primary account of
inborn
differences between human beings, it has come under the suspicion of those who hold that cultural (social and educational) factors heavily outweigh inborn, or biological, factors in their contribution to
human differences. Eugenics is accordingly often treated as an expression of class prejudice, and Galton as a reactionary. Yet to some extent this view misrepresents his thought, for his aim was not the creation of an aristocratic elite but of a population consisting entirely of superior men and women. His ideas, like those of Darwin, were limited by a lack of an adequate theory of inheritance; the rediscovery of the work of Mendel came too late to affect Galton's contribution in any significant way.

(b. July 22, 1822, Heinzendorf, Austria [now Hynčice, Czech Rep.]—d. Jan. 6, 1884, Brünn, Austria-Hungary [now Brno, Czech Rep.])

A
ustrian botanist, teacher, and Augustinian prelate Gregor Mendel was the first to lay the mathematical foundation of the science of genetics, in what came to be called Mendelism.

As his father's only son, Mendel was expected to take over the small family farm, but he chose instead to enter the Altbrünn monastery as a novitiate of the Augustinian order, where he was given the name Gregor (his birth name was Johann).

The move to the monastery took him to Brünn, the capital of Moravia, where Mendal was introduced to a diverse and intellectual community. Abbot Cyril Napp found him a substitute-teaching position at Znaim (Znojmo, Czech Rep.), where he proved very successful. However, in 1850, Mendel failed an exam—introduced through new legislation for teacher certification—and was sent to the University of Vienna for two years to benefit from a new program of scientific instruction. Mendel
devoted his time at Vienna to physics and mathematics, working under Austrian physicist Christian Doppler and mathematical physicist Andreas von Ettinghausen. He also studied the anatomy and physiology of plants and the use of the microscope under botanist Franz Unger, an enthusiast for the cell theory and a supporter of the developmentalist (pre-Darwinian) view of the evolution of life.

In the summer of 1853, Mendel returned to the monastery in Brünn, and in the following year he was again given a teaching position, this time at the Brünn
Realschule
(secondary school), where he remained until elected abbot 14 years later. These years were his greatest in terms of success both as teacher and as consummate experimentalist.

In 1854, Abbot Cyril Napp permitted Mendel to plan a major experimental program in hybridization at the monastery. The aim of this program was to trace the transmission of hereditary characters in successive generations of hybrid progeny. Previous authorities had observed that progeny of fertile hybrids tended to revert to the originating species, and they had therefore concluded that hybridization could not be a mechanism used by nature to multiply species—though in exceptional cases some fertile hybrids did appear not to revert (the so-called “constant hybrids”). On the other hand, plant and animal breeders had long shown that crossbreeding could indeed produce a multitude of new forms. The latter point was of particular interest to landowners, including the abbot of the monastery, who was concerned about the monastery's future profits from the wool of its Merino sheep, owing to competing wool being supplied from Australia.

Mendel chose to conduct his studies with the edible pea (
Pisum sativum
) because of the numerous distinct
varieties, the ease of culture and control of pollination, and the high proportion of successful seed germinations. From 1854 to 1856 he tested 34 varieties for constancy of their traits. In order to trace the transmission of characters, he chose seven traits that were expressed in a distinctive manner, such as plant height (short or tall) and seed colour (green or yellow). He referred to these alternatives as contrasted characters, or character-pairs. He crossed varieties that differed in one trait—for instance, tall crossed with short. The first generation of hybrids (F
₁
) displayed the character of one variety but not that of the other. In Mendel's terms, one character was dominant and the other recessive.

In the numerous progeny that he raised from these hybrids (the second generation, F
₂
), however, the recessive character reappeared, and the proportion of offspring bearing the dominant to offspring bearing the recessive was very close to a 3 to 1 ratio. Study of the descendants (F
₃
) of the dominant group showed that one-third of them were true-breeding and two-thirds were of hybrid constitution. The 3:1 ratio could hence be rewritten as 1:2:1, meaning that 50 percent of the F
₂
generation were true-breeding and 50 percent were still hybrid. This was Mendel's major discovery, and it was unlikely to have been made by his predecessors, since they did not grow statistically significant populations, nor did they follow the individual characters separately to establish their statistical relations.

Mendel's approach to experimentation came from his training in physics and mathematics, especially combinatorial mathematics. The latter served him ideally to represent his result. If
A
represents the dominant characteristic and
a
the recessive, then the 1:2:1 ratio recalls the terms in the expansion of the binomial equation:

(
A
+
a
)
²
=
A
²
+ 2
Aa
+
a
²

Mendel realized further that he could test his expectation that the seven traits are transmitted independently of one another. Crosses involving first two and then three of his seven traits yielded categories of offspring in proportions following the terms produced from combining two binomial equations, indicating that their transmission was independent of one another. Mendel's successors have called this conclusion the law of independent assortment.

Mendel went on to relate his results to the cell theory of fertilization, according to which a new organism is generated from the fusion of two cells. In order for pure breeding forms of both the dominant and the recessive type to be brought into the hybrid, there had to be some temporary accommodation of the two differing characters in the hybrid as well as a separation process in the formation of the pollen cells and the egg cells. In other words, the hybrid must form germ cells bearing the potential to yield either the one characteristic or the other. This has since been described as the law of segregation, or the doctrine of the purity of the germ cells. Since one pollen cell fuses with one egg cell, all possible combinations of the differing pollen and egg cells would yield just the results suggested by Mendel's combinatorial theory.

Mendel first presented his results in two separate lectures in 1865 to the Natural Science Society in Brünn. His paper “Experiments on Plant Hybrids” was published in the society's journal, V
erhandlungen des naturforschenden Vereines in Brünn
, the following year. It attracted little attention, although many libraries received it and reprints were sent out. The tendency of those who read it was to conclude that Mendel had simply demonstrated more accurately what was already widely assumed—namely,
that hybrid progeny revert to their originating forms. They overlooked the potential for variability and the evolutionary implications that his demonstration of the recombination of traits made possible. Mendel appears to have made no effort to publicize his work, and it is not known how many reprints of his paper he distributed.

In 1900, Dutch botanist and geneticist Hugo de Vries, German botanist and geneticist Carl Erich Correns, and Austrian botanist Erich Tschermak von Seysenegg independently reported results of hybridization experiments similar to Mendel's, though each later claimed not to have known of Mendel's work while doing their own experiments. However, both de Vries and Correns had read Mendel earlier—Correns even made detailed notes on the subject—but had forgotten. De Vries had a diversity of results in 1899, but it was not until he reread Mendel in 1900 that he was able to select and organize his data into a rational system. Tschermak had not read Mendel before obtaining his results, and his first account of his data offers an interpretation in terms of hereditary potency. He described the 3:1 ratio as an “unequal valancy” (
Wertigkeit
). In subsequent papers he incorporated the Mendelian theory of segregation and the purity of the germ cells into his text.

In Great Britain, biologist William Bateson became the leading proponent of Mendel's theory. Around him gathered an enthusiastic band of followers. However, Darwinian evolution was assumed to be based chiefly on the selection of small, blending variations, whereas Mendel worked with clearly nonblending variations. Bateson soon found that championing Mendel aroused opposition from Darwinians. He and his supporters were called Mendelians,
and their work was considered irrelevant to evolution. It took some three decades before the Mendelian theory was sufficiently developed to find its rightful place in evolutionary theory.

The distinction between a characteristic and its determinant was not consistently made by Mendel or by his successors, the early Mendelians. In 1909, Danish botanist and geneticist Wilhelm Johannsen clarified this point and named the determinants genes. Four years later, American zoologist and geneticist Thomas Hunt Morgan located the genes on the chromosomes, and the popular picture of them as beads on a string emerged. This discovery had implications for Mendel's claim of an independent transmission of traits, for genes close together on the same chromosome are not transmitted independently. Today the gene is defined in several ways, depending upon the nature of the investigation. Genetic material can be synthesized, manipulated, and hybridized with genetic material from other species, but to fully understand its functions in the whole organism, an understanding of Mendelian inheritance is necessary. As the architect of genetic experimental and statistical analysis, Mendel remains the acknowledged father of genetics.

(b. Dec. 27, 1822, Dole, France—d. Sept. 28, 1895, Saint-Cloud, near Paris)

F
rench chemist and microbiologist Louis Pasteur made some of the most varied and valuable discoveries in the history of science and industry. It was he who proved that microorganisms cause fermentation and disease; he who pioneered the use of vaccines for rabies, anthrax, and chicken cholera; he who saved the beer, wine, and silk industries of France and other countries; he who performed
important pioneer work in stereochemistry; and he who originated the process known as pasteurization.

Pasteur made his first important contribution to science on May 22, 1848, when he presented before the Paris Academy of Sciences a paper reporting a remarkable discovery—that certain chemical compounds were capable of splitting into a “right” component and a “left” component, one component being the mirror image of the other. His discoveries arose out of a crystallographic investigation of tartaric acid, an acid formed in grape fermentation that is widely used commercially, and racemic acid—a new, hitherto unknown acid that had been discovered in certain industrial processes in the Alsace region. Both acids not only had identical chemical compositions but also had the same structure; yet they showed marked differences in properties. Pasteur found that, when separated, the two types of crystals rotated plane polarized light to the same degree but in opposite directions (one to the right, or clockwise, and the other to the left, or counterclockwise). One of the two crystal forms of racemic acid proved to be identical with the tartaric acid of fermentation.