induction leading to the formation of empirical laws could not commence. It was, therefore, the first step in the formation of any science to discover the method or system of measure on which quantitative induction could be founded.
Although various attempts had been made in the eighteenth century by Linnaeus and others to quantify certain aspects of biological research (such as the classification of leaves and reproductive organs in plants), they were all considered, at least by nineteenth century standards, artificial, and therefore not sufficient for the basis of a quantitative science. At the beginning of the nineteenth century, however, two important developments afforded new opportunities for advancing quantitative investigations of organic phenomena. The first was the increased interest in and use of statistics. The second was the discovery of fossils of extinct organisms, whose forms were completely alien from existing flora and fauna, which focused attention on questions about the origin and dispersion of organic forms. In his search of evidence and arguments for The Origin of Species, Darwin was influenced by both of these developments, which inspired him to cultivate quantitative evidence and mathematical arguments to support his theories of variation and evolution.
Though vital statistics (numbers of births and deaths) had been collected since the seventeenth century by religious and political organizations, the number of investigations and degree of attention to their results was limited to very small audiences.2 At the beginning of the nineteenth century, however, social, political, and economic contingencies converged to create what statistical historian Harald Westergaard dubs the “The Era of Enthusiasm” for statistics (136), and Ian Hacking calls a period with “a professional lust for measurement” (5).
There is no single, agreed upon cause for this sudden interest in and collection of statistics. Some historians attribute it to the need to for precise measurement required by the Industrial Revolution, which gathered momentum at the beginning of the nineteenth century (Hacking 5). Others argue that it was the result of a sudden increase in the availability of statistical information that followed the end of the Napoleonic wars (Chatterjee 267). Yet others contend, perhaps most convincingly, that the supply of statistical data increased to meet a greater demand by governments who required quantitative data in order to make better informed political decisions and more persuasive policy arguments (Westergaard 141; Cullen 19–20; Patriarca 13–14). In particular, governments required statistics on birth and death rates as well as the resources of their domain and the domains of other nations to make rational economic policy decisions.
The statistical fever that had grabbed hold of politicians and moral philosophers in the early decades of the nineteenth century also infected geologists and botanists who were exploring the vast biodiversity of the Americas and Australia. Like political economists, they began in earnest to gather quantitative data on organic populations and the conditions under which they thrived. However, unlike their counterparts, the ends for their statistical efforts were affected by important scientific questions raised by new geological theories which assumed a dramatically older earth and grappled with new fossil evidence of organisms unlike any flora or fauna known to Victorian science. These discoveries, which challenged the tenants of the Christian doctrine of creation, encouraged investigations attempting to reconcile, to some extent, the scientific evidence with religious doctrine.
These efforts gave rise to a new field of biogeography, whose aim was to answer fundamental questions about organic populations, including: “What causes influence the thriving or extinction of particular species?”; “What is the distribution of species and genera upon the globe?”; “What is the population of any given species?”; “How can we account for the appearance of new species throughout geological time?”; and “What are the laws by which plants and animals of different parts of the earth differ?”3
Part of the spirit of this new field was that these questions needed to be answered not through classification of organisms and minerals, but rather through the juxtaposition of quantitative facts about climate, population, and location. Alexander von Humboldt, one of the early founders of biogeography, proclaims this goal in Aspect of Nature in Different Lands and Different Climates (1849):
Terrestrial physics have their numerical element, as has the system of the universe, or celestial physics, and by the united labors of botanical travelers we may expect to arrive gradually at a true knowledge of the laws which determine the geographical and climactic distribution of vegetable forms. (108)
The path towards a new biogeographical physics was laid down in works such as Alphonse de Candolle’s “Essai Elementaire de Geographie Botanique” (Elementary Essay on Botanical Geography) (1820), Robert Brown’s General Remarks, Geographic and Systemical, on the Botany of Terra Australis (1814), and Joseph Hooker’s Botany of the Antarctic Voyage, Vol. 2 (1853).4 In their texts, statistics on temperature, elevation, size of organic populations, and the size and distribution of genera and species were used to make arguments bearing on the questions of distribution, variation, origination, etc. of plants and animals.
Robert Brown’s work exemplifies the biogeographer’s efforts to use basic, arithmetical operations and quantified data to compare and make arguments about variation in organic phenomena and the relationship of this variation to geographic and climactic conditions. In the Botany of Terra Australis, for example, Brown tests the assertion commonly held by nineteenth century botanists that dicotyledonous plants outnumber monocotyledonous plants by examining whether climate affects the numbers of either type in the general botanical population: 5
With a view to determine how far the relative propositions of these two classes [dicotyledons and monocotyledons] are influenced by climate, I have examined all the local catalogues or Floras which appear most to be depended on. . . . The general results of this examination are that from the equator to about 30° of latitude, in the northern hemisphere at least, the species of dicotyledonous plants are to monocotyledonous plants as about 5 to 1 . . . and that in the higher latitudes a gradual diminution of dicotyledonous takes place, until at about 60° N. lat. and 55° S. lat. they scarcely equal half their intratropical proportion. (Miscellaneous Botanical Works 8)
In the passage Brown draws on quantitative descriptions of location and previously tabulated statistics on the number of species of each sort of plant as well as calculated ratios to describe the limits of the geographical distribution of dicotyledonous and monocotyledonous plants. He concludes, based on the data and calculations, that dicotyledonous plants are abundant near the equator but become less abundant in northern latitudes. This conclusion provides precise quantitative detail supporting what was otherwise an anecdotal assumption about the difference in dicotyledonous and monocotyledonous plants in the general population of flora. It also supplies new information about the relationship between location and the thriving of dicotyledonous plants, which was previously unknown.
Darwin and the Biogeographers
The quantitative data and mathematical methods used by Brown and other biogeographers inspired Darwin to develop quantitative/mathematical arguments about the phenomena of variation and evolution. Evidence that Darwin was inspired by their methods can be found in his reading habits, in the private thoughts he recorded in his notebooks, and in his letters discussing the construction of his arguments for The Origin of the Species.
A brief assessment of Darwin’s reading habits during the development of The Origin of the Species reveals that Darwin was familiar with the central works of biogeography and read them as he was developing his ideas for his masterwork. He was most likely introduced to them by his mentor John Henslow, who presented him, before he left Cambridge, with Humboldt’s Personal Narrative of Travels to the Equinoctial Regions of the New Continent during the Years 1799–1804 (1814–1829) in which the explorer discusses the importance of quantification in the discovery of natural laws and offers statistics on temperature, altitude, longitude and latitude, etc. for various regions and flora in South and Central America (Schweber 205). It is clear that Darwin read this book and found it important because his copy contains extensive notes. According to the compiler of Darwin’s marginalia, Mario
