Overview: Life Sciences 1800-1899

Natural history, the description and classification of natural forms, had been the main occupation of life scientists in the eighteenth century, and it expanded dramatically in the nineteenth. Voyages of exploration brought thousands of new plants and animals back to Europe from Africa, the Americas, Asia, and Australia. Improved microscopes revealed hitherto unseen microorganisms and details of anatomy. In addition, geologists began studying fossils systematically, bringing many strange and new organisms to light and giving natural history a truly historical dimension. The organic world proved to be more extensive, old, and diverse than previously imagined.

Despite the exciting findings to come, many naturalists at the turn of the nineteenth century were dissatisfied with their field. A true science, they felt, should not just describe and classify, it should explain things as well. Form, or morphology, needed explaining: Why were there so many plant and animal forms? Why did certain forms exist and not others? Why did some species have internal structures in common? Also, how did species develop and maintain their forms? Function, or physiology, needed explaining, too: How did living things work? How did function relate to form? Further important questions included why species were found in some places and not others (biogeography), how to interpret the fossil record (paleontology), and whether biological theories applied to humans.

This movement to go beyond descriptive natural history gave rise to modern biology. Indeed, the word "biology" was invented in 1800 for the new approach and the problems it addressed. Here is a sampling of the answers and explanations upon which biologists built their science.

Biologists first took Newtonian physics as a model for what scientific explanations should be like. Around 1800 men such as Johann F. Blumenbach (1752-1840) and Carl F. Kielmeyer (1765-1844) tried to explain life processes by means of special forces and laws, the way Isaac Newton had explained the movements of falling objects with the gravitational force and the laws of motion. To explain function, for example, Kielmeyer used such forces as "irritability," which made muscles contract in response to stimuli, or "sensitivity," which acted on the nerves and conveyed sense perception.

In the study of form, the old theory that embryos were preformed and only had to expand and unfold gave way to the idea of a formative force, advanced by Blumenbach, that made embryos take shape in stages. The force obeyed laws dictating the changes the embryos had to go through. Similar reasoning inspired early theories of evolution, which assumed that similar laws and formative forces produced the series of forms in the fossil record.

Evolutionist Jean Baptiste de Lamarck (1744-1829) borrowed his concept of force from the theory that heat and electricity were carried by invisible fluids. (Even today we speak of heat "flow" and electrical "juice.") Some force-bearing fluid, he suggested in 1809, made animals active and changed their forms in response either to the environment or to internal causes.

An influential alternative to the rule of laws and forces was the "idealism" of Karl E. von Baer (1792-1876) and other early morphologists. Idealists assumed that every species or natural group corresponded to an unchanging "idea" that was the model for its form. In his landmark work on embryology (1828), von Baer declared that the idea of the adult animal was present in the embryo and guided its progress. Somehow the end product caused its own development—a doctrine known as "teleology."

Biologists did not remain satisfied with special laws, forces, ideas, and teleology as explanatory devices. There were too many exceptions to the laws and questions about how the forces acted or how the idea caused its own development. They began looking inside the organism for structures and mechanisms that might cause biological processes more directly.

The cell theory of Matthias Schleiden (1804-1881) in 1838 and Theodor Schwann (1810-1882) in 1839 taught that cells were the building blocks of life and that biological explanations should involve observable cellular activity. The movement, growth, and division of cells were to explain the development, growth, and maintenance of plants and animals forms. Gregor Mendel (1822-1884), the founder of genetics, was part of this trend. He did not merely propose laws that predicted what forms would result from cross-breeding and in what ratios. He also showed how the behavior of reproductive cells could explain why the laws worked, if they contained different hereditary factors.

Physiologists studied physical and chemical processes going on in organs, tissues, and cells, and by mid-century, leading physiologists, including Hermann Helmholtz (1821-1894) and Emil DuBois-Reymond (1818-1896), called special, biological laws and "vital forces" unnecessary and unscientific. Studies of respiration and energy metabolism, begun by Helmholtz and others in the 1840s, eventually showed that processes in cells were no different, in principle, from what was observed in test tubes. Research on the electrical nature of nerve function, on fermentation, photosynthesis, and other biochemical processes helped made it clear, by the 1890s, that the laws of physics and chemistry were the only laws biology needed.

A most decisive blow against laws, forces, and teleology was dealt by Charles Darwin (1809-1882). His 1859 theory of natural selection provided a concrete biological mechanism of evolution. The tendency of living things to vary in form, the inevitability of a struggle for life among the variants, and their unequal success in producing offspring, were all observable processes that combined to cause species to change and become better adapted to their environments. The results of variation and selection were unpredictable and therefore could not be explained by laws or teleology. They had to be studied and explained like historical events.

History was the missing piece in many biological puzzles. In biogeography, it explained why similar environments often were populated by different species. Environment alone did not determine which species would live where; the movements and evolutionary changes of species also played a role. In morphology, Darwinism explained similarities among living species and between living and fossil forms by their common family histories, and a generation of morphologists, led by Ernst Haeckel (1834-1919), worked out the basic family trees.

Haeckel and Thomas Huxley (1825-1895) were among the promoters of Darwinian evolution who brought its social and theological consequences before the public. Were the human mind and moral sense products of natural selection like the body? If so, could there be objective moral standards, a soul, or any basis for religion? Could, or should, humans shape their own evolutionary future? Would it improve mankind if society and international relations were as ruthlessly competitive as Nature? Answers varied. Some "social Darwinists" argued that if struggle and selection could improve animals, then it was good for humans, too, and justified economic competition, colonialism, racism, and war. Some engaged in polemics against religion.

Others thought that the ability to cooperate would free us from natural selection and make Darwinism irrelevant in human affairs.

At the end of the century, new research directions re-emphasized the experimental methods of the physiological laboratory and used them to explore the biological questions that Darwinism had made urgent. Chief among them were the physical causes of variation, heredity, and development, as well as the interactions between organisms and their physical environment. Research in these areas laid the groundwork for the twentieth-century disciplines of developmental biology, genetics, cytology, and ecology.

SANDER GLIBOFF