Overview: Life Sciences 1900-1949

Previous Period

Three giants of nineteenth-century life sciences set the stage for many of the biological investigations undertaken in the first half of the twentieth century. Charles Darwin's (1809-1882) On the Origin of Species (1859) established the theory of evolution by natural selection and focused attention on questions of how organisms are related to each other and how life on earth has changed over time. Claude Bernard's (1813-1878) research in physiology, particularly on the chemical functioning of animal tissue, and his writings advocating the experimental method helped make biology less of a purely observational science in which most emphasis was placed on classification and on describing the anatomy of organisms. Because of Bernard's influence, biology became more experimental in the twentieth century. Louis Pasteur's (1822-1895) research on infectious disease and on the chemistry of microbes made careful microscopic and biochemical studies more crucial to the biological sciences.

Genetics and Evolution

Gregor Mendel (1822-1884) was another important biologist of the nineteenth century, but his work remained unknown for years, having been published in an obscure journal in 1869. His research on heredity in pea plants was rediscovered in 1900, and when related to the work of contemporary geneticists, led to the development of modern genetics, the study of how traits are passed on from one generation to the next. Thomas Hunt Morgan (1866-1945) and his coworkers used fruit flies with particular mutations (hereditary defects) to discover the position of genes on chromosomes, the structures in cells that had been identified as the probable seat of genetic material. Also working with fruit flies, Hermann Muller (1890-1967) discovered in 1927 that mutations can be caused by X-rays, demonstrating that such mutations are es sentially chemical changes and indicating the dangers of X-rays.

More theoretical work in genetics, particularly the development of statistical techniques by Ronald Fisher (1890-1962) and others on how rapidly a mutation could become common in a population, provided crucial information for relating genetics to the theory of evolution. This was an important contribution to what became known as the Modern Evolutionary Synthesis, which developed in the 1930s and 1940s. This synthesis was based on work not only in genetics, but also in ecology, paleontology (the study of fossils), and taxonomy (classification). All contributed to the idea that natural selection acting on random genetic variations could explain evolutionary change, and thus provided substantial support for Darwin's theory of evolution.

Developmental and Cellular Biology

Embryology, the study of the development of multi-cellular organisms, was one area of biology where a great deal of experimentation was done in the first half of the century. For example, Hans Spemann (1869-1941) found that tissue he called the "organizer," when transplanted from one embryo into another, could induce the recipient embryo to develop a whole new nervous system. There was also a strong focus on the composition and function of chromosomes, the structures that biologists linked with heredity since they seemed to reproduce and be passed on from one cellular generation to the next. Biologists also linked sex determination to specific chromosomes, which they designated the sex chromosomes. In an important discovery that set the stage for the development of genetics in the second half of the twentieth century, in 1944 Oswald Avery (1877-1955) and his coworkers identified DNA as the genetic material in bacterial chromosomes. This led to further research establishing DNA as the basis of heredity in all organisms.

Many other biochemical studies also contributed to the understanding of cellular processes. Fritz Lipmann (1899-1986) found that adenosine triphosphate (ATP) was an important energy molecule in the cell, and Hans Krebs (1900-1981) worked out the details of the citric acid or Krebs cycle, explaining how the chemical energy in sugar is transferred to ATP. Plant chemistry was also being explored, with the discovery of plant hormones that controlled many developmental processes and the identification of chlorophyll as the molecule that absorbs the Sun's energy in photosynthesis.

In terms of structural biology, Wendell Stanley (1904-1971) was the first to define the nature and organization of a virus in his research on the tobacco mosaic virus. This followed earlier work identifying bacteriophages as viruses that infect bacteria. Bacteriophages were later used in studies on genetics because they were so small and simple. For the much larger animal cells, James Gray (1891-1975) helped to establish the field of cytology, the study of cell structures, functions, and pathology. With the development of the electron microscope in the 1930s and 1940s, it finally became possible to look at viruses as well as to see much more clearly the intricate structures of cells.

Behavioral Biology

At the very beginning of the century, Santiago Ramón y Cajal (1852-1934) discovered that the nervous system was made up of a network of individual cells that do not touch, but instead send signals across microscopic gaps (synapses). Twenty years later, Otto Loewi (1873-1961) identified acetylcholine as one of the chemical signals that cross synapses. In other work on the nervous system, Charles Sherrington (1857-1952) discovered reflex arcs, in which nerve cells carry impulses into the spinal cord where other impulses are triggered that go directly out to the source of the stimulus, bypassing the brain. The other great control system of the body, the endocrine system, which releases hormones, also received a great deal of attention. William Bayliss (1860-1924) and Ernest Starling (1866-1927) discovered the first hormone, secretin, in 1902 and showed that it was involved in stimulating the secretion of digestive juices. Walter Cannon (1871-1945), one of the great physiologists of the twentieth century, found the connection between several hormones and the emotions.

It was during the first half of the twentieth century that ethology (the study of animal behavior) developed as a significant area of research in biology. Karl von Frisch (1886-1982) discovered that bees communicate through specific movements or "dances." Konrad Lorenz (1903-1989) studied imprinting in geese: the first thing they see when they hatch, usually the mother, is imprinted on their brains as the object to rigidly follow. Research was also done in behavioral ecology, the study of social insects and animal societies. The investigation of human societies flourished with anthropologists going all over the world to examine the customs of isolated indigenous populations. Franz Boas (1858-1942) studied the Indians of the Pacific Northwest and also the peoples of northern Asia, to whom these Indians are closely related. His student, Margaret Mead (1901-1978), became famous for her work on the Pacific island of Samoa.

Biology and Society

Research on human behavior showed the relevance of biology to societal issues, but during the first half of the twentieth century there were also several cases where the interpretation of biological concepts led to controversy outside of biology. One of the most famous cases was the trial of John Scopes (1900-1970), a biology teacher tried for breaking a Tennessee law that forbade teaching Darwin's theory of evolution. The public attention this trial received showed the extent of anti-evolution sentiment in the United States.

Eugenics, the concept that only those who have "good" genes should be allowed to reproduce, became a popular idea in both the United States and Europe, but by mid-century it had been discredited because of the way the idea was abused in Nazi Germany. In the Soviet Union, the director of the Institute of Genetics, Trofim Lysenko (1898-1976) distorted genetics research for his own purposes, condemning many noted Soviet geneticists and doing long-term harm to this science in his country. But there were also positive steps taken in establishing the relationship of science to society at large, especially in the United States where corporate and government support of science increased and major foundations became important patrons of scientific and medical research. There was also a great deal of agricultural research done by state universities and agro-industries that led to the development of hybrid corn and other enhanced plant strains, improved animal breeds, and the increased use of fertilizers.

The Future

The second half of the twentieth century saw the continuing growth of many areas of biology that had become important early in the century. Genetics blossomed still further after the structure of DNA was discovered in 1953; this led to huge growth in the field of molecular biology, which investigates the molecular basis of genetics. Ecology, which had grown as a science during the early part of the century with the development of such concepts as food webs and organismal communities, became an even more significant part of biology as the environmental movement emerged in the 1960s and 1970s.

ROBERT HENDRICK