Reprinted by permission of Daedalus, Journal of the American Academy of Arts and Sciences, from the issue entitled, “Science in Culture,” Winter 1998, Vol. 127, No. 1.

The central theme of the Enlightenment, enhanced across three centuries by the natural sciences, is that the phenomena tangible to the human mind can be rationally explained by cause and effect. Thus humanity can–all on its own–know; and by knowing, understand; and by understanding, choose wisely.

The idea is amplified by what Gerald Holton has called the Ionian Enchantment, the conviction that all tangible phenomena share a common material base and are reducible to the same general laws of nature. The roots of the Enchantment reach to the beginnings of Western science in the sixth century BC, when Thales of Miletus, in Ionia, considered by Aristotle to be the founder of the physical sciences, proposed that all substances are composed ultimately of water. Although the hypothesis was spectacularly wrong, the ambition it expressed–to attain the broadest possible generalization in cause-and-effect explanations–was destined to become the driving force of Western science.

The success of the scientific revolution may make this perception now appear trivially obvious. Surely, it will seem to many, coherent cause-and-effect explanation is an inevitable consequence of logical thought. But to see otherwise it is only necessary to examine the history of Chinese science. From the first through the thirteenth centuries, as Europe passed from late antiquity through the Dark Ages, science in China flourished. It kept pace with Arab science, even though geographic isolation deprived Chinese scholars of the ready-made base that Greek culture provided their Western counterparts. The Chinese made brilliant advances in subjects such as descriptive astronomy, mathematics, and chemistry. But they never acquired the habit of reductive analysis in search of general laws that served Western science so well from the seventeenth century on. They consequently failed to expand their conception of space and time beyond what was attainable by direct observation with the unaided senses. The reason, according to Joseph Needham, the principal Western chronicler of the subject, was their emphasis on the holistic properties and harmonious relationships of observable entities, from stars to trees to grains of sand.

Unlike Western scientists, they had no inclination to search for abstract codified law in nature. Their reluctance was stimulated to some degree by the historic rejection of the Legalists, who attempted to impose rigid, quantified law during the transition from feudalism to bureaucracy in the fourth century BC But of probably greater importance was the fact that the Chinese steered away from the idea of a supreme being who created and supervises a rational, law-governed universe. If there is such a ruler in charge, it makes sense–Western sense at least–to read a divine plan and code of laws into physical existence. If, on the other hand, no such ruler exists, it seems more appropriate to search for separate rules and harmonious relations among the diverse entities composing the material universe. In summary, it can be said that Western scholars but not their Chinese counterparts hit upon the more fortunate metaphysics among the two most available to address the physical universe.

Western scientists also succeeded because they believed that the abstract laws of the various disciplines in some manner interlock. A useful term to capture this idea is consilience. The expression is more serviceable than coherence or interconnectedness because the rarity of its usage has preserved its original meaning, whereas coherence and interconnectedness have acquired many meanings scattered among a plethora of contexts. William Whewell, in his 1840 synthesis The Philosophy of the Inductive Sciences, introduced consilience as literally a “jumping together” of facts and theory to form a common network of explanation across the scientific disciplines. He said, “The Consilience of Inductions takes place when and Induction, obtained from one class of facts, coincides with an Induction, obtained from another different class. This Consilience is a test of the truth of the Theory in which it occurs.”

Consilience proved to be the light and way of the natural sciences. Physics, with its astonishing congruity to mathematics, came to undergird chemistry, which in turn proved foundational for biology. The successful union was not just a broad theoretical consistency, as articulated by Whewell, but an exact folding of principles pertaining to more complex and particular systems into the principles for simpler and more general systems. Organisms, it came to pass, can be reduced to molecules whose properties are entirely comformable to the laws of chemistry, and the elements to which the molecules are composed are in turn conformable to the laws of quantum physics.

To place the organization of modern science in clearer perspective, the disciplines can be tied to the position that their entities occupy in the scale of space and time, while noting that each class of entities represents a level of organization determined by the ensemble of other entities composing them and located lower on the space-time scale.

The consilient view of the natural world is illustrated by the use of the space-time scale to define the disciplines of biology:

Evolutionary space-time. Over many generations entire populations of organisms undergo evolution, which at the most elemental level is a change in the frequencies of the genes in the organisms that compose the populations. The foremost cause of evolution is natural selection, the differential survival and reproduction of the competing genes–or, put more precisely, the differential survival and reproduction of the organisms whose traits are determined by the genes. Natural selection occurs when populations interact with their environment. The subdiscipline broadly covering the phenomena in this segment of space-time is evolutionary biology.

Ecological space-time. Evolution by changes in gene frequency is coarse grained: It becomes apparent only when the history of an entire population is watched across generations. The process of natural selection driving it is finer grained, comprising particular events that affect the birth, reproduction, and death of individual organisms. These are events that can be observed only in a more constricted space and during shorter periods of time, usually the span of a season or less, than is the case for genetic evolution. They are addressed by the discipline of ecology. (Ecology is often put under the rubric of evolutionary biology, then that subject is broadly defined.)

Organismic space-time. Natural selection acts on the anatomy, physiology, and behavior of organisms whose programs of development are prescribed by genes. These properties usually occupy millimeters to meters in space and seconds to hours in time. The subdiscipline treating them is organismic biology.

Cellular space-time. The anatomy, physiology, and behavior or organisms are aggregated phenomena of cells and tissues. Covering micrometers to centimeters, and milliseconds to full generations, they are the province of cellular and developmental biology.

Biochemical space-time. The development and function of cells and tissues are themselves the aggregate products of highly organized systems of molecules. At this latter level, space ranges from nanometers to millimeters, and time usually from nanoseconds to minutes. The responsible discipline is molecular biology.