Evolution: Topic Index

These topics were written by Dr. Francisco Ayala, Professor of Biological Sciences and Philosophy at the University of California, Irvine. He is a member of the President's Committee of Advisors on Science and Technology, and has been President and Chairman of the Board of the American Association for the Advancement of Science.

I advance three propositions. The first is that Darwin's most significant intellectual contribution is that he brought the origin and diversity of organisms into the realm of science. The Copernican Revolution consisted in a commitment to the postulate that the universe is governed by natural laws that account for natural phenomena. Darwin completed the Copernican Revolution by extending that commitment to the living world.

The second proposition is that natural selection is a creative process that can account for the appearance of genuine novelty. How natural selection creates is shown with a simple example and clarified with two analogies, artistic creation and the "typing monkeys," with which it shares important similarities and differences. The creative power of natural selection arises from a distinctive interaction between chance and necessity, or between random and deterministic processes.

The third proposition is that teleological explanations are necessary in order to give a full account of the attributes of living organisms, whereas they are neither necessary nor appropriate in the explanation of natural inanimate phenomena. I give a definition of teleology and clarify the matter by distinguishing between internal and external teleology, and between bounded and unbounded teleology. The human eye, so obviously constituted for seeing but resulting from a natural process, is an example of internal (or natural) teleology. A knife has external (or artificial) teleology, because it has been purposefully designed by an external agent. The development of an egg into a chicken is an example of bounded (or necessary) teleology, whereas the evolutionary origin of the mammals is a case of unbounded (or contingent) teleology, because there was nothing in the make up of the first living cells that necessitated the eventual appearance of mammals.

I conclude that Darwin's theory of evolution and explanation of design does not include or exclude considerations of divine action in the world any more than astronomy, geology, physics, or chemistry do.

The Darwinian Revolution

The publication in 1859 of The Origin of Species by Charles Darwin ushered in a new era in the intellectual history of humanity. Darwin is deservedly given credit for the theory of biological evolution: he accumulated evidence demonstrating that organisms evolve and discovered the process, natural selection, by which they evolve. But the import of Darwin's achievement is that it completed the Copernican revolution initiated three centuries earlier, and thereby radically changed our conception of the universe and the place of humanity in it.

The discoveries of Copernicus, Kepler, Galileo, and Newton in the sixteenth and seventeenth centuries, had gradually ushered in the notion that the workings of the universe could be explained by human reason. It was shown that the earth is not the center of the universe, but a small planet rotating around an average star; that the universe is immense in space and in time; and that the motions of the planets around the sun can be explained by the same simple laws that account for the motion of physical objects on our planet. These and other discoveries greatly expanded human knowledge, but the intellectual revolution these scientists brought about was more fundamental: a commitment to the postulate that the universe obeys immanent laws that account for natural phenomena. The workings of the universe were brought into the realm of science: explanation through natural laws. Physical phenomena could be accounted for whenever the causes were adequately known.

Darwin completed the Copernican revolution by drawing out for biology the notion of nature as a lawful system of matter in motion. The adaptations and diversity of organisms, the origin of novel and highly organized forms, even the origin of humanity itself could now be explained by an orderly process of change governed by natural laws.

The origin of organisms and their marvelous adaptations were, however, either left unexplained or attributed to the design of an omniscient Creator. God had created the birds and bees, the fish and corals, the trees in the forest, and best of all, man. God had given us eyes so that we might see, and He had provided fish with gills to breathe in water. Philosophers and theologians argued that the functional design of organisms manifests the existence of an all-wise Creator. Wherever there is design, there is a designer; the existence of a watch evinces the existence of a watchmaker.

The English theologian William Paley in his Natural Theology (1802) elaborated the argument-from-design as forceful demonstration of the existence of the Creator. The functional design of the human eye, argued Paley, provided conclusive evidence of an all-wise Creator. It would be absurd to suppose, he wrote, that the human eye by mere chance "should have consisted, first, of a series of transparent lenses ... secondly of a black cloth or canvas spread out behind these lenses so as to receive the image formed by pencils of light transmitted through them, and placed at the precise geometrical distance at which, and at which alone, a distinct image could be formed ... thirdly of a large nerve communicating between this membrane and the brain." The Bridgewater Treatises, published between 1833 and 1840, were written by eminent scientists and philosophers to set forth "the Power, Wisdom, and Goodness of God as manifested in the Creation." The structure and mechanisms of man's hand were, for example, cited as incontrovertible evidence that the hand had been designed by the same omniscient Power that had created the world.

The advances of physical science had thus driven humanity's conception of the universe to a split-personality state of affairs, which persisted well into the mid-nineteenth century. Scientific explanations, derived from natural laws, dominated the world of nonliving matter, on the earth as well as in the heavens. Supernatural explanations, depending on the unfathomable deeds of the Creator, accounted for the origin and configuration of living creatures—the most diversified, complex, and interesting realities of the world. It was Darwin's genius to resolve this conceptual schizophrenia.

Darwin's Discovery: Design without Designer

The strength of the argument-from-design to demonstrate the role of the Creator is easily set forth. Wherever there is function or design we look for its author. A knife is made for cutting and a clock is made to tell time; their functional designs have been contrived by a knifemaker and a watchmaker. The exquisite design of Leonardo da Vinci's Mona Lisa proclaims that it was created by a gifted artist following a preconceived purpose. Similarly, the structures, organs, and behaviors of living beings are directly organized to serve certain functions. The functional design of organisms and their features would therefore seem to argue for the existence of a designer. It was Darwin's greatest accomplishment to show that the directive organization of living beings can be explained as the result of a natural process, natural selection, without any need to resort to a Creator or other external agent. The origin and adaptation of organisms in their profusion and wondrous variations were thus brought into the realm of science.

Darwin accepted that organisms are "designed" for certain purposes, i.e., they are functionally organized. Organisms are adapted to certain ways of life and their parts are adapted to perform certain functions. Fish are adapted to live in water, kidneys are designed to regulate the composition of blood, the human hand is made for grasping. But Darwin went on to provide a natural explanation of the design. He thereby brought the seemingly purposeful aspects of living beings into the realm of science.

Darwin's revolutionary achievement is that he extended the Copernican revolution to the world of living things. The origin and adaptive nature of organisms could now be explained, like the phenomena of the inanimate world, as the result of natural laws manifested in natural processes. Darwin's theory encountered opposition in some religious circles, not so much because he proposed the evolutionary origin of living things (which had been proposed before, and accepted even by Christian theologians), but because the causal mechanism, natural selection, excluded God as the explanation for the obvious design of organisms.

The Roman Catholic Church's opposition to Galileo in the seventeenth century had been similarly motivated not only by the apparent contradiction between the heliocentric theory and a literal interpretation of the Bible, but also by the unseemly attempt to comprehend the workings of the Universe, the "mind of God." The configuration of the Universe was no longer perceived as the result of God's Design, but simply the outcome of immanent, blind, processes. There were, however, many theologians, philosophers, and scientists who saw no contradiction then nor see it now between the evolution of species and Christian faith. Some see evolution as the "method of divine intelligence," in the words of the nineteenth century theologian A.H. Strong. Others, like the American contemporary of Darwin, Henry Ward Beecher (1818-1887), made evolution the cornerstone of their theology. These two traditions have persisted to the present. Pope John Paul II has recently (October 1996) stated that "the theory of evolution is more than a hypothesis. It is … accepted by researchers, following a series of discoveries in various fields of knowledge." The views of "process" theologians, who perceive evolutionary dynamics as a pervasive element of a Christian view of the world, are well represented in this volume.

Natural Selection as a Directive Process

The central argument of the theory of natural selection is summarized by Darwin in The Origin of Species as follows:

As more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. ... Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of generations? If such do occur, can we doubt (remembering that more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favorable variation and the rejection of injurious variations, I call Natural Selection.

Darwin's argument addresses the problem of explaining the adaptive character of organisms. Darwin argues that adaptive variations ("variations useful in some way to each being") occasionally appear, and that these are likely to increase the reproductive chances of their carriers. Over the generations favorable variations will be preserved, injurious ones will be eliminated. In one place, Darwin adds: "I can see no limit to this power [natural selection] in slowly and beautifully adapting each form to the most complex relations of life." Natural selection was proposed by Darwin primarily to account for the adaptive organization, or "design," of living beings; it is a process that promotes or maintains adaptation. Evolutionary change through time and evolutionary diversification (multiplication of species) are not directly promoted by natural selection (hence, the so-called "evolutionary stasis," the numerous examples of organisms with morphology that has changed little, if at all, for millions of years, as pointed out by the proponents of the theory of punctuated equilibrium). But change and diversification often ensue as by-products of natural selection fostering adaptation.

Darwin formulated natural selection primarily as differential survival. The modern understanding of the principle of natural selection is formulated in genetic and statistical terms as differential reproduction. Natural selection implies that some genes and genetic combinations are transmitted to the following generations on the average more frequently than their alternates. Such genetic units will become more common in every subsequent generation and their alternates less common. Natural selection is a statistical bias in the relative rate of reproduction of alternative genetic units.

Natural selection has been compared to a sieve which retains the rarely arising useful genes and lets go the more frequently arising harmful mutants. Natural selection acts in that way, but it is much more than a purely negative process, for it is able to generate novelty by increasing the probability of otherwise extremely improbable genetic combinations. Natural selection is thus creative in a way. It does not "create" the entities upon which it operates, but it produces adaptive genetic combinations which would not have existed otherwise.

The creative role of natural selection must not be understood in the sense of the "absolute" creation that traditional Christian theology predicates of the Divine act by which the universe was brought into being ex nihilo. Natural selection may rather be compared to a painter which creates a picture by mixing and distributing pigments in various ways over the canvas. The canvas and the pigments are not created by the artist but the painting is. It is conceivable that a random combination of the pigments might result in the orderly whole which is the final work of art. But the probability of Leonardo's Mona Lisa resulting from a random combination of pigments, or St. Peter's Basilica resulting from a random association of marble, bricks and other materials, is infinitely small. In the same way, the combination of genetic units which carries the hereditary information responsible for the formation of the vertebrate eye could have never been produced by a random process like mutation. Not even if we allow for the three billion years plus during which life has existed on earth. The complicated anatomy of the eye like the exact functioning of the kidney are the result of a nonrandom process—natural selection.

Natural Selection as a Creative Process

Critics have sometimes alleged as evidence against Darwin's theory of evolution examples showing that random processes cannot yield meaningful, organized outcomes. It is thus pointed out that a series of monkeys randomly striking letters on a typewriter would never write The Origin of Species, even if we allow for millions of years and many generations of monkeys pounding at typewriters.

This criticism would be valid if evolution would depend only on random processes. But natural selection is a nonrandom process that promotes adaptation by selecting combinations that "make sense," i.e., that are useful to the organisms. The analogy of the monkeys would be more appropriate if a process existed by which, first, meaningful words would be chosen every time they appeared on the typewriter; and then we would also have typewriters with previously selected words rather than just letters in the keys, and again there would be a process to select meaningful sentences every time they appeared in this second typewriter. If every time words such as "the," "origin," "species," and so on, appeared in the first kind of typewriter, they each became a key in the second kind of typewriter, meaningful sentences would occasionally be produced in this second typewriter. If such sentences became incorporated into keys of a third type of typewriter, in which meaningful paragraphs were selected whenever they appeared, it is clear that pages and even chapters "making sense" would eventually be produced.

We need not carry the analogy too far, since the analogy is not fully satisfactory, but the point is clear. Evolution is not the outcome of purely random processes, but rather there is a "selecting" process, which picks up adaptive combinations because these reproduce more effectively and thus become established in populations. These adaptive combinations constitute, in turn, new levels of organization upon which the mutation (random) plus selection (nonrandom or directional) process again operates.

The manner in which natural selection can generate novelty in the form of accumulated hereditary information may be illustrated by the following example. Some strains of the colon bacterium, Escherichia coli, in order to be able to reproduce in a culture medium, require that a certain substance, the amino acid histidine, be provided in the medium. When a few such bacteria are added to a cubic centimeter of liquid culture medium, they multiply rapidly and produce between two and three billion bacteria in a few hours. Spontaneous mutations to streptomycin resistance occur in normal (i.e., sensitive) bacteria at rates of the order of one in one hundred million (1 x 10-8) cells. In our bacterial culture we expect between twenty and thirty bacteria to be resistant to streptomycin due to spontaneous mutation. If a proper concentration of the antibiotic is added to the culture, only the resistant cells survive. The twenty or thirty surviving bacteria will start reproducing, however, and allowing a few hours for the necessary number of cell divisions, several billion bacteria are produced, all resistant to streptomycin. Among cells requiring histidine as a growth factor, spontaneous mutants able to reproduce in the absence of histidine arise at rates of about four in one hundred million (4 x 10-8) bacteria. The streptomycin resistant cells may now be transferred to a culture with streptomycin but with no histidine. Most of them will not be able to reproduce, but about a hundred will start reproducing until the available medium is saturated.

Natural selection has produced in two steps bacterial cells resistant to streptomycin and not requiring histidine for growth. The probability of the two mutational events happening in the same bacterium is of about four in ten million billion (1 x 10-8 x 4 x 10-8 = 4 x 10-16) cells. An event of such low probability is unlikely to occur even in a large laboratory culture of bacterial cells. With natural selection, cells having both properties are the common result.

As illustrated by the bacterial example, natural selection produces combinations of genes that would otherwise be highly improbable because natural selection proceeds stepwise. The vertebrate eye did not appear suddenly in all its present perfection. Its formation requires the appropriate integration of many genetic units, and thus the eye could not have resulted from random processes alone. The ancestors of today's vertebrates had for more than half a billion years some kind of organs sensitive to light. Perception of light, and later vision, were important for these organisms' survival and reproductive success. Accordingly, natural selection favored genes and gene combinations increasing the functional efficiency of the eye. Such genetic units gradually accumulated, eventually leading to the highly complex and efficient vertebrate eye. Natural selection can account for the rise and spread of genetic constitutions, and therefore of types of organisms, that would never have existed under the uncontrolled action of random mutation. In this sense, natural selection is a creative process, although it does not create the raw materials—the genes—upon which it acts.

Natural Selection as an Opportunistic Process

Natural selection has no foresight, nor does it operate according to some preconceived plan. Rather it is a purely natural process resulting from the interacting properties of physicochemical and biological entities. Natural selection is simply a consequence of the differential multiplication of living beings. It has some appearance of purposefulness because it is conditioned by the environment: which organisms reproduce more effectively depends on what variations they possess that are useful in the environment where the organisms live. In a sense, natural selection is an "opportunistic" process. The variables determining in what direction it will go are the environment, the preexisting constitution of the organisms, and the randomly arising mutations. But natural selection does not anticipate the environments of the future; drastic environmental changes may be insuperable to organisms that were previously thriving.

Adaptation to a given environment may occur in a variety of different ways. An example may be taken from the adaptations of plant life to desert climate. The fundamental adaptation is to the condition of dryness, which involves the danger of desiccation. During a major part of the year, sometimes for several years in succession, there is no rain. Plants have accomplished the urgent necessity of saving water in different ways. Cacti have transformed their leaves into spines, having made their stems into barrels containing a reserve of water; photosynthesis is performed in the surface of the stem instead of in the leaves. Other plants have no leaves during the dry season, but after it rains they burst into leaves and flowers and produce seeds. Ephemeral plants germinate from seeds, grow, flower, and produce seeds—all within the space of the few weeks while rainwater is available; the rest of the year the seeds lie quiescent in the soil.

The opportunistic character of natural selection is also well-evidenced by the phenomenon of adaptive radiation. The evolution of Drosophila flies in Hawaii is a relatively recent adaptive radiation. There are about 1,500 Drosophila species in the world. Approximately 500 of them have evolved in the Hawaiian archipelago, although this has a small area, about one twenty-fifth the size of California. Moreover, the morphological, ecological, and behavioral diversity of Hawaiian Drosophila exceeds that of Drosophila in the rest of the world.

Why should have such "explosive" evolution have occurred in Hawaii? The overabundance of drosophila flies there contrasts with the absence of many other insects. The ancestors of Hawaiian drosophila reached the archipelago before other groups of insects did, and thus they found a multitude of unexploited opportunities for living. They responded by a rapid adaptive radiation; although they are all probably derived from a single colonizing species, they adapted to the diversity of opportunities available in diverse places or at different times by developing appropriate adaptations, which range broadly from one to another species.

The process of natural selection can explain the adaptive organization of organisms; as well as their diversity and evolution as a consequence of their adaptation to the multifarious and ever changing conditions of life. The fossil record shows that life has evolved in a haphazard fashion. The radiations, expansions, relays of one form by another, occasional but irregular trends, and the ever present extinctions, are best explained by natural selection of organisms subject to the vagaries of genetic mutation and environmental challenge. The scientific account of these events does not necessitate recourse to a preordained plan, whether imprinted from without by an omniscient and all-powerful designer, or resulting from some immanent force driving the process towards definite outcomes. Biological evolution differs from a painting or an artifact in that it is not the outcome of a design preconceived by an artist or artisan.

Chance and Necessity

Natural selection accounts for the "design" of organisms, because adaptive variations tend to increase the probability of survival and reproduction of their carriers at the expense of maladaptive, or less adaptive, variations. The arguments of Aquinas or Paley against the incredible improbability of chance accounts of the origin of organisms are well taken as far as they go. But neither these scholars, nor any other authors before Darwin, were able to discern that there is a natural process (namely, natural selection) that is not random but rather is oriented and able to generate order or "create." The traits that organisms acquire in their evolutionary histories are not fortuitous but determined by their functional utility to the organisms.

Chance is, nevertheless, an integral part of the evolutionary process. The mutations that yield the hereditary variations available to natural selection arise at random, independently of whether they are beneficial or harmful to their carriers. But this random process (as well as others that come to play in the great theatre of life) is counteracted by natural selection, which preserves what is useful and eliminates the harmful. Without mutation, evolution could not happen because there would be no variations that could be differentially conveyed from one to another generation. But without natural selection, the mutation process would yield disorganization and extinction because most mutations are disadvantageous. Mutation and selection have jointly driven the marvelous process that starting from microscopic organisms has spurted orchids, birds, and humans.

The theory of evolution manifests chance and necessity jointly intricated in the stuff of life; randomness and determinism interlocked in a natural process that has spurted the most complex, diverse, and beautiful entities in the universe: the organisms that populate the earth, including humans who think and love, endowed with free will and creative powers, and able to analyze the process of evolution itself that brought them into existence. This is Darwin's fundamental discovery, that there is a process that is creative though not conscious. And this is the conceptual revolution that Darwin completed: that everything in nature, including the origin of living organisms, can be accounted for as the result of natural processes governed by natural laws. This is nothing if not a fundamental vision that has forever changed how humanity perceives itself and its place in the universe.

Teleology and Teleological Explanations

Explanation by design, or teleology, is "the use of design, purpose, or utility as an explanation of any natural phenomenon" (Webster's Third New International Dictionary, 1966). An object or a behavior is said to be teleological when it gives evidence of design or appears to be directed toward certain ends. For example, the behavior of human beings is often teleological. A person who buys an airplane ticket, reads a book, or cultivates the earth is trying to achieve a certain end: getting to a given city, acquiring knowledge, or getting food. Objects and machines made by people also are usually teleological: a knife is made for cutting, a clock is made for telling time, a thermostat is made to regulate temperature. Similarly features of organisms are teleological as well: a bird's wings are for flying, eyes are for seeing, kidneys are constituted for regulating the composition of the blood. The features of organisms that may be said to be teleological are those that can be identified as adaptations, whether they are structures like a wing or a hand, or organs like a kidney, or behaviors like the courtship displays of a peacock. Adaptations are features of organisms that have come about by natural selection because they serve certain functions and thus increase the reproductive success of their carriers.

Inanimate objects and processes (other than those created by people) are not teleological in the sense just explained because we gain no additional scientific understanding by perceiving them as directed toward specific ends or for serving certain purposes. The configuration of a sodium chloride molecule (common salt) depends on the structure of sodium and chlorine, but it makes no sense to say that that structure is made up so as to serve a certain purpose, such as tasting salty. Similarly, the shape of a mountain is the result of certain geological processes, but it did not come about so as to serve a certain purpose, such as providing slopes suitable for skiing. The motion of the earth around the sun results from the laws of gravity, but it does not exist in order that the seasons may occur. We may use sodium chloride as food, a mountain for skiing, and take advantage of the seasons, but the use that we make of these objects or phenomena is not the reason why they came into existence or why they have certain configurations. On the other hand, a knife and a car exist and have particular configurations precisely in order to serve the purposes of cutting and transportation. Similarly, the wings of birds came about precisely because they permitted flying, which was reproductively advantageous. The mating display of peacocks came about because it increased the chances of mating and thus of leaving progeny.

The previous comments point out the essential characteristics of teleological phenomena, which may be encompassed in the following definition: "Teleological explanations account for the existence of a certain feature in a system by demonstrating the feature's contribution to a specific property or state of the system." Teleological explanations require that the feature or behavior contribute to the persistence of a certain state or property of the system: wings serve for flying; the sharpness of a knife serves for cutting. Moreover, and this is the essential component of the concept, this contribution must be the reason why the feature or behavior exists at all: the reason why wings came to be is because they serve for flying; the reason why a knife is sharp is that it is intended for cutting.

The configuration of a molecule of sodium chloride contributes to its property of tasting salty and therefore to its use as food, not vice versa; the potential use of sodium chloride for food is not the reason why it has a particular molecular configuration or tastes salty. The motion of the earth around the sun is the reason why seasons exist; the existence of the seasons is not the reason why the earth moves about the sun. On the other hand, the sharpness of a knife can be explained teleologically because the knife has been created precisely to serve the purpose of cutting. Motorcars and their particular configurations exist because they serve transportation, and thus can be explained teleologically. Many features and behaviors of organisms meet the requirements of teleological explanation. The hand of man, the wings of birds, the structure and behavior of kidneys, the mating displays of peacocks are examples already given.

It is useful to distinguish different kinds of design or teleological phenomena. Actions or objects are purposeful when the end-state or goal is consciously intended by an agent. Thus, a man mowing his lawn is acting teleologically in the purposeful sense; a lion hunting deer and a bird building a nest have at least the appearance of purposeful behavior. Objects resulting from purposeful behavior exhibit artificial (or external) teleology. A knife, a table, a car, and a thermostat are examples of systems exhibiting artificial teleology: their teleological features were consciously intended by some agent.

Systems with teleological features that are not due to the purposeful action of an agent but result from some natural process exhibit natural (or internal) teleology. The wings of birds have a natural teleology; they serve an end, flying, but their configuration is not due to the conscious design of any agent. We may distinguish two kinds of natural teleology: bounded, or determinate or necessary, and unbounded or indeterminate or contingent.

Bounded natural teleology exists when specific end-state is reached in spite of environmental fluctuations. The development of an egg into a chicken is an example of bounded natural teleological process. The regulation of body temperature in a mammal is another example. In general, the homeostatic processes of organisms are instances of bounded natural teleology.

Unbounded design or contingent teleology occurs when the end-state is not specifically predetermined, but rather is the result of selection of one from among several available alternatives. The adaptations of organisms are designed, or teleological, in this indeterminate sense. The wings of birds call for teleological explanation: the genetic constitutions responsible for their configuration came about because wings serve to fly and flying contributes to the reproductive success of birds. But there was nothing in the constitution of the remote ancestors of birds that would necessitate the appearance of wings in their descendants. Wings came about as the consequence of a long sequence of events, where at each stage the most advantageous alternative was selected among those that happened to be available; but what alternatives were available at any one time depended, at least in part, on chance events.

The Compatiblity of Teological and Causal Explanations

Teleological explanations are fully compatible with (efficient) causal explanations. It is possible, at least in principle, to give a causal account of the various physical and chemical processes in the development of an egg into a chicken, or of the physicochemical, neural, and muscular interactions involved in the functioning of the eye. (I use the "in principle" clause to imply that any component of the process can be elucidated as a causal process if it is investigated in sufficient detail and in depth; but not all steps in almost any developmental process have been so investigated, with the possible exception of the flatworm Caenorhabditis elegans. The development of Drosophila fruitflies has also become known in much detail, even if not yet completely.) It is also possible in principle to describe the causal processes by which one genetic variant becomes eventually established in a population by natural selection. But these causal explanations do not make it unnecessary to provide teleological explanations where appropriate. Both teleological and causal explanations are called for in such cases.

Paley's claim that the design of living beings evinces the existence of a Designer was shown to be erroneous by Darwin's discovery of the process of natural selection, just as the pre-Copernican explanation for the motions of celestial bodies (and the argument for the existence of God based on the unmoved mover) was shown to be erroneous by the discoveries of Copernicus, Galileo, and Newton. There is no more reason to consider anti-Christian Darwin's theory of evolution and explanation of design than to consider anti-Christian Newton's laws of motion. Divine action in the Universe must be sought in ways other than those that postulate it as the means to account for gaps in the scientific account of the workings of the Universe.

The Copernican and Darwinian revolutions have jointly brought all natural objects and processes as subjects of scientific investigation. Is there any important missing link in the scientific account of natural phenomena? I believe there is, namely, the origin of the universe. The creation or origin of the universe involves a transition from nothing into being. But a transition can only be scientifically investigated if we have some knowledge about the states or entities on both sides of the boundary. Nothingness, however, is not a subject for scientific investigation or understanding. Therefore, as far as science is concerned, the origin of the universe will remain forever a mystery.

Coda: Science as a Way of Knowing

Science is a wondrously successful way of knowing. Science seeks explanations of the natural world by formulating hypotheses that are subject to the possibility of empirical falsification or corroboration. A scientific hypothesis is tested by ascertaining whether or not predictions about the world of experience derived as logical consequences from the hypothesis agree with what is actually observed. Science as a mode of inquiry into the nature of the universe has been successful and of great consequence. Witness the proliferation of science academic departments in universities and other research institutions, the enormous budgets that the body politic and the private sector willingly commit to scientific research, and its economic impact. The Office of Management and the Budget (OMB) of the U.S. government has estimated that fifty percent of all economic growth in the United States since the Second World War can directly be attributed to scientific knowledge and technical advances. The technology derived from scientific knowledge pervades, indeed, our lives: the high-rise buildings of our cities, thruways and long span-bridges, rockets that bring men to the moon, telephones that provide instant communication across continents, computers that perform complex calculations in millionths of a second, vaccines and drugs that keep bacterial parasites at bay, gene therapies that replace DNA in defective cells. All these remarkable achievements bear witness to the validity of the scientific knowledge from which they originated.

Scientific knowledge is also remarkable in the way it emerges by way of consensus and agreement among scientists, and in the way new knowledge builds upon past accomplishment rather than starting anew with each generation or each new practitioner. Surely scientists disagree with each other on many matters; but these are issues not yet settled, and the points of disagreement generally do not bring into question previous knowledge. Modern scientists do not challenge that atoms exist, or that there is a universe with a myriad stars, or that heredity is encased in the DNA.

Science is a way of knowing, but it is not the only way. Knowledge also derives from other sources, such as common sense, artistic and religious experience, and philosophical reflection. In The Myth of Sisyphus, the great French writer Albert Camus asserted that we learn more about ourselves and the world from a relaxed evening’s perception of the starry heavens and the scents of grass than from science’s reductionistic ways. The validity of the knowledge acquired by non-scientific modes of inquiry can be simply established by pointing out that science dawned in the sixteenth century, but humanity had for centuries built cities and roads, brought forth political institutions and sophisticated codes of law, advanced profound philosophies and value systems, and created magnificent plastic art, as well as music and literature. We thus learn about ourselves and about the world in which we live and we also benefit from products of this non-scientific knowledge. The crops we harvest and the animals we husband emerged millennia before science's dawn from practices set down by farmers in the Middle East, Andean sierras, and Mayan plateaus.

It is not my intention in this section to belabor the extraordinary fruits of nonscientific modes of inquiry. But I have set forth the view that nothing in the world of nature escapes the scientific mode of knowledge, and that we owe this universality to Darwin's revolution. Here I wish simply to state something that is obvious, but becomes at times clouded by the hubris of some scientists. Successful as it is, and universally encompassing as its subject is, a scientific view of the world is hopelessly incomplete. There are matters of value and meaning that are outside science's scope. Even when we have a satisfying scientific understanding of a natural object of process, we are still missing matters that may well be thought by many to be of equal or greater import. Scientific knowledge may enrich esthetic and moral perceptions, and illuminate the significance of life and the world, but these are matters outside science's realm.

On April 28, 1937, early in the Spanish Civil War, Nazi airplanes bombed the small Basque town of Guernica, the first time that a civilian population had been determinedly destroyed from the air. The Spanish painter Pablo Picasso had recently been commissioned by the Spanish Republican Government to paint a large composition for the Spanish pavilion at the Paris World Exhibition of 1937. In a frenzy of manic energy, the enraged Picasso sketched in two days and fully outlined in ten more days his famous Guernica, an immense painting of 25 feet, 8 inches by 11 feet, 6 inches. Suppose that I now would describe the images represented in the painting, their size and position, as well as the pigments used and the quality of the canvas. This description would be of interest, but it would hardly be satisfying if I had completely omitted esthetic analysis and considerations of meaning, the dramatic message of man's inhumanity to man conveyed by the outstretched figure of the mother pulling her killed baby, bellowing faces, the wounded horse or the satanic image of the bull.

Let Guernica be a metaphor of the point I wish to make. Scientific knowledge, like the description of size, materials, and geometry of Guernica, is satisfying and useful. But once science has had its say, there remains much about reality that is of interest, questions of value and meaning that are forever beyond science's scope.