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Over the last two hundred years, the Western world has undergone a remarkable revolution in the way the living and nonliving things in the world are viewed and interpreted. Much of this change in perspective is due to the well-known work of Charles Darwin, who in many respects was the first scientist to break unconditionally with ideas associated with special creation and divine intervention in the origin and progression of life. Yet Darwin did not develop his theory solely on the facts and observations he collected himself. Rather, the development of the theory of evolution is rooted in scientific work carried out by "natural historians" who preceded Darwin by nearly two hundred years. Ironically, these sixteenth- and seventeenth-century biologists gathered data and wrote treatises for entirely different reasons and under completely different theoretical pretexts.
In the seventeenth century, the standard interpretation of the world centered on the idea of special creation and worldwide stability. Using a literal interpretation of the Old Testament and calculating the generations in it, the Irish Archbishop Ussher (1581-1656) reported that the earth was created in 4004 B.C. Later, John Lightfoot (1602-1675) of Cambridge was even more "precise" and stated that creation took place on October 23 at nine in the morning. Although it may not seem an obvious contribution to the development of evolutionary theory, this straightforward approach of viewing the world in a "rational" way signals a fundamental reason that Darwinism developed at all. The rational interpretation of the world is a basic tenet of Christianity, and in many respects this concept paved the way for the collection of the basic data used in the evolutionary synthesis. Loren Eiseley has written:
It is surely one of the curious paradoxes of history that science, which professionally has little to do with faith, owes its origins to an act of faith that the universe can be rationally interpreted, and science today is sustained by that fact. (Darwin's Century, p. 62)
Given the ever-present arguments over the creationist and evolutionist interpretations of the past, it is also curious that the concept of evolution has its ultimate roots in the Christian faith. Christianity is fundamentally different from most other religions in that it gives no credence to predestination, that there is only one God to obey (not a pantheon of lesser and often unpredictable deities), that reincarnation is rejected, and that humans have free will and decide on their ultimate destiny. This latter aspect of Christianity leads to what has been called the "germ of curiosity" and to a scientific approach named "logical positivism." Basically, logical positivism is concerned with collecting facts that are verifiable through shared observations. Mystic and supernatural phenomena are not acceptable. Another aspect of logical positivism is its emphasis on observation. Early practitioners believed that if one collected a lot of facts, the facts would order themselves into a logical framework.
Thus, in 1691, John Ray (1627-1705), a devout member of Trinity College in London, published The Wisdom of God Manifested in the Works of Creation. Firmly based in Christianity and following the doctrines of a rational world and logical positivism, Ray gave detailed descriptions of the natural world to glorify the majesty of the creation. Although at the time there was little controversy about the hand of God in the creation, Ray felt that by naming species and documenting their underlying similarities of design, he was collecting solid evidence for the creation. Ray and other natural theologians unwittingly began the movement toward interpreting the world by a noncreationist theory. They collected voluminous facts about the living world, drew conclusions about the similarity in designs, and contributed data to the model that has been called "the great chain of being." This perspective concerns the ordering of plants and animals into a connected series of lowest to highest categories and originally was used to document the sequence of events in creation. Much later, this progression of life forms was reinterpreted as evidence for evolutionary change.
Ray's classifactory scheme is not used today, but that of Karol von Linne (or Linnaeus, 1707-1778) is a fundamental part of the theory of evolution and evolutionary interpretations. Like Ray, Linnaeus was deeply religious and primarily interested in the natural world as an example of the wisdom and grandeur of God. He wrote that
man alone was capable of putting nature to his own use. He alone could appreciate the wisdom, power, and goodness displayed by nature. It was his duty, therefore, to study nature diligently that God might be glorified in His works. (The Death of Adam, p. 132)
Linnaeus' study of nature consisted of ordering the natural world into discrete categories. He is the father of taxonomy (the science of naming living things), classification (the science of grouping these organisms into a hierarchical order), and systematics (the science of determining the relationships among diverse types of organisms). His contribution, then, concerns the arrangement of a "chaotic" natural world into one characterized by order and logical consistency. Even though Linnaeus believed in manifest creation, the fixity of species (he felt that species had not changed from the moment of creation), and the unlikelihood of extinction, all of which are rejected by Darwinism, he nevertheless was a great, and again unwitting, contributor to the theory of evolution. He provided a system that rendered the complex natural world understandable.
A further step in the development of the theory of evolution was taken by Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (or simply Lamarck). Before Lamarck (1744-1829), nearly all natural theologians insisted on the stability of species. Although new varieties could be produced (for example, specific breeds of dogs, cattle, or flowers), scientists argued that the created design did not change. Lamarck argued, however, that species were not stable, that their fixity was only an illusion produced by our limited vision of time. Moreover, modern species were the descendants of extinct species that were modified over time. Lamarck, unjustly labeled the "French Atheist" because of these views, maintained that living things
feel certain needs, and each felt need, stirring their consciousness, immediately causes fluids and forces to be directed toward the point of the body where an action capable of satisfying that need can take place . . . if there exists . . . an organ appropriate to such an action, it is stimulated to act; and if no organ exists, and the felt need is pressing and sustained, little by little, the organ is produced and develops by reasons of its constant, vigorous use. (The Death of Adam, p. 160)
In this line of reasoning, species not only changed through time, but they controlled their evolutionary destiny by the workings of an inner drive to perfection. Although hazy about the origin of life (he wavered between spontaneous generation and divine creation), Lamarck felt that the Creator did instill in every living thing a will ("inner drive") to improve itself and that the cumulative effect of this universal force led to greater complexity over time. Consequently, the great chain of being or ladder of perfection was powered by natural forces. Because organisms were naturally motivated to improve themselves, they automatically moved up the ladder of perfection with God watching every step of the way.
Lamarck's contribution is significant mainly in that he provided the first attempt to deal with change in species. His model accounting for the change, however, conforms to the adage of "a theory slain by an ugly fact." The "ugly fact," which was also unknown to Darwin, is that there is no direct connection from the phenotype (outward appearance of an organism) back to the genotype (underlying genetic system). Although genes control the development and expression of a structure, the structure or changes in it have no direct link back to the genes. The connection between the genotype and the phenotype is a one-way street with information only going from the genes to the outward appearance. Changes that occur in the phenotype of an individual cannot, then, be translated back into the genetic code for expression in subsequent generations. The coding system of genetics--DNA--operates in isolation; consequently, no matter how long and hard an organism might strive to improve itself, such effects cannot have any impact beyond the lifespan of the particular individual. If the inheritance of acquired characteristics was true and there was a direct link from the phenotype to the genotype, this would be in the long run a great disadvantage to the offspring. A mother who lost all her teeth would give birth to toothless babies that would be toothless forever, fathers missing an arm could only sire children with the same missing appendage, mothers with fallen arches would only have babies with the same foot problems, and so on. The one-way street between the phenotype and the genotype provides a protection to the integrity of the genetic structure.
Another critical event leading to the
formulation of the concept of evolution was the discovery of time. With
this discovery, mainly the result of publications by James Hutton
(1726-1797) and Charles Lyell (1797-1875), the world took on a much
greater antiquity. Hutton, in his Theory of the Earth (1795), wrote
that the earth had "no vestige of a beginning, no prospect of an
end." He argued that "time which measures everything is to
nature endless and as nothing." Not widely accepted, Hutton's ideas
about time were eventually expanded and popularized by Lyell, who also
reified his ideas about the proper way to interpret the past. This
concept, known as uniformitarianism or actualism, stipulates that former
changes in the geological and biological world are the result of an
uninterrupted succession of events, controlled by the same laws that
operate in the present. The window to the past, then, is opened by
observing the forces responsible for shaping the present. A rational,
positivist interpretation of the contemporary world was reapplied by
Hutton and Lyell for studying periods of time beyond the experience of
direct observation. Such a model could not have been supported if Ussher's
4004 B.C. date was accepted, for no forces operating in the present could
possibly be fast enough to produce the kind of variation described by the
natural historians. However, given a much greater antiquity of the earth
(today confirmed by radioactive isotope dating methods), processes
affecting the biology of living things that are readily observable and
quantifiable could then be applied to prehistoric situations.
Like Lamarck, Darwin (1804-1882) rejected the idea of species stability, but Darwin's theory also broke completely with the theological overtones of Lamarck. Darwin maintained that evolution was due to naturally occurring (random) variation within a species and to the competition between and among species. Divine influence found no place in Darwin's theory. Specifically, Darwin argued:
As many more individuals of each species are born than can possibly survive; and, as consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself . . . will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form. (Origin of Species, p. 27)
From this statement, we can distill six precepts that are critical for understanding the Darwinian concept of evolution: (1) species tend to over-reproduce (spaying cats and human birth control measures are examples of our knowledge of this principle); (2) there is a struggle for existence (the fact that unchecked population growth interferes with an individual's ability to find food and a place to eat is an obvious example); (3) individuals are variable due to natural factors (we know that except in identical twins, no two individuals look alike); (4) there is a survival of the fittest (the fact that some individuals are more successful in leaving more offspring due to a physical attribute is known as fitness); (5) variations in external morphology (the phenotype) are inherited (even though offspring are not identical to their parents, there is some resemblance); (6) change or evolution takes place due to the accumulation of favorable hereditary characteristics. Thus, evolution is the result of the interaction of factors 1-5 and is natural or a fact of nature as opposed to being directed by any supreme being. Obviously, this theory of life would require a long geological span, so only Hutton's and Lyell's ideas about the great antiquity of the world could accommodate such a slow, gradual rate of change.
This new approach to nature revolutionized the way science viewed the world. The tranquil world of Lamarck and earlier philosophers was transformed into a competitive, "cruel" world by Darwin. Rather than looking for and describing the goodness of nature, scientists after Darwin were more keenly interested in how animals and plants adapted to specific environments, how they obtained their food, how their morphology was geared toward the food quest, and so on. This new approach even filtered into the arts. Poets such as Tennyson, who spoke of "nature red in tooth and claw," emphasized the competitive aspects of nature. Commenting on this new perspective, Darwin wrote:
We behold the face of nature bright with gladness, we often see the superabundance of food; we do not see or we forget, that the birds which are idly singing around us mostly live on insects or seeds, and are thus constantly destroying life; or we forget how largely these songsters, or their eggs, or their nestlings, are destroyed by birds and beasts of prey; we do not always bear in mind, that, though food may now be superabundant, it is not so at all seasons of each recurring year.
And Romanes, the nineteenth-century evolutionist, wrote:
. . . we find that more than half of the species which have survived the ceaseless struggle are parasitic in their habits, lower and insentient forms of life feasting on higher and sentient forms; we find teeth and talons whetted for slaughter, hooks and suckers moulded for torment-- everywhere a reign of terror, hunger, and sickness, with oozing blood and quivering limbs, with gasping breath and eyes of innocence that dimly close in deaths of brutal torture!
Yet, is the natural world of Darwin really "red in tooth and claw"? Natural selection is going on around you all the time, but you do not hear screams of agony or witness constant fights for survival. In fact, the major premises of Darwin's theory only suggest that animal and plant populations tend to over-reproduce, and because there is a limited supply of food and space, members of these populations are in competition with one another. Because all living things show variations in structure and form (which is partly controlled by heredity), those that possess the best morphological or structural arrangements are the ones that live the longest and produce the most offspring; that is, they are the most fit. The fittest individuals contribute the most to subsequent generations; therefore, their phenotypes become more prevalent in future generations. In Darwin's theory, there is neither the concept of an inner consciousness driving the evolutionary process toward perfection nor a reliance on the inheritance of acquired characteristics. Rather, the important idea is the one of interplay between variation and competition.
The significance of Darwin's theory cannot be overestimated. In addition to formulating a model that enables biologists to analyze the natural world, the theory brought about a major change in the way people viewed their world. The concept of divine intervention in the natural and everyday events of life ceased to be as important. Humans were lowered from the top rung of the ladder of perfection to a place among the rest of the animal and plant world, so that the forces that make otters and ants what they are also are responsible for the making of humans. The publication of The Origin of Species marks the beginning of our model of interpretation of how the world runs. This model will guide us through our study of the evolution and variation of humans.