Because April 19, 1982, marked the centennial of Charles Darwin's death, it is appropriate that we summarize some of the compelling thoughts and recall the scholarly career of this outstanding naturalist. It was Darwin who revolutionized our factual understanding and rational appreciation of the origin and development of all life on earth (including the appearance and significance of our own human species). Darwin went further than any other naturalist both prior to and during his lifetime in presenting a comprehensive and intelligible synthetic explanation of changes throughout terrestrial space and time and of the mechanism which he thought responsible for them. As a result, we still continue to learn from and build upon his original insights. Unfortunately, there are many today who either misunderstand or misrepresent Darwin's thoughts. It therefore becomes necessary to correct many misconceptions in the process of explaining the ideas of this seminal intellect.
Before Darwin
In antiquity, several naturalist cosmologists speculated on the origin of life and man's position within the nature of things. Thales claimed that life first appeared in water, and Anaximander postulated that our ancestors had once passed through a fishlike stage in the early phases of life's development and movement from water to land. Xenophanes recognized both the biological and historical significance of fossils, while Heraclitus acknowledged universal change to be the essential characteristic of reality. Empedocles even anticipated the DarwinWallace basic explanatory principle of natural selection or, as Herbert Spencer referred to it, the survival of the fittest. In his bizarre attempt to account for the origin of those first organisms from the haphazardly coming together of free-floating organs on the surface of the earth at the beginning of life, Empedocles glimpsed the need for organisms to adapt and survive in order to reproduce and endure in a changing environment. In short, evolutionary ideas or concepts were implicit, if not explicit, in some early pre-Socratic speculations on the universe.
Aristotle, the father of biology and several other sciences, although he contributed
to embryology and taxonomy, did not hold to an evolutionary interpretation of organic history. Strangely enough, he explicitly rejected the scientific value of fossils by claiming them to be mere random chance aberrations in rock strata. He even held that no living form of plant or animal had ever become extinct. One may argue that Aristotle in some cases supported the spontaneous generation of life from nonliving matter, but, for the most part, he claimed that the "Great Chain of Being" represented a terrestrial universe consisting of a static hierarchy of flora and fauna types. He likewise maintained that each kind of plant and animal had an eternally fixed natural place in this ladder of nature, which could claim the human animal, characterized by its greatest complexity of structure and degree of consciousness, as its apex. In no sense, however, did the Stagirite ever conceive of man as the end result of a dynamic process of antecedent organic development from lower to higher (that is, from earlier to later) forms.
Although the poetic natural philosopher Lucretius speculated on the evolution of the cosmos and the biosocial and cultural development of humankind, his incredibly modern ideas, formulated about two thousand years ago, were, until recently, overshadowed by the long predominant Aristotelianism and eclipsed from the general intellectual view.
In the Italian Renaissance, Leonardo da Vinci recognized the significance of fossil remains and anticipated at least geological, if not also biological, evolution. He boldly held the planet earth to be at least two hundred thousand years old! In general, however, the "Dark Ages," medieval period, and subsequent Renaissance contributed very little to biology as such, because of the concentration on theology, metaphysics, or astronomy that prevailed during those centuries.
Philosophers of the eighteenth century "Age of Enlightenment," however, returned to observing nature itself and critically reflecting upon human experience. At the beginning of that century, the eminent Swedish scientist, Carolus Linnaeus, fathered modern taxonomy. As a good Aristotelian, however, he was not an evolutionist, although he was bewildered, as a naturalist devoted to botany, by the discovery of varieties within some of those allegedly eternally fixed species he classified and described.
At the close of the 1700s and the beginning of the 1800s, the natural philosopher and invertebrate specialist, Lamarck, did uphold the evolutionary perspective. In fact, he was the first serious thinker to write a book solely for the purpose of presenting the theory of biological evolution as it applies to the history of the animal kingdom. In his major book, Zoological Philosophy (1809), Lamarck boldly presented his own arguments in favor of organic nonfixity and biological transformism. Although this volume appeared in the year of Darwin's birth and exactly fifty years before Darwin would publish his most important work on the theory of evolution, On the Origin of Species (November 24, 1859), Lamarck's controversial theory of organic history went unaccepted and unappreciated by the
scientific community of the time. This was primarily because its explanatory principles were more metaphysical than naturalistic in character, such as his resort to spontaneous generation to account for the origin of the earliest plant and animal forms, his acceptance of the laws of use and disuse and the inheritance of acquired characteristics, and his vitalist interpretation of life—all rejected by modern science.
Darwin's Contribution
As Charles Darwin (1809-1882) modestly admitted, the idea of evolution did not originate with him. Yet, one may convincingly argue that Darwin is, in fact, the central figure in the history of the science of evolution. In spite of all those early insights, from Thales to Lamarck, it fell to him to bring together into a scientific and coherent view of life all the emerging facts and relationships in the embryonic sciences of historical geology, comparative paleontology, and developmental biology (including embryology and taxonomy). With the towering genius of Darwin, evolution ceased to be a mere rational speculation on nature or a philosophical overview on the scheme of things. It became instead an all-embracing scientific theory of organic history with explanatory, predictive, and exploratory powers. In short, evolution changed from being a philosophy to being a science.
It is interesting to note that, despite his early medical and theological studies, Darwin had no formal degree in geology or biology and, in fact, never taught these subjects at a college or university. Also, from our perspective and in the light of our benefit of hindsight, many of the very instruments he used in his scientific investigations were faulty. To his immortal credit, however, he always remained open and hospitable to the theoretical implications and physical consequences of his own experiences and experiments, as well as those of other naturalists. In short, Darwin's greatest teacher was the process of nature itself.
As a young naturalist, Darwin was primarily interested in historical geology and enjoyed collecting beetles and hunting as a sport. At that time, he never questioned his fundamental religious beliefs and accepted the then-taught doctrine of the eternity of plant and animal forms on earth. However, three major influences radically shifted Darwin's early conceptual framework from recent creationism to scientific evolution and caused him to become more and more interested in biology, and eventually general anthropology, while increasingly doubting the literal meaning of his youthful religious commitments.
The three major influences on Darwin's early thought were: the Hutton-Lyell geological theory of uniformitarianism, which advocated the slow but continuous evolution of the stratigraphic structures of the crust of the earth as a result of pervasive natural forces; the global scientific voyage of H.M.S. Beagle (particularly its five-week visit to the Galapagos Islands in 1835); and the chance
but critical reading of Malthus's An Essay on the Principle of Population (1798). It is to Darwin's lasting advantage that he accepted the theory of geological gradualism and, as a naturalist aboard the Beagle, took full advantage of the opportunities for a vast range of experiences. During the Beagle voyage, Darwin became increasingly aware of the roles of camouflage and mimicry within the biological world, discovered giant prehistoric mammal fossils in Argentina, met the technologically primitive and nonliterate Fuegians at the tip of South America, witnessed the physical consequences of earthquakes, volcanic eruptions, and tidal waves on the malleable surface of the earth, and even found fossil marine specimens in rocks at the top of the Andes in Chile.
During the circumnavigation of the globe, the eccentric aristocrat and fundamentalist creationist, Captain Robert FitzRoy, encouraged Charles Darwin to collect empirical evidence in support of a literal interpretation of the story of divine creation as written in Genesis. However, to FitzRoy's displeasure and dismay, the more rocks and fossils Darwin studied and collected, the more convinced the young scientist became that the biblical account is not an adequate portrayal of the story of life. One might say that the creation-evolution controversy had its origin in the personal conflict that developed between FitzRoy and Darwin on H.M.S. Beagle during its historical journey around the world.
When Darwin returned to England in 1836, he was convinced that "descent with modification" had taken place throughout organic history. Yet, he still had no rational principle capable of empirical verification or falsification that would account for the origin of species on the earth. In 1838, a casual reading of Malthus's book gave Darwin the missing key to an understanding and appreciation of biological history in terms of evolution. According to the Malthusian principle of population, there is a discrepancy between the geometric increase in the number of organisms to be fed and the arithmetic increase in the growth of their food supply, resulting in pervasive struggle and ruthless competition in the living world. This principle gave Darwin his essential and useful explanatory device of natural selection or the survival of the fittest (today referred to as differential reproduction or extinction).
For many years, as a semi-invalid and quasi-recluse at Down House in the Kent countryside of England, the shy and gentle Darwin remained more or less isolated from the scientific community. He devoted years to empirical research, being dedicated to a vast array of subjects: orchids, climbing and insectivorous plants, the earthworm (his favorite animal), varieties of barnacles, the artificial breeding of cultivated plants and domesticated animals (especially pigeons), the origin of coral reefs and atolls, the formation of vegetable mold, and a comparative study of the emotions in nonhuman and human animals. Concerning the theory of biological evolution, Darwin merely sketched a thirty-five-page essay in 1842, which he later expanded into a 230-page manuscript in 1844. Despite continued urging and encouragement by scientific friends (notably Lyell, Huxley,
and Hooker) to publish his already formulated theory of organic history, Darwin did not do so. In fact, he left provisions in his will for his wife, Emma Wedgewood, to see to it that the proposed multivolume work on evolution would be published in the event he should die before it appeared in print. One may even argue that Darwin had no serious intention of publishing a book on the theory of evolution during his own lifetime.
But, in the late spring of 1858, Darwin received a letter and manuscript from Alfred Russel Wallace. The event was to change the course of Darwin's life and the course of science in general.
Other Contributors
There are astonishing parallels between Darwin and Wallace: each was an English naturalist who had explored South America with interests in both geology and biology; visited an archipelago (Galapagos Islands and Malay, respectively); studied orchids and collected beetles; did original research on animals such as the barnacle and the butterfly; read Paley, Humboldt, and Lyell, as well as Malthus; enjoyed reflecting in solitude; accepted the scientific theory of biological evolution as a true framework of natural history; and independently founded the concept of natural selection as the primary explanatory mechanism to account for the emergence, survival, and extinction of life forms on earth.
Darwin had developed the principle of natural selection in 1838, but never published his views on the subject (the 1842 abstract and expanded 1844 version had not appeared in print). Wallace first presented a portion of his theory of evolution in two published works, The Sarawak Law (1855) and Ternate Essay (1858).
At the Linnean Society meeting on July 1, 1858, the Darwin-Wallace positions were read, and it was agreed that priority be given to Darwin as the scientific father of the theory of biological evolution by means of natural selection (although both Darwin and Wallace had independently discovered the significance of natural selection). It must be emphasized that Darwin had a much larger volume and array of documented empirical evidence and wider range of both experiences and experiments than Wallace had ever accumulated or could ever claim. Wallace, a meritorious and respectable scientist in his own right and an honest and grateful man, loyally conceded the primacy to his friend Darwin.
As incredibly similar as these two naturalists were in 1858, in later years their interpretations of evolution increasingly diverged from each other to the point of eventual diametrical opposition. Whereas Darwin grounded his theory in mechanistic materialist terms, Wallace turned to spiritualism and argued that the essential uniqueness of the human being could not be accounted for merely through the accumulation of slight beneficial variations over long periods of time due to
the process of natural selection alone. Darwin remained a rigorous naturalist throughout his entire life. His major one-volume work in evolution, On the Origin of Species (1859), appeared in the year following the arrival of Wallace's letter.
Darwin himself never defended evolution in public or in print. He left it to others to convince the scientific community, philosophers, and theologians of the validity and soundness of his admittedly disturbing interpretation of life on earth. Likewise, he did not at this time extend his view of things to account for the origin and historical development of the human species. (Nevertheless, anyone reading Darwin's Origin carefully could easily see its far-reaching implications for understanding and appreciating the organic history of the human zoological group as a whole.)
In 1860, the vertebrate paleontologist and natural philosopher, Thomas Henry Huxley, as "Darwin's bulldog," defended the theory of evolution against the scientifically uninformed and irrelevant arguments of Bishop Samuel Wilberforce ("Soapy Sam") in a public debate at Oxford University. Although reminiscent of the Darwin-FitzRoy personal conflict during the voyage of the Beagle, neither Darwin nor Wallace was present at the debate (nor were they present at the reading of their joint paper at the Linnean Society meeting in 1858). The Huxley-Wilberforce clash exposed the theoretically biased and scientifically faulty arguments of the special-creationist bishop. Wilberforce used arguments then that are still used by creationists today—namely that evolution cannot be established using the scientific method, that variation and natural selection are inadequate as a mechanism for macro-evolution, that mutation ("monstrosity") cannot be the source of advantageous variations, and that there are gaps in the fossil record and an absence of transitional forms. Huxley provided a learned and eloquent defense of Darwinism by answering Wilberforce's claims and by carefully building a case for evolution based on factual evidence. This debate enhanced the scientific credibility of the new theory and thus gave it its first major victory.
In 1866, the Czech monk, Gregor Johann Mendel, working with the common garden pea plant, Pisum, in the Augustinian monastery of Brno, discovered the basic principles of heredity. His pioneering research, incorporating rigorously controlled experiments and the use of mathematics, unfortunately went unappreciated by the other monks. Likewise, its value and significance went unrecognized by the scientific community at that time. There is no evidence that Darwin even knew of Mendel or ever read his monograph, Experiments in Plant Hybridization (1866). Had Darwin known of Mendel's discoveries, biology may have had the synthetic theory of evolution several decades earlier. Nevertheless, Mendel is properly acknowledged as the father of the science of genetics.
Like Haeckel in Germany, Huxley in England was quick to extend the theory of evolution to account for the origin and natural history of humankind. It was not Darwin but Huxley, in his book, Evidence as to Man's Place in Nature (1863),
who first pointed out the striking and undeniable similarities between the great apes and humans. As a result, he claimed that the human species once shared a prehistoric common ancestry with its living pongid cousins.
In The Descent of Man (1871), Darwin finally joined Huxley and Haeckel in extending his own theory of evolution to explain humankind's place in biological history. However, by that time, this evolutionary battle had been generally won in scientific circles.
Early Problems
At first, the Darwinian theory of evolution had its shortcomings. At that time, the special sciences crucial for an empirical support of this conceptual scheme were not yet sufficiently developed. There were several important areas that caused Darwin trouble in presenting his theory, but the advances of science and natural philosophy in this century are increasingly modifying that theory, and only in a few instances have Darwin's own ideas needed to be rejected outright. It is surprising how enduringly valid Darwin's original writings still are in understanding and appreciating organic history on earth.
In Darwin's time, some physicists had greatly underestimated the age of our planet, claiming it to be merely about forty million years old. This presented Darwin with a problem, since it clearly did not offer enough time to account for the presumably gradual appearance of all of the plant and animal species that have ever existed on the earth. There was also the, incompleteness of the fossil record itself (one may argue that fossil remains constitute the single most convincing body of evidence for the evolution of living things throughout natural history). It was also claimed that no living intermediate or fossil transitional forms are to be found in the geosphere or biosphere. However, absolute dating techniques in modern science clearly show that the earth is about 4.6 billion years old. The paleontological record continues to grow and includes specimens of so-called "missing links" which are transitional in nature between earlier and later taxonomic categories—for example, Ichthyostega the fishlike amphibian, Seymouria the amphibian-like reptile, Archaeopteryx the reptilian bird, and Australopithecus afarensis the pongid-like hominid.
Darwin's theory was also criticized because the origination of new species is not directly observable by human beings (although varieties or "incipient species" have been seen to appear on earth and not only under laboratory conditions). The Lamarckian influence on Darwin's own theory of pangenesis is no longer accepted by the scientific community. Unaware of the Mendelian principles of genetics, Darwin reluctantly had to fall back upon a particulate interpretation of inheritance, which did not distinguish between body cells (somatic cells) and sex cells (gametes). Darwin's hereditary units or gemmules were held to be
produced directly by the various organs of a living body and, as a result,
subject to use and disuse as well as the inheritance of acquired
characteristics. This Lamarckian element in Darwinism was an attempt to account
for the seemingly rapid evolution of life within a geologically short period of
time.
Darwin's theory of descent with modification by means of natural selection stressed the struggle for existence among individuals and, as a result, underestimated the equally weighty and no less true elements of cooperation within a population as an aspect of group behavior (brought out in Kropotkin's study of such altruistic behavior patterns in his book, Mutual Aid: A Factor of Evolution, 1902). Today this phenomenon of cooperation is seen to be a crucial element in the preservation and evolution of some species, especially our own.
Darwin's gradualism did not allow for any sudden leaps or saltations in organic history. It assumed a rather smooth and uniform process of biological change. But today, with a better perspective on the fossil record, some paleontologists are adopting the Eldredge-Gould hypothesis of "punctuated equilibria." This is the view that the origin of new species is a more or less rapid process throughout organic history, taking often as little as one hundred thousand years. A number of intermediate steps do occur, as Darwin proposed, but these steps are telescoped together in this relatively short span of time (geologically speaking) and in small isolated populations. This explains the absence of many transitional fossils. However, because some fossil sequences are rather complete, Darwin's gradualism and the newer punctuated equilibria need not be seen as necessarily mutually exclusive mechanisms. In my opinion, both of these mechanisms have probably played a role in the origin of new species; thus, it might be proper to speak of "punctuated gradualism."
Modern Developments
The scientific evidence continues to support the theory of evolution. Neo-Darwinism or the modern synthetic theory of biological evolution is grounded primarily in random genetic variability and the necessity of natural selection (as such, Darwin's and Mendel's conclusions represent the essential features of the foundation of evolutionary biology in the last half of this century). There is, in fact, new and growing evidence that supports a broad application of the theory of evolution: astrochemistry and astrophysics support a process cosmology; historical geology supports continental drift (plate tectonics); recent hominid fossil discoveries shed light on the origins of humankind (such as the Laetoli footprints and the fossil material of Australopithecus afarensis); the emerging science of sociobiology points to the direct relationship between genetic inheritance and animal activity; biochemistry and systematics, as well as the recent research in genetic engineering, continue to support the historical continuity and essential
unity of all living things on earth; and speculations in the emerging science of exobiology suggest that life may exist in many parts of our physical universe.
The latest studies in primate ethology demonstrate that, in terms of genetic makeup and behavior patterns, the human animal is closer to the great apes (orangutan, chimpanzee, and gorilla) than even Huxley, Haeckel, and Darwin had thought in the 1800s. Indeed, some scientists and natural philosophers argue that humans differ merely quantitatively rather than qualitatively from these three pongids.
It is apparent that, in the history of science and for ages to come, Charles Robert Darwin will undoubtedly continue to stand as one of the most fertile, powerful, and influential seminal intellects ever generated by our evolving species. The time-tested truth of the essential core of his theory of evolution, despite all the unavoidable modifications and corrections it has sustained and will continue to sustain in the future as a result of further advances in the sciences, cannot be ignored.
Just as the Bruno-Galileo conceptual revolution of the Italian Renaissance shifted the center of the universe away from our earth to elsewhere (be it the sun as with Galileo or the belief that reality has no fixed center and no fixed circumference as with Bruno), so the Darwinian worldview removes the attention from humankind as the special animal in the cosmos and makes possible the existence of evolving life and intelligence elsewhere in the material universe. To reject Darwin's theory altogether, as some misguided fundamentalists are urging us to do, would leave our species without a scientific compass upon the high seas of an unknown and highly problematic future, pregnant perhaps with wondrous opportunities but also with significant dangers.
We will undoubtedly continue to move ever further beyond Darwin—but never without him.