Our
understanding of the world is built up of innumerable layers. Each layer is
worth exploring, as long as we do not forget that it is one of many. Knowing
all there is to be known about one layer—a most unlikely event—would not teach
us much about the rest. The integration of the enormous number of bits of
information and the resulting vision of nature take place in our minds; but the
human mind is easily deceived and confused, and the vision of nature changes every
few generations. It is, in fact, the intensity of the vision that counts more
heavily than its completeness or its correctness. I doubt that there is such a
thing as a correct view of nature, unless the rules of the game are stated
clearly, undoubtedly, there will later be other games and other rules.
Erwin Chargaff, Heraclitean Fire
Up until 1953
it was still possible to believe that there was something fundamentally and
irreducibly mysterious in living protoplasm. No longer. Even those philosophers
who had been predisposed to a mechanistic view of life would not have dared
hope for such total fulfillment of their wildest dreams.
Richard Dawkins, River Out of Eden
Beginning around Aristotle’s time (4th century B.C.), philosophers believed that the orderly way in which organisms grow and develop could be credited to a vitalistic principle, an influence that was beyond human comprehension and thus considered not within reach of investigation. This vital “force” was a manner of identifying the cause behind a prevailing worldview which, in pre-Christian times (and with roots going back at least as far as ancient Egypt), could broadly be considered pantheistic.[1]
As the scientific revolution gathered steam it increasingly became apparent that most observed phenomena were completely natural and could be understood and described without invoking mystical forces. (Well into the 19th century, in certain fields—embryology, for instance—the intermingling of naturalistic and supernatural explanations was still practiced by reputable scientists.) Galileo, Kepler, and Newton in turn demonstrated the inestimable worth of mathematics as a way of describing the cosmos, which contributed to an even more compellingly mechanistic worldview. Ernst Mayr, in his last book, This is Biology, describes the intellectual mood of this era:
Substantial numbers of people who cared deeply about such matters clung to an enduring intuitive sense that living things possessed qualities that could never be accounted for by physicalism (defined as the belief that physical entities are all that exist). A sort of countermovement resulted, manifesting in different forms at different times; this philosophical vitalism originated in the 17th century and held sway until the mid-1800s. Though never a unified “movement,” it was a reaction to mechanistic thinking, and its proponents focused on various issues they felt physicalism failed to take into account: the origin of adaptations and behaviors, the mystery of development and regeneration…the very nature of what animated living things.
The influential French philosopher Henri Bergson, shortly after the beginning of the 20th century, popularized the notion of an élan vital. The idea briefly took on a mantle of scientific respectability in the early 1900s when German embryologist Hans Driesch discovered that embryos, mutilated in the earliest stages of their cellular multiplication, could recover and develop into more or less normal organisms. This, and other remarkable aspects of growth and development, led him to that the emergence of the correct form of any organism—in all its intricate complexity—must be under the influence of some guiding life force, which he called entelechy. (He actually borrowed this term from Aristotle who coined it to mean “the condition of a thing whose essence is fully realized; actuality.”)
Driesch knew well that the ordering properties of entelechy were in conflict with everyday physical forces and laws and emphasized in his writings that it was a natural (as opposed to a mystical or metaphysical) factor that acted on normal developmental processes. He suggested that, whatever it was, entelechy operates by influencing the timing of molecular interactions in a manner that promotes a cooperative, holistic pattern of development. While his ideas were never absolutely discredited, they never advanced scientifically, being resistant not only to some form of experimental proof, but even to real conceptual coherence—virtually inevitable, given their nebulous nature. Driesch’s ideas have subsequently been revisited by others in slightly different forms but for similar reasons never gained traction.
Contrary to how naïve any vitalistic theories appear today, vitalism was, in its time, a legitimate alternative—not just to mechanism but to the more sophisticated physicalism as well. Adherents of both schools were passionate in their beliefs and there were repeated periods of struggle between the ideologies. After all, physicalists of the mid- to late-19th century employed their own nebulous concepts and poorly defined terms to describe phenomena that could not yet be understood. In addition, they often failed to address the main concerns of their intellectual adversaries.[3] Nevertheless, with unrelenting scientific advances, vitalism gradually faded into the background, in large part due to increasingly being seen as a metaphysical program unable to come up with coherent theories subject to being tested.
Cells were unknown before English polymath Robert Hooke, peering through an early microscope at a thin slice of cork, saw tiny and apparently empty four-sided compartments that reminded him of monks’ cubicles. Hooke had no idea what these minute chambers were but certainly would not have imagined he was observing the building blocks of all living things. Early microscopists were still influenced by a holdover from ancient Greek philosophy—atomism—and assumed that the basic constituents of life were invisible, indivisible, indestructible particles. (Not to be confused with the modern, scientific conception of atoms.)
By the end of the 18th century it was an accepted fact that cells were the fundamental components of plants but it was not until the 1820s that French botanist Henri Dutrochet first proposed that they were not just structural entities but physiological as well. Owing to his discovery of osmosis[4] and careful studies of respiration,[5] Dutrochet is considered the father of cell physiology. A confirmed anti-vitalist, his work was always focused on demonstrating that physics and chemistry lay behind life processes.
Dutrochet’s work led to a more wide-ranging cell theory that was independently put forward by two Germans: botanist Matthias Schleiden and a colleague, zoologist Theodor Schwann. In 1838, Schleiden proposed that all parts of a plant were composed of cells and that new cells arose from the nuclei of older cells, which were formed in some sort of unspecified crystallization process. (While the gist of Schleiden’s premises were correct, almost all the details were based on erroneous speculations.) The following year, Schleiden and Schwann had a conversation involving plant cells’ nuclei. Schwann recalled having observed similar structures in tissues from frog embryos.[6] Recognizing an important finding, they compared resemblances and confirmed a connection between the two phenomena. Schwann realized that animals as well as plants were composed of cells and that cells—not organs and tissues—were the elementary units of life. Shortly thereafter he published a paper on his ground-breaking hypothesis. Mayr: “Few publications in biology have ever caused such a sensation as Schwann’s magnificent monograph. It demonstrated that animals and plants consist of the same building blocks—cells—and that a unity therefore exists throughout the entire organic world…. It was a vigorous endorsement of reductionist thinking.”
By 1852, after years of painstaking observation, the Polish embryologist Robert Remak concluded that binary fission—that is, dividing in two—was the only means by which animal cells could multiply. He established without doubt that new cells were not the result of productions of the nuclei or unformed substances in intercellular spaces (the erroneous hypotheses of Schleiden and Schwann, respectively). His investigations, while slow to gain acceptance, paved the way to an entirely new model of how organisms developed. Unacknowledged in his lifetime (and even to this day), it was Remak’s work that helped clarify the muddled views surrounding animal cells’ origins.
At the beginning of the 20th century, cell theory had achieved a degree of coherence: it was recognized that both plant and animal tissues are composed of cells; that new cells arise through binary fission; that all organisms start out as a single cell formed by the union of egg and sperm; that these germ cells each carried a set of hereditary elements, or factors (later, genes); that these factors were duplicated during cellular division, becoming two identical sets of genetic material (chromosomes); and that each new cell thus received a copied set of factors from the parent cell. It was a start.
Mendel’s recently exhumed research results provided solid evidence that heredity was indeed controlled by molecules, providing a significant boost to Loeb’s (and other committed mechanists’) investigations. And it was Loeb who insightfully recognized that Mendel’s findings pointed the way to biology’s next big mission: to discover the chemical substances within chromosomes that were responsible for passing on hereditary traits. Though it may have taken longer than expected, biochemists James Watson and Francis Crick made a monumental breakthrough in the early 1950s that would all but finish off vitalism. Boyce Rensberger noted that “by applying a purely reductionist approach to the study of life, they would vindicate the mechanist view spectacularly with the discovery of…DNA and the cracking of the genetic code.”
The announcement of DNA’s discovery via a two page article in the April 1953 issue of Nature began a whole new chapter of modern life; from a cultural standpoint, science’s role in everyday living was a perfect addition to the atmosphere of optimism and progress following WW II’s end. Religious views continued to be influenced by the lasting impact of Darwin’s radical ideas; as his theory of natural selection gained ever greater acceptance, people felt the wider effects of being further liberated from the church’s stifling dictates and lingering superstitions (a course unwittingly first set in motion by Newton). Even devoutly religious people saw the light and were tentatively embracing a perspective permitting both God and science to illuminate their worldview. The never-ending introduction of fantastic new machines and technologies, plus an escalating adoption of mechanical terminology (and, later, computer jargon) to describe biological processes, lent credence to the notion that living things are basically machines as well—a supposition that has only grown stronger with passing time. Even after three centuries of determined study, our overall conception of nature is far from settled. The whole enterprise is a work in progress and our current views, the product of history, mental effort, sweat, and serendipitous accident. One thing is certain: life is a curious and extraordinarily convoluted affair.
©2017
Tim Forsell
[1] Pantheism is the belief that the Universe (or nature as
the totality of everything) is identical with divinity, or that everything
composes an all-encompassing, immanent god. Pantheists thus do not believe in a
distinct personal or anthropomorphic god. Such concepts date back thousands of
years, and some religions in the East continue to contain pantheistic elements.
[2] An aside: this was Mayr’s last book, published when he
was ninety-three.
[3] Mayr again: “It is ironic that the physicalists
attacked the vitalists for invoking an unanalyzed ‘vital force,’ and yet in
their own explanations they used such equally unanalyzed factors as ‘energy’
and ‘movements.’ The definitions of life and the descriptions of living
processes formulated by the physicalists often consisted of utterly vacuous
statements. For example, the physical chemist Wilhelm Ostwald defined a sea
urchin as being, like any other piece of matter, ‘a spatially discrete cohesive
sum of quantities of energy.’… [Pioneer embryologist] Wilhelm Roux…stated that
development is ‘the production of diversity owing to the unequal distribution
of energy.’ These [and other] physicalists never noticed that their statements
about energy and movement did not really explain anything at all.”
[4] The tendency of a solvent—such as water—to diffuse from
a region where dissolved substances are less concentrated to one where they are
more so. Unless checked, osmosis continues until the concentrations of the
substances are in equilibrium.
[5] The movement of oxygen (from air) to tissues and cells
and subsequent elimination of carbon dioxide (as a waste product).
[6] It should be noted that little was then known about
animal cells; in contrast to plants, it was much harder to prepare animals’
relatively delicate tissues for study under a microscope. Also, animal cells
are typically much smaller than those of plants.
[7] Two decades passed before the re-emergence of Mendel’s
work revealed the significance of Flemming’s own important findings. His
identification of chromosomes and mitosis are thought to be among the 100 most
important scientific discoveries.
[8] Humorous historical facts worth knowing: The press’
coverage of Loeb’s discovery evidently gave birth to the (mis)use of that
hackneyed expression. According to Boyce Rensberger, “Loeb’s experiments, in a
seaside laboratory and on marine organisms, became so mixed up in the popular
mind with the allegedly mysterious powers of the sea that unmarried women were
advised not to bathe in the ocean. Childless couples, on the other hand, rushed
hopefully to beach resorts. Loeb even received letters from desperate couples
asking him to give them a child.”