Introduction: Deduction vs. Induction
In the history of science, spontaneous generation and abiogenesis have been used as synonyms describing the same phenomenon, i.e. an event by which animate life formed from inanimate matter. If I were an ancient Greek philosopher, like Aristotle or Anaximander, I would arguably feel right at home using either term to explain how life originated, e.g. Anaximander (610-546 BCE) hypothesized humans spontaneously formed out of mud exposed to sunlight. The idea humans emerged out of something like mud agreed with the worldview of the ancient Greeks because they believed everything was composed of a combination of earth, air, fire and water. The concept of spontaneous generation, or abiogenesis, was developed well before the advent of the modern sciences of chemistry, biology, physics or geology.
For all their cultural achievements the ancient Greeks conducted not a single experiment to confirm or falsify even a single assumption they made about physical reality (not a one). Instead, they trusted their ability to intuit or think up answers. (In philosophy, this type of reasoning is called a priori reasoning or deduction: through deduction we can come up with all sorts of conclusions about physical reality like mice are the product of dirty shirts, wheat, etc. without any need to confirm or disprove a hypothesis.)
Aristotle (384-322 BCE) deduced larger objects by their nature were heavier and therefore fell to the ground faster than smaller objects. Aristotle’s view was considered authoritative until an experiment falsifying this assumption was finally conducted in Pisa (some 1900 years by students of Galileo). Once experimental science came in to widespread use—with the work of Galileo, Isaac Newton and Sir Francis Bacon—we reduced our dependency upon deduction, replacing it with an increasing use of inductive reasoning: through induction we “induce” or “compel” nature to relinquish her secrets by conducting experiments; that is, we aren’t satisfied by simply deducing an answer to a complex question; rather, we look for real or material causes to explain why the world works as it does.
Abiogenesis as a Scientific Concept
Not unlike Aristotle’s teaching on gravity, the ancient and pre-scientific concept of spontaneous generation persisted for centuries unchallenged; that is, until an alternative explanation for life’s origins was proposed by Charles Darwin (1809-1892 AD) in his book Origin of Species (published in 1859). Darwin’s work presented a different explanation for how life possibly emerged on Earth: life began as something simple, and over the enormous span of geologic time, evolved in to something more and more complex and various. The problem with evolutionary theory, at least as it existed in the 19th century, was it still did not explain why life began in the first place; it explained how natural selection produced a variety of life forms but did not explain the origin of life (attempts would come later). For this reason spontaneous generation continued to be regarded as a useful idea well into the 19th century.
As our understanding of the cell and life cycles improved in the latter 19th century, scientists placed increasing emphasis on looking for material causes for observed effects in biology and in the study of disease in particular. In this context, Louis Pasteur (1822-1895) developed a germ theory of disease whereby disease was understood as the product, not of the work of evil spirits, but of microscopic disease causing pathogens. In other words, people (well, most of us) abandoned magical explanations preferring to explain reality by appealing to observable mechanisms. Science posits the existence of any organism—whether we are talking mice, bacteria or alligators—is explainable through an appeal to a series of natural processes interacting with one another in a chain of causality. No spontaneity required.
Historically speaking, the words abiogenesis and spontaneous generation have been used interchangeably in the same sense the words hot and warm are used in order to refer essentially to the same thing. Honestly, some ideas are so simple we can be careless with language without risking or losing too much in the translation. This is case with the terms spontaneous generation and abiogenesis if we are just speaking off the cuff and talking in general terms as opposed to specific concepts.
Where we get in to trouble, however, is mistaking the two words for the same concept. Spontaneous generation was coined by Aristotle who attempted to explain the mysterious appearance of flies from rotting meat; whereas abiogenesis is a modern term used in reference to a chain of causality leading to the appearance of life from inanimate matter. The French philosopher and logician Peter Abelard (1079-1142 AD) argued that for the sake of clarity we must make deliberate and good use of the appropriate words when communicating with one another (or else we cannot expect to both get at the truth or transmit it accurately).
Abelard had four recommendations for those of us hoping to practice clear thinking (the third of which is most relevant to the topic at hand):
1). Use systematic doubt and question everything.
2). Learn the difference between statements of rational proof and those merely of persuasion.
3). Be precise in your use of words while expecting precision from others.
4). Watch for error (even in Holy Scriptures).
Mark Twain, an early 20th century American author, echoing Abelard observed the difference between using the right word and the almost right word was the distance between saying “lightning” instead of “lightning bug.” The way we use words matters and certainly shouldn’t become a barrier to understanding.
Confusion in Secondary Classrooms
Despite the conceptual differences between the two terms, I’ve come across science texts used in secondary classrooms that continue to use the abiogenesis/spontaneous generation interchangeably. In my own academic experience, I’ve never come across any serious evolutionary biologist who confuses the two.
In the case of the overall origins of life, the term abiogenesis is used in modern science to describe the eventual product of a lengthy, gradual process whereby the interplay of a combination of elements like carbon, hydrogen, oxygen, nitrogen mixing about in pools for hundreds of millions of years, etc. were exposed to a combination of radiation, heat, pressure, electricity, etc. inevitably forming in to simple organic compounds (due to chemical reactions).
During the Miller-Urey experiment in 1953, the conditions hypothesized as necessary (articulated above) for the development of life were simulated. During this experiment, scientists were able to generate or grow amino acids from a primordial solution (it should be noted that this experiment is ongoing and continues to generate amino acids even in the present day). Yet, the only thing “spontaneous” about generating these acids is that one could not exactly predict the exact moment the solution would produce an organic compound; however, we could and did predict that the primordial solution was capable of eventually producing organic compounds with the passage of time.
(There’s an interesting caveat here with respect to the Miller-Urey experiment. The scientists involved have acknowledged it is problematic to posit life emerged from their hypothesized primordial pools. Click here to visit a Scientific American blog discussing some of the associated problems with the experiment.)
Chemistry, biology and physics being what they are it is inevitable molecules and compounds are created through the sheer number of interactions between matter. The product of these interactions, in this case amino acids, are properly understood as organic by definition, i.e. “Of, relating to, or denoting compounds containing carbon.” Amino acids, however, are not properly understood as “living.” They are simply the building blocks of life. We are, however, still left with the task of bridging the gap between inanimate and animate (or to be a little more precise bridging the gap from simple amino acids to RNA, from RNA to DNA, and then from DNA to the development of complex organisms).
Lastly, although when these compounds formed they did so “suddenly” but there was no massive or categorical leap from one thing (a log) turning in to something completely different (an alligator).
Conclusion: Using Words Correctly Matters
The terms abiogenesis and spontaneous generation are not properly regarded in science as equivalents. I’ve read no serious modern biologist who has ever confused these two terms with one another when popularizing scientific ideas, e.g. Richard Dawkins, Stephen Gould, or Ken Miller. Again, yes, you could describe the moment something organic appeared by saying it was something spontaneously generated, but the idea that dust, rather than eggs, generated dust mites is now considered an absurd and unsupportable concept. The differences in the two terms, despite some incidental denotative similarities, point to two fundamentally different conceptions of reality, e.g. spontaneous generation reflects a pre-scientific worldview without any need for proof while abiogenesis reflects a modern scientific worldview whereby phenomenon are understood to exist as part of a chain of causality (no magic involved) which is both discoverable and falsifiable.
Why would a high school text use these terms interchangeably? I cannot answer this question without first taking a look at the background of the text’s authors and the context in which the book itself was written; it’s not as though mistakes or errors cannot creep in to a high school text book. In my honest opinion, I view any unqualified and continuing association of the two terms in any text as both problematic and confusing. (Though to be fair if a student or teacher did not have the knowledge or awareness of the history of the two concepts, there’d be no reason to suppose a logical problem would exist in treating them as equivalents.) In the end, text book creators can and do make errors; moreover, not every scientist is necessarily an expert on the history of science.
The fundamental issue I have with the unquestioned interchangeability of these terms, therefore, is in one sense literary-philosophical and one part historical: philosophically speaking, if we treat these two ideas as identical concepts we commit a sort of categorical error because they do not describe the same process; and historically speaking, one concept continues to be used by serious scientists (abiogenesis) while the other is best reserved for conversations around a discredited notion relating to dirty clothes and mice.
Students and teachers need to appreciate that words, concepts and beliefs, etc. come from somewhere; that these words have a beginning; that they do not just appear as if out of nowhere (spontaneously generated); and when we understand the history of a term’s usage we begin to appreciate how our knowledge and conceptual understanding is a the process of unfolding.