Understanding Evolution

Introduction

Natural selection is the most popular natural explanation for the emergence of Earth’s vast biosphere. In 1859, Charles Darwin, the father of the modern theory of evolution, introduced this concept in The Origin of Species.

Perhaps, the two most popular classroom examples are the Galápagos finch beaks and the development of microbial resistance. Surprisingly, however, while both illustrate adaptation, neither has been observed to progress to form a new species, i.e., “The Origin of Species.”

These two examples illustrate the larger issue with Darwin’s “Origin of Species” theory: the disconnect between adaptation and speciation. Fortunately, understanding these disconnections scientifically provides insight into deciphering evolution facts from fiction.

V.I.S.T.A.

Niles Eldredge (pictured left), of the American Museum of Natural History, introduced the V.I.S.T.A. framework to codify the principles of Darwin’s theory. Within this framework, Eldridge identifies five structural principles of natural selection: variation, inheritance, selection, time, and adaptation.

Eldredge proposed that Darwin’s “Origin of Species” theory was based on inferences from these five observed biological principles. Interestingly, Darwin carefully crafted the title of his book –

“On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life.”

The full title represents two disconnected processes. While “The Origin of Species” infers a process of speciation, “Preservation of Favoured Races” refers to a process of conservation. However, in the text, Darwin fused these two disconnected processes under a single framework: natural selection.

Natural Selection

Natural selection, a cornerstone concept in modern biology, plays a pivotal role in shaping Earth’s vast biosphere. In the wake of more than a century of research, scientists increasingly recognize Darwin’s concept of natural selection as two distinct processes: microevolution and macroevolution.

Microevolution is an adaptive process within a species, while macroevolution is a process of speciation that produces new species. Darwin envisioned both as driven by natural selection. An abundance of scientific evidence supports microevolution. However, the scientific evidence for macroevolution has never been directly observed or successfully tested.

This evolutionary disconnect in Darwin’s theory stems from the conclusions constructed using different methods of study. While the adaptive changes of microevolution are directly observable, macroevolutionary changes have never been directly observed.

As published in 1859, macroevolution was presumed to be an extension of continuous microevolution. However, as will be discussed, twentieth-century biotechnological advances challenged his presumption.

The source of Darwin’s divergent concept stems, in part, from technological grounds and, more importantly, from his study method.

Study Method

Darwin’s study method approach used deductive reasoning, reasoning based on assumptions rather than direct observation. The two methods of reasoning for studying nature are deduction and induction. While primarily drawing from deductive reasoning, Darwin did use inductive reasoning, but only by inference, not from empirical observation.

Inductive reasoning based on empirical observation distinguishes science from philosophy. While reasoning is used in both approaches, there are significant differences in their predictive value. Reasoning independent of direct empirical observations is not inductive reasoning. When reasoning is detached from direct observation, it ceases to be inductive and becomes either deductive or speculative.

Inductive reasoning extracts concepts drawn only from direct, repeatable, descriptive, and measurable observations. Conclusions drawn only from repeatable observations are inductive reasoning. Philosophy, by contrast, does not require repeatable direct observations.

History demonstrates how these approaches, philosophical or scientific, can lead to vast differences in understanding nature.

Philosophical Approach

While a philosophical approach allows flexibility without strict principles, scientific approaches are principled and use systematic and structured methods. Understanding the distinction, Darwin claimed to have used the scientific approach. In his Autobiography, Darwin recorded that he began with “True Baconian principles and without any theory collected facts” in 1837.

Bacon’s systematic method of studying nature launched the Scientific Revolution – principles of science are still essential in the twenty-first century. Perhaps, to disguise his approach, Darwin quoted from Francis Bacon in the opening pages of The Origin of Species – in all six editions.

“… let no man out of a weak conceit… think or maintain, that a man can search too far or be too well studied in the book of God’s word…”

Even though inferring adherence to Baconian principles and “God’s word,” Darwin didn’t. When questioned by Cambridge alumnus Henry Fawcett in 1861 following “The Great Debate,” Darwin recommended abandoning the principles of science –

“How odd it is that everyone should not see that all observation must be for or against some view if it is to be of any service.”

After 1837, philosophy incrementally replaced Baconian principles. Philosophical approaches continue to be widely practiced in the twenty-first century. Without any supportive evidence, Astrobiologists at NASA extended Darwin’s hypothesis to define what life is –

“Life is a self-sustaining chemical system capable of Darwinian evolution.”

The concept of macroevolution and NASA’s definition of life may be logical deductions. However, without empirical support and testing, neither idea is scientifically valid.

Scientific Approaches

Science is a systematic process of understanding the natural world using empirical evidence, observation, experimentation, testing, and inductive analysis. With a scientific approach, the causes and effects in nature can be validated or falsified; philosophical approaches can’t. Darwin’s power of natural selection argument illustrates the problem using an intellectual approach –

“I can see no limit to this power [natural selection] in slowly and beautifully adapting each form to the most complex relations of life.”

However, Darwin’s analysis lacked empirical evidence. Therefore, his approach was philosophical, not scientific – a ubiquitous approach applied throughout The Origin of Species. Modern scientists now understand, through testing, that natural selection limits itself to what already exists.

A scientific approach is the only proven method to unlock nature’s mysteries; however, scientifically validating a theory is challenging. And, as essential as a scientific approach is, only repetitive testing can maintain its validation. In the words of Albert Einstein (pictured right) –

“No amount of experimentation can ever prove me right; a single experiment can prove me wrong.”

Nevertheless, under the guise of science, Darwin generated one of the most contentious theories in the history of science. Since then, “The Great Debate” over the validity of evolution continues into its second century.

“The Great Debate”

Inspired by Darwin, “The Great Debate” continues into the twenty-first century. Samuel Wilberforce (pictured left) and Thomas Huxley (pictured right) launched the debate in 1860 following the publication of the Origin of Species in 1859.

Huxley held a gold medal award in biology from the University of London, but did not qualify for a university degree. Samuel Wilberforce graduated with a “first-class degree” in mathematics and classics from the University of Oxford and was appointed Dean of Westminster Abbey.

As the son of William Wilberforce, the leader of Britain’s abolitionist movement, Wilberforce’s debating roots ran deep. Huxley, known as Darwin’s Bulldog, confronted Wilberforce, a critic of Darwin’s hypothesis, with each side declaring victory. By twenty-first-century standards, philosophy on both sides drove the debate, not science.

The outcome illustrates how different approaches, even among the highly educated, may lead to different interpretations of nature – even when using the same evidence. The philosophical approach searches for the meaning and purpose of the biosphere. By contrast, the scientific approach searches for the natural laws governing the biosphere.

By Investigation Evolution, “The Great Debate” continues, loaded with evidence from fields of science inconceivable in the nineteenth century.

Tools of Science

Science is a systematic, principled approach to unlocking nature’s hidden mysteries. Its approach includes objective observation, quantitative and qualitative assessments, and testing. Analyzing empirically obtained observations using inductive reasoning is crucial to the scientific method.

Science and philosophy differ vastly in their goals and methods. While science aims to understand nature’s laws, philosophy seeks to understand knowledge, reality, and existence.

Science is constrained to analyze empirical evidence inductively. By contrast, philosophy is free of constraints to explore abstract concepts using logic and reason. As a result, a philosophical approach can be influenced by investigator bias, as Darwin practiced.

The tools for scientifically validating a law of nature, such as natural selection, are not in philosophy’s tool chest.

Testing in Moths

In the mid-twentieth century, the first scientific test of natural selection was on moths. British geneticist Bernard Kettlewell (pictured left) tested the role of natural selection by observing the effect of industrial pollution on the coloring of peppered moths (pictured right). By observing how dark moth populations gradually surpassed light-colored moths, Kettlewell concluded that industrial pollution induced adaptive darkening through natural selection.

In 1959, Kettlewell published the results of his study, “Darwin’s Missing Evidence,” in Scientific American. British geneticist Philip. M. Sheppard called the phenomenon –

“… the most spectacular evolutionary change ever witnessed and recorded by man.”

Kettlewell’s study validated the adaptive role of natural selection. As industrial pollution decreased, the dark and light moth populations gradually returned to their pre-industrial levels. Therefore, Kettlewell’s peppered moth studies demonstrated how adaptations within a species can align with environmental changes.

Testing in Bacteria

Richard Lenski (pictured left), a professor at Michigan State University, explored the role of natural selection further in microbes. In the longest evolution laboratory experiment in the history of biology, Lenski tested the transition into a speciation process – macroevolution. Can adaptive changes transition into a speciation process? In 1988, Lenski launched the test.

Although adaptive changes developed in Escherichia coli following exposure to varying environments (pictured on the right), no evidence of macroevolution was observed. In 2017, writing for Science Alert, Fiona MacDonald placed the comparison between bacteria and human evolution into context –

“Scientists have spent the past 30 years carefully tracking evolution across more than 68,000 generations of E. coli bacteria – the equivalent of more than 1 million years of human evolution.”

Like Kettlewell, Lenski began and ended with the same species—Escherichia coli. Macroevolution never happened. Lenski transferred the study to Jeffrey E. Barrick at the University of Texas in 2022. Since then, the testing has continued. However, Barrick has not published evidence supporting Darwin’s “origin of species” concept.

Empirical observations in moths and experimental testing in bacteria provide scientific support for the concept of microevolution. However, the concept of macroevolution has not yet been scientifically validated. Science provides finely tuned processes powered to separate facts of nature from fictional stories.

Nicholas Copernicus (1473-1543) introduced a radically new way of separating facts from fiction, later known as the Scientific Method. A Prussian Renaissance mathematician and astronomer, Copernicus broke philosophy’s academic domination, revolutionizing the method for studying nature.

Science Testing Methods

The introduction of scientific principles unleashed a global Scientific Revolution, overturning ancient Greek dogmas. In the sixteenth century, Nicholas Copernicus (1473-1543) (pictured left) flipped Aristotle’s geocentric view of the universe. Using objective observations and repetitive empirical observations, Copernicus inductively concluded that the Sun, not Earth, was the center of our solar system, a heliocentric theory.

This new approach ignited a cultural and scientific revolution in the study of nature. Francis Bacon (1561-1626) later further formalized Copernicus’s approach. The systematic principles of Bacon’s approach, known as the scientific method, establish clear boundaries between science and non-science. The scientific method is an empirical method for acquiring knowledge about nature.

The critical components of science include formulating hypotheses through inductive reasoning based on objective observations and testing them.

Scientific Method

Francis Bacon (pictured right), co-founder of the Royal Society, formalized and systematized Copernicus’s approach. However, Darwin upended Bacon’s principles, switching from objective observations with inductive reasoning to subjective observations with deductive reasoning. Notably, Darwin never performed any testing. According to Darwin, objective observations are counterproductive –

“How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service.”

When questioned by American naturalist Asa Gray about his study approach, Darwin candidly replied in 1859 –

“What you hint at generally is very, very true: that my work is grievously hypothetical, and large parts are by no means worthy of being called induction, my commonest error being probably induction from too few facts.”

Bacon’s scientific principles, grounded in objective observations, inductive logic, and experimental testing, remain modern science’s premier investigative standard. Applying Bacon’s approach can help validate the laws of cause and effect in nature, such as Isaac Newton’s (pictured left) laws of gravity and motion. Lenski’s ongoing study on E. coli evolution is an example of applying the scientific method in biology.

However, experimental testing is not always feasible. Naturalists use an observational or historical science approach when experimental manipulations are not feasible.

Observational Science

The observation science approach uses the scientific method but replaces manipulative experimental testing with non-manipulative testing. This testing validity approach is the primary study method in scientific fields such as physics, chemistry, geology, astronomy, and health and population sciences.

Rather than identifying cause-and-effect relationships using experimental testing, observational science aims to identify associations between variables. As Kettlewell’s moth study is a classic example, sequencing genomes (pictured right) is a modern example of observational science.

Observational science cannot validate a theory with absolute certainty; it only validates its probability.

Historical Science

The study of ancient biology, known as paleontology, began with ancient Greek philosophers. As the only direct evidence for ancient Earth, paleontology is an essential field for scientifically validating the hypothesis of evolution. Studying ancient artifacts is known as historical science, which applies scientific principles of observation to the phenomena of past events.

The emergence of advanced biotechnologies beginning in the late twentieth century extended the reach of modern paleontology. Scientists can now extract and analyze the genetic material in fossils.

As the only discipline that directly studies early life, historical science is crucial for testing the validity of evolution.

Degrees of Testing Validity

These different scientific approaches have different degrees of testing validity. The word “valid” originates from the Latin word validus, meaning strong. Experimental testing differentiates the scientific method from other scientific approaches by manipulating testing variables. Hence, the scientific method is science’s most rigorous method of testing.

The scientific method can validate the laws of cause and effect in nature. For example, Newton manipulated weights and distances to validate the law of gravity (pictured right). However, Lenski never validated natural selection’s role in speciation, i.e., “the origin of species.”

By comparison, observational and historical sciences use probabilistic calculations when variable manipulation is not feasible for testing. Unlike the scientific method, neither observation nor historical science can definitively prove or disprove a theory – only probabilities.

Darwin’s Approaches

Popularized by Aristotle in Western academia, Darwin’s approach to natural selection originated in Greek philosophy. While Darwin highly regarded Bacon’s scientific method, he simultaneously downplayed the importance of scientific principles. In the words of evolutionary biologist Francisco Ayala –

“There is a contradiction between Darwin’s methodology and how he described it for public consumption.”

Although portrayed as a scientist, Darwin’s approach was inconsistent with scientific principles. The influence of Darwin’s practice of blending philosophy with science continues as a ubiquitous practice within Western academia.

NASA’s definition of “life” exemplifies the popular acceptance of Darwin’s blending approach of philosophy and science. A “self-sustaining chemical system” has yet to be observed and tested.

Charles Darwin

Darwin’s Red Notebook (1837) and “I Think” Tree of Life (pictured left) illustrated his approach. “I think” had replaced his “I observed” approach just months after returning to England on the HMS Beagle. The letters A, B, C, and D, representing different “species,” were speculations but never observed in nature.

After more than two decades, in The Origin of Species (1859), Darwin replaced his “I Think” drawing with a diagram (pictured right) in which different “species” were speculations depicted as letters and numbered letters, also never observed in nature. Darwin argued –

“The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth.”

However, unlike Newton, Darwin never defined the meaning of his letters. Precise definitions lay the foundation for scientific progress, enabling effective communication and collaboration. The influence of family history and contemporary philosophical currents formulated the framework of Darwin’s hypothesis of natural selection, replacing objective observations.

Erasmus Darwin

Charles Darwin aligned with the ideological perspectives of his grandfather, Erasmus Darwin (pictured right). As a highly educated Freemason, he was a sought-after physician, even by King George III. At the time, the increasing popularity of the Age of Enlightenment endeavored to blur the distinction between science and philosophy.

In his two-volume Zoonomia, the Laws of Organic Life (1794-96), Erasmus encouraged readers to use their imaginations, arguing –

“Would it be too bold to imagine that all warm-blooded animals have arisen from one living filament, which the great First Cause endued with animality… possessing the faculty of continuing to improve by its own inherent activity, and of delivering down these improvements by generation to its posterity, world without end?”

Philosophy Driven

In the last chapter of The Origin of Species, Darwin acknowledged his philosophical approach using logical arguments, writing –

“As this whole volume is one long argument… “

While enjoying international popularity, he was less popular among his colleagues at The Royal Society.

Royal Society Colleagues

The Royal Society, co-founded by Francis Bacon in 1660, remains the first and longest-running scientific organization in Western Civilization. As the organization that distinguished science from the influence of philosophy, the Society emerged as a cornerstone institution guiding the Scientific Revolution. The Society sets standards and recognizes and awards scientific advancements.

Principally, the Society upheld the inductive principles of science, rejecting philosophical and logical deductive arguments. To reflect its mission, the Society adopted the motto – Nullius in Verba – meaning “take nobody’s word for it.”

Darwin Then and Now is an educational resource on the intersection of evolution and science, highlighting the ongoing challenges to the theory of evolution.

Move On

Explore how to understand twenty-first-century concepts of evolution further using the following links –

- The Understanding Evolution (current page) category showcases how different investigative approaches can lead to diverse conclusions. Subcategories include –
  - Studying Evolution explains how key evolution terms have changed since The Origin of Species was published in 1859.
  - What is Science explains Charles Darwin’s approach to science and how modern science approaches are used for different investigative purposes.
  - Evolution and Science feature study articles on how the scientific evidence influences the current understanding of evolution.
  - Theory and Consensus feature articles on the historical timelines of the theory and Natural Selection.
- The Biography of Charles Darwin category showcases relevant aspects of his life.
- The Glossary defines terms used in studying the theory of biological evolution.

Explore Darwin’s five principles of natural selection, coined in the acronym V.I.S.T.A –