Definitions and Comparisons in

Logical Scientific Evaluation

of Evolution and Creation

by Craig Rusbult, Ph.D.

This paper does not evaluate theories of evolution or creation.
Instead, it examines principles of logic, and develops guidelines
for how theories about origins should be compared & evaluated.

Does "evolution" have a consistent definition?

If not — if evolution has many meanings that can

change — then we cannot logically evaluate it
unless the intended meaning is clarified.

1. Comparisons and Definitions 
2. The Many Meanings of Evolution 
3. The Many Meanings of Creation 
4. Comparisons that are Logically Valid 
5. Shifts of Meaning (how & how, and why) 

      1. Comparisons and Definitions

      Logical Comparisons
      An important principle for scientific evaluation, logical comparison, is illustrated by asking whether a theory proposing that John is an Olympic Weightlifter (OW) is supported by observing that John can lift a hat and place it on his head.  Yes, the OW theory predicts that John can lift the hat, and he does.  But plausible alternative theories — like "John is a weakling" or "John has average strength" — are also compatible with this result, so the observation offers little support for OW.
      When we see John lift a hat, the appropriate response is "So what?"  To justify a response of "Wow!", the evidence must be more relevant (for comparing OW with competitive theories) and more impressive.  For example, if we saw John lift a heavy weight, close to the world record, this would provide strong evidence for the plausibility of OW, since this observation is much less compatible with the alternative theories.  The principle of logical comparison says, "To distinguish between these competitive theories, we must focus on their differences (they disagree about John's ability to lift the near-record weight), not their similarities (they all agree that John can lift the hat)."
      This principle of logic is often ignored when origins theories are evaluated.  Instead of using logical comparisons, scientists and educators often claim support for evolution because "it can lift hats" instead of focusing their attention on questions that are more challenging (for evolution) and more useful (for evaluation).  A framework for logically comparing origins theories is outlined in Section 4.

    Precise Definitions
      We cannot logically compare theories unless each theory is precisely defined.  In science and education, we can improve the accuracy of our thinking and communication by using two important words — evolution and creation — with precision and consistency.  Since each of these words can have many meanings, confusion is possible.  But if we decide that confusion is undesirable, we can use precise definitions that minimize the possibilities for confusion and misunderstanding.  This worthy goal is the focus of Sections 2 and 3: The Many Meanings of Evolution, and The Many Meanings of Creation.  Then, building on this foundation of conceptual clarity, a framework for logically comparing origins theories is outlined in Section 4.

      The perils of imprecise definitions are illustrated by a sneaky car salesman who buys your seat cover for $1000 and sells you a new Porsche for $5000.  Did you get a good deal?
      The "Olympic Weightlifter" illustration is borrowed from a prominent philosopher, Elliott Sober, who is a critic of Intelligent Design.


      2. The Many Meanings of Evolution
      To logically evaluate evolution, we must carefully define each concept that is called "evolution" and critically examine the relationships between these concepts.
      In general, evolution is any process of gradual change.  In biology, evolution (E) is a change in the gene pool of a population.  But "evolution" can also refer to fossil progression, common descent, micro-E within a species, macro-E to produce a new species (*), neo-Darwinian subtheories proposing that E occurs by specific mechanisms — involving the production of genetic variation, expression of genetic variation in individuals, change of gene frequencies in a population, and production of new species, plus macro-evolutionary scenarios (details) — or a Total Macro-E claim that all biodiversity and biocomplexity was produced by the cumulative effects of natural macro-E.   { In addition, a nonscientific meaning of E is a claim — made by some atheists (Richard Dawkins,...) and some Christians — that "evolution is inerently atheistic" so theistic evolution is impossible. }
      * macro-evolution can range from minor macro-E (which occurs, for example, when two groups within a species become isolated from each other, then evolve independently until they can no longer interbreed, thus forming two species that are very similar) to major macro-E.
      In our pursuit of conceptual clarity, one option is to replace the word "evolution" (which has many meanings) with many words (each with one meaning), as I've done above.  In this context the goal of conceptual clarity is to be certain, each time "evolution" is discussed or evaluated, that the meaning is precise and clear.
      In Section 4, we'll examine four types of evolution that can be components in an origins theory:  1) small-scale E (micro-E and minor macro-E);  2) an old earth with fossil progressions;  3) full common descent;  4) Total Macro-E by natural mechanisms.


      3. The Many Meanings of Creation
      In a common cultural stereotype, there is one Judeo-Christian theory of creation.
      In reality, four basic creation theories are compatible with a basic Judeo-Christian doctrine of theistic creation:
      In young-earth creation (yeC), everything in the universe was miraculously created in a 144-hour period less than 10,000 years ago.  Later, most of the earth's geology and fossil record were formed in a global flood.
      In old-earth creation (oeC), also called progressive creation, at various times during a long history of nature (spanning billions of years) God used miraculous-appearing theistic action to create.  There are two kinds of oeC:  oeCindependent proposes independent creations "from scratch" so a new species would not necessarily have any relationships with previously existing species;  oeCmodification proposes creation by an extensive modification (by changing, adding, or deleting) of the genetic material for some members (or all members) of an existing species.  Each type of oeC proposes a history that combines miraculous-appearing creations (independent or by modification) with natural-appearing evolution.
      In theistic evolution (TE), also called evolutionary creation, natural evolution was God's method of creation, with the universe designed so complex life would naturally evolve.  Theistic Evolution and Theology

      A design theory is not a creation theory.  A theory of intelligent design, which claims that a particular feature was produced by design-directed action rather than undirected natural process, is restricted to claims that that can be scientifically evaluated.  A basic design theory does not claim that, based on scientific analysis, we can distinguish between supernatural design-action (in creation) and natural design-action (in non-creation), it just claims that "design-directed action did occur."  All theories of divine creation propose some type of intelligent design, but in our current culture a theory of Intelligent Design usually has a narrower definition, as explained in Four Types of Design.
      Here is a simple analysis of relationships between the narrow-definition Intelligent Design (in science) and creation (in theology):
• a creationist can accept a totally natural evolution with non-Design (science) and propose evolutionary creation (science + theology), or
• a creationist can reject a totally natural evolution and accept Design (science) and propose progressive creation (science + theology), or
• a person can reject a totally natural evolution and accept Design (science) and say "I don't know" or "I'm not going to tell you" when asked about creation (theology).

      What is my position?  I'm flexible and willing to change, but currently I think the most plausible creation theories in biology are "independent creation of the first life, then old-earth creation by genetic modification," because the most credible scientific theories include some design-directed action.  But the purpose of this page is to show how all theories, not just my own, should be logically compared and evaluated.


      4. Logical Comparisons of Origins Theories
      The table below lists four components of evolutionary theory (described in Section 2) and shows whether each creation theory affirms this component (YES) or denies it (no).  This lets you see the similarities and differences between neo-Darwinian "totally natural evolution" (atheistic, agnostic, or theistic) and three modern creation theories, plus outdated creation theories from two centuries ago.

theory components
(for each type of E, does
a theory say yes or no?)
creation by
of 1800
micro-E and minor macro-E YES YES YES YES no
old earth with basic fossil-E YES
full common descent
YES no no no
natural Total Macro-E YES no no no no

      This table uses accurate definitions of 4 modern theories, and allows logical comparisons:
      All modern theories agree (YES YES YES YES) about "micro-E and minor macro-E" so evidence for micro-E and minor macro-E does not help us distinguish between neo-Darwinian evolution and any of the three modern creationist theories.  And evidence for an old earth (with evolutionary fossil progressions) is not evidence against the two old-earth theories, which say "YES YES".
    Similarly, evidence for common descent (such as homologous adaptations of previously existing structures, vestigial structures, "molecular clock" analyses, and a sharing of pseudogenes, Hox genes, and genetic code) can count against one old-earth theory (with independent creation) but not another (with creation by genetic modification).  { All modern creationists accept partial common descent, but some say "no" to a claim about full common descent. }  Are design and descent compatible?
      Obviously, logical comparison is important.  To distinguish between two theories, we must focus on evidence about disputed components (where one theory says yes and the other says no), not shared components (where both say yes, or both say no).  For example, the table above shows that most "evidence for evolution" (for minor macro-E, old-earth fossil progressions, and full common descent) is not evidence for Total Macro-E when it is compared with old-earth creation by genetic modification.

      In this table the information above is arranged in a different way, to clearly show — for each comparison of two theories — the disputed components (in black) that should be the focus of attention, and the shared components (in gray) that are not relevant:

What ideas should
(and should not)
be compared in
each two-theory
The two theories that are being compared
agree about the GRAY components, but
disagree about the BLACK components.
totally natural
evolution of
all organisms
old earth

total E
old earth

total E
old earth
total E
old-earth creation
(by macromutation
of genetic material)
old earth

total E
old earth
total E
old-earth creation
(with independent
old earth
total E
young-earth creation
(with independent
creations )

note:  This table oversimplifies some relationships.  For example, oeC-independent and yeC-independent will disagree in some details of their theory-based predictions (about data that is currently unknown) and retroductions (to explain data that is already known) regarding minor macro-E, but "micro-E" is GRAY because the existence of micro-E (and minor macro-E) is consistent with either theory.


      5. Shifts of Meaning (how & how, and why)

      How to Produce a Shift
      • evolution-shifts:  Often, support is illogically shifted from a strongly supported meaning of evolution — such as basic "old earth" progressions in the fossil record, micro-E changes (like those that produce drug-resistant bacteria), or minor macro-E (that produces a new-yet-similar species) — to a less strongly supported meaning (like Total Macro-E).
      • creation-shifts:  Evidence against young-earth creation is often shifted onto old-earth creation.  { What are the practical results in education? }  And the important scientific differences between two old-earth theories — independent creation and genetic modification — are ignored. 
      With an evolution-shift the implied support for evolution increases, and with a creation-shift the implied support for creation decreases.  But in each case the shift (and associated implication) is not logically justified.

      How to Avoid a Shift
      • minimizing evolution-shifts:  Each evolutionary sub-theory (as described in Section 2) is supported by different evidence, and should have different plausibility.  We need conceptual clarity;  the sub-theories of evolution should be precisely defined and their relationships should be carefully analyzed, because if there is only "evolution" it is easy to assume that evidence for some aspects of evolution necessarily provides strong support for other aspects.  When we estimate the plausibility of an extrapolation from micro-E to Total Macro-E, there should be a rigorous evaluation for each step connecting the intermediate levels.  This evaluation should be based on tight logic, not loose language that allows a transfer of support from one level to another.  { Perhaps advocates of evolution can make a strong case for moving from lower levels of E to Total Macro-E, but the process of "extrapolating between levels" should be explicitly recognized. }
      • minimizing creation-shifts:  We should understand what each creation theory proposes, then compare these theories with each other and with theories of evolution, to see where they agree and disagree.  In a comparative evaluation we should focus on the differences between competitive theories, instead of wasting time on questions where both theories agree.  When we ask, "Does this evidence really matter?", we see that most of the evidence typically proposed in support of evolution is irrelevant when comparing Total Macro-E with old-earth creation by genetic modification or with a basic theory of intelligent design.

      strong support for Total Macro-E requires strong answers (but not proof) for tough questions:
      1. For each step in a macro-E scenario, how many mutations and how much selection would be required, how long would this take, and how probable is it?  {more about rates and complexity}
      2. Could a step-by-step process of evolution produce systems that seem irreducibly complex (because all parts seem necessary for performing the system's function) since there would be no function to "select for" until all parts are present?   Are questions allowed?
      another question, related to irreducible complexity, is even more challenging:
      X. Could a nonliving system naturally achieve the minimal complexity required to replicate itself and thus become capable of changing, in successive generations, by neo-Darwinian evolution?  For the past five decades, scientists have been learning that what is required for life seems much greater than what is possible by natural process.  { This question is "X" because it's separate from neo-Darwinian theory, which simply assumes the existence of an organism that could reproduce, and doesn't try to explain how the first living organism became alive. } { more about the first life

      Why do shifts occur?
      Shifts of meaning can arise from an intention to mislead, inadequate understanding of concepts, lack of communication skill, or (in one type of shift) a narrow focus on the most vocal form of creationism.
      But value judgments (about the relative importance of various evaluation criteria) can also provide a logical reason to ignore distinctions between theories.  For example, if a young earth is all that matters, all old-earth theories will be opposed with equal vigor because their differences will seem less important than their old-earth similarities.  And for someone whose main goal is to avoid any implication that God has "interfered with nature," all creationist theories are equally guilty.
      Value judgments are an essential part of making decisions, but they should be logically analyzed to determine whether they are contributing to inaccurate scientific evaluations.

      The Main Theme of Sections 1-5
      The quality of our thinking and evaluating, in science and education, will improve when we use precise definitions and logical comparisons, when we accurately understand all theories, explicitly acknowledge their similarities and differences, and use this knowledge in our evaluations and communications.

This page is a condensed summary of an older full-length page and is further condensed in FAQs: basic & medium & short.

The mini-sections below continue the process of trying to improve conceptual clarity, by precisely defining concepts and making distinctions between concepts that are related yet different.

      Precise Definitions
      Are definitions important?
      Imagine that "car" and "seat cover" are words with many meanings, and each word can mean just the car's seat cover, or its body, engine, drive train, gas tank, hood ornament, or the whole car.
      Will you say "yes" if a car salesman puts his hand on the cheap seat cover of your new car and says, "Will you sell me this seat cover for $1000?"  Then he points to a shiny new Porsche and says, "Do you want to buy this car for $5000?"  Of course, you would sell your seat cover for $1000, and you would buy the Porsche for $5000.  But unless you get a precise definition of what "seat cover" and "car" mean, in writing, you might lose your car and $4000, and end up with only a shiny new hood ornament.
      Yes, precise definitions are important in this imaginary scenario, and in real life.  For example, similar shifts of meaning often occur in education about evolution.

      mechanistic theories of evolution propose specific natural causes of evolution.  In neo-Darwinian theories, Darwin's basic ideas are combined with modern genetics, mathematical population analysis, and molecular biology;  modern neo-Darwinism is a broad umbrella of scientists who disagree about some questions (such as gradualism versus punctuated equilibrium) but agree on major concepts.  neo-Darwinian theories of evolution propose mechanisms for:
      (1) producing genetic variation in a population through introducing new genetic material (by mutation, duplication followed by mutation, or gene inflow) and shuffling old material (by gene crossovers and sexual reproduction);  (2) expressing genetic variation in the characteristics (physiology, structure, behavior,...) of individuals;  (3) causing changes in gene frequencies in a population through natural selection (by differential rates of survival and reproduction for individuals or groups), random genetic drift (especially in small subpopulations), and gene inflow or outflow;  (4) producing new species by reproductive isolation (due to geography, behavior, physiology,...).  These mechanisms are explained in Understanding Evolution.
      During their studies of bio-E, scientists can use available data to construct descriptive and causal scenarios, to determine what happened and why.  Evolutionary scenarios for the history of life can involve many factors, including selection, drift, and isolation, relationships among species (competition and mutualism,...), climate shifts and continental drifts, linked genes and developmental regulators, changes in the functions of enzymes & organs, and more.  Scientists can ask a variety of questions and seek answers in various ways, such as estimating the rates of evolutionary change and the importance of different causal factors, while contributing to the construction of theory-based models for the long-term, large-scale changes of Total Macro-E.

      Is DESIGN defined by DESCENT?
      Does a theory of design have to deny descent?  No, because full common descent is only one component of naturalistic evolution, which could be false even if common descent was true.  A theory of design can affirm common descent, or deny it, or just say "I don't know" because a basic design theory — which claims only that "design-directed action did occur" — doesn't have to explain the details about how, when, why, and who.
      But conventional theories of neo-Darwinian evolution — which claim "Total Macro-E by undirected natural process with no design" — require full common descent, plus an old earth.  Therefore, some proponents of design argue against full common descent (or an old earth) because they think this is justified by the evidence and will be helpful in providing evidence against non-design evolution, even though it isn't necessary because a discontinuity in descent is only one of several possible ways that evolution might be false.
      Other proponents of design, including myself, think the scientific evidence is consistent with full common descent (and an old earth) but not Total Macro-E. *  If logical scientific evaluation provides support for the plausibility of a full common descent, arguing against descent is counter-productive in building a case for design because this will focus attention on aspects of biology where (I think) the evidence is consistent with neo-Darwinian theory, and will distract attention from important questions — about rates of change, irreducible complexity,... — where evidence indicates that a theory of Total Macro-E may be incorrect.  {But I'm open to the possibility that descent is almost-full but not totally-full, and am willing to seriously consider evidence for this. }
      To make a logical evaluation based on evidence about descent, we must think in terms of (at least) four theories: Total Macro-Evolution (Descent-NonDesign) and oeCmodification (Descent-Design) which affirm full descent, plus oeCindependent and yeC (both are NonDescent-Design) which deny full descent although they affirm partial descent.  In a three-way logical comparison, evidence for full descent counts for both Descent-NonDesign and Descent-Design, relative to either theory of NonDescent-Design, old-earth or young-earth.  But evidence for full descent (or against it) does not help us distinguish between Descent-NonDesign and Descent-Design, since they agree about descent.

      Is EVOLUTION defined by DESCENT?
      Above, I explain why design is not defined by descent, which also may not define evolution.  Advocates of naturalistic evolution often defend their claim that "evolution is fact" by pointing to the history of biological development in the fossil record.  And they often define the essence of evolution as full common descent.  But full descent is accepted by Michael Behe, so why is there such a strong reaction against Behe — by not allowing him to ask his questions about irreducible complexity in science journals (*) — if the essence of evolution is descent, rather than a history that is 100% natural?
      * from Critical Thinking in Closed Science: "Consistent with the standards of modern molecular biology, Behe is encouraging a detailed examination of evolution, at a deeper level with higher standards.  As expected, his challenges have stimulated creative thinking and... have served as a catalyst for action by defenders of evolution who want to show he is wrong, and by proponents of design.  .....  Perhaps, when the evidence and arguments have been thoroughly examined and debated, when more experiments and analyses have been done, Behe's ideas will be shown to be wrong.  But critical thinking should be allowed in science, so there should at least be some recognition — by allowing publication in science journals — that his questions are important and are worthy of being asked."

      Is proof possible in science?
      Although in mathematics or formal logic it is possible to prove truth or falsity, in science it is more useful to think in terms of the relative amounts of evidence-based support for a theory and against it.  In science we cannot logically prove that a theory (proposing either design or nondesign) is true or false, but scientists can develop a logically justified confidence in the truth or falsity of a theory.  As a reminder that the outcome of theory evaluation is an educated estimate rather than a claim for certainty, it is useful to think in terms of a theory status, which can range along a continuum from low to high, to describe the degree of confidence in a theory.   {more about design & proof}

      Young-Earth Creationism:
      What are the practical results in education?
      In the past four decades, since the revival of flood geology in 1961, the most prominent advocates of young-earth views have framed the origins question as "Christianity versus atheism" with Christianity represented by only young-earth creation, with old-earth creation excluded from consideration.  In American education, the practical results have been:
      1) an increase in the perceived plausibility of evolution, because in a scientific competition that includes only two models (young-earth creation and old-earth evolution) evolution will "win points" simply because it proposes an old universe, and all evidence for an old earth becomes evidence for evolution;
      2) a decrease in the willingness of science teachers to criticize evolution based on scientific evidence and logical evaluation, because teachers don't want to give credibility to the young-universe theories that usually have accompanied criticisms of evolution, and because they mistakenly assume that legal prohibitions against teaching young-earth creationism also apply to any serious questioning of evolution.

This website for Whole-Person Education has TWO KINDS OF LINKS:
an ITALICIZED LINK keeps you inside a page, moving you to another part of it, and
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Here are other related pages:

Logical Evaluations of Evolution
(a longer version of this page)

Critical Thinking about Evolution in Public Education

and from a variety of authors,
Origins Education in Public Schools
Biological Evolution — Principles & Questions

This page is

Copyright © 2002 by Craig Rusbult, all rights reserved