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29+ Evidences for
The Scientific Case for Common DescentVersion 2.85
Copyright © 1999-2004 by Douglas Theobald,
Posted January 17, 2005
Permission is granted to copy and print these
pages in total for non-profit personal, educational, research, or critical
Evolution, the overarching concept that unifies the biological sciences,
in fact embraces a plurality of theories and hypotheses. In evolutionary debates
one is apt to hear evolution roughly parceled between the terms "microevolution"
and "macroevolution". Microevolution, or change beneath the species level, may
be thought of as relatively small scale change in the functional and genetic
constituencies of populations of organisms. That this occurs and has been
observed is generally undisputed by critics of evolution. What is vigorously
challenged, however, is macroevolution.
Macroevolution is evolution on the "grand scale" resulting in the origin of
higher taxa. In evolutionary theory it thus entails common ancestry, descent
with modification, the genealogical relatedness of all life, transformation of
species, and large scale functional and structural changes of populations
through time, all above the species level (Freeman and
Herron 2004; Futuyma 1998; Ridley 1993).
Common descent is a general descriptive theory that concerns the genetic
origins of living organisms (though not the ultimate origin of life). The theory
specifically postulates that all of the earth's known biota are genealogically
related, much in the same way that siblings or cousins are related to one
another. Thus, macroevolutionary history and processes necessarily entail the
transformation of one species into another and, consequently, the origin of
higher taxa. Because it is so well supported scientifically, common descent is
often called the "fact of
evolution" by biologists. For these reasons, proponents of special creation
are especially hostile to the macroevolutionary foundation of the biological
This article directly addresses the scientific evidence in favor of common
descent and macroevolution. This article is specifically intended for those who
are scientifically minded but, for one reason or another, have come to believe
that macroevolutionary theory explains little, makes few or no testable
predictions, is unfalsifiable, or has not been scientifically demonstrated.
A Critique of
Douglas Theobald's "29 Evidences for Macroevolution"
Lawyer, Churches of Christ minister, and young-earth creationist
Ashby Camp argues that the evidence is insufficient to establish that
all organisms share the same biological ancestor.
Responds to Ashby Camp's "Critique"
The author of this essay has written a response to Camp.
What is Universal Common Descent?
Universal common descent is the hypothesis that all living, terrestrial
organisms are genealogically related. All existing species originated gradually
by biological, reproductive processes on a geological timescale. Modern
organisms are the genetic descendants of one original species
or communal gene pool. Genetical "gradualness", a much misunderstood term, is a
mode of biological change that is dependent on population phenomena; it is not a
statement about the rate or tempo of evolution. Truly genetically gradual events
are changes within the range of biological variation expected between two
consecutive generations. Morphological change may appear fast, geologically
speaking, yet still be genetically gradual (Darwin 1872, pp.
312-317; Dawkins 1996,
2002, pp. 150-152; Mayr 1991, pp.
1983). Though gradualness is not a mechanism of evolutionary change, it
imposes severe constraints on possible macroevolutionary events. Likewise, the
requirement of gradualness necessarily restricts the possible mechanisms of
common descent and adaptation, briefly discussed below.
Common Descent Can Be Tested Independently of
In this essay, universal common descent alone is specifically considered and
weighed against the scientific evidence. In general, separate
"microevolutionary" theories are left unaddressed. Microevolutionary theories
are gradualistic explanatory mechanisms that biologists use to account for the
origin and evolution of macroevolutionary adaptations and variation. These
mechanisms include such concepts as natural selection, genetic drift,
sexual selection, neutral evolution, and theories of speciation. The
fundamentals of genetics, developmental biology, molecular biology,
biochemistry, and geology are assumed to be fundamentally correct—especially
those that do not directly purport to explain adaptation. However, whether
microevolutionary theories are sufficient to account for macroevolutionary
adaptations is a question that is left open.
Therefore, the evidence for common descent discussed here is independent of
specific gradualistic explanatory mechanisms. None of the dozens of predictions
directly address how macroevolution has occurred, how fins were able to
develop into limbs, how the leopard got its spots, or how the vertebrate eye
evolved. None of the evidence recounted here assumes that natural selection is
valid. None of the evidence assumes that natural selection is sufficient for
generating adaptations or the differences between species and other taxa.
Because of this evidentiary independence, the validity of the macroevolutionary
conclusion does not depend on whether natural selection, or the inheritance of
acquired characaters, or a force vitale, or something else is the true
mechanism of adaptive evolutionary change. The scientific case for common
descent stands, regardless.
Furthermore, because it is not part of evolutionary theory, abiogenesis
also is not considered in this discussion of macroevolution: abiogenesis is an
independent hypothesis. In evolutionary theory it is taken as axiomatic that an
original self-replicating life form existed in the distant past, regardless of
its origin. All scientific theories have their respective, specific explanatory
domains; no scientific theory proposes to explain everything. Quantum mechanics
does not explain the ultimate origin of particles and energy, even though
nothing in that theory could work without particles and energy. Neither Newton's
theory of universal gravitation nor the general theory of relativity attempt to
explain the origin of matter or gravity, even though both theories would be
meaningless without the a priori existence of gravity and matter.
Similarly, universal common descent is restricted to the biological patterns
found in the Earth's biota; it does not attempt to explain the ultimate origin
What is Meant by "Scientific
Evidence" for Common Descent?
Scientific theories are validated by empirical testing against physical
observations. Theories are not judged simply by their logical compatibility with
the available data. Independent empirical testability is the hallmark of
science—in science, an explanation must not only be compatible with the observed
data, it must also be testable. By "testable" we mean that the hypothesis makes
predictions about what observable evidence would be consistent and what would be
incompatible with the hypothesis. Simple compatibility, in itself, is
insufficient as scientific evidence, because all physical observations are
consistent with an infinite number of unscientific conjectures. Furthermore, a
scientific explanation must make risky predictions -- the predictions should be
necessary if the theory is correct, and few other theories should make the same
As a clear example of an untestable, unscientific, hypothesis that is
perfectly consistent with empirical observations, consider solipsism. The
so-called hypothesis of solipsism holds that all of reality is the product of
your mind. What experiments could be performed, what observations could be made,
that could demonstrate that solipsism is wrong? Even though it is logically
consistent with the data, solipsism cannot be tested by independent researchers.
Any and all evidence is consistent with solipsism. Solipsism is unscientific
precisely because no possible evidence could stand in contradiction to its
predictions. For those interested, a brief explication of the scientific method
and scientific philosophy has been included, such as what is meant by
"scientific evidence", "falsification", and "testability".
In the following list of evidences, 30 major predictions of the hypothesis of
common descent are enumerated and discussed. Under each point is a demonstration
of how the prediction fairs against actual biological testing. Each point lists
a few examples of evolutionary confirmations followed by potential
falsifications. Since one fundamental concept generates all of these
predictions, most of them are interrelated. So that the logic will be easy to
follow, related predictions are grouped into five separate subdivisions. Each
subdivision has a paragraph or two introducing the main idea that unites the
various predictions in that section. There are many in-text references given
for each point. As will be seen, universal common descent makes many specific
predictions about what should and what should not be observed in the biological
world, and it has fared very well against empirically-obtained observations from
the past 140+ years of intense scientific investigation.
It must be stressed that this approach to demonstrating the scientific
support for macroevolution is not a circular argument: the truth of
macroevolution is not assumed a priori in this discussion. Simply put,
the theory of universal common descent, combined with modern biological
knowledge, is used to deduce predictions. These predictions are then compared to
the real world in order see how the theory fairs in light of the observable
evidence. In every example, it is quite possible that the predictions could be
contradicted by the empirical evidence. In fact, if universal common descent
were not accurrate, it is highly probable that these predictions would fail.
These empirically validated predictions present such strong evidence for common
descent for precisely this reason. The few examples given for each prediction
are meant to represent general trends. By no means do I purport to state all
predictions or potential falsifications; there are many more out there for the
inquiring soul to uncover.
Are There Other Scientifically Valid
The worldwide scientific research community from over the past 140 years has
discovered that no known hypothesis other than universal common descent can
account scientifically for the unity, diversity, and patterns of terrestrial
life. This hypothesis has been verified and corroborated so extensively that it
is currently accepted as fact by the overwhelming majority of professional
researchers in the biological and geological sciences (AAAS 1990; NAS 2003; NCSE 2003; Working Group
2001). No alternate explanations compete scientifically with common descent,
primarily for four main reasons: (1) so many of the predictions of common
descent have been confirmed from independent areas of science, (2) no
significant contradictory evidence has yet been found, (3) competing
possibilities have been contradicted by enormous amounts of scientific data, and
(4) many other explanations are untestable, though they may be trivially
consistent with biological data.
When evaluating the scientific evidence provided in the following pages,
please consider alternate explanations. Most importantly, for each piece of
evidence, critically consider what potential observations, if found, would be
incompatible with a given alternate explanation. If none exist, that alternate
explanation is not scientific. As explained above, a hypothesis that is simply
compatible with certain empirical observations cannot use those observations as
supporting scientific evidence.
How to Cite This Document
Many people have asked how to cite this work in formal research papers and
academic articles. This work is an online publication, published by the
Talk.Origins archive. There are standard academic procedures for citing
online publications. For example, if you last accessed this page on January 12,
2004, and used version 2.83, here is a reference in formal MLA style:
Theobald, Douglas L. "29+ Evidences
Macroevolution: The Scientific Case for Common Descent." The Talk.Origins
Archive. Vers. 2.83. 2004. 12 Jan, 2004
For more information about citing online sources, including MLA, APA, Chicago, and
CBE styles, see
the formal style guidelines given in the book Online!: a reference
guide to using internet sources.
"... there are many reasons why you might not understand [an explanation of
a scientific theory] ... Finally, there is this possibility: after I tell you
something, you just can't believe it. You can't accept it. You don't like it.
A little screen comes down and you don't listen anymore. I'm going to describe
to you how Nature is - and if you don't like it, that's going to get in the
way of your understanding it. It's a problem that [scientists] have learned to
deal with: They've learned to realize that whether they like a theory or they
don't like a theory is not the essential question. Rather, it is
whether or not the theory gives predictions that agree with experiment. It is
not a question of whether a theory is philosophically delightful, or easy to
understand, or perfectly reasonable from the point of view of common sense. [A
scientific theory] describes Nature as absurd from the point of view of common
sense. And it agrees fully with experiment. So I hope you can accept Nature as
She is - absurd.
I'm going to have fun telling you about this absurdity, because I find it
delightful. Please don't turn yourself off because you can't believe Nature is
so strange. Just hear me all out, and I hope you'll be as delighted as I am
when we're through. "
- Richard P. Feynman (1918-1988),
from the introductory lecture on
quantum mechanics reproduced in QED: The Strange Theory of Light and
Matter (Feynman 1985).
American Association for
the Advancement of Science (1990) Science for All Americans. http://www.project2061.org/tools/sfaaol/sfaatoc.htm
Darwin, C. (1872) The Origin of Species. Sixth
Edition. The Modern Library, New York.
Dawkins, R. (1996) The Blind Watchmaker. New
Feynman, R. P. (1985) QED: The Strange Theory of
Light and Matter. Princeton, NJ: Princeton University Press.
Freeman, S. and Herron, J. C. (2004)
Evolutionary analysis Third edition. Upper Saddle River, NJ:
Futuyma, D. (1998) Evolutionary Biology. Third
edition. Sunderland, MA: Sinauer Associates.
Geological Society of
America (2001) "Evolution." http://www.geosociety.org/aboutus/position.htm
Gould, S. J. (2002) The Structure of Evolutionary
Theory. Cambridge, MA: Belknap Press of Harvard University Press.
Mayr, E. (1991) One Long Argument. Cambridge,
Harvard University Press.
National Academy of
Sciences. (2003) multiple statements. http://www.nationalacademies.org/attic/evolution/index.html
National Center for
Science Education. (2003) "Voices for Evolution: Statements from Scientific
and Scholarly Organizations."
A compilation of statements from 47 of the
world's largest and most prestigious societies of professional research
scientists, on the importance of evolutionary theory.
Rhodes, F. H. T. (1983) "Gradualism, punctuated
equilibria, and the origin of species." Nature 305: 269-272.
Ridley, M. (1993) Evolution. Boston: Blackwell
Working Group (2001) "Evolution, Science, and
Society: Evolutionary biology and the national research agenda." American
Naturalist. 158: S1. Endorsed by:
Institute of Biological Sciences,
American Society of Naturalists,
Animal Behavior Society,
Ecological Society of America,
Genetics Society of America,
Society for Molecular Biology and Evolution,
Society for the Study of
Society of Systematic
Full-text at http://www.rci.rutgers.edu/~ecolevol/fulldoc.pdf