Intelligent Design is a well-worn concept in theological
argument. Since ancient times, the harmony and complexity of natural organs
and systems have served as "proof" for the existence of God. In modern times
before Darwin (1859), William Paley (1802) was the most famous proponent of
this idea. Remember the watch found on the heath? Paley supposed that, just
as the discovery of such an intricate mechanical setting would be proof of a
human designer, so the intricate mechanisms of the natural world, such as
the human eye, prove the existence of a benevolent, divine designer. Today
design has new currency in the latest anti-evolution thrust. Pennock gives a
list of its academic sponsors (Pennock 1999, 29) and cites Philip Johnson as
"the most influential new creationist and unofficial general" of the
Intelligent Design school. Johnson is a retired professor of law at the
University of California at Berkeley and author of Darwin on Trial
(1991) and Defeating Darwinism (1997). Since the word design
itself implies plan or purpose, it appears redundant to say "intelligent
design" unless one means to imply intelligence of the highest order or
divine intelligence. Despite its abstract aura, the origin of the term is
undeniably religious.
By their own definition, creationists believe that the
world in general, and mankind in particular, are designed and exist for a
divinely ordained purpose (Pennock 2001). Therefore, creationists reject the
possibility that new species appear through evolution by common descent,
which proceeds without a preordained purpose. They offer as the
alternative Intelligent Design: the purposeful fashioning of each species by
an intelligent designer-by implication God. Like its forerunner, creation
science, this movement presumes that by undermining Darwinism they ensure
Intelligent Design reigns as the sole available alternative, ignoring
numerous other creation myths. A full defense of evolution is available
elsewhere; our purpose in this short article is to cite some cases
incompatible with Intelligent Design.
Does the real world show evidence of wise, omniscient
design? To be plausible, an argument must take all the facts into account.
The scientific study of biology shows us that existing species have serious
flaws, belying claims of a beneficent creator. Intelligent design spokesmen
ignore vestigial organs, anatomical inefficiency, destructive mutation, the
sheer wastefulness of natural processes, and the findings of molecular
genetics. The constant interplay of random mutations honed by selection
pressures during evolution produces many instances of poor design. What
follows are a few of the less technical of the hundreds of examples of flaws
noted by paleontologists and other students of evolutionary processes.
Vestigial Features
Darwin was not only convinced by the success of evolution
in explaining numerous instances of common descent, but also by its ability
to account for vestigial organs, "parts in this strange condition, bearing
the stamp of inutility." These organs are of little or no current use to an
organism but are probable remnants of an earlier form from which the
organism evolved. Intelligent Design has no explanation for these organs. As
Stephen Jay Gould has put it, "Odd arrangements and funny solutions are the
proof of evolution-paths that a sensible God would never tread but that a
natural process, constrained by history follows perforce" (Gould 1980; Gould
in Pennock 2001, 670). Let's look at some examples.
Cockroaches and other insects may grow an extra set of
wings, as did their fossilized ancestors. Unlike most other snakes, boa
constrictors possess small vestigial hind legs. Crabs possess small useless
tails under their broad, flat bodies, remnants of some ancestral form.
Flounders lie flat on the sea floor and in the adult both eyes are on the
same side of the head, but when young the eyes are on opposite sides of the
head and one moves to the other side! The earlier stage is a clue to an
evolutionary path. The result is a wrenched and distorted skull.
The frigate, a non-aquatic bird, does not benefit from the
webbing on its feet. In flightless birds the number of usable limbs is
reduced from four to two with the presence of two non-functional limbs.
Penguins possess hollow bones although they do not have the same need for
minimal body weight as flying birds. Otherwise fully aquatic animals such as
sea snakes, dolphins, and whales must rise to the surface to breathe air.
Modern whales exhibit several non-functional vestigial traits. Fetuses of
baleen whales bear teeth that are absorbed as the fetus matures; adult
baleen whales do not have teeth.
Paleontologists proposed that whales had evolved from land
mammals with legs, and therefore, in an example of its predictive power, the
theory of evolution forecast that legs would be found on fossilized whales.
In recent years the evolution of whales from now extinct land mammals has
become well documented through newly found fossils from the Eocene epoch,
about 50 million years ago (Wong 2002). The fossilized whales contain
well-defined feet and legs. In modern adult whales, the front legs have
evolved into flippers and the rear legs have shrunk so that no visible
appendages appear. Hindlimbs still appear in the fetuses of some modern
whales but disappear by adulthood. Externally invisible, vestigial
diminished pelvic bones occur in modern adult whales. Evolution accounts for
these useless vestigial elements as leftovers in the development of whales
from land mammals, but they remain unaccounted for by Intelligent Design.
Anatomical Inefficiency
Some anatomical features that may be useful to a creature
do not show efficient design one could term intelligent. They testify
instead to the process of natural selection. Tails have a widely varied role
in mammal bodies. They appear essential for monkeys, but the small, wispy
tail in a large elephant seems useless. Tails are absent in adult apes and
humans, except they appear in early embryos and are residual in the coccyx
at the end of the vertebra. In some human babies a residual tail is clipped
at birth.
Why should moles, bats, whales, dogs, and humans among
others possess forelimbs based on the same bones that have been adapted in
each case unless inherited from a common ancestor? Starting from scratch, an
engineer could do a better job in each case. In pandas a normally small bone
in the wrist has undergone significant enlargement and elongation so it is
opposable as a thumb to the other five fingers, enabling them to strip
leaves from a bamboo stalk (Gould 1980; Gould in Pennock 2001, 669). To
achieve this feat, the thumb muscles normally assigned to other functions
have been rerouted. It is difficult to see how this anatomical architect
would receive another commission.
The early embryos of most animals with backbones have eyes
on the sides of the head. In those such as humans that develop binocular
vision, during development the eyes must move forward. Sometimes this
forward movement is incomplete and a baby is born with the eyes too far
apart.
In mammals the recurrent laryngeal nerve does not extend
directly from brain to larynx, but upon reaching the neck bypasses the
larynx and drops into the chest where it loops around a lung ligament and
only then retraces up to the larynx in the neck. While a one-foot length of
nerve would be required for the direct route from brain to larynx in
giraffes, the actual length of the doubled-back nerve from the chest of
giraffes may reach twenty feet (K.C. Smith in Pennock 2001, 724-725).
There are many features of human anatomy we might wish
were better designed. Our jaws are a little small to accept wisdom teeth
that are often impacted and may need pulling. The openings of our tubes for
breathing and swallowing are so close that we often choke. In humans the
appendix serves no apparent purpose, but it is infection-prone, leading to
inflammation and potentially fatal appendicitis. In men the testes form
inside the abdomen and then drop through the abdominal wall into the
scrotum, leaving two weak areas that often herniate, requiring surgery to
relieve pain. Also in men the collapsible urethra passes though the prostate
gland that enlarges in later life and impedes urine flow. Anatomists cite
many more examples of such inefficient or useless structures, such as
nipples in male primates.
Creationists often cite the human eye as a model of
perfection for which Darwinism cannot account, claiming that such a complex
organ could not be created by natural selection. But throughout the animal
kingdom eyes have evolved many times, presumably beginning with plentiful
photosensitive material followed by a stepwise incremental buildup over
generations to the current organs. And the human eye is far from a model of
perfection. In all vertebrate eyes the "wire" from each of three million
light-sensitive retinal cells passes in front of the retina, and the
collection is bundled into the optic nerve, creating a blind spot. This
set-up is just the reverse of what any designer would construct: wires
leading away from the backside, not light side, of the light-sensitive cells
(Dawkins 1987). On the other hand, the wires do lead from the backside of
the separately evolved eyes of the squid, octopus, and other cephalopods.
Why does the designer favor squid over humans?
Instead of the efficiency and elegance one expects from
Intelligent Design, we see numerous vestigial characteristics and instances
of poor design. Such anomalies are both expected and accommodated by
evolution. Only evolution offers a self-contained explanation of why more
than 99 percent of the species that have lived on Earth are extinct. What
sport does a benevolent, omniscient, and omnipotent deity receive from
visiting on humans and other mammals all sorts of afflictions including
parasitic bacteria, viral diseases, cancer, and genetic diseases?
These and many other examples suggest that any Intelligent
Design must have been undertaken by a committee of fractious gods who could
not agree. Taken at face value, invocation of Intelligent Design supports an
argument for polytheism.
Of course creationists might respond to these and other
examples by saying that the ways of God are mysterious and inscrutable, and
that we are not wise enough to comment on the means by which he achieves his
ends. If anyone offers this argument, what gives him license to propose
Intelligent Design as the means by which God achieves his ends? Such a
personal view is patently religious, and does not belong in any science
classroom.
Destructive Mutations
The study of molecular evolution strongly reinforces and
extends the classic whole animal conclusions for evolution, while appearing
whimsical at best for an intelligent designer. Modern evolutionary theory
regards genetic mutation in the DNA of a species as the source of favorable
variations that nature selects for their value in aiding the survival of an
individual. But mutation occurs randomly, and in most cases the variation is
harmful and results in miscarriage, deformity, or early death. Such
mutations are passed from one generation to the next, sometimes lurking in
recessive genes until they meet a recessive partner. One example is cystic
fibrosis, which causes mucus buildup in lungs, liver, and pancreas. Sickle
cell anemia results in poor blood circulation, general weakness, and when
inherited from both parents, painful crises owing to sickling and clumping
of the red cells. Phenylketonuria prevents infant brain development.
Muscular dystrophy wastes muscles and often leaves the victim helpless. In
other cases such mutations are dominant. Huntington's Disease causes gradual
deterioration of brain tissue in middle age. Hypercholesterolemia causes
heart disease due to cholesterol build-up. Neither intelligence nor design
seems at work in producing such cruel mutations, though modern evolutionary
theory fully accounts for nature's fickleness.
Discoveries of Molecular Genetics
In the genetic material, DNA, the sequence of four nucleic
bases furnishes three-letter code words for the sequence of twenty amino
acids that occur in proteins. Owing to similarities among the properties of
some of the twenty amino acids, substitutions may occur without consequence
for proper protein folding and function. For many animals it has proved
possible to follow the sequences of both nucleic bases in DNA and amino
acids in proteins to spot the changes that have occurred over time. One
example is the blood protein hemoglobin, which is a tetramer composed of two
alpha and two beta chains working in concert to bind four oxygen molecules.
For the beta chain of hemoglobin, the number of amino acid differences
compared to that in normal adult humans of 146 amino acids appears in
parentheses after the listed animal: gorilla (1), gibbon (2), rhesus monkey
(8), dog (15), horse and cow (25), mouse (27), chicken (45), frog (67), and
lamprey (125) (Campbell 1987). Clearly, species more closely related to man
have fewer differences from humans in their hemoglobin. Since each amino
acid substitution requires millions of years to occur, a time scale for
branching descent from a common organism according with evolutionary theory
is more probable than creation by an intelligent designer.
The known library of DNA and protein sequences is now so
huge that numerous comparisons between organisms are possible. If evolution
had not already been elaborated by Darwin, we would be led to it by the more
recent results of substitutions in molecular sequences. Many amino acid
substitutions result in inactive mutant proteins that are not further
elaborated by the organism, if it survives the mutation. On the other hand,
many substitutions do not impair function and result in amino acid sequence
variation of a functional protein, as in the example of the beta chain of
hemoglobin above. Furthermore, in humans there are more than 100 amino acid
substitutions in the 146-amino-acid beta chain of normal adult human
hemoglobin that still yield a functional protein, and most carriers are
unaware that they bear a hemoglobin variant. On the other hand, the
substitution of only the third amino acid in the beta chain of human
hemoglobin gives rise to an aberrant hemoglobin that aggregates within and
produces sickling of the red cell with consequent reduced oxygen-carrying
capability. This kind of trial-and-error probing involving numerous inter-
and intra-species amino acid substitutions has evolution written all over
it; it is very difficult to ascribe any design or anything intelligent to
this process.
Human Nature
Is it any more than an overweening human ego that proposes
intelligent design for such a poorly designed creature? In this egoism,
creationists confirm in a perverse way that they have great difficulty
rising above their animal origins. It is by reducing influence of ego that
the nobler aspects of human nature emerge in humanistic values, values which
have been appropriated by some religions.
Of course, evolutionary history fails to induce the warm
and fuzzy feeling inspired by Intelligent Design. People would rather
believe in a benevolent creator who cares for them. Evolution offers no
mercy for the individual or species that lack the traits enabling them to
compete in the struggle for food or adapt to changing environments. Fossil
evidence shows the number of species that have failed these trials. An
Intelligent Designer would create only successful species, but evolutionary
theory can account for the many unsuccessful ones. If Intelligent Design
fails so badly to account for the real world, aside from the emotional
appeal of a wise providence, is there any justification for its continued
promotion?
Addendum: The Law of Evolution
We end with a comment on the status of evolution-as fact,
"just a theory," or something in between. In the physical sciences there are
many observations or facts that have given rise to generalizations: two of
these are the law of conservation of matter and the law of definite
proportions (which states that when two or more elements combine to form a
compound they do so in definite proportions by weight). The statements of
facts and their convenient generalization to laws are expressed in terms of
macroscopically observable and weighable quantities. The overarching
explanation for these laws is achieved in atomic theory, which is expressed
in terms of invisible atoms and molecules. No one thinks that atomic theory
is "just a theory," for it possesses extraordinary explanatory power and
provides the context in which many of the conveniences of our civilization
depend. Thus we proceed from many observations or facts to their
generalization in terms of laws, both levels macroscopic, to a theory
expressed in terms of invisible entities.
If we now apply this scheme to biology, we see that the
concept of evolution is at the law level, as it summarizes the results of a
large number of observations or facts about organisms. The analogous theory
is natural selection or other means by which evolution is achieved. Unknown
nearly 150 years ago to Darwin, explanations of macroscopic evolution in
terms of microscopic genes and molecular sequences of nucleic bases in DNA
are known to us. Placing the concept of evolution at the law level clarifies
its status; it is not a theory.
In contrast, the premise of Intelligent Design fails to
meet even the most fundamental elements of rational inquiry. By being able
to account for everything by divine edict, Intelligent Design explains
nothing.