By Jonathan Wells
Icons of Evolution is a critical examination of some of the best-known examples traditionally used in biology textbooks to support Darwinian evolution. Jonathan Wells, who held a PhD in molecular and cell biology from the University of California, Berkeley, examines these familiar examples and asks a fundamental question: Do they actually demonstrate what textbooks often claim they demonstrate?
Rather than attempting to address every aspect of evolutionary theory, Wells concentrates on a series of highly recognizable examples—what he calls the “icons of evolution.” He compares their textbook presentation with evidence from the scientific literature and argues that important qualifications, contrary evidence, or limitations have often been omitted.
The Ten Icons
Wells examines ten major examples frequently associated with the teaching of evolution:
The Miller-Urey Experiment
The famous 1953 experiment produced some organic molecules under simulated atmospheric conditions. Wells questions whether the atmospheric mixture used in the experiment adequately represents conditions on the early Earth and whether the experiment demonstrates the origin of life.
Darwin’s Tree of Life
The branching tree is used to represent the common ancestry of living organisms. Wells examines whether biological and fossil evidence produces the simple branching pattern commonly portrayed or a substantially more complicated history.
Homology in Vertebrate Limbs
Similar patterns in the bones of vertebrate limbs are frequently presented as evidence of common ancestry. Wells asks whether similarity itself explains common ancestry and examines difficulties involved in explaining homologous structures through developmental genetics.
Haeckel’s Embryos
Ernst Haeckel’s famous embryo drawings were historically used to illustrate similarities among vertebrates during development. Wells examines the history and accuracy of these illustrations and argues that important differences between early vertebrate embryos have often been obscured.
Archaeopteryx
With its combination of avian and reptilian characteristics, Archaeopteryx became one of the most famous fossils associated with evolution. Wells discusses what the fossil can—and cannot—tell us about the origin of birds.
Peppered Moths
Changes in the proportions of light and dark peppered moths during industrialization became a classic textbook example of natural selection. Wells does not dispute natural selection in the moth populations; instead, he questions aspects of the experimental evidence and the way photographs and the example itself were historically presented.
Darwin’s Finches
Changes in Galápagos finch beaks provide measurable evidence of natural selection. Wells asks whether such changes demonstrate the larger claim that natural selection can generate fundamentally new biological forms, noting that observed changes can fluctuate with environmental conditions.
Four-Winged Fruit Flies
Mutations can produce fruit flies with an additional pair of wings. Wells examines whether such mutations provide evidence for the creative power attributed to mutations in large-scale evolutionary change, emphasizing that the additional wings are abnormal rather than functional innovations.
Fossil Horses
Horse fossils have often been arranged to illustrate evolutionary development through geological history. Wells discusses how the familiar linear sequence has been replaced by a much more branching and complex picture.
Human Evolution — the Ultimate Icon
The familiar illustration showing a progression from an ape-like ancestor to a modern human has become one of the most recognizable images of evolution. Wells argues that such images can give an impression of certainty and direct ancestry that goes beyond what individual fossil discoveries establish.
A Question About Evidence
The central theme of Icons of Evolution is broader than whether a particular textbook illustration is inaccurate.
Wells distinguishes between observational evidence and the interpretation placed upon that evidence.
Natural selection can be observed. Mutations occur. Fossils document organisms that lived in the past. Organisms share many structural and genetic similarities.
The question Wells raises is whether these observations by themselves establish all of the larger conclusions commonly drawn from them—particularly the claim that mutation and natural selection are sufficient to account for the origin of fundamentally new biological structures and forms.
His criticism is therefore directed especially toward cases where relatively limited empirical observations are presented as demonstrations of much broader evolutionary claims.
Science Should Remain Open to Critical Examination
A major message of the book concerns the way science is taught.
Wells argues that students should not simply be shown selected examples and told what conclusions to draw from them. They should also learn about the limitations of the evidence, competing interpretations, unresolved questions, and changes that have occurred as scientific knowledge has developed.
From this perspective, questioning an evolutionary explanation is not the same as rejecting science. Scientific theories should remain open to testing and criticism, and textbook examples should accurately reflect the evidence on which they are based.
The book consequently challenges readers to distinguish between what has actually been observed experimentally or historically and what has been inferred from those observations.
Why Icons of Evolution Remains Significant
When Icons of Evolution appeared in 2000, it generated substantial controversy. Wells’s criticisms were challenged by defenders of evolutionary biology, some of whom argued that he misrepresented the relevant science or exaggerated the significance of textbook inaccuracies. The book nevertheless became an influential work within the Intelligent Design movement and stimulated continuing debate about how evolutionary evidence should be presented in education.
Wells subsequently returned to many of these questions in Zombie Science: More Icons of Evolution, published in 2017, where he revisited earlier examples and considered additional subjects including DNA, whale evolution, the human appendix and “junk” DNA, the human eye, antibiotic resistance, and cancer.
Conclusion
Icons of Evolution invites readers to look beyond familiar textbook illustrations and examine the scientific evidence behind them.
Jonathan Wells’s central contention is not simply that individual illustrations or experiments have sometimes been presented incorrectly. His broader argument is that the strength of the evidence should determine the strength of the conclusion.
The Miller-Urey experiment, peppered moths, Darwin’s finches, fossil sequences, embryo similarities and genetic mutations are all legitimate subjects of scientific investigation. Wells asks whether they demonstrate the full evolutionary conclusions frequently associated with them—or whether the evidence supports more limited conclusions.
Whatever position readers ultimately take on evolution or Intelligent Design, the book raises an important methodological principle: