Darwin: Discovering the Tree of Life Book

When the American Museum of Natural History prepared an exhibit to mark the 200th anniversary of Charles Darwin's birth (and the 150th anniversary of the publication of his book On the Origin of Species, it gave its curator, Niles Eldredge, an opportunity to write a companion volume to be published in conjunction with the exhibit. Mr. Eldredge is a prominent evolutionary biologist, and is known as the co-originator of the theory of punctuated equilibrium (more about that later).

Notwithstanding Eldredge's professional standing, however, the result is somewhat disappointing. The book follows a well-beaten path in covering Darwin's life and thinking, and contains little if anything that has not been covered earlier and more thoroughly in biographies of Darwin, histories of science, and Darwin's own books.

The last section of Discovering the Tree of Life, where the author attempts to refute doubters of the theory of evolution, is perhaps its most notable part. I am somewhat hesitant to address this subject. The theory of evolution by natural selection makes sense to me, I am not among the doubters, and I am well aware of the vilification that doubters face.

At the same time, one must acknowledge that the gaps in the evidence for evolution are profound. Darwin himself was concerned about the enormous gaps in the fossil record, and said so in The Origin of Species and other writings. Indeed, the theory of punctuated equilibrium, which made Eldredge's reputation, was conceived as a way of explaining these gaps in the record. Under the theory of punctuated equilibrium, species remain unchanged for long periods of time. Then, when the conditions for the evolution of new species are present, new evolve in an eyeblink (in terms of geological time). As a result, intermediate forms are unlikely to be captured by the fossil record.

Given that Eldredge made his reputation by finding a way to explain away (or attempt to explain away) the gaps in the evidence of evolution, one would think that he would be especially circumspect in his criticism of those who draw different conclusions from the incomplete and imperfect evidence. Yet, he is anything but. Eldredge views dissenters as religious nut cases and cartoonish troglodytes, and is not shy about describing them as such. Yet, these same troglodytes clearly have gotten under Eldredge's skin, causing him overstate the evidence for evolution.

For example, biologists have used anatomy to classify living things in species, families, orders, and other successively broader groupings at least since the time of Linnaeus. Modern genetic analysis shows that organisms which resemble each other physically also tend to be closely related genetically. Eldredge asserts that evolution must have been the cause of this resemblance, and that, therefore, it shows that life must have evolved over time. It is established, however, that genes are what cause various physical forms to develop; change a creature's genes, and you will change its appearance and other characteristics. This is so regardless of what (or who) is causing the genes to change. As a result, it does not prove evolution by natural selection.

Eldredge further points out that life forms gradually radiate outward: take almost any species of living thing, and some species will resemble it closely, some will differ by a somewhat larger degree, and so on until hardly any similarity is apparent beyond the fact that both are alive. Eldredge argues that since this is what one would expect if one life form evolves into another under the pressure of natural selection, this pattern provides further evidence of natural selection. However, if life were created by a superior intelligence (be it God or a race of super-smart aliens from outer space), there is no reason why that Creator could not choose the same pattern for his or her creations. As a result, this fact does not mean that evolution by natural selection must be taking place.

Eldredge also argues that extremely limited examples of evolution have been observed in the wild. For example, a team of scientists has documented changes over time in the bill size of certain finches in the Galapagos Islands in response changing weather conditions and seed size. (Ironically, this study concerns the same finch species which inspired Darwin to articulate his theory of evolution by natural selection.) Eldredge also mentions the well-known example of the moth species in northern England which was brown during pre-industrial times so it would be inconspicuous while resting on trees, turned grayish during the Industrial Revolution when air pollution discolored the tree bark, and then gradually evolved back to brown in the second half of the twentieth century when air pollution was brought under control. Other examples of such limited changes also exist: many disease organisms have become resistant to antibiotics, and insect pests have become resistant to insecticides, exactly as one would expect under the theory of evolution.

These examples show that relatively small changes can take place under natural forces. However, the "big" questions remain unanswered. The biggest question of all is how inanimate matter "evolves" into life. Scientists have no idea, and the theory evolution by natural selection does not provide an answer. Scientists also have no idea how consciousness and self-awareness arise, even though they have built computers which vastly exceed the mental capacity of any living creature in many ways. Once again, evolution by natural selection does not provide an answer. Indeed, there is no direct observational proof even that one species can evolve into another, similar species. Domestic dogs have faced intense breeding pressures for thousands of generations (controlled, of course, by their owners, not natural selection), and under these pressures such radically differing breeds as St. Bernards and chihuahuas have appeared, but at the end of the day they all still are dogs. Dogs have not evolved into something else, and, so far as we know, are no closer to this transition than they were 10,000 years ago.

All of this tells me that while evolution by natural selection seems to make sense, by no means has it been proven beyond doubt. Room remains for alternative theories of how life appeared and how it may change over time. Therein lies the fascination of science: there always is something more to learn. The fact that our knowledge always is incomplete requires one to keep an open mind, rather than allow beliefs to harden into dogma.

That is what Niles Eldredge is unwilling to do. The reason why is unclear; perhaps he believes that questioning the theory of evolution is tantamount to questioning the value of his life's work, and he is not willing to take that step. This rigidity is perhaps the greatest shortcoming of Eldredge's thinking, and of this book.