In honor of Charles Darwin’s birthday on February 12th, I am posting a series of diaries on Darwin and his theory. My first entry [1] in this miniseries covered the basics of Darwin’s theory of evolution. My second essay [2] described the "Intelligent Deception Lobby." In this essay, I wish to discuss some of the objections that have been made regarding his theory and show how more than 100 years of research have done nothing but bolster or minorly modify Darwin’s theory.

Ever since Charles Darwin first published Origin of Species, many who see his theory as somehow detracting from religion have tried to tear it down. They have pretty much failed from the start and the more we have learned of biology, the more evolution has been supported, if occasionally modified. Interestingly, most objections to Darwin’s original theory were recognized and brought up by Darwin himself in Origin of Species. Far from avoiding or denying potential problems, Darwin approached them head on, giving his hypotheses as to how the problems would be solved over time. In general, his hypotheses have proven quite correct.

There are three particular objections that are often brought up to try and discredit evolution. First there is the problem of the gradual evolution of complex organs, such as the eye. How can random variation acted on by natural selection produce an organ as intricate and complex as the eye? Second there is the problem of intermediate species. If evolution is a slow and gradual process, why do we never see the intermediate species, the “missing links,�? either alive or in the fossil record? These two problems can be called the Problems of Missing Intermediates and can be solved by, in essence, pointing out that a.) intermediates will be rare and rapidly replaced by improved versions, and b.) in reality, intermediates CAN be seen in both instances. I will address these momentarily.

The third problem is, to some degree, more philosophical than scientific. Some argue that it is nothing but a theory of “chance,�? whereby random events produce wonderful things like eyes and wings. Much like an infinite number of monkeys on typewriters banging out Shakespeare’s plays, this sounds very unsatisfying and even impossible. Put in somewhat scientific terms one could say that it violates the Second Law of Thermodynamics that dictates that, in essence, order cannot arise out of disorder without substantial input of energy. Chance cannot bring about order.

This objection is completely based on a false assumption: that evolution involves chance alone. To quote Richard Dawkins from his introduction to the 2003 Everyman’s Library edition of Darwin’s Origin of Species and Voyage of the Beagle (Darwin):

“The objection to Darwinism that it is a theory of ‘chance’ is one of the most popular and most foolish of all. Mutation is indeed random, although only in the sense that it is not directed towards improvement. Natural selection is quintessentially the opposite of random. Any fool can see that random chance cannot put together living complexity. That is precisely why Darwinism is necessary. It is a preposterous irony that the statistical improbability of living organization is regularly advanced as though it counted against Darwinism, rather than in favor of it.�?

In other words, although mutation, the basis for variation, is indeed random to a large degree, that is only one part of Darwin’s theory. The part that gives evolution its direction, if you want, is selection, both natural and sexual. There is no mere chance to evolution. It is directed by the pressures of the environment in which an organism lives. That is the very essence of Darwin’s theory! Those who argue that it is a theory of mere chance have misunderstood the theory.

Now I want to address the first two objections I mentioned. How can something as complex as the eye be formed by small evolutionary changes and where are the intermediate forms of organs like the eye? And, why don’t we see many intermediate species, either alive or in the fossil record, showing us the many gradations that take us from varieties within a species to separate species?

I will first address some things that apply to both. First off, the fossil record is not a complete record of evolution. Only a tiny fraction of all living organisms have become fossilized. Eons of the past in vast parts of the world have never survived in the fossil record. Conditions have to be just right for fossils to form. Even once formed, they can be destroyed by erosion and weathering. Finally, for us to ever see fossils they have to be exposed in just the right way at just the right time. Metaphorically, we are looking at a gigantic encyclopedia where most volumes are missing, the volumes we do have are missing pages, and the surviving pages are smudged. We cannot expect to have a complete fossil record wherein we can see every intermediate form through out evolution. Darwin himself went into this in great, almost excruciating, detail.

Another thing that Darwin himself points out about these objections is that imperfect intermediates are likely to be seen only in a small, isolated population for a short period of time. It is the MOST successful forms (either of organs or entire organisms) that compete the best and hence replace earlier, less successful intermediate forms. Intermediates IN GENERAL will be relatively rare and present for a short period of time on a geological scale compared with the more successful complete forms. So we are far more likely to only see the most successful forms of organs and organisms most of the time. As Darwin himself puts it (Darwin):

“When we see any structure highly perfected for any particular habit, as the wings of a bird for flight, we should bear in mind that animals displaying early transitional grades of the structure will seldom continue to exist to the present day, for they will have been supplanted by the very process of perfection through natural selection.�?

In some ways these points eliminate the problems of the missing intermediates. But one wants to say, “Yeah, but why don’t we see ANY intermediates?�? Even if they are rare and short lived, why aren’t any alive TODAY?

The answer is they are alive and we do see them. These objections are not only refutable logically as above, but they plain aren’t true! Intermediate organs were mentioned by Darwin himself, and intermediate species were observed even in the period immediately after Darwin published.

Taking the question of the evolution of a complex structure like the eye, Darwin points out that in Arthropods (or Articulata as they were called in Darwin’s time) such intermediate, imperfect eyes DO exist in living organisms. Again, from Darwin himself (Darwin):

“…In the Articulata we can commence a series with an optic nerve merely coated with pigment, and without any other mechanism; and from this low stage, numerous gradations of structure, branching off in two fundamentally different lines [two different kinds of complex Arthropod eyes], can be shown to exist, until we reach a moderately high stage of perfection. In certain crustaceans, for instance, there is a double cornea, the inner one divided into facets, within each of which there is a lens-shaped swelling. In other crustaceans the transparent cones which are coated by pigment, and which properly act only by excluding lateral pencils of light, are convex at their upper ends and must act by convergence; and at the lower ends there seems to be an imperfect vitreous substance.�?

In other words, you CAN see various stages of the evolution of the eye in living animals. From a simple pigmented optic nerve, through various simple structures up to the full compound eye of the fly, all are seen within the same broad category of animals.

To discuss intermediates between full speciation, I have to go to other sources than Darwin himself. As early as 1863, Henry Walter Bates observed speciation in action. From Janet Browne’s biography of Charles Darwin (Browne):

“…Bates gave an eyewitness account of the origin of species in nature. Two Amazonian butterflies, the black-and-crimson-spotted Heliconius melpomene and the Heliconius thelixope, if taken separately, were perfectly distinct species. Bates discovered four or five transitional forms living in particular geographical areas in between the two, each connected by a chain of gradations. The intermediate forms were not hybrids. They were geographical races, each on their way to becoming a separate species.�?

Other examples have been observed. One of the most striking and yet mundane are sea gulls. Gulls are an example of a phenomenon called a “ring species�? where each neighboring population in a range of an organism can interbreed and represent mere varieties, but the opposite ends of the range have populations that cannot interbreed and are, by all definitions, separate species. From Carl Zimmer’s companion book to the 2001 PBS series, Evolution (Zimmer):

“In the North Sea, for instance, there is a species of bird known as the herring gull. It has a grey mantle and pink legs. If you move west through its range, you come across more herring gulls…which look essentially the same as the ones in the North Sea, except for a few minor differences in their coloring. But by the time you reach Canada, the differences become stark, and in Siberia, the gulls have a dark grey mantle and legs that are less pink than yellow. Yet despite these differences, they are still scientifically classified as the herring gull (although their common name is the vega gull). Keep moving through Asia and into Europe, and the gulls continue to get darker and more yellow-legged…all the way to the North Sea where your journey began. Here these gulls, known as the lesser black-backed gulls, live alongside the gray-mantled, pink-legged herring gulls.

“Because the two groups of birds look so different and do not mate, they are treated as two separate species. Yet lesser black-backed gulls and herring gulls live at two ends of a continuous ring, inside of which all the birds can mate with their immediate neighbors. A ring species is exactly what you’d expect given the way mutations arise and spread.�?

Nothing could prove Darwin’s hypothesis better than this! Here is speciation IN ACTION with two separate species side by side and a continuous series of gradations that can be followed that takes you from one to the other. Every step of the way is right there for us to see. Ring species like the gull are the most definitive proof of Darwin’s theory you can get.

Intermediate organs and intermediate species right in front of us. So much for the problems of the missing intermediates. The intermediates can indeed be found in some cases. You can’t expect all intermediates from all of evolution to be found because of the issues I brought up earlier. But we can be satisfied that intermediates DO exist and can be used as very strong supports for the theory of evolution.

Theories are never “PROVEN�? in a definitive sense. They are DISproven if contrary evidence is found. Sometimes a simple change in the theory can be made to accommodate the contrary evidence, preserving the basic theory in a modified form. Other times evidence so contrary is discovered that the entire theory has to be thrown out. If each new piece of evidence is in agreement with the theory, then that theory has support. Evolution has never been disproven. It has frequently been supported by more and more data. Arguably, some new data, such as mass extinctions from comet impacts, has required minor modifications of Darwin’s theory, such as “punctuated equilibrium.�? But no major alterations to the basic design of “variation, selection, speciation�? has been required. These foundations of Darwin’s theory have ONLY been supported by the extraordinary advances in molecular biology (DNA and protein structure as the bases of variation), ecology (a better understanding of how natural selection and sexual selection work) and the discovery of more fossils and of phenomena like “ring species.�? The HUGE amount of new discoveries has only strengthened the more than 100-year old theory Darwin came up with. That is an astonishing robustness that has been matched by hardly any other theories in history. Newtonian physics can boast a longer period of dominance, from the 17th to 20th centuries when Einstein had to come up with some modifications. But not much else can boast as great a success as Darwinian evolution.

And 2005 brought even more support for Darwin’s theory. From the December 23rd issue of the journal Science:

“News
BREAKTHROUGH OF THE YEAR:
Evolution in Action
Elizabeth Culotta and Elizabeth Pennisi

Amid this outpouring of results, 2005 stands out as a banner year for uncovering the intricacies of how evolution actually proceeds. Concrete genome data allowed researchers to start pinning down the molecular modifications that drive evolutionary change in organisms from viruses to primates. Painstaking field observations shed new light on how populations diverge to form new species--the mystery of mysteries that baffled Darwin himself. Ironically, also this year some segments of American society fought to dilute the teaching of even the basic facts of evolution. With all this in mind, Science has decided to put Darwin in the spotlight by saluting several dramatic discoveries, each of which reveals the laws of evolution in action…

Probing how species split
2005 was also a standout year for researchers studying the emergence of new species, or speciation. A new species can form when populations of an existing species begin to adapt in different ways and eventually stop interbreeding. It's easy to see how that can happen when populations wind up on opposite sides of oceans or mountain ranges, for example. But sometimes a single, contiguous population splits into two. Evolutionary theory predicts that this splitting begins when some individuals in a population stop mating with others, but empirical evidence has been scanty. This year field biologists recorded compelling examples of that process, some of which featured surprisingly rapid evolution in organisms' shape and behavior.

For example, birds called European blackcaps sharing breeding grounds in southern Germany and Austria are going their own ways--literally and f iguratively. Sightings over the decades have shown that ever more of these warblers migrate to northerly grounds in the winter rather than heading south. Isotopic data revealed that northerly migrants reach the common breeding ground earlier and mate with one another before southerly migrants arrive. This difference in timing may one day drive the two populations to become two species.

Two races of European corn borers sharing the same field may also be splitting up. The caterpillars have come to prefer different plants as they grow--one sticks to corn, and the other eats hops and mugwort--and they emit different pheromones, ensuring that they attract only their own kind.

Biologists have also predicted that these kinds of behavioral traits may keep incipient species separate even when geographically isolated populations somehow wind up back in the same place. Again, examples have been few. But this year, researchers found that simple differences in male wing color, plus rapid changes in the numbers of chromosomes, were enough to maintain separate identities in reunited species of butterflies, and that Hawaiian crickets needed only unique songs to stay separate. In each case, the number of species observed today suggests that these traits have also led to rapid speciation, at a rate previously seen only in African cichlids…�?

This is just a sampling of the massive progress that has been made in one year alone, all completely in agreement or modifying in only minor ways Darwin’s theory. Since Darwin’s time we have figured out the basis of variation on the molecular level (mutations leading to different structure or expression of proteins), we have further characterized the details of how both natural and sexual selection work, and we have captured speciation in action several times. Ladies and gentleman, I think we have to recognize that Charles Darwin’s theory of evolution is one of the most brilliant and most insightful scientific theories in the history of our species and it is WAY past time for it to be considered controversial. New studies are bound to modify his theory from time to time, but Darwin’s theory is something we should cherish as a deep understanding of how life works.

Bibliography:

Browne, Janet; The Power of Place: Charles Darwin, the Origin and After, Knopf, 2002.

Darwin, Charles; Origin of Species and Voyage of the Beagle, Everyman’s Library 2003 edition.

Zimmer, Carl; Evolution: the Triumph of an Idea, companion to the PBS series, Harper Collins, 2001.