Peter Sutton (Crossfire, March 5 to 11), in an article that relies on a book by Michael Denton, writes that “the theory propounded by Charles Darwin and his followers still remains to be proved conclusively”. Denton has led Sutton astray by criticising evolution without first troubling to understand the process.
The article states that molecular biologists are challenging orthodox Darwinism. Some are merely resurrecting a very old approach: that great complexity cannot be explained by natural processes. A theory of this kind published in a recent book proved null and void because the author did not realise that neutral structures (neither useful nor harmful) can survive in species for lengthy periods, and this error undermined his arguments.
The most common source of confusion about evolution is a failure to distinguish between the fact of change over time on the one hand, and the quite separate matter of how change is brought about (natural selection) on the other.
It is a fact that populations change over time. Fast-breeding species reveal this. Bacteria evolve resistance to antibiotics. Insects evolve resistance to pesticides.
The explanatory power of change over time is powerful. It makes sense of the fossil succession through geological time; vestigial organs (remnants of previously useful organs, like human body hair); different degrees of anatomical, molecular and DNA similarity between species; geographical distribution of species (related species on neighbouring islands and on the nearest mainland); and many more biological facts that would be utterly mysterious if evolution had not occurred.
The argument about there being no fossil transitional forms (links) is incorrect. Not only have links between groups been found – such as the thousands of mammal-like reptiles of the Karoo, showing every permutation of the transition from reptiles to mammals – but also successions of fossils so similar to each other that it is hard to know how to divide them into species.
The fossil hominid succession from Australopithecines to Homo sapiens is an example.
It is ridiculous to argue that “an infinitude of connecting links are crucial to the theory”. If just one fossil of an extinct species resembling a living form had been found, and no others, it would require an explanation. And the explanation would have to be changed over time.
If, one day, natural selection theory proves to be wrong in some respect, this will not alter the fact that change occurs and that new species emerge from old.
Natural selection is the mechanism Darwin proposed for evolutionary change. Mechanisms, or explanations of facts, are called theories. If a theory survives long-term examination (Darwinism is 140 years old) its reliability is highly probable. If it is actually seen in action, it could be said to be “proved conclusively” though theories can be modified over time so scientists don’t use such dogmatic terms.
Here is one example among many: an unusually large El Nio affected seed plants on an island so radically that the average size of beak of a population of finches changes significantly in one season. Scientists studied the process in detail and showed that natural selection was the mechanism of change. Scientists often use natural selection to produce new strains of bacteria.
Sutton’s article claims that Darwin’s theory is in doubt when it comes to macro-evolution. In fact, there is much fossil evidence of “macro- evolution”. In any case, the distinction between micro- and macro-evolution is artificial because evolution is a continuum.
Change occurs within an isolated population, generation after generation (micro), until it reaches a point where its members cannot breed with other populations of the same species. Natural selection over long periods of time produces species that are grouped into genera, families, orders, classes (macro). There is no break at any point. The mechanism is natural selection every step of the way, and large changes result from cumulative small changes.
Sutton says Darwin knew his evidence was in many ways insufficient, but this is not so. His theory lacked only one element. Darwin could see that variety exists in species and he proposed that selection operates on variety, but he did not understand how it arises.
The answer has been known for almost a century. Chromosomal and genetic recombinations and mutations produce variety and novelty. The melding of natural selection with genetics in the 1930s and 1940s resulted in “the New Synthesis”, which some call neo- Darwinism, and information about DNA has completed Darwin’s elegantly integrated theory.
Finally, all the arguments in the second half of the article depend on the erroneous assumption that evolution depends on chance. Variety in populations is indeed a matter of mutations and chance assortment of genes. However, far more offspring are produced than can survive, and natural selection weeds out those that are less well camouflaged, or slower to run away, or whatever.
This wholesale death is neither accidental nor random. It is stringent and precise. Those individuals less well adapted to the prevailing conditions do not survive to pass on their genes.
If the environment changes, the character of the population shifts because different kinds of individuals start surviving: those best adapted to the new conditions. If, despite huge numbers and frequent mutation, no individuals fit a new environment well enough to survive selection, the species becomes extinct. Far more species have met this fate than are alive today. “Fitness”, incidentally, is more than survival. It is defined by the number of offspring produced in a lifetime.
Natural selection is extremely fine-tuned and can operate on minute differences between individuals. Such selection, among millions of individuals, over millions of generations, has results that our generation-bound brains cannot comprehend.
As Darwin wrote, it is difficult to believe that structures like eyes evolved, though he argued convincingly that they did. People cannot understand or imagine how. But the animal kingdom has every kind of eye from a simple light sensitive spot to the mammalian version. And our eyes are by no means perfectly or logically constructed. A good designer would have done a lot better. Natural selection has to make do. Design errors like our bad backs and troublesome sinuses are good evidence that natural selection shaped us.
Sutton suggests that natural selection is an integral part of modern biology only because there is no alternative theory. On the contrary, it is a theory that makes sense of what was previously an inexplicable, disconnected array of biological facts, and no alternative is needed.
Jane Dugard is a zoologist with experience in research, teaching, writing and publishing