Macroevolution: The Skeptic’s View
Skeptics question whether random mutations plus natural selection can produce the evidence observed in the world around us.
The adaptive changes of microevolution include such things as color; proportions of existing body parts, or which of the existing genes are most often expressed in a given environment. These are commonly observed and plentiful examples of evolution. Another example sometimes given is the mutation that produces sickle cell anemia and a number of other genetic diseases. Microevolution is the sense of evolution that everyone agrees to exist.
But what about macroevolution, the evolutionary changes that might produce not only new and substantially different species but also lead to new families, class, order, and phyla? When pressed for examples of macroevolution the Neo-Darwinianist come up short. The example of the four-winged fruit fly was often given in the past, but it is now recognized that the extra wings do not have muscles attached and they actually get in the way of the functional wings creating a disability rather than an advantage. These four-winged fruit flies survive only with the help of laboratory technicians. Clearly beneficial structural changes in complex organisms seem to be wholly lacking.
For thousands of years man has deliberately, carefully and selectively bred dogs, cattle, and other animals without ever producing any structural changes. There have been changes in color and body proportions, but no beneficial structures that did not exist before, even though novelty can be socially and economically valuable. This fact seems to demonstrate that there are some built-in limits to possible biological change.
Over the last century scientist have experimented with short-lived organisms to try to demonstrate macroevolution as well as microevolution. These organisms were subjected to conditions that would generate many mutations and selection was used to try to accumulate changes to produce something structurally new. These experiments have produced a wealth of knowledge and an array of interesting mutations, but no beneficial structural changes. Careful manipulation to obtain the coincidence of three different mutations will produce the four-winged fruit fly with its disabled flight, but nothing much better.
The simple fact is that the vast majority of mutations are detrimental, although a few are neutral. But it is highly debatable if there are any clearly beneficial mutations in complex organisms because they all carry some negative consequences. If any actually exist, they are exceedingly rare. Further the simple fact is that mutations have not been observed to accumulate into beneficial structural changes.
In the last few decades of scientific progress many exciting milestones have been passed bringing new understanding of the intricate, amazing and complex biochemical working of biological machines. The result has been that some scientists think that most of the biochemical subsystems of these biological machines cannot be reduced to a simpler form and still maintain any useful functionality. That also means that they could not arise from a simpler form. This concept has become known as ‘irreducible complexity’ and it stands as a potential disproof of the current theories of macroevolution.
But what about the fossil record? Doesn’t the succession of fossils over geologic time demonstrate macroevolution? It is not at all clear that science understands the relationships between the succeeding fossil types. There is a substantial diversity of opinions among experts about these relationships in the ‘tree of life’. Often the proposed transitional forms contain structural elements that don’t fit into the proposed developmental path. A good example is the commonly asserted evolution of birds from the theropod dinosaurs, which run around on two legs like birds. But the theropods do not have hip a structure like birds; they have a different kind of hip structure similar to reptiles. There is a type of dinosaur that has a hip structured like birds but that type includes Stegosaurus and Triceratops, which are otherwise not much like birds.
This patchwork of fossil facts often frustrates attempts to put them together into the simple connections they seem to imply. One paleontologist has written, “when discussing organic evolution the only point of agreement seems to be ‘it happened.’ Thereafter there is little consensus, … Constructing phylogenies is central to the evolutionary enterprise, yet rival schemes are often strongly contradictory.” [ Morris, p.1]. Many experts look to genetics and biochemistry to resolve the contradictions through comparing the details of proteins in apparently related organisms but this has produced many surprises and more confusion. Molecular research often enough describes molecular connections that do not correspond to the phylogenies suggested by fossils [Morris, Lee, Patterson, Woese]. Not only do they suggest surprising connections they also suggest multiple origins and developmental pathways for life’s chemical machinery. [Doolittle, Leipe, Peterson]
As geologists have refined our knowledge of the Cambrian Explosion they have come to realize that most of the basic body forms developed in a very short time geologically. Some propose a time span of only five to ten million years more than five hundred million years in the past. A few more basic forms followed soon after. The appearance of the new body forms is so rapid in the Cambrian explosion that there is no apparent connection with a common ancestor. This rapid ‘explosion’ of new forms is very different from the conventional picture of the ‘tree of life’. The tree of life suggests a single origin of life followed by a slow steady increase in the basic body forms and variations on those basic forms. But this picture is not what the fossil record shows.
Many organisms have changed very little or not at all since their first appearance in the earth’s fossil record. These are often called living fossils and a few examples are Neopilina mollusks, horseshoe crabs, tuatara lizard, coelacanth fish, cockroach, gingko and wollemi pine trees, and many others. If random mutations plus natural selection is the only principle controlling the development of life forms, why do so many life forms remain so little changed through multiple suggested geologic periods of time while enduring changing environments and mass extinctions?
In short, the conventional Neo-Darwinian view of evolution has many serious weaknesses and some outright failures. There is a definite need for new ideas and innovative thinking ‘outside the box’. New hypotheses that might lead to new and better theories about the origin and history of life are definitely needed. Students need to be made aware of these weaknesses and failures so that they can understand and evaluate new ideas as they come along to influence both science and society. They also need to be able to see the challenges and opportunities that a future in science holds for them.
References might be omitted for a textbook version. Reference articles are provided for statements that might seem unsupportable to the uninformed. The reference authors make some similar statements about the facts in question even though they are not in any way skeptics of evolution as a whole.
Simon Conway Morris, “Evolution: Bringing Molecules into the Fold,” Cell 100 (2000):1-11.
Michael S. Y. Lee, “Molecular phylogenies become functional,” Trends in Ecology and Evolution 14 (1999): 177-178.
Colin Patterson, David M. Williams, and Christopher J. Humphries, “Congruence Between Molecular and Morphological Phylogenies,” Annual Review of Ecology and Systematics 24 (1993): 153-188.
Carl Woese, “The universal ancestor,” Proceedings of the National Academy of Sciences USA 95 (1998): 6854-6859.
W. Ford Doolittle, “The nature of the universal ancestor and the evolution of the proteome,” Current Opinion in Structural Biology 10 (2000):355-358.
Detlef D. Leipe, L. Aravind, and Eugene V. Koonin, “Did DNA replication evolve twice independently?” Nucleic Acids Research 27 (1999): 3389-3401.
Scott N. Peterson and Claire M. Fraser, “The complexity of simplicity,” Genome Biology 2 (2001):1-7.