This page in brief
Evolution is now accepted in the scientific world as the way the human race came to be living on earth. But many people oppose it, saying the evidence is against it, and it has not been proven. Are their objections to evolution reasonable?
This page outlines briefly the reasons to believe evolution occurred, and some of the main objections – gaps in the fossil record, the Cambrian explosion, transition processes, irreducible complexity, and the origin of life. I conclude that there are still some aspects of evolution that are not yet explained, especially the origin of life, but there is sufficient evidence to accept the main tenets of evolution.
The science of biological evolution
A summary of the findings of mainstream evolutionary science is provided in a statement by the InterAcademy Panel. It includes such conclusions as the age of the earth (about 4.5 billion years) and of life on earth (more than 2.5 billion years), the evolution of life via mutation and natural selection, and the use of the scientific method to investigate such matters.
Scientists generally believe that the gradual evolution of life over a long period of time is a proven fact, but that some of the mechanisms and processes remain uncertain. A summary of the evidence for evolution is provided by the University of California and BioLogos:
- Fossils provide an incomplete, but nevertheless convincing, picture of the evolution of life. Combined with radiometric dating and mapping of rock strata, relative ages can be estimated and the evolutionary “tree” described.
- Homologies are similar anatomical or cellular structures in different animals, suggesting common descent – e.g. many animal forelimbs share the same set of bones – humerus, radius, and ulna.
- Ideas like natural selection can be tested by modern day experiments that show the feasibility of this mechanism.
- DNA can identify common ancestors, the developments of different species, migration paths and genetic similarities between species, all indicators of common descent. I think this may be the most convincing evidence for evolution – see DNA, genes and human history.
What’s all the fuss about?
Many people, especially believers in various religions, contest some of these facts, or the common interpretations of them. Here is a summary of some of the main areas of contention.
Evolution is essentially a slow and gradual process of accumulation of small changes, and the fossils discovered so far only record a small percentage of the plant and animal species which have existed. One might expect the fossil record to include fossils randomly from the entire process of evolution, however, while most major groups and species are represented among the fossils, relatively few transitional fossils have been found to fill the gaps. Critics of evolution argue that this invalidates evolution as a process that produces the complexity of life we see around us.
But evolutionists explain this situation as follows:
- One would not expect large numbers of fossils to be found because the particular conditions required for fossils to form do not occur everywhere, and, of these, only a relatively small percentage are likely to be unearthed.
- Because of variations in the types of plants and animals, and the geographic conditions in which they lived, one would not expect an even distribution of fossils across all species.
- Some evolutionists, notably the late Stephen Jay Gould, believed the fossil record indicated a “punctuated equilibrium” in which periods of little change were followed by periods of great change, rather than a slow linear process.
- Transitional species may not have been in existence for long periods of time, and hence would naturally be less likely to appear in the fossil record.
- Many transitional fossils have been found, including some whose non-existence had once been considered as most damaging to evolution.
It seems this objection is reasonably answered, although continued lack of success in finding some transitional fossils may eventually throw doubt on some current understandings of processes. Check out references on gaps in the fossil record.
The fossil record for the Cambrian Period, more than 500 million years ago, shows the relatively sudden appearance (over a period of perhaps 5-30 million years), without previous ancestors or transitional forms, of most of the phyla known today. (Phyla are major groupings of plants and animals based on their body plan. There are about 35 phyla today, and most appeared, or are believed to have originated, in the Cambrian Period). At first sight, this appears contradictory to Darwinianism, and very difficult to explain.
The Darwinist responses include:
- Contradiction – it simply didn’t occur, it isn’t possible, and the evolution of new phyla actually took longer than the current fossil record may suggest.
- There were earlier ancestors, but their fossils have not been preserved because they were not organisms that commonly left fossils.
- There was a long period before the Cambrian where genes developed to a certain stage, which then allowed the new phyla to develop relatively quickly.
- There were, perhaps, special conditions (for example increased oxygen levels) which led to this rapid growth.
This still looks to be a small difficulty for evolutionary theory – the several different explanations indicate that a satisfactory understanding has not yet been reached. Nevertheless, it seems wise to give science the benefit of the doubt here. See references on the Cambrian explosion.
The evolution of life requires numerous small changes to cumulatively lead to new and more “advanced” species. And for natural selection to operate as a mechanism for this change, every step in the process must confer a survival advantage so that the organism survives to allow the next step in the process. Much debate centres around whether plausible processes can be found that explain the evolution of complex biological body parts, such as the eye.
Of course it isn’t possible to demonstrate the evolution of new species with new biological functions in a laboratory, so ‘demonstration’ generally involves understanding how the new organism is related to its ancestor organism, determining what changes in anatomical structure are required, showing from the fossil record or some form of modelling, that such changes could have occurred, and demonstrating how each of the major steps had survival value (perhaps by showing homologies – examples of similar structures which “work” in present day organisms).
Using such processes, evolutionary scientists have explained many difficult to imagine transitions. Many others remain to be explained, but it is claimed that this is only a matter of time.
More than a decade ago, biochemist Michael Behe introduced the idea that the structure of some living cells is “irreducibly complex”, meaning that their functioning is so dependent on all of their components that they could not evolve from a simpler structure.
This is a more significant challenge to evolution, but it is generally accepted that he has not yet demonstrated his case. For example, evolutionists claim to have shown workable transitions to systems, such as the bacteria flagellum and the cilium (two biological “machines” used for propulsion) which Behe claimed were irreducibly complex. It remains to be seen whether the concept of irreducible complexity can be shown to be true in any situation.
This one is tricky to assess. Scientists often claim that transitional processes have been demonstrated or proven, when in fact they have generally only been shown to be feasible – they cannot be established by the normal scientific method of repeatable observation (see quote below from WF Doolittle). A more modest claim would seem in order. See here for references on the transition processes and irreducible complexity.
The evolution of life is one thing, but evolution requires the existence of a primitive organism to begin the process. (Strictly speaking, the theory of evolution does not address the origin of life.) How did life originate?
It is not easy to define the characteristics of life, but the following abilities are generally part of the definitions:
- to process energy to perform other functions;
- to respond to stimuli and adapt to its surroundings;
- to grow and regenerate worn components; and
- to store information that allows replication.
For the earliest forms of life to be able to perform these functions is no mean feat.
Hydrogen, oxygen, carbon and nitrogen have to be formed into amino acids. Scores of amino acids must then be linked together in an appropriate sequence to form protein molecules and the nucleic acids which make up genetic code. Then a hundred or more protein molecules must combine to form a living cell. That such complex processes could occur naturally is almost beyond belief, and critics of evolution can outline many barriers that must be overcome, and for which current explanations do not appear to be satisfactory.
Science has not as yet been able to demonstrate how it all might have occurred. Many proposals have been examined and none has been found likely at this stage. The methods being used for this research cannot yield the near-certainty that science usually seeks, and some critics will undoubtedly continue to argue that natural forces alone cannot explain the origin of life. Francis Crick, one of the discoverers of the structure of DNA, wrote in 1981: “The origin of life appears to be almost a miracle, so many are the conditions which would have had to be satisfied to get it going.”
Scientists believe thay have made progress on this research and are confident that they will one day be able to demonstrate the process by which life arose. In 2004, biologist W Ford Doolittle wrote:
Origins-of-life science is still very much a work in progress. The sensible bet is that chemists will close this particular gap …. within the next decade. Yet a decade later, Paul Davies can say:
The origin of life is one of the great outstanding mysteries of science.
Abiogenesis, the beginning of biological life out of chemical components, remains more uncertain than other transitions discussed above. Those committed to a belief that only natural processes can be involved will continue to strive for a feasible process, whereas others may well continue to question the evidence. See here for references on the origin of life.
Most science depends on observation of the world or of controlled experiments, in a systematic manner which leads, in the end, to a high level of statistical confidence in the results. However evolutionary science has more limited opportunities to observe of experiment, and must often proceed by less direct methods.
The following (from The Origin and Early Evolution of Life by W. Ford Doolittle, Biochemistry Professor, Dalhousie University, Canada) is instructive:
Questions about the past – whether in cosmology, geology, paleontology, archaeology, or human cultural and political history – are different. We cannot do experiments in the past, so any attempt to reconstruct it must be based on indirect and inferential methods.
Evolutionary biologists who seek to reconstruct life’s history have three such inferential methods: (1) comparisons of the properties of living species; (2) study of relics, such as biological and chemical fossils, or apparently primitive features retained by modern cells; and (3) feasibility experiments. The comparative approach can in principle take us back to the last common ancestor of all currently living things, and the fossil record (biological and chemical) may go a bit further, to something close to the first cells. For the origin of earthly life itself, and perhaps even up through the appearance of the earliest true cells, we must rely on feasibility experiments. In these experiments, hypotheses about what might have happened in the past are shown to be plausible by demonstration that similar events can be made to happen today, in the lab.
Certainty and completeness in reconstructing life’s ancient history will never be possible, nor indeed are they possible even in reconstructing the very recent history of a nation or society. But it would be foolish to deny that we already know a tremendous amount, or that what we do know provides a compelling story of how past became present.
Scientists sometimes speak as if many of the details of evolution are more certain than they can actually be. No matter how unsatisfactory explanations about any part of the process are, especially about the beginning of life, evolutionary scientists will nevertheless assume that a naturalistic explanation will be found. However the above quote suggests that the processes which originated life probably cannot ever be “proven”, and may be as much a corollary of a naturalistic worldview.
We have good reason to trust science generally, but the fact that such doubts and questions tend to be shouted down or ridiculed rather than addressed leaves me feeling a little uncomfortable.
Humility rather than hubris
This brief survey suggests that evolutionary science may sometimes deliver less than its most enthusiastic supporters claim, especially when applied to the long-ago questions of the origin of life. It appears that theories about individual evolutionary processes can be verified and falsified, but the basic assumption that the whole evolutionary process can be explained in natural terms appears to be unfalsifiable (i.e. no matter what, scientists will keep on saying there is a naturalistic answer). To be sure, science explains a lot, and we can happily accept its findings, but a degree of humility is preferable to hubris when drawing conclusions.
On the basis of the above discussion and the references, it is safest to conclude that there is no reason to significantly argue against the findings of evolutionary science. It may be that some aspects of current thinking about evolution, and especially about the origin of life, are in error, and certainly some are presently unknown, but I think there are more important matters for non-scientists to consider without arguing about evolution. It would therefore be helpful if evolution, or any other scientific matter, was considered as the explanation of how processes on earth “work”. We are each then free to decide if we think God, something else, or nothing, is the best explanation of the cause “behind” the processes.
Evolution raises questions about whether belief in God is reasonable now we better understand how human evolved. These questions are discussed in Evolution and God.