The world is full of diversity- plants, animals, microscopic organisms. Where did they come from? Two major explanations have been proposed: creation and evolution. What are the major lines of evidence that support each of these explanations? What are the major difficulties for these explanations? This paper will attempt to address these questions.
Defining some terms
The term evolution has been used with so many different meanings that it has lost much of its precision. When Darwin first proposed his theory of descent with modification, "evolution" meant the organized development of an embryo into an adult. Biologists of that time were seeking for a "law of species", because they wanted to explain life in terms of natural laws and natural mechanisms. Later, the term was used to indicate an unguided, random process. Some scientists define evolution as change over time, but use it to mean universal common ancestry. To clarify my argument here, I present definitions of several terms below:
Variation: Individual differences within a species (e.g., dogs).
Speciation: Production of new species due to loss of ability to interbreed (e.g., European shrews).
Diversification: Speciation plus variation (isolation, divergence); (e.g., kangaroos).
- Creationists misuse this term to refer to any kind of change they think is plausible.
- It is more widely understood to mean the process by which changes occur among or within populations of a species.
- Creationists misuse this term to mean any change in species that seems too great to be plausible. This is too imprecise, and not the ordinary meaning.
- Change in species to the extent that new genera or higher taxa are produced (Simpson). This is probably the usual meaning of the word. For our purposes, it is somewhat unsatisfactory because of it focuses on modification of morphological structures rather than on their origins.
- Any of the definitions given above may be called evolution. It is important to be aware of the differences in the definitions.
- Change over time. This is a popular definition, but does not help clarify the differences between creation and evolution. The issue can be clarified by identifying which of the following characteristics is involved:
- Speciation (e.g., the "evolution" of new species of oak trees by loss of ability to interbreed)
- Molecular changes (e.g., the "evolution" of hemoglobin in vertebrates)
- Morphological variation (e.g., the "evolution" of size differences in cats)
- Morphological diversification (e.g., the "evolution" of diversity in mice)
- Morphological specialization (e.g., the "evolution" of teeth in mammals)
- Morphological restructuring (e.g., the "evolution" of additional groups of reptiles, such as turtles)
- Morphological increase in complexity (e.g., the "evolution" of the eye in animals)
- Theory of Universal Common Ancestry ("TUCA"; e.g., bacteria- man). This is a key difference between creation and evolution: have all organisms descended from a common ancestor, or are there separately created groups?
"Evolution" is a term used with many definitions. Use of the term can easily result in confusion. In discussing change in species, terms should be clearly identified. The definition of evolution that gives the clearest distinction from creation is that evolution is the theory of common ancestry of all organisms.
Evidence supporting the theory of universal common ancestry (TUCA)
Several lines of evidence indicate that species have the potential for change, and that changes in species have occurred, and are occurring today. The major points of support are listed below:
- Experimental selection shows that species possess sufficient variability to permit significant change. Breeds of dogs vary as much as different genera of wild dogs. All species exhibit variation when studied closely.
- Similarities in organisms, morphological and molecular, are explained by common ancestry. "Homology" refers to an inherited feature shared by two or more species, that has been modified in different ways in the species being compared. The vertebrate forelimb is an example of a homologous structure; it is modified into an arm in humans, a paddle in whales, a wing in bats, and a foreleg in horses. Similar molecular characteristics may also be regarded as homologous. The genetic code and molecular metabolism are common to virtually all organisms, and are thought to have been inherited from a common ancestor, hence homologous.
- The hierarchical organization of taxonomy is explained by common ancestry. Recently diverged species form closely packed clusters; these clusters are more distantly spaced because they represent more ancient divergences. For example, cats, dogs and bears each include a group of similar species, thought to have diverged relatively recently. Each of these closely packed clusters of species can be clustered more loosely in the group carnivores. The different groups of carnivores are thought to have diverged from each other more anciently. This pattern applies to both morphology and to molecular sequences.
- Restricted geographical distribution of groups of species is explained by common ancestry. Groups of similar species are often restricted to a particular geographic region; examples- kangaroos, sloths, lemurs, African antelope. Their presence together, and absence in other regions, is explained if they diversified in that region from a common ancestor.
- The fossil record shows different species in successive layers, with more familiar types concentrated in the upper layers. Certain fossils are always found in the same sequential relationship, whenever they are found in the same region. This is explained if different species lived at different times, the former species being the ancestors of the later species.
- The fossil record contains numerous examples of species that are arranged in a morphological sequence. One famous example involves the "mammal-like reptiles." A group of extinct reptile-like fossils is found, beginning near the top of the Paleozoic rocks. These fossils are known as synapsid reptiles. Their lower jaws have the structure of a reptilian jaw. In the lower Mesozoic layers, similar fossils are found, but with more mammal-like lower jaws. These are followed by fossils with completely mammal-like jaws. Evolutionary theory explains this sequence as showing the development of mammals from reptile-like ancestors.
Philosophical and Theological Support
- The theory of universal common ancestry is based on a mechanism that can be studied scientifically. A testable explanation is considered superior to statements that explain an observation as caused by unspecified supernatural activity.
- The theory of universal common ancestry through natural law can explain the existence of death and pain without invoking a creator god who is responsible for evil, either through design or through indifference.
- The theory of evolution has strong explanatory power; it explains many different kinds of observations. The ability of the theory to explain so many observations makes the theory appear reliable.
Numerous lines of evidence support the capacity of species to change, and refute the theory of fixity of species. Evolutionary theory provides a logical explanation for many different observations.
Evaluation of support for TUCA
How would a creationist respond to the evidence for common ancestry? Some possible creationist responses are given below.
A creationist response to the biological support for TUCA
Four lines of biological evidence for TUCA were described above: experimental selection; homology; hierarchical taxonomy; and biogeography. Each one of these falls short of the support needed for TUCA.
Experimental selection has shown that species have an impressive capacity for change and variation. However, selection experiments have not resulted in any new morphological structures or new types of organisms. Change does not appear to be progressive, but is restricted to producing variations of existing characteristics. Multiple separate ancestries seem to be required to explain biodiversity.
The notion of "homology" actually presents severe problems for evolutionary theory. We can observe the similarities in the structural design of vertebrates, but the developmental stages are surprisingly different in the different vertebrate groups. This suggests substantial genetic differences in the processes controlling development in these groups. If the processes are so different, can we be certain the effects are truly homologous? In contrast, the eyes of insects and vertebrates have been interpreted as non-homologous.
It seems unlikely that such structurally different eyes could be derived from a common ancestor, and it seems unlikely that their supposed common ancestor would even have eyes at all. Yet the genetic switch controlling eye development appears to be highly similar in insects and vertebrates. If such similar developmental genes can produce eyes that perform the same function, but appear to have independent origins, where is the homology? Perhaps the term has no real biological meaning, but is simply a term for an idealized concept in evolutionary theory. Biodiversity can be explained as the result of multiple separate ancestries in which the Creator created a diversity of "biosystems", often using similar principles of design.
The hierarchical taxonomic pattern also has shortcomings. The actual data is full of inconsistencies, which are interpreted as evolutionary losses, reversals and parallelisms. Similarities and differences among organisms often show conflicting patterns. One characteristic may group species A with species B to the exclusion of species C. Yet a different characteristic may group species A with species C to the exclusion of species B. For example, birds have some features similar to reptiles, other features similar to mammals, and yet other features that are unique to birds. This problem increases with the number of groups included in the study. This pattern can be explained as the result of separate creative acts in which appropriate features were used in different groups as needed.
Geographical distributions indicate common ancestry only for lower taxonomic categories. Endemic groups are most common at the Family level or lower. Few Orders are endemic to a particular region. Thus common ancestry is suggested primarily among members of families and genera. For example, the sloth family is restricted to tropical America, and its members might well share a common ancestry. The Order Edentata (including the sloths, armadillos and anteaters) is one of the few living Orders with a geographically restricted distribution. All living members of the Order Edentata are restricted to tropical America (except one kind of armadillo that lives in the southern United States). However, a probable fossil edentate (an anteater) has been found in Germany, showing the group apparently has existed in other places. The existence of numerous distinct groups with worldwide distributions can be explained as the result of separate ancestries.
A creationist response to the paleontological support for TUCA
Two lines of paleontological evidence for TUCA were presented: increasing modernness, and morphological series. These two patterns in the fossil record are some of the most difficult patterns for creationists for explain. Yet it is important for creationists to address them. How would a creationist explain these patterns?
As noted above, creationists do not have a really satisfactory explanation for the increasing modernness of fossils. One suggestion is they might be the result of sequential destruction by the expanding flood. Those groups that were buried first by the flood would be least likely to have any survivors still living. Those groups that were last to be buried would be those with the greatest chance to survive the flood. This explanation would work well except for those groups saved in the ark. Why should the pattern seem to apply also to terrestrial vertebrates?
The answer to this is not clear, and creationists need to study this problem more to attempt to understand it. Various suggestions have been made. One is that post-flood survival of the terrestrial vertebrates depended survival of their food sources. Another is that the post-flood ecology favored those groups that lived at the highest elevations, which were last to be buried. A third suggestion is that the organisms God intended to destroy were killed first, and the ones to be saved were destroyed and buried later in the flood.
Certain fossils form morphological series that appear consistent with evolutionary theory. The synapsid ("mammal-like") reptiles are an example. Evolutionary theory provides a ready explanation for this sequence; creationist theory does not. Some discussion of this problem is given below. Before addressing this question, it should be noted that there are many groups that suddenly show up without identifiable ancestors. Examples include the sharks, bony fish, frogs, salamanders, dinosaurs, ichthyosaurs, turtles, lizards, snakes, crocodilians, primates, rodents, bats, edentates, and many others. Abrupt appearance is a pervasive pattern in the fossil record.
A creationist could give a variety of responses to the questions regarding morphological series such as the synapsid reptiles. First, although the fossil series of mammal-like reptiles is impressive, there are numerous large morphological gaps among the synapsid reptiles and between them and modern mammals. None of them can be confidently identified as directly ancestral to any of the others.
It is sometimes claimed that an ancestor has been found for a particular group, such as birds or mammals or whales or humans. However, a close, critical examination of such claims invariably reveals that the fossil in question is not believed to be an actual ancestor of the group, but merely a representative of a group that included the actual ancestor. Such fossils can be interpreted instead as representatives of extinct groups that had nothing to do with the ancestry of the group in question. The lack of identifiable evolutionary ancestors, including forms within morphological series, is a significant problem for evolutionary theory, but is consistent with the theory of multiple separate ancestries.
A second creationist response is that the fossil sequence appears to be the result of the catastrophic destruction of the world, which was supernaturally directed, and most of which occurred in about a year. The problem for creationists is not so much that morphological series exists, but that we do not have a ready explanation as to why they came to be buried in that sequence.
This reflects our ignorance the of pre-Flood world and the sequence of events during the Flood. The burial sequence of the mammal-like reptiles might reflect an ecological sequence of flood destruction. Further study may shed additional light on this question. However, no one has any experience with world-wide catastrophes, and it is difficult to imagine what could or could not happen.
Finally, for the sake of argument, even if a few morphological series seem problematic for creationists, this still does not explain the origins of the other groups, especially those involved in the "Cambrian Explosion. There does not seem any reasonable way to avoid the necessity of an intelligent creator and multiple separate ancestries. If this is true, explanations that depend entirely on the absence of intelligent intervention should be evaluated with caution. Bias against a creator may cause one to miss the obvious.
A creationist response to the philosophical support for TUCA
Three philosophical arguments for TUCA were presented: a mechanism that can be studied; avoiding the necessity of postulating an evil god; and the ability of the single theory to explain so many observations. However, none of these arguments is compelling. The fact that a theory proposes a mechanism that can be studied says nothing about whether the theory is actually true. It only indicates whether it can provide employment opportunities for scientists. The presence of evil does not require postulating an evil god; a good God may permit evil in order to preserve freedom, while assuring the eventual elimination of evil. The ability of the theory to explain many observations is a good point, but is weakened by the failure of the theory to explain many other observations. A theory that explains only part of the observations cannot be regarded as conclusive. This applies also to creationist theory. Neither theory can be conclusively demonstrated, and philosophical considerations are likely to be the most important factor determining which theory a person prefers.
There is good evidence that species are variable, and it appears that many varieties and species can be produced from a single ancestor. However, it does not appear that species can produce new morphological structures or produce more complex descendants. Another theory is needed to explain the rest of the evidence.
Evidence for Multiple Separate Ancestries
Numerous lines of evidence suggest that species do not all have a common ancestry. Many features of living organisms are more easily explained by a theory of multiple separate ancestries (TMSA). Some of the major evidence will be described below.
- Experimental selection shows limited variation in species. Nothing equivalent to a new type of organism, or a new organ, has ever been produced through experimental selection. Dogs are always dogs; variation may be impressive, but it is not progressive. The theory of separate ancestries can explain why there are so many different types of organisms, each with limited variability.
- Different groups of organisms have their own system of gene interactions and embryological development. For example, reptiles, amphibians and birds follow quite different pathways of embryological development. Each group probably has some unique genes and gene interactions, although study of this topic is still in the early stages. Each group passes through a similar blastula stage in development. Why do different gene interactions produce temporarily similar morphological effects; yet, why are the adult stages so different? In contrast, similar genes may produce different results. For example, flies and humans have a similar gene that controls development of the eye, but their eyes have a radically different structure. These questions are easily answered by the TMSA, in which similar principles and materials were arranged in different ways in different "biosystems."
- Many groups are separated by both quantitative and qualitative differences in genetic information. The exact genetic composition of living species is unknown, except for a very few simple organisms. However, it seems clear that some species possess genes that are not present in other species. For example, mammals have placental hormones that are apparently not present in other groups. There are probably thousands of other examples of genes that are unique to a particular group. The addition of genetic information by any means other than the activity of an intelligent creator requires a series of events that are so highly improbable that no other theory seems plausible.
- Some groups have morphological structures not present in other groups. It is implausible to think that new morphological structures can grow from nothing. Living organisms possess many and varied types of morphological structures, which are restricted to certain groups of organisms. Each new organ requires genetic information for its own development and genetic information for coordination of its function with the rest of the body. Development of new morphological structures is not seen in laboratory experiments; nor is it seen in the fossil record. The only plausible method of developing new morphological structures is through the creative activity of an intelligent being.
- The fossil record shows separate groups throughout. Fossil groups rarely if ever merge into common ancestry in the fossil record, except perhaps for a few examples at the lower taxonomic levels such as species and races. The larger groups, such as Phyla and Classes, maintain their separate identities right down to the lowest levels of the geologic column. This supports TMSA.
- Additional groups of fossils show up abruptly throughout the geologic column. The famous "Cambrian Explosion" includes most Phyla and Classes of living organisms that have enough hard parts to produce fossils easily. Even if one believes that the fossil record represents long ages of time, the "Cambrian Explosion" indicates separate ancestries for at least the major groups of organisms. Other examples of abrupt appearance extend that conclusion to groups of lower taxonomic rank. Taxonomic categories are subjectively determined, so one cannot make a blanket generalization linking limits to change with specific taxonomic categories; each case requires separate consideration and testing.
- Systematic gaps in taxonomy imply multiple separate ancestries. Relatively small, but significant, gaps appear between nearly all fossil species. Much larger gaps appear between higher taxa, such as Orders, Classes and Phyla. When viewed over time, gaps in the fossil record should be random. Instead, they are systematic. This is contrary to expectation. Although it is explained as an incomplete fossil record, it seems strange that the biggest gaps in the fossil record should occur where the greatest amounts of change are proposed. For example, there are many fossil mollusks and many fossil arthropods, but no fossils that show a reasonable link between the two groups.
Philosophical and Theological Support
- Scripture describes separately created groups. Genesis 1 gives separate mention to the following groups: plants yielding seed; fruit trees (v. 11); sea monsters (whales?); aquatic creatures; birds (v 21); cattle; creeping things; beasts of the earth (v 25); humans (v 27). The created groups are generally identified by habitat rather than group name. It seems clear from the reading that each group, e.g., "creeping things", consists of many distinct types, all created at the same time.
- The theory of universal common ancestry requires death before Adam's sin. According to TUCA, billions of individuals lived and died long before humans evolved. This disconnects the causal relationship of death and sin. Attempts have been made to distinguish the moral implications of human death from those of animal death, but TUCA provides no plausible basis for such a distinction. The Genesis story of TMSA explains the moral difference between humans and animals.
- The theory of universal common ancestry implies that God is evil. Evolution depends on the elimination of species due to resource shortages, competition, predation, and other factors we recognize as evil. If these are not the natural result of human sin, then they would appear to be the result of God's free choice. Such a god would be less moral than we are. TMSA explains the origins of the separate groups without invoking an evil god.
The theory of multiple separate ancestries explains most of the pertinent data. I think it does so more effectively than does the theory of universal common ancestry. Support for TMSA is based on observations in biology and paleontology, and by philosophical and theological arguments. TMSA cannot be proved scientifically, but it is a successful theory in explaining the origins of biodiversity.
Discussion of TMSA
The theory of multiple separate ancestries provides a good explanation for a wide variety of scientific observations. Christians may wish to know how it relates to the Bible, and how it might be used. These two topics are discussed below.
The possibility of change in species is Biblical
Change in species is part of the biblical view (Genesis 3). According to Genesis 3, nature was cursed, resulting in changes in species. Changes in plants would result in production of thorns and thistles. Changes in plant growth would produce weeds and require hard work. Changes in snakes would result in the need for crawling on their bellies. Changes in the nature of animals must have occurred to produce predators and parasites. These changes are often said to be "the result of sin." This implies some kind of genetic mechanism, such as a "creative curse" or satanic experimentation. Some such change might be neutral, but most of it would probably be degenerative.
A genetic mechanism for producing variation may be part of God's contingency plan for a world ruled by Satan. Today's environment is much different from the originally created world. If plants and animals had not been created with the ability to adapt, it is likely that most of them, perhaps all, would be extinct by now. Genetic variability may be God's way of providing for the survival of the living diversity He created.
Changes in species have produced new species. A cluster of similar species may have come from a common ancestor, but separated clusters may represent different separately created "ancestors." Creationists often use the term "Genesis kinds" to represent the species originally created by God. The Bible briefly describes the creation of many different "kinds" of animals, verifying this idea. However, creationists often add to the scriptures the notion that God prohibited animals from changing. The idea that species are fixed is not a biblical idea, but one derived from the philosophy of the ancient Greeks. The Bible does not set any limits on how much species can change; but it does state that God created many kinds in the beginning.
Similarities among groups of similar species may be due to common design rather than common descent. A good design may be useful in more than one place. It appears that the Creator used similar kinds of design features in similar kinds of organisms. Evolutionists may interpret these similarities as the result of evolution, but creationists are free to interpret them as the result of common design.
Some possible criteria for identifying species with a common ancestry
It seems reasonable that the original species, created for a world without sin, might have produced descendants with variations that we recognize as different species. How might we identify such cases?
I will propose three criteria for identifying common ancestry. First, if the differences between two or more species are no greater than the kind of variation seen within a single species, it is reasonable to suppose they might have a common ancestry. This criterion is probably met in many cases by species within a single genus. Second, if two or more species are able to hybridize and produce offspring, whether sterile or fertile, common ancestry should be suspected. Horses, donkeys, and zebras are an example, and we suspect they all descended from a common ancestor. Third, if comparison of two or more species shows that none of them has any unique genes or unique elements in their developmental programs, they are candidates for common ancestry. Our knowledge of this point is very incomplete, and it is not possible to test this criterion at present.
We should attempt to derive some criteria for identifying separate ancestries. A species which has unusual genes or a unique developmental program probably does not share a common ancestry with those lacking these features. Species that have different morphological novelties probably have different ancestries. Species or groups mentioned in the creation account of Genesis would have been separately created. Failure to hybridize may suggest, but does not prove, separate ancestries. A species that does not exhibit significant variation in a feature that distinguishes it from another species probably have separate ancestries.
"Evolution," science and history
Many people do not realize that "science" is a word with different meanings. In the context of the origin of biodiversity, the differences are of critical importance. "Historical science" is fundamentally different from "experimental science." In experimental science, the initial conditions are specified, and the result observed. So long as the initial conditions remain unchanged, the same result is expected. In historical science, only the results can be seen. The initial conditions are unknown. If the initial conditions are outside our experience, we cannot know what they were. If the initial conditions were purposefully arranged by divine intervention, we will easily be confused unless enlightened by divine revelation.
I claim that TUCA is not a scientific hypothesis, but a presupposition of evolutionary theory. Most people think of science as operating through experiment. In this sense, "TUCA" is not scientific, because it is not subject to experiment. TUCA is a presupposition of evolutionary theory. In a more technical sense, science means hypothesis testing. In this sense, TUCA is not scientific either, because common ancestry is assumed, not tested. To my knowledge, no evolutionist has ever constructed a test for common ancestry.
Science and scripture
No theory of the past has all the answers. Neither creation nor evolution explains everything we see. There are many unanswered questions about the past regardless of what one believes. One cannot make an absolute determination based solely on scientific evidence. Two factors stand out in influencing one's position.
- The relative confidence one places in revelation. One critical point in evaluating the evidence is the relative confidence one places in revelation. Those who value revelation highly will undoubtedly be biased toward believing in creation. Those who do not value revelation must depend on other lines of evidence. There is a significant number of people who do not value revelation highly, yet who doubt the theory of evolution. However, those who reject revelation are probably more likely to accept evolutionary theory, simply for lack of a better alternative.
- Whether one wishes to exclude God altogether from any potential explanation. A second critical point is whether one wishes to exclude God altogether from any potential explanation. Those who favor explanations that do not include any possibility of supernatural activity will reject creation. Having done this, evolution in some form is the only alternative theory. Those who are willing to accept theories that include the possibility of divine activity are likely to find evolution implausible. Many will find creation to be an attractive explanation for biological diversity.
"Evolution" has so many meanings that it is likely to be confusing to state whether it is true or not. Universal common ancestry is an assumption made by many scientists, but there is much evidence against it. The theory of multiple separate ancestries provides a good explanation for most observations concerning biodiversity. For those who do not wish to rule out God's purposeful activity in nature, it is quite reasonable to conclude that the origins of biological diversity involved separate acts of creation by an intelligent being.