The Cambrian Explosion is often posed as a challenge for evolution because the sudden burst of change in the fossil record appears to be inconsistent with the more typical gradual pace of evolutionary change. However, although different in certain ways, there are other times of very rapid evolutionary change recorded in the fossil record -- often following times of major extinction. The Cambrian Explosion does present a number of challenging and important questions because it represents the time during which the main branches of the animal tree of life became established. It does not create a challenge to the fundamental correctness of the central thesis of evolution, the descent of all living species from a common ancestor. This important period in the history of life extended over millions of years, plenty of time for the evolution of these new body plans (phyla) to occur. Furthermore, the fossil record provides numerous examples of organisms that appear transitional between living phyla and their common ancestors. The ongoing research about the Cambrian period is an exciting opportunity to advance our understanding of how evolutionary processes work, and the environmental factors shaping them.

The major animal body plans that appeared in the Cambrian Explosion did not include the appearance of modern animal groups such as: starfish, crabs, insects, fish, lizards, birds and mammals. These animal groups all appeared at various times much later in the fossil record.³ The forms that appeared in the Cambrian Explosion were more primitive than these later groups, and many of them were soft-bodied organisms. However, they did include the basic features that define the major branches of the tree of life to which later life forms belong. For example, vertebrates are part of the Chordata group. The chordates are characterized by a nerve cord, gill pouches and a support rod called the notochord. In the Cambrian fauna, we first see fossils of soft-bodied creatures with these characteristics. However, the living groups of vertebrates appeared much later. It is also important to realize that many of the Cambrian organisms, although likely near the base of major branches of the tree of life, did not possess all of the defining characteristics of modern animal body plans. These defining characteristics appeared progressively over a much longer period of time.⁴

Interpretations of the “Cambrian Explosion”

Not all scientists accept the idea that the Cambrian Explosion represents an unusually rapid evolutionary transition. The fossil record is notoriously incomplete, particularly for small and soft-bodied forms. Some researchers argue that the apparent rapid diversification of body plans is an artifact of an increase in the rate of fossilization, due in part to the evolution of skeletons, which fossilize more effectively.⁵ Many of the early Cambrian animals possessed some type of hard mineralized structures (spines, spicules, plates, etc.). In many cases these, often very tiny, mineralized structures are all that are found as fossils. There were major changes in marine environments and chemistry from the late Precambrian into the Cambrian, and these also may have impacted the rise of mineralized skeletons among previously soft-bodied organisms. ⁶

Most scientists are persuaded that something significant happened at the dawn of the Cambrian era and view the Cambrian Explosion as an area of exciting and productive research. For example, scientists are now gaining a better understanding of what existed before the Cambrian Explosion as a result of new fossil discoveries. Recent discoveries are filling in the fossil record for the Precambrian fauna with soft-bodied organisms like those in the Ediacaran Assemblages found around the world.⁷ Late Precambrian fossil discoveries also now include representatives of sponges, cnidarians (the group that includes modern jellyfish, corals and anemones), mollusks and various wormlike groups. Some of the new fossil discoveries, in fact, appear to be more primitive precursors of the later Cambrian body plans. The discovery of such precursors shows that the Cambrian organisms did not appear from thin air.⁸ Further discoveries will no doubt reveal more clearly the relationship of Precambrian organisms with the creatures found in the Burgess Shale and Chengjiang deposits.⁹

Genomic studies provide further insights into the origins of the Cambrian Explosion. Although the genetic divergence of organisms would have preceded the recognition of new body plans in the fossil record, accumulating genomic data is broadly consistent with the fossil record.¹⁰ Both point to the rise of the bilateria (bilaterally symmetric invertebrate animals) in the latest Precambrian Ediacaran, and their ecological explosion in diversity in the Cambrian.

Unanswered Questions

The sudden change of the Cambrian Era was, in relative terms, not too sudden for the process of evolution. The changes during the Cambrian Era did not occur over decades, centuries, or even thousands of years; they occurred over millions of years—plenty of time for evolutionary change. However, for millions of years beforehand, body plans of animals had remained relatively constant. Not until this time period did a significant change occur. The remaining questions are: What triggered the Cambrian Explosion? And why did so much change occur at this time? Several different theories address the origin of the Cambrian Explosion, proposing that dramatic environmental changes must have opened up new niches for natural selection to operate upon. These proposals include the runaway glaciation theory,¹¹ which proposes that glaciers briefly covered much of the earth, and the resultant loss of habitat created bottlenecks where evolution could act more rapidly. Another theory suggests that a change in atmospheric oxygen led to this sudden burst in evolutionary changes.¹² Yet another proposal is that major changes in the seafloor, from algae mat-covered surfaces in the late Precambrian to soft muddy bottoms later in the Cambrian, had dramatic evolutionary and ecological impacts.¹³

The Cambrian Era Fossils, Providing Answers

While the causes of the Cambrian Explosion remain a topic of open and exciting debate, the continued fossil discoveries from the Cambrian and Precambrian Eras are bringing more clarity to the evolutionary puzzle. These fossils provide valuable insight, particularly for envisioning the common ancestors of diverse groups. For instance, both vertebrates (fish) and echinoderms (sea urchins, starfish) are part of the group called deuterostomes. Without fossil evidence, it is hard to envision what a common ancestor would look like for these very different creatures. The Cambrian fossils are filling in the picture.¹⁴

Behe suggests that the parts of irreducibly complex biological structures would be useless unless they appear all together, and evolution has no mechanism to build complex structures like this. Natural selection, after all, works just one step at a time. Furthermore, natural selection has no foresight. Put simply, if a change is going to be preserved, that change will generally need to confer some extra benefit—no matter how small—to the next generation. Behe has oversimplified things a little. Evolutionary theory predicts that in small populations, neutral changes—and even changes that are slightly deleterious—will survive sometimes. Still, in general, he is correct. So let’s examine what evolutionary biologists believe about how complex structures are built.

A Seemingly “Irreducibly Complex” System

As Scott Gilbert shows in his textbook Developmental Biology, Eighth Edition, the evolution of the interconnecting bones of the middle ear illustrates how supposedly irreducibly complex structures can in fact be generated by the stepwise process of gradual change and natural selection. Fish, for example, have a special system called the lateral line system that extends along the length of their bodies and enables them to detect vibrations in the water. They also have an inner ear, which is useful for balance and supplements the lateral line system in detecting vibrations. With the movement of certain water-dwelling species to land, the lateral line system became obsolete because what was needed was a way of amplifying the vibrations in air, not water. A bone that had previously been used as a support for the skull became the stapes. Along with supporting the skull, the stapes also transmitted sound vibrations—which come in part through the skull and jaw—to the inner ear. How do we know it’s the same bone? By examining its embryological origin in fish and reptiles. In reptiles, there is just one bone that transmits air vibrations to the inner ear: the stapes.

We can also trace the origin of the two other middle ear bones, the incus and malleus, by looking at fossils from the time of the origin of mammals about 230 million years ago. Until that point, two bones—the articular and quadrate bones—served as the hinge of the jaw. Investigators, however, believe they carried out a second function. Because they were located adjacent to the stapes, it is likely they also aided in transmitting sound vibrations to the stapes.

Here is where the story gets especially interesting. Right at the time of the origin of mammals it turns out there were several species—perhaps many, paleontologists are sure they don’t have all of the transitional species preserved in the fossil record—that had a double hinge at the jaw. Not only did the articular/quadrate bones serve as a hinge, but another pair of bones, the dental/squamosal bones, served that purpose as well. So the articular/quadrate bones, which transmitted sound, no longer had to also serve as a jaw-hinge. This second function became redundant because there was another set of bones doing the same thing.

With that redundancy, the articular/quadrate bones of the jaw were free to become the incus/malleus of the middle ear. We have a record of the transition, and we have a record of the building of a so-called irreducibly complex structure. Parts that were initially used for one function became, for a period of time, useful for two functions. Then, one function was refined while the other function became redundant or unnecessary. In other words, parts that were initially used for one purpose become co-opted for another purpose; and looking back through the fossil record, we can see the intermediates.

The Bacterial Flagellum

In Darwin’s Black Box, Behe focuses on three things he considers to be irreducibly complex: the bacterial flagellum, the blood clotting cascade and the immune system. The elements of these systems are molecular in nature and therefore the evolutionary intermediates are somewhat harder to document. Interacting molecules are not preserved for historical analysis like fossil bones of the skull and middle ear. In his book, Behe suggests that biochemistry gives no clue as to how complex interacting parts like these might have come about, and he confidently states that investigations have run up against a blank wall.

It has now been 13 years since Darwin’s Black Box was written. The structures and processes Behe chose to focus on have been studied quite extensively. Although it is impossible to go back and analyze step by step what actually did happen, much evidence for straightforward evolutionary explanations has accumulated over the years. The diversity in a given structure that we see when we compare different species tells us a great deal about how that structure might have come about.

Consider the bacterial flagellum, the example most commonly used to illustrate the principle of irreducible complexity. First, it is important to point out that the bacterial flagellum comes in many different varieties, sometimes with profound differences between one species and another. This alone illustrates that the flagellum is probably not irreducibly complex. It can be altered, and when it is altered, it does not necessarily lose its function.

There are many species of bacteria, for example, that use the basal parts of the flagellum to deliver toxins into their host. A different set of bacterial species uses a portion of the flagellar machinery for another purpose. Species of the genus Buchnera live inside the sheltered environment of aphid cells in a symbiotic relationship. These bacteria no longer need flagella. However, each tiny Buchnera cell is studded with hundreds of copies of the flagellar base. As a recent paper in the journal Trends in Microbiology shows, the purpose now is to serve as a passageway for the export of proteins and other material into the surrounding environment—the aphid cell in which the bacterium resides. So while we cannot follow the sequence of events step by step to illustrate how the various types of flagella have arisen, we can see how they have changed and, in some cases, even taken on whole new functions. The term for adapting a structure for a different purpose than that for which it originally arose is “exaptation.” This is one important way in which complexity arises.

That is not the whole story, however, because individual parts have to be added into the structure as it becomes more complex or takes on new function. Where do those parts come from? Recently, investigators have shown that the key protein in the molecular motor that causes the flagellum to rotate has a very similar structure to another protein that is used to transport magnesium into and out of cells. Both protein molecules have sections that fold in almost exactly the same manner, and when we analyze the order of their building blocks (amino acids), we see profound similarities. This illustrates a second principle in building complexity: It is done by co-option. Parts that are used for one purpose are co-opted to take on a second function as well. Sometimes, the instructions to build a part are encoded by identical duplicate genes. When that happens, co-option is especially straightforward. One set of instructions for making the original part is preserved while the duplicate set of instructions can gradually be modified through mutation and natural selection, allowing the part to become better and better at carrying out its new function. This illustrates a third principle of assembling complexity: adaptation through natural selection.

Even more revealingly, the supposedly irreducibly complex bacterial flagellum turns out not to be irreducible after all. For example, there is a protein at the base of the flagellum, an ATPase, that drives the key structural subunit (flagellin) of the long hollow tube through its inner core, causing the flagellum to grow in length. Yet, it has been shown that flagellin can be transported to the end of a flagellum without this ATPase. The protein that was thought to be one of the flagellum’s most important parts can be done away with. This illustrates a fourth principle of building a complex structure: redundancy. Inside of cells, there is often more than one way to accomplish a particular purpose; as evolution “tinkers” with a complex structure, there is likely to be redundancy with certain parts at certain stages. One of these redundant mechanisms may become more specialized, and even perfected, as time goes by.

The Eye

Another system that is often held up as an example of irreducible complexity is the eye. People often ask: What good is a partly assembled eye? Is there any logical series of steps that could result in the creation—through the process of natural selection—of a structure so elegant as the eye of an eagle? What would be the starting point, anyway?

Watch "The Evolution of the Eye" from PBS' Evolution: "Darwin's Dangerous Idea".

All light-sensing devices in the animal world make use of a single light-sensitive molecule, retinal, which is derived from Vitamin A. Retinal can change its shape when it absorbs a photon of light. This molecule is always complexed with a protein known as an opsin. The two work together to sense light.

By analyzing the arrangement of the building blocks, or amino acids, in opsin, it is possible to show that all opsins are derived from a single ancestral gene. What purpose could the retinal/opsin combination have had in the earliest days of animal history? It likely functioned to detect light in order to set the internal body clock that regulates the 24-hour cycle of biological processes, known as the Circadian rhythm. In recent years, it has become apparent that living processes inside of cells are tuned to function in a manner that is synchronized with the cycle of sunlight.

Circadian rhythms function throughout the living world, including single-cell organisms. It seems likely, then, that the simplest light-detecting device arose through exaptation of a molecular device that was used to detect light—not so that an organism might move toward or away from the light, but so it could reset its molecular clock. Even the origin of opsin illustrates a basic principle of building complexity, co-option. Opsin is one of many G-protein receptors, which have come to take on many different functions through the history of life. When coupled with the light-sensitive molecule retinal, a G-protein receptor allows the cell to be sensitized to the presence and absence of light. Although we have no fossilized transitions that allow us to trace the various eye intermediates that have occurred in animal history, as we do with the middle ear, we do have a myriad of light-sensing devices in the animal kingdom that allow us to piece together how sophisticated eyes could have been created through a gradual process driven by natural selection. (You can read more about the prospective intermediates that exist in the animal world in a wonderful paper by Ryan Gregory.)

If you choose to explore eye development in detail, be watching for examples of exaptation, co-option, step-by-step adaptation and redundancy. For example, you will note that the evolution of the lens illustrates co-option and redundancy. There are two ways to focus the image on the light-receiving cells at the back of an eye. One way is through an independent lens. The other way is through the transparent cornea in front of the lens. The lens is simply transparent crystallized protein molecules that are assembled in such a manner that they bring the image into sharp focus. There are a variety of proteins that can be crystallized to serve as an effective lens. It turns out that, depending on the evolutionary lineage, various proteins—including enzymes such as alcohol dehydrogenase (an enzyme for breaking down ethanol), glutathione S transferase and protein chaperones—are used for this purpose. This is a simple example of co-option and redundancy functioning together as part of the tinkering mechanism used for building a complex structure like the eye.

Two-thirds of animal phyla have some sort of light-sensing device. Although all of these light-sensing devices make use of retinal and opsins, there are differences in structure that we can trace to differences in evolutionary origin. In his 2003 book, Life’s Solution, Simon Conway-Morris documents at least seven independent origins of the eye resulting in very similar outcomes. For example, the eye of a squid and the eye of a mammal work in a remarkably similar manner. However, the ways the two eyes are constructed during development are quite different. Differences in structure are constrained by how particular bodies are constructed as the embryo develops. Eyes also bear telltale signs of the fact that there has been a certain amount of jury-rigging in their construction. They are not perfect. They have blind spots, are subject to retinal detachment, glaucoma and macular degeneration, all of which are a function of the history of how the eye has been assembled through time.

Read how a recent study has shot down the idea that protein transport is irreducibly complex.

Although we don’t have the eye intermediates preserved in stone the way we can see the simpler assembly of the parts of the mammalian middle ear, we do have a vast array of eye structures in the animal kingdom, any one of which might appear to be irreducibly complex but which, in fact, has been put together through a set of processes that has included exaptation, co-option, step-by-step adaptation and some redundancy at various stages along the way. Indeed, these eye structures themselves are likely intermediates. Everything changes as it passes through the eons of time. This is the legacy of creation through the process of natural selection.

It would be difficult to give a short answer to this complex question.  From all we know about the state of the Earth 3 to 4 billion years ago and what we know about the complexity of the building blocks of life — DNA, RNA, amino acids, sugars — no entirely plausible hypothesis for the spontaneous origin of life has been found.  Because the topic does not have as many potentially useful applications as other areas of science, less research has traditionally been performed in this area. However, scientists are currently approaching this challenge from a number of different perspectives.¹ The fact that there is no answer today does not mean there will be no answer tomorrow.  Though an explanation for the origin of life is currently elusive, this does not mean divine intervention is the only possible explanation. There are many unexplained natural phenomena; the origin of life is simply a particularly compelling example of an unsolved mystery we would like to understand.

Clarifications

In discussions about the origin of life, an important first step is clarifying what is meant by life.  The first forms of life on Earth were probably very different from what we would call life today.  It may be tempting to think of life as anything containing the DNA double helix seen in many life forms today.  However, the main property required for early life is self-replication. The earliest self-replicating systems could have been made out of DNA, RNA or some other basic building blocks.  The key feature of such systems would have to be the ability to gather chemicals from the local environment and make copies of themselves.  All life on Earth contains carbon as an essential elemental building block.²  Carbon is the simplest element capable of forming the remarkably complex molecules that are so prevalent in life forms. Therefore, it is likely carbon was involved from the beginning.  Compounds containing carbon are generally categorized as organic; and exploring the natural mechanisms that create complex organic compounds is a main focus in research on the origins of life.

It is also important to keep in mind the age of the Earth. The Earth is approximately 4.5 billion years old.  All evidence suggests that the Earth was inhospitable to life for the first 700 million years, largely because it was so hot. However, the Earth gradually cooled, and 4 billion years ago it became more hospitable. Within little more than 100 million years, the first single-cell life forms appeared.³  Where did these organisms come from? And what were their capabilities?  Although we do not know the path that led to these early bacterial forms, it seems likely DNA had emerged as the information molecule by this time.  Microbiologist and physicist Carl R. Woese suggests there was a considerable amount of lateral gene transfer among the first forms of bacteria called archaebacteria.⁴ Lateral gene transfer, which is the movement of genes from one bacterium to another, would have enabled the exchange of genetic material, and it would therefore expedite the process of diversification of biological function acted upon by natural selection.  How these first organisms ever developed in the first place is the topic of the following discussion.

The Miller-Urey Experiment

Charles Darwin is often credited for the original “warm little pond” hypothesis, which proposes life may have formed from a combination of inorganic compounds and energy.⁵ Soviet biochemist Aleksandr Ivanovich Oparin revisited this idea and proposed life formed in an environment that lacked oxygen but was energized by sunlight.⁶  These kinds of ideas are the basis of much research of life’s origins, including the famous Miller-Urey experiment.

In 1953 at the University of Chicago, Stanley Miller and Harold Urey tackled the problem of the origin of life by reproducing the conditions they believed to be present on the primitive Earth when life originated.  By zapping a mixture of water and inorganic compounds with electricity, they produced organic compounds including amino acids, the building blocks of protein.⁷ This result catalyzed further experiments — and at least to some, it appeared that the solution to life’s mystery was about to unfold. 

A subsequent discovery by Joan Oro at the University of Houston, published in 1961, demonstrated that an essential component of DNA — adenine — as well as several amino acids could be formed by heating the inorganic compound hydrogen cyanide in water-ammonia.⁸  Though this work potentially contributed useful pieces to the puzzle,⁹ Miller-Urey type experiments have fallen short of providing a full answer to how life originated.  It’s one thing to have organic compounds present, it’s quite another to have them form a self-replicating system.

Recently, these initial results were revisited with more sensitive methods. Researchers discovered additional amino acids and other building blocks formed during the Miller-Urey experiments that they originally had not realized.¹⁰ Miller continued a variety of experiments to pin down life’s origins and, though the mystery remained unsolved, members of his lab discovered amino acids and other building blocks for life can also form from inorganic compounds in extremely cold environments.¹¹

How Life Came Together

Explanations of how the amino acids, nucleotides and sugars were formed, how they assembled in the form of DNA and RNA, and then how these building blocks of life came to replicate themselves and acquire the enzymes to facilitate this process, are all still speculative.  Many interesting ideas are being researched, however, including the deep sea vent theory,¹² radioactive beach theory¹³ and crystal or clay theory.¹⁴ Another opinion, held by Francis Crick and others, is that the only explanation for life on Earth is that it came from another planet.¹⁵  However, this type of explanation only pushes the question farther back: How did this extraterrestrial life originate? A compelling explanation of the origin of life here on Earth has not yet emerged.

Evolutionary theories of how life originated fall in two main camps: the gene first hypothesis and the metabolism first hypothesis. The gene first hypothesis currently focuses on RNA rather than DNA, as certain RNA molecules have shown the ability to function as enzymes, suggesting RNA could have both carried information and copied itself.  From this point of view, RNA preceded both DNA and protein synthesis.  On the other hand, the metabolism first hypothesis argues the molecules of prebiotic materials formed chemical cycles and networks of chemical reactions that gave rise to primitive metabolic systems.  These metabolic systems existed before RNA and provided the environment for RNA replication to later emerge.  Despite the exploration of numerous avenues of research, both theories currently lack conclusive evidence.  While researchers have recently generated self-replicating RNA from prebiotic molecules in the laboratory,¹⁶ it is difficult to understand how RNA — a notoriously unstable polymer — could have supported self-replicating systems in the hostile chemical and thermal environment of early planet Earth.

Conclusion

The study of life's origins is an exciting area of research.  The jury is still out on how life first emerged. A simple response would be to give a God-of-the-gaps explanation: that some supernatural force, namely God, must have intervened to bring life into being.

See "What is evolution?".




 

But consider the timeline of these scientific quandaries.  Life on this Earth appeared approximately 3.85 billion years ago, yet serious scientific study of its origins began just 60 years ago.  A convincing scientific explanation may still emerge in the next 50 years. Though the origin of life could certainly have resulted from God’s direct intervention, it is dangerously presumptuous to conclude the origin of life is beyond discovery in the scientific realm simply because we do not currently have a convincing scientific explanation. Although the origin of life is certainly a genuine scientific mystery, this is not the place for thoughtful people to wager their faith. All that has happened in the history of life has happened in response to God's creation command (John 1:3).  Furthermore, God is immanent in creation, upholding the natural laws.  Colossians 1:17 tells us, "He is before all things, and in him all things hold together."  What we do not know at this point is the extent to which God may have intervened supernaturally in the history of life.  Some believe that the creation command was carried out through the natural laws which have been continuously upheld by the ongoing presence of God in creation.  Others believe that since the God of the Bible and the God we experience in our lives intervenes in supernatural ways at times, that this would also likely have been true in the history of life itself.  Neither of these views are inconsistent with scientific findings.  The important thing is that in the BioLogos view, God’s sustaining creative presence undergirds all of life’s history from the beginning to the present.

Finally, as a purely technical matter, the theory of evolution does not propose an explanation to the question of the origin of life at all. The theory of evolution becomes relevant only after life has already begun.

The existence of God is an enduring and popular philosophical problem. Many arguments claiming to prove the existence of God have been proposed througout the centuries, often on the basis of some feature of the natural world. There have also been attempts to disprove the existence of God, which is a more complex task. Consider how much easier it is to establish that there is a black swan somewhere on the Earth compared to establishing that there isn’t one. G.K. Chesterton made this point: “Atheism is the most daring of all dogmas, for it is the assertion of a universal negative.”¹

Popular arguments for the existence of God include the cosmological argument, the ontological argument, the moral law argument, and the argument from Design. The argument from Design is a more general version of the narrower perspective about irreducible complexity that forms the core of the Intelligent Design movement. Each of these arguments supports a certain belief in a creator. The response to many of these arguments, however, is: 

“If God created the world, what created God?”

This is a reply that requires serious consideration. It suggests that certain arguments for God’s existence only push the question of beginnings one step farther back. It also suggests that any God complex enough to account for all of creation would necessarily be complex enough to require an explanation.  Richard Dawkins is one of the strongest proponents of this argument.

An Answer From Doctrine?

In many faiths, God’s origin is straightforward. Christian doctrine teaches that God is eternal and thus had no beginning. The Psalms speak clearly about God’s eternal nature, affirming, but never defending God’s existence:

“Before the mountains were born or you gave birth to the earth and the world, even from everlasting to everlasting, you are God.” ²

“For a thousand years in Your sight are like yesterday when it passes by, or as a watch in the night.” ³

These verses, and many others like them, highlight the complexity of God’s relation to time. Theologians have debated the relationship of God to time for centuries and no doubt will continue to do so. It is a question that we probably cannot answer. In one thoughtful response, God is the creator of time itself, and thus exists outside of time seeing all of history at once. Verses like those above are often used to support this view. On the other hand, this view is often critiqued by Biblical scholars including Clarke Pinnock, John Sanders and Gregory Boyd⁴, who point out that God is portrayed in scripture as acting in time. For example, when God is negotiating the fate of Sodom and Gomorrah with Abraham (Genesis 18), or lamenting having created humans at the time of Noah (Genesis 6:5-8), God certainly seems to be in time and responding to the unfolding course of events. But of course, given the difficulty our time-limited minds have in grasping this philosophical problem, there is no compelling reason that God could not be both outside of time and capable of acting within it.

An Answer From Definition?

Answers from religious doctrine are rarely adequate for nonbelievers. In fact, many fervent believers in God reject the argument about God’s timelessness because even timeless beings need explanations for their existence. But if God is the creator of all things, and yet also requires cause, we face an infinite regress of causes. The only way to avoid this infinite regress problem is to state — as Christian theology has always done — that God is the first cause and is entirely self existent, meaning the reason for God’s existence is contained within the very definition of God.

While this viewpoint certainly may be attractive, it still fails to convince skeptics who are more likely to favor the idea that the universe contains within itself the reason for its own existence. If that could be true of God, why couldn’t it be true of the universe? There is certainly reason to be skeptical about the common sense intuition that everything must have a cause or that everything must have a reason to be as it is. This perennial assumption has been challenged by the physics of the 20th century that uncovered a mysterious quantum world where things often do not appear to have reason to be the way they are.

The common sense assumption that everything must have a cause or a reason to be as it is also suffers from what is called the fallacy of composition. This fallacy comes about when we assume that properties of the parts apply to the whole. For example, just because every member of the human race has a mother, we cannot infer that the human race itself has a mother. Similarly, a collection of spherical things would not itself have to be spherical. In discussions about the origins of the universe, we would say that just because every individual part of the universe has a cause, that does not mean that the entire universe has a cause.

The realization that our universe had some sort of beginning has opened up exciting new conversations about origins. In some ways, a universe with a beginning seems to beg for a cause. But if the universe came into being from nothing , it becomes deeply problematic to speak of anything having caused the universe to exist. Some cosmologists would argue that our universe is the result of an uncaused quantum fluctuation. Such fluctuations do not have causes in the traditional sense, so they argue this does away with our universe needing a cause. But there is a significant problem that  the vacuum that fluctuates is not nothing. Quantum vacuums — which are what you get when you remove from space all the particles and energy — are real. They have activity, laws and rules. Our universe may have fluctuated into existence from such a vacuum, but the vacuum remains unexplained.

Cosmologist Lee Smolin suggests in Life of the Cosmos, that black holes can give birth to new universes.⁵ He proposes that our present universe emerged out of a black hole in some other “meta-universe.” And perhaps our universe is presently birthing new universes. Such a process, while clearly speculative, provides a caution against extrapolating from common sense notions of causality to philosophical conclusions about the nature of all of reality.

An Answer From Plausibility

The difference between the theist and atheist positions on this topic is that by assuming that everything — including the universe — has to have a cause, then the atheist is left with a dilemma of what or who that first cause might have been. For the theist, the answer is God, but a satisfactory reason must be found why God should be exempt for the need for a cause. Such a response is available through the Augustinian concept that God is not limited in space and time, and  therefore the argument of needing a first cause loses its power.

On the other hand, if not everything needs to have a cause, the theist and atheist have no grounds for arguing this part of their case.

But the argument can be reframed in a way that is more sensitive to postmodern intuitions about causation and the importance of starting points. Suppose as a religious believer you ask the question, “What kind of a universe is most compatible with my belief in an eternal God?” In this case the response affirms but does not prove the reality of God. The universe that we experience appears to have had a beginning; it appears to be finely tuned for life; it appears to have a place for love and purpose. These appearances affirm as plausible your prior belief in God.

See "What is the 'fine-tuning' of the universe, and how does it serve as a 'pointer to God'?"

 

Now suppose you start from the atheist assumption. In this case the universe must not really be as it appears. It cannot have a real beginning, be tuned for life and love, and purpose can’t be anything other than illusory epiphenomena — the curious byproducts of chemistry and physics. The whole picture has a claustrophobic bleakness.

Bertrand Russell, one of the most brilliant and ruthlessly honest atheists of the 20th century, captured this sense of despair in A Free Man’s Worship:

“That man is the product of causes which had no prevision of the end they were achieving; that his origin, his growth, his hopes and fears, his loves and his beliefs, are but the outcome of accidental collocations of atoms; that no fire, no heroism, no intensity of thought and feeling, can preserve an individual life beyond the grave; that all the labors of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system, and that the whole temple of man's achievement must inevitably be buried beneath the debris of a universe in ruins – all these things, if not quite beyond dispute, are yet so nearly certain that no philosophy which rejects them can hope to stand. Only within the scaffolding of these truths, only on the firm foundation of unyielding despair, can the soul's salvation henceforth be safely built.“ ⁶

In contrast to this view, the theist can affirm that the wonders encountered in the world are real, that they belong, and are a reflection of the glory of the creator whose mysterious power upholds everything.

Conclusion

The world disclosed by modern science is far subtler and nuanced than the world in which philosophers and theologians have lived for the past few centuries while formulating their arguments about the mysterious relationship between God, the physical world, time and causality. Nevertheless, no development in contemporary science poses a particular challenge to the view that God is creator. And some developments, like the discovery of fine-tuning in the physical laws, are supportive of traditional affirmations. The common-sense assumptions that have historically undergirded this entire discussion, however, need reconsideration in the face of recent scientific developments. We must be intellectually humble in making claims about God as creator. But we can also state confidently that denials that God is creator are fraught with even more unresolvable difficulties and ultimately provide a far less satisfactory grounding for a worldview in which meaning and purpose play important roles.

Many voices today say that science and Christianity are opposed to each other. Some atheists claim that science has debunked religion and superstition of all forms. Many in the general public think that the church is anti-science. And within the church, science is often portrayed as challenging important Christian beliefs. None of these voices, however, hint at the positive and fruitful relationship between Christianity and science. Here we review several ways to view the relationship between science and Christianity.

Are Christianity and science at war?

When creation and evolution clash in a courtroom, the daily news fills up with stories suggesting that there is some profound conflict between science and Christianity. Inevitably, someone mentions the historical incident of Galileo. Galileo was charged with heresy by the church in 1633 for teaching that the Earth orbits the Sun. From Galileo to textbook battles, the hasty conclusion is that science and Christianity are engaged in an endless debate, fundamentally opposed to each other.

For a review of Galileo and other historic interactions between science and Christianity, see “Christianity and Science in Historical Perspective” by Ted Davis (blog series, PDF) and “The Galileo Affair: Emblematic or Exceptional?” by Matt Rosano (blog)

Yet the Galileo incident and today’s conflicts are often about much more than the particular claims of science or faith. Personalities, politics, and culture wars all come into play when drawing the battle lines. In many instances, science and scientists are not themselves in conflict with Christian belief. In fact, Galileo himself was a Christian who believed “that the glory and greatness of Almighty God are marvelously discerned in all His works and divinely read in the open book of Heaven”¹ Many scientists then and now² are Christians who see no conflict between their scientific work and their faith. Most things studied via the natural sciences—such as the migration patterns of birds or the interior of atoms—do not raise any theological or Biblical concerns.

The “warfare” model, then, is not very helpful for understanding evolution and Christianity, since it assumes conflict from the start. A few particular areas of scientific study—like the big bang and evolution—do raise concerns for Christians, but most of the BioLogos website (see Questions by Category on the right) is devoted to showing that evolution and Christianity are not truly at war. In the rest of this answer, we’ll explore other models for the working relationship between science and Christianity.

Mark Noll, a leading historian and evangelical, gives 16 reasons why the warfare model is a mistake. (blog series)

Are Christianity and science completely separate?

One way to erase the conflicts between science and Christianity is to view them as entirely separate endeavors, with different purposes, methods, and bodies of knowledge. This view emphasizes that science is a system of knowledge about the world and its behavior, whereas religion is about morality, God, and the afterlife. Thus, Christianity and science cannot conflict, because they are addressing different sorts of questions.³

This model has some weaknesses (see below), but it does help us understand some important aspects of the relationship. Many apparent conflicts between science and religion occur because of a lack of understanding of the fundamental differences between the two. When someone claims that the Bible answers a scientific question, and another claims that science answers a question about God, the conflict immediately flares up. Many conflicts become enflamed because participants forget that Christianity and science do generally address very different questions.

This model also reminds us that science is not the only source of knowledge. There are many sorts of questions that simply do not fall under the domain of science. Borrowing an example from the Rev. John Polkinghorne, there is more than one answer to the question of “Why is the water boiling in the tea kettle?”⁴ The scientific answer might be “the water is boiling because at this temperature it undergoes a phase transition from liquid to vapor.” Another acceptable, though nonscientific, answer is “the water is boiling because I put the kettle on the stove.” A third answer might be “the water is boiling because my prayer partner is coming over for tea.” None of the answers is wrong; rather, each gives a different perspective on the question. The scientific answer does not tell the whole story. Science cannot answer questions like “Is my friend trustworthy?” or “Is this poem well written?” Science is tremendously successful in understanding the physical world, but we should let that tempt us to think it can be used to understanding everything in life.

Artist Mark Sprinkle writes on the importance of music and poetry in understanding God’s world.

Science cannot answer the question “Does God exist?” Some people argue that God’s existence is actually a scientific claim that could be tested like a chemical reaction. But science studies the natural world, not the supernatural. No amount of scientific testing or theorizing could prove or disprove the existence of a supernatural creator. The claim that “God exists” is a metaphysical one, not a claim about nature or physical laws

Though science cannot prove or disprove God’s existence, it can provide clues that support belief in God. See “What is the fine-tuning of the universe?” and “On what grounds can one claim that the Christian God is the creator?”

This model also reminds us that the Bible is not the only source of knowledge. The Bible is silent on most of the topics that concern scientists, like protons, photosynthesis, penguins, and Pluto. The Bible is not a science textbook, in the same way that it is not a textbook of plumbing, agriculture, or economics. Instead, God teaches us about these things through his general revelation in the created order.

However, this model has some significant weaknesses. It isolates religion from science, which can be a first step in marginalizing religion from public discourse. By defining religion and science as separate, this model doesn’t help us understand the interactions they do have, either negative or positive. The model also sets science on its own, apart from religion, while Christians believe that no part of our lives is outside of our walk with God.

Science and Christianity interact, correcting and enhancing each other

While many questions can be clearly categorized as “science” questions or as “Bible” questions, other questions are on the boundary. For topics like evolution, medical ethics, and climate change, we need to consider both science and faith when seeking out God’s truth. For such complex questions, we need all the knowledge and wisdom we can get, rather than handicapping ourselves by looking only to science or only to the Bible. If we look to only one or the other, we will get a distorted view of the issue. As Pope John Paul II wrote,

Science can purify religion from error and superstition; religion can purify science from idolatry and false absolutes. Each can draw the other into a wider world, a world in which both can flourish.⁵

God reveals himself in the book of Scripture and the book of Nature. To learn more about God and his work, we study both books. When one book is confusing or ambiguous, insights from the other book can help us understand it. In both revelations, we look for the underlying truth of who God is and how he made the world. Rev John Polkinghorne wrote, “Science and theology have things to say to each other, since both are concerned with the search for truth attained through motivated belief.”⁶

For more on God’s two revelations, see “Can Science and Scripture Be Reconciled?”

Faith can have a positive impact on science by guiding the practical application of scientific discoveries. With the rapid advance of science and technology, many ethical questions are facing our society. Development of safe nuclear energy is not far from the development of nuclear weapons, new medical imaging techniques save lives but are too expensive for the poor, and DNA testing improves treatment of genetic disorders at the risk of the results being misused.⁷ To address these complex questions, we need both science and the moral grounding of religion. We can’t just give a quick answer from the Bible without studying the scientific complexities, nor can we look to science alone to guide ethical decisions. Christianity and other religions lay the groundwork for the moral standards that are essential for the appropriate use of science and technology.

Science also has a positive impact on the faith of the believer. The Bible teaches that “The heavens declare the glory of God” (Psalm 19:1). Christians see God’s glory when looking up at the stars, and in colliding galaxies seen through a telescope. God’s glory is revealed in the beautiful symmetry of a maple leaf, and in the complex biochemical activity inside each cell in that leaf. Science and technology have shown us much more of God’s creation than was known in Biblical times, revealing more and more of God’s glory.

See “Science as an Instrument of Worship” by Jennifer Wiseman (PDF) (blog series)

Finally, Christianity can provide the belief framework for how and why we do science. Christians need not set aside their faith when they sit down to do science. Read on to the next question for more.