Transitional Fossils

Some time ago, the Discovery Institute’s Casey Luskin commented on the human origins exhibit at the Smithsonian Institution, suggesting that palaeoanthropologists use evolutionary theory to describe the progression of the human lineage even when they don’t have transitional fossils with which to work. He writes:

What's ironic, however, is that if you ask the question How Do We Know Humans Evolved? the answer you’re given is, “Fossils like the ones shown in our Human Fossils Gallery provide evidence that modern humans evolved from earlier humans.” So whether you find fossils or you don’t, that’s evidence for evolution.

Indeed, it has become an article of faith for those espousing both the young earth creation (hereafter YEC) model and many who hold to the intelligent design model that transitional fossils do not exist and therefore evolution has not taken place. Support for this position usually entails attacking the weak areas of the fossil record, where burial processes have left us little with which to work, or the creation of straw men arguments in which transitional fossils are defined in such a way that none could ever be found. Often this centers on the concept of “missing link,” a term that is habitually used in the popular press and young earth creation and intelligent design literature when referring to fossil remains but which has little to no meaning for biologists or palaeontologists. As Ahlberg and Clack (Ahlberg and Clack 2006) write:

But the concept has become freighted with unfounded notions of evolutionary ‘progress’ and with a mistaken emphasis on the single intermediate fossil as the key to understanding evolutionary transitions. Much of the importance of transitional fossils actually lies in how they resemble and differ from their nearest neighbours in the phylogenetic tree, and in the picture of change that emerges from this pattern.

Contrary to common misconceptions, the fossil record does not record one single lineage for any family of organisms but rather a series of branches, with many related species coexisting synchronously. Darwin hypothesized that the evolutionary record reflected this bushiness and drew such a diagram in his journal. At the time, though, he had little in the way of fossil evidence to back up this position. Much has changed since his day.

An analogy for understanding this “bushiness” was best described by Prothero and Buell (Prothero and Buell 2007). They suggest that the reader consider his or her own genealogy. You and your siblings are the direct descendents of your parents and, while you are similar to them, each of you has different characteristics not shared with them as well as characteristics that you do share. Your parents have siblings as well (your aunts and uncles), and your grandparents are their last common ancestors. These siblings have their own children (your cousins), who have different and similar traits relative to their parents. They are broadly recognizable as being related to you (“oh, I see you have Aunt Edna’s nose”) but three or four generations out, they will become less and less so. These are the “nearest neighbours” that Ahlberg and Clack describe. In this analogy, each of these cousins represents a transitional form from what was (your grandparents) to what will be down the road.

For example, no one would confuse a frog with a salamander but if you trace the fossil record of each back in time, eventually you encounter a fossil, Gerobatrachus hottoni which was recently discovered (Anderson et al. 2008) that is best described as a “frogamander,” having the basal characteristics of both frogs and salamanders. Had we seen such an animal at the time, it is likely we would not have found it remarkable because it would have resembled the species around it. One lineage eventually diverged into frogs, salamanders and other amphibians. Most (just like Darwin proposed in his tree diagram with the little hatch marks at the tip of many branches) went extinct.

Taxonomy and the Beginnings of Human Origins

All life is classified based on a system devised by Carolus Linneaus in 1735 in his remarkable work Systema Naturae. This system gives all recognized species an individual place based on a system of hierarchy. The study of classification is known as taxonomy. A taxonomic ranking for humans would be this:

When a fossil is excavated, the first thing that the palaeontologist does is make a taxonomic assessment of where it fits in a sequence of known fossils. Traits that are shared with other like species or genera are referred to as primitive traits. Examples of this in humans are five fingers and the presence of three arm bones. We share this with all mammals. Traits that are new or are not shared with other like species are referred to as derived traits. Examples of this in humans are the skeletal changes in the pelvis and the foot to allow for walking upright. We do not share these with any other primates.

Transitional fossils in the human fossil record are distinguished at both the genus and species level. This group includes the extinct genera Ardipithecus and Australopithecus and the current genus Homo. All species except Homo sapiens are extinct. Much of the recent study of early humans focuses on the transition from Ardipithecus (‘Ardi’) to Australopithecus (‘Lucy’ and similar fossils) and from Australopithecus to Homo, the genus that led eventually to us. While each of the australopithecine species identified in the fossil record has derived characteristics that separate them from their ancestors and from each other, only one led to the genus Homo.

In future posts, I will describe the evidence for human evolution and why this evidence is compelling. It suggests that we have had a long, varied history filled with great leaps of change, crushing defeat, and eventual expansion into all areas of the globe.

Notes

Ahlberg, P. & J. Clack (2006) A firm step from water to land. Nature, 440.

Anderson, J. S., R. R. Reisz, D. Scott, N. B. Frobisch & S. S. Sumida (2008) A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders. Nature, 453, 515-518.

Prothero, D. & C. Buell. 2007. Evolution: What the fossils say and why it matters. Columbia Univ Pr.

These were just a few of the questions that motivated us at BioLogos to commission a survey of pastors on origins.  In 2012, the Barna Group conducted 743 telephone interviews with pastors from across the US, from churches big and small, and from all Christian denominations.  This comprehensive, in-depth survey provides a fascinating analysis of views held by clergy today.   In the coming month, we’ll be digging deeper into the survey results, but for now, here are some key highlights:

#1: Pastors hold a diversity of views on origins.

Overall, while a slight majority of the pastors surveyed fall under the label of Young Earth Creationism (54%), sizeable portions of clergy accept Progressive Creation (15%) and Theistic Evolution (18%).

The numbers varied widely based on a number of factors, however. Pastors of mainline churches were most likely to accept Theistic Evolution, while non-Mainline, Charismatic, and Southern Baptist pastors were overwhelmingly Young Earth Creationists. Pastors of larger churches were also more likely to accept Theistic Evolution.

Regionally, the highest percentage of YEC pastors was found in South, while the highest percentage of pastors accepting TE was in the Midwest. Pastors from the western states were the least likely to accept TE.

#2: Most pastors think science and faith questions are important.

Regardless of their views, the majority of pastors surveyed feel that the Church needs to look at how it handles issues of science. 72% of pastors with YEC views and 73% of pastors with TE views agree with the statement that “the Christian community needs to take a serious look at its understanding of science and human origins in order to maintain its witness in the world.” (The numbers are slightly lower for pastors who hold to Progressive Creation and who are uncertain).

Similarly, 66% of YEC pastors and 61% of both TE and Progressive Creation pastors agree that “younger adults today are more concerned than ever about whether faith and science are compatible.”

#3: Clergy think disagreements on science and faith harm our witness (but for different reasons).

Clergy across all three viewpoints feel that disagreements are harming the Church’s outreach, but they differ in how they view that harm.

YEC pastors overwhelming agreed (85%) that “Christian disagreement on matters of creation and evolution is compromising our witness to the world.” However, a majority of TE pastors disagreed with the statement (63%).

Conversely, a majority of TE pastors (63%) agreed that “The church’s posture toward science prevents many non-Christians from accepting Christianity,” while a majority of YEC and Progressive Creation leaning pastors disagreed (59%).

#4: Pastors aren’t avoiding science.

The majority of pastors think that addressing issues of science for their congregations is an important part of their work. Of those surveyed, 72% felt that addressing science issues in the local community was somewhat (51%) or very (21%) urgent. When asked about science on a national and global level, even more pastors felt that addressing science issues is important (43% somewhat and 46% very). Furthermore, 79% of pastors included scientific themes in at least one sermon in the past year, and 40% had included them in at least ten sermons.

The majority of clergy across all four viewpoints also agreed with the statement “Just as scripture should influence human interpretation of science, science should also inform our understanding of scripture.” The numbers were highest for TE pastors and those who are uncertain (81% and 72%, respectively), though over half of YEC and PC pastors also agreed (52% and 65%, respectively).

Finally, although YEC’s are more reluctant than other pastors to say “science should inform understanding of scripture, they strongly agree (84%) that “The Christian community needs a greater commitment to showing how young earth creationism is consistent with science.”

#5: However, they are concerned about evolution for biblical reasons.

Over half of pastors said they had “major concerns” about the idea that God used evolution. The main reasons for that concern were that the idea “undermines the authority of Scripture” (64%), “views portions of the Bible as non-literal, like Genesis” (62%), “raises doubts about a historical Adam and Eve” (61%), and “raises questions about how and when death and sin entered the world” (59%). However, 26% of pastors saw no concern with the idea that God used evolution.

#6: The majority of clergy accept parts of scripture as symbolic.

60% of the pastors surveyed felt that “some portions of the Bible are symbolic, but all that it teaches is authoritative.” Clergy whose views fall under theistic evolution and progressive creation were more likely to accept this statement (79% and 73% respectively), but a sizeable number of YEC pastors (40% among the core followers and 49% among those leaning towards YEC) also agreed with the statement.

#7: Clergy are concerned that changing their views on origins might compromise their ministry.

Over half of pastors (58%) who fell under the YEC category agreed that “If you publicly admitted your own doubts about human origins, you feel you would have a lot to lose in your ministry.” 41% of pastors in the Progressive Creation group also agreed with the statement. Pastors who were uncertain or who fell under the Theistic Evolution group were less concerned, with only 26% and 17% respectively agreeing with the statement.

What does it mean for humanity to be created “from the dust of the ground?”

In many ancient Mesopotamian creation stories, human beings were depicted as deriving from some physical part of the gods. Often this was the result of conflict: humans arose from the blood, flesh or tears of gods slain by other gods. Humans created in this fashion were supposed to serve the gods by performing menial work that the gods had tired of doing themselves. The lot of humanity, then, was one of violence and servitude.

In the Israelite creation stories reflected in Genesis 1 and 2, however, humans are made from the ordinary material of creation: “dust.” Humans are made of earth-stuff, not god-stuff.

At first glance, it may seem that this lowers the status of the human creature. We might ask the question raised by Eliphaz in the book of Job:

Can a mortal be more righteous than God?
Can even a strong man be more pure than his Maker?
If God places no trust in his servants,
if he charges his angels with error,
how much more those who live in houses of clay,
whose foundations are in the dust, who are crushed more readily than a moth! (Job 4:17-19)

Indeed, our humble origins ought to remind us of the fragility of our lives. As the Psalmist says,

You turn people back to dust, saying, “Return to dust, you mortals.”
A thousand years in your sight
are like a day that has just gone by,
or like a watch in the night.
Yet you sweep people away in the sleep of death—
they are like the new grass of the morning:
In the morning it springs up new,
but by evening it is dry and withered.

The elements of which our bodies are made are ordinary and abundant. Science tells us that approximately ninety-three per cent of the mass in a living human body is comprised of elements first formed through nuclear fusion in the hearts of stars. Through almost unimaginably vast and ancient cycles of stellar formation and supernova explosions, this “stardust” of elements has been spread throughout the universe. It is as though God scattered the stars across space and time to seed the universe for life, including your life and mine. And we are thereby inseparably connected to each other, to the air we breathe, to the ground we tread, to all the creatures that fill the skies and crawl upon the earth and teem in the seas, to the depths of all the heavens. We are not transcendent of creation. We are creatures.

Yet we are creatures into which God breathed the “breath of life.” We are stardust and more than stardust. We are not reducible to our constituent chemicals. A “man” or a “woman” is not just a gooey sack of water, carbon and trace elements. Hydrogen, oxygen and carbon are not aware of their own existence. These elements cannot reason or pray or love or write poems. Conjunctions of these elements cannot carry any persistent identity across time. They do not exercise will or intentionality or agency. They are not “selves.”

Most of the cells in a human body are in constant flux: aging, dividing, dying, being replaced. The surface layer of human skin is renewed completely about every two weeks. An adult’s skeleton is entirely remade over approximately ten year periods. It may be that only the neurons of the cerebral cortex and a few other types of cells persist throughout the lifetime of a human body. And eventually, it all does return to “dust.”

Yet we think of ourselves as persisting over time, as comprising an “identity,” a “self.” Perhaps the cerebral cortex provides the stable biological platform for identity and selfhood, but something new emerges from the chemical-electrical soup, new patterns of organization, a different level of causation. We can even make choices that reshape ourselves, both physically and psychologically. The very wiring of our brains changes when we make conscious choices. Mind is both shaped by matter and supervenes on matter.

Materialists who wish to collapse all of human identity into brain chemistry overstep the bounds of “science.” A fundamental principle of scientific practice is testability: is it possible to demonstrate empirically whether a proposition is false ? As Saint Augustine observed many centuries ago, the fact that I acknowledge I could be “wrong” about something means that I am a “self” who is capable of making real choices about things that are in fact true or false. “Si fallor, sum” Augustine said – if I can doubt, if I can be wrong, then I must exist. One who is a true materialist “all the way down” cannot test his or her materialism. There is no possibility of “being” right or wrong, indeed no possibility of “being” – there is nothing but chemistry.

Spiritualists who wish to degrade matter in favor of the soul or spirit likewise are not expressing a Christian anthropology. Indeed, one of the first heresies that encountered the early Christian church was Gnosticism. A core belief of Gnosticism was that matter, including the human body, was essentially evil. Salvation for the Gnostics involved the soul’s escape from the prison of embodiment and materiality. The Gnostics treated the body either with disdain – engaging in extreme ascetic practices – or with antinomian abandon – engaging in extreme sexual license. Either way, their practices were rooted in the belief that matter and the body were unimportant. It’s easy to see how this view continually creeps into both our popular culture and our Church cultures.

Christian theology asserts that humans are spiritual creatures, a unity of body and spirit or “soul,” integrated, not reducible downwards to mere matter or upwards to mere spirit. Perhaps there is no better way to bring these themes together than with a Psalm — here is Eugene Peterson’s paraphrase of Psalm 139 in The Message:

God, investigate my life; get all the facts firsthand.
I’m an open book to you;
even from a distance, you know what I’m thinking.
You know when I leave and when I get back;
I’m never out of your sight.
You know everything I’m going to say
before I start the first sentence.
I look behind me and you’re there,
then up ahead and you’re there, too—
your reassuring presence, coming and going.
This is too much, too wonderful—
I can’t take it all in!

Is there any place I can go to avoid your Spirit?
to be out of your sight?
If I climb to the sky, you’re there!
If I go underground, you’re there!
If I flew on morning’s wings
to the far western horizon,
You’d find me in a minute—
you’re already there waiting!
Then I said to myself, “Oh, he even sees me in the dark!
At night I’m immersed in the light!”
It’s a fact: darkness isn’t dark to you;
night and day, darkness and light, they’re all the same to you.

Oh yes, you shaped me first inside, then out;
you formed me in my mother’s womb.
I thank you, High God—you’re breathtaking!
Body and soul, I am marvelously made!
I worship in adoration—what a creation!
You know me inside and out,
you know every bone in my body;
You know exactly how I was made, bit by bit,
how I was sculpted from nothing into something.
Like an open book, you watched me grow from conception to birth;
all the stages of my life were spread out before you,
The days of my life all prepared
before I’d even lived one day.

Genesis 8:1: But God remembered Noah and all the wild animals and all the domestic animals that were with him in the ark. And God made a wind blow over the earth, and the waters subsided; 2 the fountains of the deep and the windows of the heavens were closed, the rain from the heavens was restrained, 3 and the waters gradually receded from the earth.

The Flood narrative of Genesis 7-9 has played a prominent role in science and religion debates for over three hundred years and gave rise in earlier centuries to geological theories such as old earth catastrophism. While literary studies have uncovered the chiastic structure of the Flood story (see Gordon Wenham, “The Coherence of the Flood Narrative” Vetus Testamentum 28 (1978):336-48) and with it the theological pivot point of the entire narrative (Gen. 8:1 – “And God remembered Noah…), much of the popular attention remains on the questions regarding details (Is there THAT much water in the world to cover ALL the mountains to a depth of 15 cubits? Could you really fit two or seven of every animal species in an ark that size?)

Looking at a smaller matter, we find at the beginning and the middle of the narrative indications of an ancient Near Eastern worldview. As the story is told, the flood was not merely the result of excessive rain, but actually the convergence of the waters above the earth with the waters below the earth. It is, as one translation puts it, as if the sluice gates at the deep and of the heavens were thrown open and water poured in from above and below. This is a consistent picture from the Old Testament of a three-tiered universe—a dome above the earth holding back the heavenly waters, a flat earth with water on its surface, and water under an earth which is held up by pillars.

That the story is told using the cosmology of its time should not be unduly unsettling, nor that the story is reinterpreted as new understandings of the universe come into favor. By way of example, consider John Calvin and his understanding of the structure of the universe. Although committed to the principle of sola Scriptura, Calvin recognized that the Bible would have been written in terms its original recipients would have understood.

Calvin inherited the medieval cosmology of his time, a way of viewing the world heavily influenced by Greek thought and one which was about to receive shocks from astronomers such as Copernicus and Galileo. But not just yet. Calvin still subscribed to the common conception of his day in which the four elements—earth, air, fire, and water—comprised the earthly sphere and possessed unique characteristics. The nature of air and fire was to rise, while the nature of earth and water is to sink. Earth, being heavier than water, should sink to the center of the cosmos and water should compose the next layer. Both earth and water are spherical, i.e., naturally form spherically around the cosmic center. Thus the heavier spherical element of earth should be encased entirely within the lighter spherical element of water.

Notice what this does to the flood story. For Calvin, the amazing thing is that the world isn’t constantly under water and subject to flooding. In the cosmology of Calvin’s day, it does not take an act of God to cause a universal flood, but rather an actively present and restraining hand of God to keep the waters back in everyday circumstances and make inundation by water something other than universal.

Obviously, Calvin was wrong. Or perhaps we should say that medieval cosmology was flawed and justifiably gave way to new conceptions of the universe. The answer is not to return to an ancient Near Eastern cosmology, but to reinterpret cautiously within new and better cosmologies and to pay closest attention to the text and the theology of scripture.

The geological and planetary sciences bring their own unique contributions and are of more interest than the latest expedition to discover the ark on Mt. Ararat. Is the flood story a universalization of a catastrophic regional event that burned itself into the psyche of ancient cultures in the Mediterranean basin? Various theories regarding a Black Sea venue for a catastrophic flood event are still in process of being sorted out. It’s intriguing. Or the question where the water on Planet Earth comes from? Was it always here as an emanation of vapors from the earth’s crust in its early formation, or has it accumulated over eons through the steady bombardment of earth by small, icy comets? It’s an intriguing scientific question that is in the midst of determination through testing.

Preaching Suggestions

When preaching on the story of the Flood, it is easy to get lost in the debates over particulars. As mentioned elsewhere, to tackle all the peripheral issues threatens to turn a sermon into a geology lecture. Other settings are better suited to addressing those questions, and those are best addressed open-endedly.

A brief explanation of ancient Near Eastern cosmology can be helpful to contextualize the story. If there are those who are tempted to think that a cosmology embedded in the Bible must be inspired and definitive, one can note that cosmology has changed by the New Testament. The Bible itself isn’t wed to a particular structure of the universe.

What is important is to keep the theology of the text front and center, and in that theology there are at least three non-negotiables from the flood narrative. First, human sin and violence threatens to undo a good creation (the flood is a de-creation event, a return of the waters mentioned in Genesis 1:2). Second, God remembers Noah, and never forgets his promises. Third, the end of the flood is a covenant with the whole earth regarding the stability and endurance of the natural order.

Conversations about science and faith can be like that. People hold clearly discordant points of view, and it would be dishonest to ignore the conflict. Yet some voices emphasize the dissonance without any note of harmony to put it in context. Too often, science and faith becomes a hostile battle of worldviews, sounding angry, dissonant chords even among fellow Christians. But civil, gracious dialogue is possible. On the BioLogos Forum, we invite authors from a range of positions, including some that don't agree with all our beliefs, but we strive to set these dialogues in a context of respect and civility. When authors are fellow Christians, we don’t shy away from disagreements, but remember the broader context of our unity as fellow believers, the harmony that binds us together.

My own story is more harmonious than dissonant. My interest in music was paralleled by my interest in math and science and my involvement in church. My family and teachers encouraged my interests in science, and I remember how fun it was to play math games with my dad and brother. And every week we were in church: twice on Sunday, plus Wednesday night club, youth group activities, and Bible quizzing. While my church accepted the young earth position, they didn’t emphasize it, and I was never told that a particular science view was essential to being a Christian. When I encountered the evidence for the age of the universe and the evolution of life, I also found Christian authors who showed me how this scientific evidence could fit with Christian beliefs.

But others have experienced more dissonance. Nearly four years ago, Dr. Francis Collins launched this website with the story of a young university student in the midst of a profound personal crisis, what Dr. Collins called “a wrenching crisis of worldviews shaking her deepest foundations.” Without a context of harmony, too many people – young and old – feel they have to choose between two incompatible positions, either Christian faith or the findings of science. BioLogos exists to show another way. We hold fast to the authority of the Bible and the core beliefs of Christianity, and at the same time, accept the rigorous conclusions of mainstream science.

It is with these chords of dissonance and resolution in mind that I come to this opportunity to lead BioLogos. I have long sensed God’s calling to serve the church as part of this dialogue. Some of you know of me from a book I wrote in 2007 with my husband Loren, called Origins. I’ve been speaking and writing on science and faith for many years, but I did this around the edges of my primary career of teaching and research in astronomy. While I thoroughly enjoy teaching students and doing research, over the last year I have recognized God’s hand in leading me to shift my fulltime work to the science and faith dialogue. Now I’m looking forward to using and developing my gifts in service of BioLogos.

Joining me as a new member of the leadership team is Dr. Jeff Schloss, who will serve as our Senior Scholar. Many of you are already familiar with his work, and know he brings not only a strong track record of scholarship in evolution and philosophy, but tremendous skill in communicating to lay audiences. Jeff and I share a deep commitment to the unity of the body of Christ and a desire to remove barriers for people to come to Christ. I am delighted to have him on board.

Jeff and I inherit a strong and vibrant organization from our outgoing President, Dr. Darrel Falk. Darrel brought his deep love and concern for the church, along with his considerable creativity and hard work, to this effort. We plan to continue and build on the excellent programs he established.

One of the pleasures of my first few weeks on the job has been getting to know the BioLogos staff. Kathryn, Lisa, Stephen, Mike, Laura J, and LeAnne each bring key skills to the organization, as well as energy and a passion for the mission of BioLogos. The team keeps BioLogos functioning behind the scenes, from finances to computer programming to event planning. Two team members, Mark Sprinkle and Tom Burnett, have decided to move on to other opportunities after a year of dedicated service to BioLogos. As web editors, Mark and Tom revamped the blog, making it a forum for rich scholarly dialogue and vibrant testimonies, and drawing in new authors to write on a great mix of topics. They also organized the archived material, so that the best of BioLogos is readily accessible. We wish them well in their new endeavors. Joining the BioLogos team is Emily Ruppel as Interim Web Editor. You may know Emily from her work to develop and edit the e-zine God & Nature for the American Scientific Affiliation; she will join us part time at BioLogos while she continues to work with ASA.

We believe God has great things in store for BioLogos. We will continue to focus on connecting with scholars, pastors, teachers, and lay people, but in the months ahead, we will also be sharpening our vision and engaging afresh in strategic planning. We’ll be considering new audiences, new programs, and new priorities. I invite your comments below on directions you’d like to see BioLogos take.

In just a few years, this organization has impacted the lives of thousands of Christians and brought an important voice to discussions taking place within the church. Thanks to the strong support from The John Templeton Foundation and many other generous donors, the vision of Francis Collins is thriving. BioLogos is on the cusp of enormous opportunities and huge potential. While transitions are times of risk and vulnerability, they are also times of great opportunity. My prayer is that God will give us wisdom and guidance to be good stewards of this opportunity. May God continue to use BioLogos to bring harmony to a conversation that has emphasized dissonance for far too long.

For more than a century, evangelicals and fundamentalists have typically rejected both evolution and higher biblical criticism. Sometimes there are good reasons: the claims of some biblical scholars are so outrageous and the claims of some scientists so anti-religious, that a strongly negative response is entirely appropriate. Too often, however, the evangelical encounter with modern science conforms to what historian Mark Noll has called “the scandal of the evangelical mind”—namely, “that there is not much of an evangelical mind.” Attitudes toward science have been crucial to this analysis. As Noll says, “since 1960 creationism has done more than any other issue except abortion to inflame the cultural warfare in American public life.” (p. 192)

Readers who want to know more about Noll’s book and its reception should go here and here. His conclusions about evangelicals and science are fully consistent with those I am about to present.

Evangelicals in Tension with Science

Evangelicals exhibit considerable tension and ambivalence when it comes to science, especially human evolution. On the one hand, evangelicals enthusiastically embrace the findings of science, when it comes to most applications in medicine and engineering. They also accept the experimental sciences, such as physics, chemistry, physiology, or thermodynamics. They have no problems with gravitation, the periodic table, the circulation of the blood, or the law of entropy. Here, their attitude is highly empirical: if it can be shown from repeatable experiments and observations, it’s true and presents no challenge whatsoever to religious belief.

On the other hand, evangelicals are quite hesitant to accept some conclusions of the so-called historical sciences, such as geology, cosmology, and evolutionary biology. Fundamentalists reject the very legitimacy of those sciences, and have created their own alternative explanation, “creation science,” which comports with their particular views of biblical authority and hermeneutics. Evangelicals are more ambivalent. As we’ve seen, many evangelicals accept the big bang and modern geology, with a 4.65 billion-year-old earth and the enormously long history of living things before humans arrived on the planet. But evolution–understood here to mean the common descent of humans and other organisms–presents very serious problems for many, perhaps most, evangelicals. This motivates them to look for alternative views.

The alternatives evangelicals embrace are precisely those we have studied in this series. Some eagerly support the YEC view. Others prefer one of the many varieties of the OEC view. Many like the strident tone of the ID movement, with its vigorous assault on biological and cultural “Darwinism” and its near-universal rejection of human evolution. For most evangelicals, however, TE is probably not a viable option at present, for biblical and theological reasons.

Reconciling Evolution with Scripture

Most evangelicals do not see any reasonable way to combine human evolution with the following beliefs:

• the uniqueness of humans, who alone bear the “image of God”
• the fall of Adam and Eve, the original parents of all humans, from a sinless state, by their own free choices to disobey God
• the responsibility of each person for their own actions and beliefs, within a universe that is not fully deterministic
• the redemption of individual persons by the atoning sacrifice of Christ.

Evangelicals cannot and must not be separated from these crucial beliefs about human dignity, freedom, responsibility, sin, and redemption. The 64-dollar question is: can these beliefs be maintained without simultaneously affirming the necessity of an historical, separately created first human pair? The answer is probably in the hands of evangelical academics, especially theologians and biblical scholars. Can they be persuaded that the scientific evidence for evolution is sufficiently strong to warrant a re-examination of the traditional view? Can a credible gospel and credible science be harmonized?

There exists an enormous gap between popular conceptions of science–conclusions, methods, and attitudes–and those of scientists themselves. This gap is not unique to science among practitioners of specialized knowledge, and it is not unique to evangelicals among the lay public. But it is real and very significant, and it affects theologians and biblical scholars no less than anyone else. Those who try to bridge this gap are mostly scientists (in their role as educators at colleges and universities and insofar as they write books for lay readers) and science journalists. Many influential members of those professional communities are skeptical or even strongly hostile toward Christian beliefs, and this can exacerbate an already difficult state of affairs. If ways can be found to popularize good science, while showing appropriate sensitivity to the concerns of evangelicals, it would be a very good thing.

Signs of Hope

Certainly there are reasons to hope. The conversation about science and religion is considerably broader now than it was at the time of the Scopes trial in 1925. Back then, many Protestants faced a very grim choice. On the one hand, they could follow politician William Jennings Bryan and the fundamentalists, rejecting modern science in the name of biblical authority and orthodox beliefs. On the other hand, they could follow theologian Shailer Mathews and the modernists, rejecting biblical authority and orthodox beliefs in the name of modern science. There was no one out there like John Polkinghorne, Francis Collins, Joan Centrella, Owen Gingerich, Simon Conway Morris, William Phillips, or Ian Hutchinson—to name just a few of the many top scientists today who accept evolution while affirming the divinity of Jesus, the bodily resurrection, and the actual divine creation of the universe. But they are all scientists, not theologians (except for Polkinghorne, who is both). In Galileo’s day, it was the scientists who eventually convinced the theologians and biblical scholars to accept Copernicus’ theory of the earth’s motion around the sun. But, it took a long time, and the process was difficult and often painful. Thus far, the biblical scholars and theologians who have tried to move the conversation forward have not been very well received, as Richard Ostling has so capably reported. I suspect we are in for more of the same.

It’s Your Turn to Talk

That’s what I think. What do you think? I’ll mainly be listening quietly, since I’ve now said all I wanted to say. Thank you all for hanging in there for ten months—far longer than I had originally anticipated. After a short respite I’ll return with a new series, but I’ll keep the topic under wraps for the time being.

Augustine had a great deal to say about those chapters in Genesis that are especially controversial within Christianity today. In fact, Augustine dedicated about as much as any other Christian writer to the first few chapters of Genesis, so there is little guesswork we have to do in ascertaining what he believed Scripture to claim about creation. First of all, Augustine clearly rejected the notion that God had created the earth in six 24-hours periods. Instead, he believed that the universe was created instantaneously, and that the six days reported in Genesis were a metaphor for the various levels of dimensions of the created realm—something akin to what ancients referred to as the ‘Great Chain of Being’. But this is not to say that Augustine believed that the world was created as it is today in that instant. Rather, he affirmed that God created the world with inchoate potential for further development, like an acorn that will grow into a great tree when planted in the ground.

Augustine therefore affirmed that Creation has evolved and continues to evolve, though not driven by random natural processes, as affirmed by classical Darwinism. Instead, such evolution is governed providentially both via the inchoate potentialities present in the world from its beginning and by God’s ongoing governance of the universe.⁴ We should be careful not to turn Augustine too quickly into a modern advocate of theistic evolution, but the similarities are nevertheless significant. Augustine affirmed these ideas not on the basis of an attempt to accommodate Scripture to scientific discovery, but based upon his own reading of Scripture! Indeed, I think it fair to say that the great father of Western Christianity was something of a proto-evolutionary theist, and therefore one whose work deserves far more attention by those seeking to be faithful to both Scripture and Christian tradition while making sense of the claims of contemporary science.

Of course, we need to be careful not to push such claims too far. Augustine himself resists such a move by recognizing both the contingency of human interpretations of Scripture and the dangers of unintentionally imposing our own views on Scripture. A rather long, but significant quote from Augustine makes this point all too clear:

Let us suppose that in explaining the words, “And God said, ‘Let there be light,’ and light was made,” one man thinks that it was material light that was made, and another that it was spiritual. As to the actual existence of “spiritual light” in a spiritual creature, our faith leaves no doubt; as to the existence of material light, celestial or supercelestial, even existing before the heavens, a light which could have been followed by night, there will be nothing in such a supposition contrary to the faith until unerring truth gives the lie to it. And if that should happen, this teaching was never in Holy Scripture but was an opinion proposed by man in his ignorance.

On the other hand, if reason should prove that this opinion is unquestionably true, it will still be uncertain whether this sense was intended by the sacred writer when he used the words quoted above, or whether he meant something else no less true. And if the general drift of the passage shows that the sacred writer did not intend this teaching, the other, which he did intend, will not thereby be false; indeed, it will be true and more worth knowing. On the other hand, if the tenor of the words of Scripture does not militate against our taking this teaching as the mind of the writer, we shall still have to enquire whether he could not have meant something else besides. And if we find that he could have meant something else also, it will not be clear which of the two meanings he intended. And there is no difficulty if he is thought to have wished both interpretations if both are supported by clear indications in the context.

Usually, even a non-Christian knows something about the earth, the heavens, and the other elements of this world, about the motion and orbit of the stars and even their size and relative positions, about the predictable eclipses of the sun and moon, the cycles of the years and the seasons, about the kinds of animals, shrubs, stones, and so forth, and this knowledge he holds to as being certain from reason and experience. Now, it is a disgraceful and dangerous thing for an infidel to hear a Christian, presumably giving the meaning of Holy Scripture, talking nonsense on these topics; and we should take all means to prevent such an embarrassing situation, in which people show up vast ignorance in a Christian and laugh it to scorn. The shame is not so much that an ignorant individual is derided, but that people outside the household of the faith think our sacred writers held such opinions, and, to the great loss of those for whose salvation we toil, the writers of our Scripture are criticized and rejected as unlearned men.

If they find a Christian mistaken in a field which they themselves know well and hear him maintaining his foolish opinions about our books, how are they going to believe those books in matters concerning the resurrection of the dead, the hope of eternal life, and the kingdom of heaven, when they think their pages are full of falsehoods on facts which they themselves have learnt from experience and the light of reason?

Reckless and incompetent expounders of holy Scripture bring untold trouble and sorrow on their wiser brethren when they are caught in one of their mischievous false opinions and are taken to task by those who are not bound by the authority of our sacred books. For then, to defend their utterly foolish and obviously untrue statements, they will try to call upon Holy Scripture for proof and even recite from memory many passages which they think support their position, although they understand neither what they say nor the things about which they make assertion.⁵

I am tempted here to let Augustine have the final word, but I think there are three final points worth highlighting here as a way of connecting this quote to the two books theory and thereby concluding our discussion of Augustine:

1. The Book of Nature is clearly revelatory of God’s providential work in Christ, and even nonbelievers are capable of comprehending its complex order through the proper use of reason and experience (i.e. science properly understood).
2. The Book of Scripture is clearly revelatory of God’s providential work in Christ, and therefore is true and authoritative in all matters. The problem is that we often misinterpret Scripture by imposing our own preconceptions upon it rather than allowing it to speak for itself.
3. God’s two books can and should be read together in harmony when we are open to allowing them to speak for themselves on their own terms. Ultimately, they cannot contradict each other because the source of both is the same God and if they seem to be in contradiction it is because we have misread one or both of them, and we need to be willing therefore to allow ourselves to be open to thinking about either one in different ways, trusting that God will ultimately lead us to see the truth of the whole.

Notes

4. In truth, these two kinds of providence are one and the same for Augustine because God in some ‘stands’ outside of time as its eternal creator. So, for Augustine, eternality is not everlasting time, but the complete lack of temporality altogether. In this sense, all of creation at all times is eternally present to God, and there is ultimately no difference between God’s governance over creation at its beginning from God’s governance at any other moment in its history. In a way, God governs all of history all at once.
5. This quote is excerpted from St. Augustine, The Literal Meaning of Genesis, 2 vols., translated and annotated by John Hammond Taylor, SJ (Paulist Press, 1982), volume one of which can be read here.

The inevitable companion to the idea that the Church has held back scientific progress is that we must look outside Christendom to discover the origin of modern science. But this is also false. Modern science stands as one of the great achievements of Western civilization. And, despite what we have often heard, it is certainly an achievement of the West, not of Islam, China or even ancient Greece. Many historians of science are still reluctant to admit this. This may be because the fad of post-modernism bit them hard and has refused to let go. They have developed a habit of praising Arabic and ancient Greek science as successful on their own terms but they have lost sight of the fact that, viewed objectively, the theories advanced by early science were quite false.

Of course, we should have respect the Greek and Islamic natural philosophers who struggled to comprehend the world. But most of what they taught, through no fault of their own, was woefully inaccurate. This was because their aims for science were nothing like ours. They wanted to understand nature in terms that made sense of their ethical or religious beliefs, and formed their theories accordingly.

To take just one example, pre-modern medicine was an unmitigated disaster, far more likely to kill patients than cure them. Treatments such as bleeding and purging could only weaken the constitution of the sick, reducing their bodies’ capacity to fight off infection. It is no surprise to find that the most celebrated doctor of antiquity, Galen of Pergamum (left), considered himself as much a philosopher as a healer. Given the ineffectiveness of learned physicians, it’s little wonder that people put so much stock in miracles and magic. Perhaps the most surprising thing is that doctors were able to maintain their professional status through all the centuries that they could do little more that hasten their clients to the grave. Luckily for us, we can be much more confident that modern medicine really can cure us of many diseases. So the history of science should be the story of how we went from being fundamentally wrong about the natural world to being, in large part, right.

Science as we imagine it today, with laboratories, experiments and a professional culture, is a recent phenomenon that did not appear until the nineteenth century. But its origins can be found much earlier and we usually look for them in the period known as the ‘scientific revolution’. It is commonly believed that the recovery of Greek philosophy during the Renaissance gave Western civilization the inspiration it needed to launch this revolutionary way of looking at the world. In this view, hardly anything of consequence for science occurred between the fall of Rome and the era of Copernicus and Galileo. Carl Sagan produced a timeline of scientific progress in his book Cosmos (1980) showing nothing at all happening between AD415 and AD1543. But this is an illusion foisted on us by the same mentalité that declared science and religion must be in conflict. The truth is that to understand why modern science arose uniquely in the West, we have to travel all the way back to the Middle Ages.

Dispelling Myths

Before we do that, we should finally dispose of the two myths about scientific progress that we noted above. Firstly, as we have seen, the popular view remains that religion has held back science at every opportunity. Many people still believe that science has advanced by fighting superstition and making the world safe for rational enquiry. It is true that certain religious doctrines contradict some scientific discoveries. The creation/evolution controversy is a case in point, but such quarrels have been surprisingly rare. Even the infamous trial of Galileo, the other example of conflict most often cited, was an aberration in the Catholic Church’s usual supportive attitude towards science.

On the other hand, the problems with the thesis that science and faith are locked in a historical conflict are formidable. For a start, the so-called ‘scientific revolution’ in the seventeenth century coincided with the period when Christian belief in Europe was at its strongest. Only after science had triumphed did religion start to suffer any sort of decline. And, if Christianity really had tried to hold back scientific progress, the chances are that it would have succeeded. Modern science would not have arisen in Christian Europe at all.

As it happens, much of the evidence marshaled in favor of the conflict thesis turns out to be bogus. The Church never tried to outlaw zero or human dissection; no one was burnt at the stake for scientific ideas (not even Giordano Bruno); and no educated person in the Middle Ages thought that the world was flat, whatever the Bible might imply. Popes have had better things to do than banning vaccination or lightning conductors on churches. The thought of a pope excommunicating Halley’s Comet is absurd, but this has not prevented the tale of Calixtus III (right) doing just that from entering scientific folklore. It is remarkable that authors today, who consider themselves skeptics, can swallow some of these stories whole. Carl Sagan introduced his readers to a ‘baloney detector’ in his book, The Demon-Haunted World (1997). It is a great shame he never used it on his own writings. He presented a completely fictitious account of the murder of the pagan philosopher Hypatia in Cosmos and falsely blamed Christians for the destruction of the Alexandrian library.

Zealous Victorian historians did find occasional examples of ecclesiastical stupidity, such as the Boston pastor who warned that lightning strikes caused earthquakes. They rewrote history to make these marginal figures into leaders of opinion. Religious dissidents who paid the ultimate price for their faith were recast as champions of reason. Pope Boniface VIII issued a bull intended to stop crusaders sending their bones home for burial; he would have been most surprised to hear that, according to Andrew Dickson White, he had legislated against human dissection. Whenever a priest questioned a scientific theory, which they often did in their capacity as amateur scientists, this was held up as an example of religious obstruction. Historians have been debunking these legends for over a century now, but they continue to be recycled by each new generation.

The role of ancient Greek and Islamic thought

The other myth about the rise of science is that westerners only had to pick up the baton from the ancient Greeks, or, as has been more recently alleged, the Islamic caliphate. In reality, modern science is qualitatively different from the natural philosophy practiced by the likes of Aristotle or Avicenna. Aristotle started from the passive observation of nature and then built up a system based on rational argument. This had two enormous disadvantages: compared to controlled experiments, passive observation is usually misleading; and not even Aristotle’s powers of reason could prevent blunders in his arguments.

His discussion of motion is a case in point. He observed that everyday objects tend to stop when nothing was pushing them. From this observation, he deduced the principle that all moving objects must be moved by something else. He elevated this principle to the status of a logical certainty and then used it to explain other kinds of motion. He even thought that it successfully proved the existence of God. If the universe as a whole is full of movement, he argued, it requires an exterior unmoved mover,—that is, God—to keep it going. But of course, Aristotle’s initial observation was just a specific instance without any general applicability. We now know that objects do not stop when there is no force on them. They tend to keep going in a straight line: a principle enshrined as Newton’s First Law. Other observations led Aristotle to decree it certain that a vacuum can never exist; that heavy objects fall faster than light ones and that the earth must occupy the centre of the universe. All wrong. Aristotle, alas, was mistaken about almost everything. This was not because he was a fool but because he was practicing a natural philosophy that could never lead to true theories.

Alhazen

Islamic science suffered from similar drawbacks. Advances made by Muslim natural philosophers were significant, but rather more modest than we are usually led to believe. The importance of Alhazen’s investigations into the properties of light is indubitable. They were used by Roger Bacon in his own writings on perspectiva and thence were integrated into the modern theory of vision developed by Johannes Kepler. Even so, Alhazen’s experimental method was limited and not carried forward by his immediate successors. Similarly, the intuition of Ibn al-Nafis, in the thirteenth century, concerning the circulation of blood between the heart and the lungs is deeply impressive. But there is no evidence that he had any impact on the rediscovery of this phenomenon by Michael Servetus and Realdo Columbo three centuries later.

Consequently, we should be skeptical about some of the claims made for Islamic science in some recent television shows and books, not to mention in Wikipedia. That said, the misattribution of scientific advances to Islamic sources has sometimes been the fault of the pioneers who actually discovered them. Alchemy is a case in point. During the Middle Ages, it was customary for Christian alchemists to write their treatises under the name of the fabled Arab savant Geber. It is not surprising that later historians mistakenly assigned developments such as the first production of powerful acids as well as the isolation of alcohol to Geber himself. Alcohol was even assigned an Arabic name by Christian authors. We now know that he probably did not write any of the works attributed to him.

On the other hand, there was one towering exception to the rule that early science tended to be bunk: both the Greeks and Arabs excelled in mathematics. This was because pure rationalism works a treat when it is restricted to geometry and arithmetic. The imams had plenty of practical uses for math, as well: the Muslim calendar follows the moon and not the solar year, while mosques had to be orientated towards Mecca. Both these religious problems required mathematical solutions. It’s also said that the complicated rules of Islamic inheritance made algebra indispensable. Even our word algebra is a corruption of al-jabr, the name of an Arabic textbook widely used by Christians.

Despite these genuine contributions, it is nevertheless fair to say that neither Aristotelian rationality nor Islamic mathematics was the key to the developments that made the modern world possible. As we shall see in the second part of this essay tomorrow, the very different cultural situation in medieval Europe allowed for Aristotle’s faulty method to be criticised by the Catholic Church, meaning that previously forbidden ideas could flourish. The Church also made natural philosophy a compulsory part of the course that it required trainee theologians to follow. So, unlike in Islamic madrassas, science had a central place in Christian centers of learning. Indeed, it was a Christian worldview that proved especially compatible with—even necessary for—the rise of modern science.

Some implications and conclusions of Theistic Evolution

Bernard Ramm argued for just such a position in The Christian View of Science and Scripture, even though he was an OEC, not a TE. Denis Lamoureux takes it further in his recent book, I Love Jesus & I Accept Evolution. A glance at the table of contents shows that he emphasizes the presence of “ancient science in the Bible” and teaches us how to interpret the Bible in light of this. Just as we don’t take biblical astronomy “literally,” with its 3-tiered universe, we shouldn’t take biblical biology “literally,” with its fixed species and separate creations a few thousand years ago.

For a concise description of Complementarity, I borrow the words of Stanford physicist (now retired) Richard Bube, who wrote three books about science and Christianity, taught a course about it for decades, and edited the Journal of the American Scientific Affiliation (now called Perspectives on Science & Christian Faith) for many years. In his book, Putting It All Together, Bube presented seven “patterns” for relating science to faith (here and here), ending with his personal favorite, Complementarity, described as follows:

“Science and theology tell us different kinds of things about the same things. Each, when true to its own authentic capabilities, provides us with valid insights into the nature of reality from different perspectives. It is the task of individuals and communities of individuals to integrate these two types of insights to obtain an adequate and coherent view of reality.” (p. 166)

I’ll offer my own example to illustrate this model. Everyone reading this column originated in the union of two cells, one from each parent. Everyone reading this is also created in the image of God. Each of these two sentences is true, but the truths they proclaim are of a different order. The first neither implies nor negates the second. You can see where this is going: for TEs, the truth (in their view) that we are descended from other primates neither implies nor negates the truth that we are created in the image of God.

The Complementarity view, as I’ve briefly presented it, might seem quite shallow—nothing more than the simple, unsupported claim that science is about HOW and religion is about WHY. Readers who want a subtler account are invited to study Christopher Rios’ article about its development. Rios quite properly stresses the work of two important British scientists from the last century, quantum chemist Charles A. Coulson and his friend, brain theorist Donald M. MacKay, one of the most prolific and thoughtful Christian thinkers of his generation. If you don’t know MacKay, I unreservedly recommend that you get acquainted, but his work is so wide-ranging that I am hesitant to recommend a single starting place. Evolution was not one of his chief interests (I don’t offer him as a prime example of TE per se), but I can’t think of anyone who wrote more about the Complementarity model of science and Christian faith.

Physicist-theologian John Polkinghorne can also be understood as a proponent of Complementarity, though I would not characterize his position solely in those terms. His overall vision captures the essence of Complementarity: theology complements the limited picture of reality given to us by science; it goes beyond science, providing a larger metaphysical framework within which both nature and the science of nature are more intelligible (see below for more). Many of his books are conceptually deep, discouraging casual readers, but they are also eloquent and very creative, making the hard work of reading them time well spent. There simply is no good substitute for diving into them yourself. I’ve reviewed one of his recent books here.

(INVITATION: If you would like to take part in a full discussion of one of his books here at BioLogos, at some point down the road, please let me know, either in a comment below or privately (tdavisATmessiahDOTedu). Don’t make the commitment lightly—you would be expected to purchase and read the book—but please take the invitation seriously and respond accordingly.)

A theology of nature starts from the assumption that God exists and then seeks to understand the whole of nature in light of this. Polkinghorne does this in many of his books (see the review linked above for some specific examples). Natural theology, on the other hand, is the effort to demonstrate God’s existence (including some of God’s attributes, such as power, wisdom, and goodness) from reason or nature, without appealing to the Bible. Many Christian authors since the patristic period have done this, often citing the first chapter of Romans, though some of the most important have had doubts about the value of the whole enterprise; two prominent examples would be Blaise Pascal (see the article by George Murphy here) and John Henry Newman.

The golden age for natural theology lasted from the late 17th century (when Boyle and Newton were outspoken advocates of using science to argue for God’s existence) down through the mid-19th century, when Darwinian evolution provided a serious challenge to natural theological arguments based on “contrivances,” aspects of nature that appeared to be exquisitely crafted for a specific purpose by the Creator. Although it’s not true “That Darwin Destroyed Natural Theology,” (see the chapter by Jon Roberts here), it is true that TE authors no longer appeal to intricate biological “contrivances” to make their case. Prior to Darwin, a leading natural theologian, the great scholar William Whewell, had already made the case for a different type of natural theology in his famous contribution to the Bridgewater Treatises, a series of eight books on natural theology from the 1830s: “But with regard to the material world, we can at least go so far as this;—we can perceive that events are brought about, not by insulated interpositions of divine power, exerted in each particular case, but by the establishment of general laws” (Astronomy and General Physics Considered with Reference to Natural Theology, p. 356 in the fifth London edition of 1836). Ironically, Darwin placed this very passage directly opposite the title page in On the Origin of Species (1859).

Just a few years later, a Unitarian chemist from Harvard, Josiah Parsons Cooke, Jr., replied to Darwin in a book called Religion and Chemistry; or, Proofs of God’s Plan in the Atmosphere and Its Elements (1864). Cooke got around Darwin by inquiring into the basic properties of matter itself—the features of the physical universe that make biology possible at all. “There is abundant evidence of design in the properties of the chemical elements alone,” he argued, especially as they combine to make the unique substance we call water. Natural theology had found a more solid foundation, “which no theories of organic development can shake.”

Contemporary TEs do pretty much the same thing. They look for evidence of “design” or “purpose” in the nature of nature itself, not in biological “contrivances.” Discussions of the “fine tuning” of the universe are common in TE literature, including Francis Collins’ book, The Language of God and Ken Miller’s book, Finding Darwin’s God. Philosopher Robin Collins (who is writing a superb book about the fine tuning of the laws of nature) provides a helpful introduction to the terms and the issues here. Polkinghorne raises fundamental questions about the very intelligibility of nature in the wonderful title chapter in Belief in God in an Age of Science. Let’s pay careful attention to what he says about his overall approach:

“This new natural theology differs from the old-style natural theology of Anselm and Aquinas by refraining from talking about ‘proofs’ of God’s existence and by being content with the more modest role of offering theistic belief as an insightful account of what is going on. It differs from the old-style natural theology of William Paley and others by basing its arguments not upon particular occurrences (the coming-to-be of the eye or of life itself), but on the character of the physical fabric of the world, which is the necessary ground for the possibility of any occurrence (it appeals to cosmic rationality and the anthropic form of the laws of nature) ... [Consequently] the new-style natural theology in no way seeks to be a rival to scientific explanation but rather it aims to complement that explanation by setting it within a wider and more profound context of understanding. Science rejoices in the rational accessibility of the physical world and uses the laws of nature to explain particular occurrences in cosmic and terrestrial history, but it is unable of itself to offer any reason why these laws take the particular (anthropically fruitful) form that they do, or why we can discover them through mathematical insight.” (pp. 10-11)

Looking Ahead

Sorry to stop mid-stream, but this is enough for now. This discussion resumes in about two weeks with more implications and conclusions of TE. There should be enough here to keep us going until then!

The Denisovans, an extinct hominid group that interbred with modern humans, made the news again lately with the publication of a more detailed study of their genome. One of the many interesting findings was that the Denisovans share the same chromosome 2 fusion that modern humans have. In this post, I review what we know about the origins of human chromosome 2, and then discuss the new Denisovan findings and their implications.

The origins of human chromosome 2: a brief review

Though I have discussed the evidence for a fusion event leading to human chromosome 2 before, perhaps a brief review of the evidence is in order. The human genome is made up of 23 pairs of chromosomes (for a total of 46 chromosomes). This makes us something of an oddity among living great apes, all the rest of whom have 24 pairs of chromosomes (for a total of 48). Given that there are many independent lines of evidence that support the conclusion that we share a common ancestor with other great apes, this poses something of a conundrum: how is it that our species arrived at this specific chromosome number? If we were to represent this “problem” on a phylogeny, or tree of relatedness, it would look something like this (not to scale):

Our closest living relatives, chimpanzees and bonobos, both have 48 chromosomes, as do all other great apes such as gorillas and orangutans. This pattern has one of two explanations, one of which is much more likely than the other. Either the common ancestor to these species had 48 chromosomes, and there was an event that reduced that number to 46 specifically on the lineage leading to humans (option A), or the common ancestor species had 46 chromosomes, and there were independent, repeated events that increased chromosome number in all other great ape species (option B). We can compare these options by placing the required event(s) on the phylogeny (again, not to scale):

It should be obvious that the option that requires the fewest events is the more likely one – in this case option A with an event that reduces chromosome number in the lineage leading to humans. The other option, that of repeated, independent events to increase chromosome number, remains a formal, but unlikely, possibility. Events that reduce chromosome number are not frequent occurrences, so Option A is more likely than Option B.

We can also find further support for Option A, because it predicts a specific type of event, namely one that reduces chromosome number. Since loss of a large amount of chromosomal material is almost always detrimental, we need an event that reduces chromosome number without losing information. One way for this to happen is for two chromosomes to fuse together and become one. Initially, this event would produce an individual with 47 chromosomes, where two different chromosomes get stuck together. Contrary to what is often assumed, this individual would be fertile and able to interbreed with the others in his or her population (who continue to have 48 chromosomes). In a small population, over time, two relatives who both have one copy of the fusion chromosome may mate and produce some progeny with two copies of the fused chromosome, or the first individuals with 46 chromosomes. Since either a 48-pair set or a 46-pair set is preferable for ease of cell division, this population will either eventually get rid of the fusion variant (the most likely outcome), or by chance will switch over completely to the “new” form, with everyone bearing 46 chromosome pairs. While not overly likely, this type of event is not especially rare in mammals, and we have observed this sort of thing happening within recorded human history in other species. Some mammalian species even maintain distinct populations in the wild with differing chromosome numbers due to fusions, and these populations retain the ability to interbreed.

Further evidence for a fusion event in the lineage leading to modern humans comes from comparing synteny, or gene locations and orders on chromosomes within modern great apes – an issue we have discussed here before. In brief, what we see in human chromosome 2 is exactly what we would predict for a fusion event. When compared to other great apes, we see the genes on human chromosome 2 match up, in order, with two smaller ape chromosomes. We also see that sequences used at the tips of chromosomes are present at the proposed fusion site, and that human chromosome 2 has not one but two sites for the cell cytoskeleton to attach to for cell division – but that one of the sites is mutated and not functional, though it lines up precisely with the location of this site on the appropriate ape chromosome. Together, this evidence consistently supports both common ancestry for humans and great apes, and specifically that the difference we see in our chromosome numbers arose due to a single fusion event. I briefly discussed this evidence in my last post where I describe how I teach some of this material and the compelling impact it has on students exploring the evolution question for the first time.

Enter the Denisovans

With that as background, we are now prepared to appreciate a new finding that comes from genomics work done on the Denisovan hominids, an archaic species that is more closely related to Neanderthals than to us, but that nonetheless interbred with some anatomically modern humans as they migrated out of Africa and populated the globe. (For those not familiar with the Denisovans, or the evidence for our interbreeding with them, both Darrel Falk and I have written on this previously, here and here). Recently, a more detailed understanding of the Denisovan genome was published, and nested in the new information is the discovery that the Denisovans share the 46 chromosome set with the same fusion that we have. This strongly supports the hypothesis that the fusion event predates the separation of our species. If we were to represent this on a phylogeny, we can now place this event with more accuracy than before (as before, the phylogeny is not to scale):

Despite this new information, one obvious question remains. Did the Neanderthals also have the 46-pair set? From looking at the phylogeny above, we can see that the most likely answer is that they did, since the fact that the Denisovans had it strongly implies that the last common ancestor of humans and Neanderthals / Denisovans had it as well, and the Neanderthal-Denisovan split comes later. While the Denisovan DNA samples are of high enough quality to make this assessment, we do not yet have Neanderthal DNA of high enough quality to do the same analysis with current methods (though one additional feature of the new work on the Denisovan genome is developing more sensitive DNA sequencing techniques that may resolve this question in the future).

In other words, this fusion seems to be an ancient one, predating our species by several hundred thousand years. Present estimates of the last common ancestor between humans and Neanderthals / Denisovans range at about 800,000 years ago.

Implications for understanding our “becoming human”

The main implication from this work is that it places the fusion event well before the advent of our species. I’ve often chatted informally with Christians about evolution, and at times some have thought that this fusion event was what “started” our species, or made our species unable to interbreed with other groups. Some have even suggested that perhaps the fusion event was what produced the first human (i.e. Adam).

Note that thinking this way suggests a misunderstanding of how chromosome fusions occur and what effect they have on their hosts. A fusion does not precipitate a speciation event, but rather the individual with the fusion remains a part of his or her population, and able to interbreed, even if with reduced fertility. Also, there is no necessary biological effect or change that the fusion produces on the appearance of the organism. These misunderstandings aside, however,what this new evidence shows is that this fusion event took place long before modern humans arose at around 200,000 years ago. Indeed, the 800,000 years ago date for the last human - Denisovan common ancestor means that this is the most recent date possible for the fusion. While it is an interesting piece of our evolutionary history, it doesn’t seem to have much to do with how we came to acquire the traits that set us apart from, and ultimately outcompete, other similar species.