Today's video is courtesy of filmmaker Ryan Pettey, director/editor of Satellite Pictures and features physicist Ard Louis.

In today's video, Oxford physicist Ard Louis discusses the famous debate between renowned evolutionary biologists Stephen Jay Gould and Simon Conway Morris. Gould believed (and wrote in his book Wonderful Life) that if the "tape" of evolution were rerun, the chance that anything like human intelligence would emerge is essentially zero. In other words, humanity is here through random accident. Gould pointed to the work of Morris and fellow scientists in their research of the Burgess Shale as evidence for this view.

However, Morris himself disagrees, pointing to what is called evolutionary convergence. As Morris notes, there are numerous examples of identical features evolving multiple times throughout the history of life independently. Morris believes that if the tape of life were replayed, we would see something like humans emerge. A Christian might say, it looks like we were planned.

Some Christians might find Simon Conway Morris' viewpoint, with its implicit teleology, more attractive. Others, perhaps motivated by a high view of providence, may find Gould's emphasis on contingency equally congenial to their faith. What do you think?

As we noted in our response to the June article in Christianity Today “The Search for the Historical Adam,” the evidence for gradual creation is overwhelming, with more studies supporting the evolutionary process being published each year. We’ve looked at many of these evidences: from fossils, from comparative anatomy, from genetics. Today, we’d like to highlight for our readers a compelling video from the annual TED Conference featuring geneticist Svante Pääbo. You may remember Pääbo from his efforts to extract and sequence DNA from 30,000(+) year old Neanderthal bones (we mentioned his work here).

In this eighteen minute video, Pääbo covers a lot of ground, noting several lines of genetic evidence for the evolution of modern humans from earlier hominids in Africa, as well as for the interbreeding between early humans and Neanderthals. We’ve covered some of this data before, but it’s particularly compelling to hear it described by one of the scientists leading the field of study.

However, our goal at The BioLogos Foundation isn’t just to make the Church aware of the fascinating and convincing scientific evidence for gradual creation. As we have said before:

BioLogos exists to help Christians think carefully about the ramifications of these new data in light of long-standing traditional ways of viewing human creation. We have some re-thinking to do, but it can be done and will be done within the context of a Christian faith that is fully orthodox and thoroughly evangelical. Any time we draw closer to truth, to God’s truth, we have nothing to fear. There is still much to learn, but we can look back at what we have learned with awe—absolute awe.

It is truly amazing that we know so much now about our early days. For example, Africans do not have DNA which is specifically derived from Neanderthals, whereas people in the rest of the world do carry a small amount. This confirms the picture of human history derived from studying fossils. Neanderthal bones have not been found in Africa, so it isn’t surprising that their DNA is not there either. The fact that non-Africans have some of the DNA found in Neanderthal bones confirms that which geneticists knew from other studies: we have two distinct groups of human ancestors—those who left Africa in ancient times and those who stayed.

God chose to reveal himself and to begin working with a distinct sub-group of ancient humans, those descended from Abraham and Sarah. To Abraham, God made a marvelous promise. Drawing his attention to the stars above, God said that someday Abraham’s descendents would outnumber the countable stars in the universe. And so it came to be. Indeed through our adoption into the family, we are all children of Abraham. The God of Abraham is our God too and each one of us is one of those stars too numerous for Abraham to count.

Sometimes, it seems that we are uncomfortable with the notion that God made us through a gradual process that included apes in our family tree. It is almost as though we would prefer dirt to apes. Perhaps, in at least some cases, this is due to an inadequate appreciation for the fact that God loves, really loves, all of creation, not just us. As special as we know we are, we can’t read Psalm 104, Genesis 1, Genesis 9 (where the covenant is not just with Noah but with all living creatures), or Job 38-41 without being reminded that all living creatures are God’s creation (see here). The Neanderthals, the Denisovans, Homo erectus, and the australopithecines were God’s creation too! Still, we modern humans have been singled out. We’ve been called out.

True our family tree, as Pääbo shows here, is intriguing. But let us never forget, that the most important thing about this tree is that God is the vine which exists at its core, and we are called to be the branches which bear fruit. The fact that many of us have a small amount of Neanderthal DNA, some of us have Denisovan DNA, and others have neither is interesting, but it is really just a side issue for people of faith. As a result of God’s visit to Abraham, followed eventually by God’s taking on flesh in the person of Jesus of Nazareth, we can all know God as our heavenly Father. We are children of God and as such, we are God’s representatives. We are called to image God. We are called to love God. And we are called to love each other and to deeply respect all that he has made.

In our previous essay, we learned that a tree summarizing species relationships can be built using DNA information, and how we can use DNA as a “molecular clock” to date ancient events. Both of these methods have made specific predictions about the origin of whales. If evolution is true: whales are related to the even-toed hoofed mammals and should share common ancestors with them; transitional fossil forms dating from about 45 to 50 million years ago should be found which can be shown to be related to both the even-toed hoofed mammals and modern whales; whales are most closely related to modern hippos, and should share a common ancestor with them.

What other types of information might we be able to use to construct a phylogenetic tree (i.e. a family tree) of species relationships? It turns out that characteristics of body structure also can be used – for example, the presence or absence of certain bones, or the specific shapes of those bones. An advantage of using bony features is that they can be recovered from fossils, whereas DNA (with only certain limited exceptions) must come from living organisms.

We can also derive functional information from an examination of bony features. The various protrusions, bumps and knobs found on bones usually have important implications. For example, smooth rounded areas at the ends of bones allow them to fit together and move easily. The shapes of such surfaces determine which bone motions are “allowed” or “disallowed”. Consider, for example, the motion of the forearm against the upper arm at the elbow. This is a “hinge” joint, whose normal motion is defined by the shapes of the upper arm bone and one of the forearm bones, where they meet each other. You might normally exercise the action of this hinge joint when you pick up a cup of coffee, bring it to your mouth, then set it back down again. Let’s try to imagine another motion. For this exercise we first need to get our arm into the proper starting position. Place your arm at your side, bent at the elbow at a ninety degree angle, with your palm up. Now, while keeping your palm up, let’s attempt to move your arm only at the elbow (no shoulder motion – that’s cheating!). Now swing your forearm out to the side and attempt to end up with your fingers pointed directly away from your side. Most of you will not be able to do this. If you can, it’s because your shoulder is rotating in spite of yourself. This motion at the elbow is normally not allowed. Hence a careful analysis of bone shapes can allow us to infer how the bones were used. This in turn can assist us in the task of phylogenetic (evolutionary) classification of organisms. That is, we will have more confidence in the grouping together of animals in our tree diagram if corresponding bones are used functionally in the same way.

Therefore we would expect that we could use various bony features to help us examine the predictions generated by our previous look at different types of DNA data. Are there any bony features that are particularly relevant to the even-toed hoofed mammals? Well, it turns out that there are. These are mainly running animals, and there are several features of their ankle bones, which taken together define the “allowed” motions which make them efficient runners. If one takes the various ankle bones of a large group of mammals, examines them carefully to note their shapes, scores that information into a table, then uses a computer program to build a phylogenetic tree, it turns out that all the even-toed hoofed mammals are placed together. So far, so good. But what about whales? Well, now we have an obvious problem. Modern whales are very specialized, - they have flippers which correspond to the forelimbs, and they have almost no hind limbs! I say “almost” because they do have small pelvic bones, which are not attached to the rest of their skeletons. But they certainly have no ankles. This is where the fossils should come in – if evolution is true, we should expect to be able to identify transitional fossils which are ancestral to whales which contain the characteristic ankle bony features of the even-toed hoofed mammals.

Now let’s look at bony features from the whale perspective. We have already mentioned the almost complete loss of hind limbs, and the presence of forelimbs modified into flippers. In addition, as air breathers, whales have a blowhole at the top of their skull. And as powerful swimmers, which use a large tail fluke in vertical motions, whales have enormous sets of muscles which attach to enlarged projections from their vertebral column. So if evolution is true, we should begin to see fossil forms which manifest changes in bony features which correspond to the gradual accumulation of these whale-like characteristics. However, we still need more, because these various bony features all would be expected to occur in largely or exclusively aquatic forms. We might expect this to correspond to the later stages of a transition from terrestrial even-toed hoofed mammals. But what about the earlier stages? It would be very helpful if we had some “defining” characteristic of whales, similar to the ankle structure of even-toed hoofed mammals.

It turns out that the structure of the bones of the skull and ear apparatus of whales are highly modified to allow efficient hearing underwater. The mechanical aspects of efficiently receiving sound through water are somewhat different than receiving sound travelling through air. If evolution is true, we should expect to be able to find key transitional fossil forms with a progressive series of modifications of the skull and ear bones, features which would not be found in any other mammals.

Now that we know what we should expect to see, if evolution is true, let’s look at what has actually been found in the fossil record. Over the last fifteen years or so, a series of fossils, many of them discovered in the Indian subcontinent, have fulfilled nearly all of our predictions.^1,2 Let’s look at the figure below (Figure 1), reproduced from a recent popular book on evolution.³ This shows a series of fossils, arranged in approximate chronological order, with a modern whale at the top. How old are these fossil forms? The entire fossil progression illustrated occurs from a little over 50 million years ago to about 40 million years ago. So a remarkable alteration in general body form occurred in a little over 10 million years. This time frame agrees well with the previous prediction from the DNA “clock” that we discussed in our previous essay. Second, the general change in body shape corresponds to what we predicted in our discussion of whale bony features above. That is, there is a gradual elongation and streamlining, there is a modification of the forelimb into flippers and progressive reduction of the hindlimb, the nostrils for breathing move toward the top of the skull to form a blowhole (not obvious from the diagram), and the vertebrae develop enlarged projections to support the attachment of swimming muscles.

Figure 1: Skeletons and Body Forms of Modern Whales and Fossil Ancestors
The reconstructed skeletons (black) from modern whales (top) and various ancestral skeletal forms (series below) are in chronological order (from Pakicetus up). Indohyus is an extinct whale “cousin”. Relative body size, to scale, is indicated by the gray shapes at the right of each animal.

There is probably little question that the last fossil species in the figure (Durodon) is well on the way to becoming a modern whale. However, it might be argued by a skeptic that the earlier species (like Rhodocetus, Ambulocetus, or Pakicetus), despite the “cetus” (whale) part of their names, are not so obviously “whale-like” that they deserve to be considered as fossil whale ancestors. However, remember the characteristic whale skull modifications for hearing? It has been shown very clearly that throughout this series of fossil species, the various bony changes necessary to support efficient hearing in water were being acquired in a stepwise fashion. Organisms earlier in the sequence had skeletal characteristics consistent with them being able to hear well in both air (using the “classic” mammalian hearing apparatus), and newly acquired changes to also allow better hearing in water. Later organisms in the sequence become increasingly specialized for hearing in water only.⁴

What of the earliest fossil shown in this diagram –Pakicetus? Careful examination shows that it has the features we would predict for an early whale ancestor. It has the ankle bone characteristics of the even-toed hoofed mammals (in fact these features are also found in several of the later fossil forms as well, ensuring their continuity). This confirms one of the predictions made by the DNA evidence we discussed earlier. Furthermore, it has some of the modifications of the skull bones necessary for more efficient underwater hearing, which were previously documented only for modern whales and their later (more obvious) ancestors.⁴ These features are also shared with the “whale cousin” Indohyus.⁵ Preservation of more of the skeleton of this latter species has allowed detailed analysis indicating characteristics likely shared with whale ancestors. Indohyus was probably a wading animal, which spent much of its time in the water. It appears to have fed mostly on land, so it is suggested that resort to the water was made to escape predators.⁵

Finally, we need to look back at the last prediction from our previous DNA evidence, namely that modern whales are most closely related to hippos. If evolution is true, we should expect to find fossil forms linking these two modern groups. This has proven to be a tougher nut to crack, mainly because the ancestral whales first appear about 50 million years ago in what is now south Asia, and the hippo family first appears about 15 million years ago, in Africa. The most recent tree diagram, produced by using a combination of skeletal features and DNA data, still supports this family connection, as shown by the following figure (Figure 2).⁶

Figure 2: Phylogenetic Tree Showing the Relationship of Modern Whales to Living and Extinct Even-Toed Hoofed Mammals
This tree is based on both bony features and DNA data. The organisms presented in blue are semi-aquatic or aquatic forms. Organisms shown in green are terrestrial even-toed hoofed mammals (Artiodactyls). In black is shown a member of the odd-toed hoofed mammals. In red is an extinct fossil ancestor group. (This figure is adapted from Fig 1a in Reference 6).

The blue lines in the diagram show species in which the skeleton is specially thickened, and the bone structure more dense. This is an adaptation which allows wading animals (like modern hippos and the fossil Indohyus) to be good “bottom-walkers” (it prevents them from floating due to lighter body tissues), and allows fully marine organisms (like modern whales) to have “neutral buoyancy” (so they don’t always tend to pop up to the water surface, like a cork). There has also been progress in clarifying the relationships between fossil ancestors of hippos and those of modern whales. A recent study of hippo evolution, based only on skeletal characteristics, has conclusively shown that the hippo family are descended from an extinct group of fossil Artiodactyls, known to go back more than 40 million years, and whose fossils are from southern Asia. Furthermore, this study produced a phylogenetic tree predicting that this extinct hippo ancestor group also shared a common ancestor with the fossil whales.⁷ Thus the investigation of hippo origins is independently leading us back toward the origin of whales. However, in this study the statistical support for predicted common ancestor of the ancient hippo group and the ancient whale group is not as strong as scientists would like to consider this “case closed”. What is necessary is more fossils, of the appropriate age in order to complete the story of hippo evolution. We still need that to fill in the details of the predicted relationship of hippos to modern whales.

Thus the “Whales’ Tale” is not yet complete. It is a story of scientific discovery in progress. As we finish, let’s briefly summarize what we have found out. Different types of DNA evidence agree that modern whales are most closely related to the even-toed hoofed mammals, despite the obvious great changes in limb anatomy of the modern whales. This prediction has been amply confirmed by the fossil record. The DNA sequence evidence predicted a time frame during which critical early events in evolution of whale ancestors should occur. This prediction has also been amply confirmed. Finally, DNA evidence predicts that modern whales are most closely related to hippos. There is some fossil evidence supporting a predicted common ancestor, but more data is needed. A final caution to possible sceptics – this state of “unfinished business” is precisely how the scientific process works. There is no “crisis”. There is no indication that evolution is not true. There is simply the ongoing work of mapping out of various lines of evidence. A scientific conclusion is considered well supported if “all roads lead to Rome”. In the case of whale evolution it might be prudent to say that the evidence has not quite converged in Rome yet, but that we are now in the suburbs. That is precisely what makes science interesting and fun. Stay tuned!

The next blog in this series can be found here.

References:

1: Thewissen J.G.M., Williams E.M., Roe L.J. and Hussain S.T. 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature. 413: 277-281.

2: Gingerich P.D., ul Haq M., Zalmout I.S., Khan I.H., Malkani M.S. 2001. Origin of Whales from Early Artiodactyls: Hands and Feet of Eocene Protocetidae from Pakistan. Science. 293:2239-2242.

3: Coyne, J.A. 2009. Why Evolution is True. Viking Penguin, New York. Pg 50.

4: Numella S., Thewissen J.G.M., Bajpai S.,Hussain T., Kumar K. 2007. Sound Transmission in Archaic and Modern Whales: Anatomical Adaptations for Underwater Hearing. The Anatomical Record. 290:716-733.

5: Thewissen J.G.M., Cooper L.N., Clementz M.T., Bajpai S., Tiwari B.N. 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature. 450:1190-1194.

6: Geisler J.H. and Theodor J.M. 2009. Hippopotamus and whale phylogeny. Nature. 458:E1-E4.

7: Boisserie J.-R., Lihoreau F., Brunet M. 2005. The position of Hippopotamidae within Cetartiodactyla. Proceedings of the National Academy of Sciences U.S.A. 102(5):1537-1541.

As we have seen, speciation (the events that lead to reproductive isolation between populations of organisms) can be a prolonged and complex process. Populations can become isolated geographically (e.g. through migration) and begin to accumulate genetic differences that may raise a barrier to reproduction between them. This barrier may only be a partial barrier, however. The stickleback populations we discussed previously are an example: the first event leading to speciation was physical separation when some marine fish colonized new freshwater habitats. Even after significant differences accumulated between the marine and freshwater forms, a second wave of colonization of fresh water by the marine form brought the two groups into contact again, leading to some genetic exchange even as the two groups remained largely distinct. At the point of the second colonization, whether one or two species is/are present is a point of discussion: the case can be made for either. A scientist arguing for one species would point out that the two groups can still produce fertile offspring, whereas a colleague might argue for two based the distinct characteristics and ecological niches of the two populations, as well as the observation that the hybrids resulting from interbreeding are not as well adapted to either niche. The point is clear: speciation, as a slow process, is a gradient, and a clear line of demarcation cannot be drawn on a gradient. To return to our flip-book analogy, every adjacent page is only slightly different from the pages on either side. If we compare widely separated pages, the differences are clear. The point is that there is no single page in between them that we can identify as the point where the images “became different.”

While this discussion might seem a little academic and uninteresting (perhaps because one might discount such events as mere ‘microevolution’ of sticklebacks), we have recently learned that similar events shaped human speciation. As far as we can tell, sticklebacks are not aware of, nor concerned about, the theological implications of how they came to be, but we certainly are for our own species (and perhaps even for sticklebacks). What was once an area of interest mainly for specialists is about to become a topic of intense discussion among evangelicals: we have only recently learned that a portion of the lineage leading to modern humans interbred with other hominid species they encountered as they migrated out of Africa ~50,000 years ago. In order to explain what happened, let’s pick up the tale at an earlier point, around 450,000 years earlier.

Out of Africa, twice over

Somewhere between 500,000 and 300,000 years ago, the ancestors of the Neanderthals (Homo neanderthalensis) left Africa and migrated into the Middle East region, and from there on to Europe and parts of Asia. (Recall that human ancestors, at this point, are all still in Africa, and will stay put until around 50,000 years ago). Neanderthals persisted in the Middle East and Europe until ~30,000 years ago, meaning there was a time where the humans leaving Africa about 50,000 years ago could have interbred with them before they went extinct. This remained an open question until techniques improved to recover and sequence ancient DNA. It is now possible to obtain and sequence DNA from Neanderthal remains, and the complete genome sequence of Neanderthals was published in early 2010. The results were fascinating: DNA sequence comparisons between the two species indicates that modern, non-African humans have about 1-4% Neanderthal DNA in their genomes. This variation, however, is not present in sub-Saharan Africans, since they are descended from humans that did not leave Africa and and thereby, because of geographical separation, never had the opportunity to interbreed with Neanderthals. We also know that the group that left Africa went through a reduction in population size to a about 1200 individuals (a genetic bottleneck), whereas those that stayed behind maintained a larger population size (about 6000) over the same period.

New details

In addition to this information, we have recently discovered a new hominid species from Asia, as Darrel Falk recently highlighted here on BioLogos. This species, named the “Denisovans” is known to us only from a few bone fragments and one molar, but - wonder of wonders in this age of paleogenomics - this was enough for us to determine its complete genome sequence. The results were, again, fascinating: the Denisovans are relative of Neanderthals that split off from them after their common ancestor left Africa. The Neanderthals went west to Europe, and the Denisovans colonized Asia (and evidence suggests they were quite widespread). Even more interesting is that comparing Denisovan and human DNA indicates that some humans (modern Melanesians) have about 5% Denisovan DNA in their genomes. This variation is not found in Europeans or Africans.

Putting the story together

Assembling all of this information reveals the following tale: the common ancestor of Neanderthals and Denisovans migrated from Africa to the Middle East between 500,000 and 300,000 years ago, leaving a population behind that would eventually become modern humans (at around 200,000 years ago). In the Middle East, the populations destined to become Neanderthals and Denisovans part ways, with their differences accumulating over the next several hundred thousand years to make them distinct species. When a population of modern humans leave Africa around 50,000 years ago, they encounter, and breed with, Neanderthals shortly after. This genetic exchange is small, since there are partial reproductive barriers in place, but a small fraction of Neanderthal DNA becomes established in this lineage. Groups from this population then part ways, with some migrating into Europe and others into Asia. This latter group then encounters the Denisovan hominids, interbreeds with them, and a fraction of Denisovan DNA takes hold as a result. This population goes on to colonize southeast Asia, Oceania and Australia, where we see this variation today in Melanesians. Modern humans thus have different evolutionary trajectories: Melanesians have both Neanderthals and Denisovans in their lineage, Europeans have Neanderthals, and Africans have neither.

New data, new questions

Even as I stand amazed in what God has revealed to us about our origins through science, I know that this new information will be difficult for some within the evangelical community to accept. Moreover, it is almost certain that some Christian groups, unfortunately, will misrepresent this data to their constituents (whether intentionally or not), and thus spread confusion that hinders the needed theological conversation. Still, I have reason for hope: God has seen it fit to reveal this information to us, and that suggests that He believes the evangelical Christian community is ready for this conversation to happen. As Darrel mentioned at the end of his recent piece, we at BioLogos want to assist our evangelical sisters and brothers in this conversation in any way we can, in full confidence that it can be done in an edifying way:

BioLogos exists to help Christians think carefully about the ramifications of these new data in light of long-standing traditional ways of viewing human creation. We have some re-thinking to do, but it can be done and will be done within the context of a Christian faith that is fully orthodox and thoroughly evangelical. Any time we draw closer to truth, to God’s truth, we have nothing to fear. There is still much to learn, but we can look back at what we have learned with awe—absolute awe.

In the rest of the series, we will look closely at the evolutionary explanation for the blueprint. That explanation postulates that tetrapod limbs arose during a particular era in life's history, and that they arose as modifications of the fins of fish. And the evolutionary explanation isn't just an interesting idea. It's a comprehensive explanation – it helps us to understand bones, fossils, genes, chemical signaling systems. It provides a coherent framework for understanding why limbs are the way they are, and how they got that way.

Comparing the anatomy of tetrapod vertebrates and fish

The idea that tetrapods arose from fish is not new; E.D. Cope proposed in 1892 that tetrapods descended from lobe-finned fish. (Modern lobe-finned fishes include coelacanths and lungfish, and comprise one of two divisions of the bony fishes. The other division, the ray-finned fishes, includes most familiar kinds of fish.) In the early days, biologists inferred ancestral relationships between species largely through comparative anatomy and embryology: they would carefully classify organisms according to their structure (including their structure during development) and look for relationships that generated nested hierarchies. A simple nested hierarchy goes something like this: 1) animals with backbones; 2) animals with backbones and limbs; and 3) animals with backbones, limbs, and hair. Animals in group 3 also belong to groups 1 and 2, while animals in group 2 also belong to group 1, and so the groups together define a nested hierarchy. Such studies alone could have led some scientists to infer an ancestral relationship between fish and tetrapods, and perhaps those studies did convince them. But then there were fossils of various types of fish and other vertebrates, many long extinct. That fossil record was relatively sketchy in 1892, but it nevertheless led Cope and others to conclude that certain fish had given rise to tetrapods at a particular time in natural history.

The fossil record shows a fish-to-tetrapod transition

Here are some basic findings from the fossil record that suggest a fish-to-tetrapod transition and that have been known for decades:

• Fish, including fish with bones, lived on the earth before tetrapods appeared. Specifically, fossils of bony fish first appear in rocks from about 420 million years ago.

• Tetrapods appear in the fossil record at a particular point in history and then persist and diversify in subsequent eons. Their arrival was long thought to have occurred about 365 million years ago, although some recent findings have challenged that hypothesis.

• Tetrapods that still had some fishy features were prowling the planet 365 million years ago.

• Lobe-finned fish that were starting to look more like tetrapods were eating other fish about 385 million years ago.

Even many decades ago, there were hints that something interesting happened between 400 million years ago and 365 million years ago. Let's take a close look at the ancient animals that suggest the fish-to-tetrapod transition.

Ancient animals

The most primitive known tetrapods for which we have skeletal remains lived 365 million years ago. They were undeniably tetrapods, but there was definitely something fishy about them. (Heh heh.) One of the most famous of these creatures is Acanthostega, discovered in 1987 by British paleontologist Jennifer Clack and pictured below. Acanthostega is a card-carrying tetrapod, with fingers and toes. But it has a fish tail, with fin rays. Another well-known primitive tetrapod is Ichthyostega, which lived around the same time as Acanthostega. Like Acanthostega, it is a true tetrapod, but has several odd fish-like structural features. For example, its skull is more fish-like than that of Acanthostega. In summary, both Acanthostega and Ichthyostega already used the limb blueprint, even though both also had some fish-like anatomical characteristics. Their presence 365 million years ago shows that tetrapods must be at least that old, and their mixture of anatomical features suggests that the transition happened not long before that.

And what about the lobe-finned fish that looked a bit tetrapod-ish? That animal is Panderichthys, described as “vaguely crocodile-shaped” with skeletal features that were tetrapod-like. Specifically, this ancient fish had tetrapod-like “shoulders,” and recent analysis found some finger-like bones at the ends of the fins. The creature also had a breathing hole on the top of its head. These fish lived around 385 million years ago.

The hunt for the earliest tetrapods

Taken together, these observations suggested that the fish-to-tetrapod transition occurred between 385 and 365 million years ago. Eager to see what that transition looked like, scientists began to look for 375 million-year-old rocks in which they might find animals at the beginning of tetrapod-hood. They wanted to catch evolution in the act.

Let's stop and think about this, because it's cool and because it's important to note the extent to which evolutionary biology is hypothesis-driven. Critics of evolution sometimes portray the theory as an untestable historical conjecture, depicting it as fundamentally different from experimental science in the lab. But the hunt for the earliest tetrapods was an effort to test a hypothesis that had generated a prediction. Based on the hypothesis that lobe-finned fish were ancestors of tetrapods, scientists predicted that intermediate animals, “fishapods,” would be found in the gap between Panderichthys and Acanthostega. To evaluate the prediction, all they needed to do was find some suitable 375 million-year-old rocks.

Neil Shubin describes that search in the first chapter of Your Inner Fish. He and his colleagues found suitable rocks in the islands of the Arctic: the right age, nicely exposed (by erosion), and representative of the kind of environment that their quarry would frequent – freshwater streams. They made their biggest discovery on their last trip (“a do-or-die situation”) in 2004. That discovery was Tiktaalik roseae, the “fishapod.”

The “fishapod”

Tiktaalik roseae is one of the most extraordinary fossil intermediates ever described, and its public debut in 2006 was front-page news. An artist's conception of the animal is pictured below.

There are several aspects of the anatomy of Tiktaalik that earn it the title “fishapod.” Like a good fish, it had scales and webbed fins. Like a tetrapod (more specifically, like a crocodile), it had a flat head, with eyes on the top of the head, and it had a neck. But what about those fins? Or are they limbs? Remarkably, the answer seems to be, “both.”

The fins of Tiktaalik were part fish fin, part tetrapod limb. On the outside, they looked like fins, with webbing. On the inside, though, these fins were clearly tetrapod-like. Amazingly, the fins of Tiktaalik were built using a primitive version of the limb blueprint: one bone, two bones, blobs, digits. As Shubin writes in Your Inner Fish, “We had a fish with a wrist.” (The Tiktaalik roseae web site at the University of Chicago is a great source for images and more information.)

Let's address three questions about Tiktaalik that might have occurred to you. First, why might animals like Tiktaalik have developed tetrapod-like fins? Shubin and his colleagues suggest that these limb-like fins may have been useful for doing “push-ups” in the shallow water. (Like Panderichthys, Tiktaalik had a breathing hole on top of its head and was clearly adapted for living and moving in shallow water.) Second, is Tiktaalik an ancestor of all tetrapods? No, not necessarily. What Tiktaalik shows us is that animals were developing tetrapod features in the context of fish bodies, and Tiktaalik shows us the context (shallow water) in which this likely occurred. But that doesn't mean that our lineage arose from Tiktaalik itself. Finally, is Tiktaalik now the oldest tetrapod? No, apparently not. For one thing, Tiktaalik is truly transitional, and probably therefore not worthy of full tetrapod membership. But more notably, data published in 2010 show that tetrapods are a lot older than was thought at the time of Tiktaalik's discovery. The new findings show footprints that are unmistakably those of a tetrapod, in rocks about 395 million years old. Surprisingly, then, tetrapods were already on their way long before Neil Shubin's specimen lived. Tiktaalik is truly a fish/tetrapod intermediate, which was living at the same time as animals that were fully tetrapods. A simple story of succession, in which intermediates disappear and are replaced by less intermediate types, seems to be an oversimplification.

In conclusion, the fossil record provides evidence that the fins of fish and the limbs of tetrapods are related by ancestry: limbs seem to be modified versions of fins. What other evidence supports this proposal? In the next post, we will turn to developmental biology, and explore the meaning of the term 'homology.'

Further reading:

Neil Shubin (2009) Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body. New York: Vintage Books.

Carl Zimmer (2006) A Fin is a Limb is a Wing: How Evolution Fashioned its Masterworks. Online at NationalGeographic.com.

Tiktaalik roseae website at the University of Chicago.

Jennifer Clack's website at the University of Cambridge.

Images are from Wikipedia.

Many scientists think that evolution is a directionless process, one in which humans are merely an accidental byproduct. In a recent episode of the award-winning radio program “To the Best of Our Knowledge” (produced by Wisconsin Public Radio, and reposted above, with permission), however, esteemed paleontologist Simon Conway Morris of Cambridge University explains a different view of evolution. Conway Morris has catalogued plentiful examples of evolutionary convergence, in which different organisms arrive at the same function through different evolutionary pathways, including the trait of intelligence. He examines the ability of the octopus to gaze, learn and play, and compares it to the intelligent behaviors of dolphins and the tool making ability of certain crows. Given enough time and resources, he says, every ecological niche will be filled up by some kind of life form. One of these niches is that for highly intelligent life, a niche occupied by us, Homo sapiens. If the tape was rewound and evolution started over from scratch, Conway Morris says, the evolutionary details would be different, but the end result would be similar: a species characterized by intelligence and complex civilization.

While several esteemed scientists, including atheist Richard Dawkins, and Brown University cell biologist, Kenneth Miller, agree with Simon Conway Morris, most (according to Dawkins) do not accept that evolution can have this sort of directionality. Sean Carroll, leading evolutionary biologist and Vice-President of the Howard Hughes Medical Institute, says that animals merely “exploit what’s available,” with no necessary end. Little, he believes, is inevitable. “With a few other rolls of the dice”, he says, evolution would have resulted in a significantly different assortment of organisms. Noted philosopher of science, Daniel Dennett, agrees with Carroll. Just as the origin and wide-spread diversity of creatures like marsupials (mammals with a pouch) was not inevitable, he says, so the evolution of intelligent human-like beings was not inevitable either. Dennett goes on to say:

The idea that this whole great universe was in some sense designed or intended for us strikes me as just bizarrely self-involved (chuckles)—one of the most stunningly narcissistic visions that I’ve ever encountered. It seems unlikely, don’t you think?

In complete contrast Conway Morris says:

The universe from a theistic viewpoint, from a Christian viewpoint, is utterly contingent. It needn’t exist at all, more particularly it could be anything which God so chose. Science is an open-ended adventure; we don’t know where it’s going to end. People who think religion is simply a set of answers to keep you comfortable are, I’m afraid, sadly mistaken—it is an open-ended adventure. We don’t know, really, what the nature of the universe is. We don’t know why we have our moral, ethical, intellectual and poetic capacities. I know they come from an evolutionary basis, I have no quarrel with that. But so far as I’m concerned, we are going on to completely new territory and my view would be that in fact the religious instincts and the religious teachings actually tell us something real about the world. They’re not simply fairy stories.

So is the near-certainty of human life front-loaded from the beginning? Was it predetermined from the Big Bang that human beings would eventually arise? Was it predetermined that God’s natural activity—that activity which upholds the universe and maintains all that is within it—would be sufficient for the eventual development of humans? Alternatively, was supernatural activity required for the creation of the human body? Does the Bible dictate one way or the other? Is it somehow less God’s creation if it took place through God’s natural activity? Is it somehow more God’s creation if supernatural activity was required? These are questions for theologians. Science is taking us up to edge as Conway Morris brilliantly shows. There, we meet the theologians, and there, we begin the journey’s next phase.

I encourage you to listen to the above recording. The deeper we explore creation, the more we see and appreciate its beauty. So also, and even more significant, the deeper we embed ourselves in God's written and Living Word, the more confident we become of “Romans 8:26-39”. We are loved. More than we can possibly imagine, we are deeply embedded in the love of God. This, truly, is "Life's Solution."

]]> Thu, 11 Aug 11 02:15:51 -0700 Darrel Falk http://biologos.org/blog/nprs-adam-and-eve-story?utm_source=RSS_Feed&utm_medium=RSS&utm_campaign=RSS_Syndication http://biologos.org/blog/nprs-adam-and-eve-story?utm_source=RSS_Feed&utm_medium=RSS&utm_campaign=RSS_Syndication All science can say is that there was never a time when only two people existed on the earth: it is silent on whether or not God began a special relationship with a historical couple at some point in the past. This subtle but extremely important point was missed entirely in the NPR story. The conversation regarding the historicity of Adam and Eve, described so clearly in the cover story of the June issue of Christianity Today, continues in an unlikely place—at National Public Radio. If you haven’t already heard it, you’ll want to listen to this story. BioLogos Senior Fellow Dennis Venema does a beautiful job summarizing the genetic data in a non-technical way, and Karl Giberson addresses the serious danger to the Church if we ignore this data. While we at BioLogos appreciate many aspects of the story, we need to make one all-important clarification: the debate over the historicity of Adam and Eve is primarily a theological debate, one that is more complex than the story lets on. All science can say is that there was never a time when only two people existed on the earth: it is silent on whether or not God began a special relationship with a historical couple at some point in the past. This subtle but extremely important point was missed entirely in the NPR story. It is a consideration that we raise repeatedly at BioLogos. See, for example this article by Daniel Harrell and this series by Denis Alexander.

Evangelical Christians have long suspected there are allegorical components to the Genesis story—a talking snake, for example—but as to whether Adam and Eve were not real people, there has been much more hesitancy--and for theologically important reasons. The science itself is silent—the most it can say is that there were never just two individuals who were the sole genetic progenitors of the entire human race. Several independent lines of genetic evidence unambiguously point to this conclusion. Science also make it very clear that humans developed through an evolutionary process. As Christians, we interpret all this in light of our belief in God as Creator.

It is important for Evangelicals to know that science is silent on the historicity of two people named Adam and Eve, just as it is silent on the existence of persons named Abraham, Isaac, and Moses. Adam and Eve may well have been two real people, who through the grace of God entered into a paradisiacal relationship with him, until—tragedy of tragedies— they allowed their own self-centered desires to reign in their hearts, instead of their love for God. Although genetics convincingly shows that there was never a time when there were just two persons, the Bible itself may even provide hints of the existence of other people—likely we’ve all wondered about those hints since we were children. “Did Cain marry his sister?” we want to know. “Who were the people that Cain was afraid of as he wandered the earth after killing Abel? If they were his brothers or nephews, why didn’t the author refer to them that way?” The author doesn’t seem to be as puzzled by this as we are. We’ve always known about those little pointers—in fact, ancient interpreters wrestled with them too, long before Darwin or modern genetics appeared on the scene. So it ought not to necessarily surprise us for genetics to come along and confirm that, sure enough, there were others around at the time of Adam and Eve.

The NPR story, as much as we appreciate it, implies that, according to science, there are only two options for Christians—dismiss the conclusions of science, or dismiss the notion of a historical couple named Adam and Eve. This is simply not the whole story. Any dismissal of a historical couple, who entered into relationship with God only to sin and break that relationship, is going to have to come from theology. There is no scientific reason to upset that theological apple cart. Indeed as scientists, we must respect the theological diversity of Evangelicalism.

Science is an amazing tool that gives insight into our world, one which is so effective that it is allows us to become virtually certain about some things. The earth does revolve around the sun. The universe was created over 14 billion years ago. All species came about through a gradual process that included natural selection, genetic drift and sexual selection. Christians should see all of this as the product of God’s masterful plan and ongoing activity. Christians should also see that science is silent on the existence of a specific first couple who enjoyed a special relationship with God. Exploring that is beyond the purview of science.

As I wrote last week, the data are clear that humans have been created through an evolutionary process and there was never a time when there was a single first couple, two people who were the progenitors of the entire human race. Within that framework, BioLogos does not take a position on the existence, in history, of two unique individuals, Adam and Eve. This is a theological question, not a scientific one. We recognize that now that the scientific consensus is clear, having become substantiated even further through genetics, there will be many fine theological minds on both sides of the historicity question. Our task is to help the Church come to appreciate that mainstream science and Christianity can co-exist in harmony. We’re happy to stand back and watch as the theologians work through the historicity question. Indeed, some of that conversation may well take place on these pages.

What pleases me most about the C.T. editorial is that it shows the willingness of the C.T. editorial staff to pay close attention to scientific consensus. Look at what they say:

Sometimes, Christian ways of thinking must adjust. Two famous names—Copernicus and Galileo—tell that tale. Other times Christian thinkers adopt some of what scientific research suggests, but hold firm on key aspects of biblical knowledge. The name B.B. Warfield tells that tale…

As the article goes on, the editors also make this statement:

Now we come to another great moment of tension between Christian readings of Scripture and science…

Christians have already drawn the line: there must be an original pair of humans endowed with soul—that is, the spiritual capacity to relate to God in the special way Genesis describes.

Having explained why the line must be drawn at a first couple, the editorial goes on to briefly discuss ways of bringing harmony between the science and traditional Christianity:

Hebrew thought offers one clue to resolving this tension: The corporate nature of humanity. Scripture often calls groups of people by the name of their historical head. Israel is an obvious example. So are Canaan and Cush.

At times, Scripture also holds groups of people morally responsible for the actions of some of their members.

Thus some have suggested—as does John Collins in “Did Adam and Eve Really Exist?” (Crossway, 2011)—that if both biblical and scientific clues suggest a larger population contemporary with Adam and Eve (Whom did Cain marry? Whom did God protect him from?), we can still conceive of Adam and Eve as leaders of that original population. That suggestion has the virtue of embracing both a prehistoric couple and a prehistoric population.

Finally, and all importantly:

At this juncture we counsel patience. We don’t need another fundamentalist reaction against science. We need instead a positive interdisciplinary engagement that recognizes the good will of all involved and that creative thinking takes time. In the long run, it may be the humility of our scholars as much as their technical expertise that will bring us to deeper knowledge of the truth.

The C.T. editorial, in other words, has shown that in their view mainstream evangelical Christianity and mainstream science can co-exist in harmony. There are still many details to be worked out and much conversation lies ahead, but there is reason for optimism. The findings of science and the evangelical approach to Christianity need not be at dead end anymore, and we are thankful that the editorial staff of “Christianity Today” is clearing away the barriers and beginning to pave the way.

As we move forward, the conversation ought to focus on matters about which we can all agree. This is part of the reason that BioLogos has begun a Saturday sermon series, which currently focuses on a set of sermons delivered by Pastor Tim Keller of Redeemer Presbyterian Church in New York City. I have now listened to the second sermon in this series four times and every time I hear it, I glean some new truth that leaves me in complete awe of our Creator and the never-ending depth of a theology thoroughly grounded in Genesis. Each week we post a four minute excerpt, a brief summary, and then a link to download the entire sermon. We are encouraging people to come back after listening to the whole sermon to “talk” about it if they so desire. So far, it has largely been the atheists who have been chomping at the bit to enter into conversation. That’s not what we want though, especially when I suspect that they have not even listened to the sermon. We hope that a large group of fellow believers will listen to these sermons together as we are all drawn into a spirit of celebration for the beauty of the creation story as fully revealed in Genesis, Romans and Revelation.

The reason that I am advocating Pastor Keller’s messages as the rallying point around which we can all gather is that as one listens to what he has to say, there is very little with which any of us Christians would disagree, regardless of our perspective on details. As I listened again to last Saturday’s sermon, The First Word, I thought to myself that if I were a young earth creationist, I could embrace almost everything he said and grow richly closer to God in the process. However, that would be equally true if I was a Reasons to Believe, old earth creationist, or a William Dembski I.D. theorist, or, of course, a BioLogos evolutionary creationist. The fact is that we are all one. We can all rally around the Word as expounded by pastors such as Dr. Keller. Sure we’ll look at some parts differently—but when we are all hearing the Word together, we can all celebrate its message as it speaks to the heart and soul of who we are as Christians. As we do that—together—we will all, with one voice be able to cry out in unison—“Christ in you—the hope of Glory!” The atheists will look on and wonder what is happening, but what they will see as we all celebrate and worship together is the radiant face of Jesus—the Body of Christ in unison celebrating the beauty of the Creation story as it is completely fulfilled in our Lord.

Editor's Note: Please see Darrel's follow up comment below (#62248) for some clarification on the piece and BioLogos' position on Adam and Eve. Also the first two sentences of the second paragraph have been modified slightly to ensure that the BioLogos position is clear.

Today we post the final installment in our four-part "Distinctions" series. This video was directed by Loretta Cooper, President of Clarity Media Strategies and was scripted by Loretta Cooper and BioLogos Program Director, Kathryn Applegate.

Narrator: What does it mean to be human? For the Christian, the answer is complex. In part, it is a reflection of being created in the image of God with free will and common values. But does the science of human evolution pose a threat to that uniqueness?

Lee Strobel: But in the last 150 years, science has failed to substantiate Darwin’s claims of macro-evolution.

Mike Riddle: The Bible teaches that God created all creatures after their kind; there was not one common ancestor everything evolved from.

Ken Ham: You know, through this nation, whole generations of young people are being taught in the public schools that there is no God, life evolved by natural processes, and that very much determines their morality, how they view themselves, their purpose and, meaning in life, and so on.

Narrator: Not all Christians view evolutionary science as a threat to their faith, and not all scientists see human evolution as a strictly materialistic process. There are those in both communities who believe the explanation is much more complex, including Dr. Rick Potts. Dr. Potts is one of the world’s leading paleoanthropologists, and the curator of (anthropology at) Smithsonian’s Museum of Natural History.

Rick Potts: What we’ve found is that part of our message is that an aspect of being human has been the process of becoming human that scientists have been able to uncover, and that includes the amazingness, if you will, of the fact that human beings today are connected to all other living creatures. There is this vast kinship that all creatures share on earth, and that is a beautiful thing.

Narrator: But the idea of common ancestry is anything but beautiful to many conservative Christians. It’s a prospect that has caused consternation among American evangelicals dating back at least to the Scopes Trial in 1925. Others, however, insist that there is nothing in common ancestry that should alarm those who have observed nature and who study the character of creator God.

Denis Alexander: When we talk about common ancestry, we don’t mean we are descended from the apes, we mean that we shared a common ancestor with the apes about six million years ago, plus or minus a little bit. And so the apes have been evolving their own particular way and we have been evolving our way. But the fact that we are all linked up in this evolutionary, historical way, I think is a just wonderful drama, a theater. And to me, anyway, I find it a privilege that I should be connected up to all these wonderful creatures.

Greg Boyd: And on the one hand I want to fully acknowledge that we human beings are in a class by ourselves, and that we are radically unique in God’s plan because we are to have dominion and to be the stewards of the planet and things of that sort. So I want to totally affirm that. On the other hand, if you totally separate humans from the rest of the animal kingdom, then you miss the beautiful continuity that is there, and part of the fear, I think, for people in thinking that we in any way came from apes is that it undignifies us. Well, it doesn’t. On the other hand, if our dignity has to be all at their expense then we have all the dignity and they have none, if we are in competition with them, and then we exploit them. There is a dignity to human beings that animals don’t have, but on the other hand, there is a worth and a value there that we need to respect.

Narrator: Any honest dialogue about the origins of humanity must acknowledge that some scientists and some Christians will never find common ground on this issue. But for those willing to engage in the conversation with prayerful hearts and open minds, the dialogue can lead us to glimpses of our Creator that inspire awe and worship.