Introduction

The earth is billions of years old. This means that the long time spans required for evolution did in fact occur. But did evolution actually happen? We need to look for evidence of gradual change and common descent, and our first place to look is the fossil record. The fossil record provides a unique view into the history of life, showing the forms and features of species through time. As we encounter species long extinct, we begin to comprehend the scope of God’s creative work.

The overall picture of the fossil record is change through time with an increase in complexity of life. Rocks over 1 billion years old exhibit only fossils of small, single-celled organisms. Moving to rocks 550 million years old, there are also fossils of simple, multicellular animals. At 500 million years ago (MYA), we find ancient fish without jawbones, and at 400 MYA we find jawed fish. Gradually, new types of animals appear: amphibians at 350 MYA, reptiles at 300 MYA, mammals at 230 MYA, and birds at 150 MYA.1 Even within these groups, there has been major change through time. For example, dinosaurs dominated reptile fossils from 230-65 MYA, early birds had teeth and tails, and early mammals were no larger than a mouse.2 As the rocks become more and more recent, the fossils look increasingly like animals observed today.

Clearly, through time there has been significant change in the organisms present on earth. An important question is whether the fossil record supports the claim that new species arise through gradual change – a key requirement of evolution. To answer this, four examples will be examined from Darrel Falk’s discussion in Coming to Peace With Science.

Continue: Transition to Land

Transition to Land

Land animals (tetrapods) first appear in the fossil record in rocks around 370 million years old. In older rocks, only sea creatures are found. The most notable structures of these new land animals were the legs, found in the same place as the fins of the sea creatures.

Until recently, there was no clear connection between the fish and the tetrapods – the fossils were either one or the other. Then, in 1998, scientists found a fossilized fin of just the right age (370 million years) with 8 digits and a distinct humerus, radius, and ulna – like an early tetrapod. However, the fin was clearly from a fish – strong evidence of a transitional form.

Other evidence can be found in the early tetrapods.  For example, living terrestrial vertebrates never have more than five digits on their limbs. In history, this rule has only been violated a few times, and all the exceptions are found in a narrow range around 370 MYA. Both these findings – a fish fin with tetrapod-like bones, and exceptions to the maximum-of-five rule – occur right as land animals first appeared on the scene, strongly indicating gradual change.3

A particularly interesting transitional form was discovered in northern Canada in 2006; named Tiktaalik, this species had forelimbs with the properties of fins but the ability to support weight on land. The fossil was found in a rock formation which is about 375 million years old.4 Again, the transitional form was found at just the right time period.

Continue: Turtles

Turtles

Turtles have a distinct body plan with the characteristic protective shell. Compared to other vertebrates, this body plan is very old and relatively unchanging. The first fossilized turtles appeared in rocks 210 million years old. But is there evidence for the gradual formation of turtles?

Consider the following: at 255 MYA, there are fossils of creatures with “small, bony plates in the center of their backs.”5 These plates were not large enough to provide protection and insulation like a turtle shell; rather, they are thought to have given structural support to the backbone. Then, at 248 MYA, there are fossils of one species with bony plates (not fused) covering most of its back, and another species with fused plates covering the entire back. These plates were similar (though not identical) to true turtle shells, and these species also had other skeletal features similar to turtles.6

The key point is that these fossils are found at “just the right time” in the fossil record: right before the turtle fossils appear.

Continue: From Reptiles to Mammals

From Reptiles to Mammals

Another example showing evidence of gradual change is in the transition from reptiles to mammals. Mammals first appear in the fossil record around 230 million years ago, some 70 million years after reptiles first appeared.

There is an interesting group of reptiles, the cynodonts, which first appeared around 260 MYA and became increasingly mammal-like in more recent fossils (~245 MYA). Mammalian ears have three special bones (the malleus, incus, and stapes) that detect vibrations and allow hearing. They also have a jaw with two bones that make up the hinge, the dentary and squamosal. Cynodonts had only one bone (the stapes) in their middle ear, and their jaw hinge was formed by two different bones, the articular and quadrate, which were found close to the stapes.

Here things get interesting. Just before mammals appeared, there were species of cynodonts with a double jaw hinge: a dentary-squamosal hinge (like in mammals) and further back the “old fashioned” articular-quadrate hinge. The articular-quadrate hinge was right up against the ear drum, and appears to have served two roles: the role of a hinge, and the role of transmitting sound vibrations. It appears that the articular and quadrate bones were slowly taken up into the ear as the dentary and squamosal took over for the jaw.

Until this time, there had never been creatures like these cynodonts, and soon after mammals appeared, they went extinct. Here again, the fact that they show up at just the right time is strong evidence of gradual change.7

Continue: Whales

Whales

A final example of gradual change can be found in the fossil record of whales. Even though it is believed that land animals evolved from water animals, whales are an exception.  They are mammals, and so are believed to have evolved from land animals at a later time.

Whales have a characteristic “fat pad,” a structure that allows jaw vibrations to be used for hearing. Recently, a 52-million-year-old whale fossil, Pakicetus, was found in Pakistan. It was clearly a small (wolf-sized) whale, but it had no fat-pad, and its teeth were very much like the terrestrial animals already thought to be related to whales.

Then scientists found fossils of a more recent (40 MYA) and larger (50 feet) whale species, Basilosaurus. This whale is remarkable because it had a small but well-formed mammalian limb. However, it was very distinct from Pakicetus, which had a stronger resemblance to terrestrial animals. 

Then, a new species of whales was found that fit between Pakicetus and Basilosaurus. This new species, Ambulocetus was a classic transition species with “full-length hind limbs and a tail.” More and more fossils continue to be found, further illustrating the gradual change and connecting the whales to the ancestors of the hippopotamus.8

Continue: Why Are There No More Transitional Forms?

Why Are There No More Transitional Forms?

The important point from the examples above is that the transitional-type fossils regularly show up at just the right time, right when we are expecting to see a change from one type to another.  Yet, a common complaint is that there are very few transitional forms. It is certainly true that many lineages cannot be traced smoothly – there are “gaps” in the fossil record.

There are several responses to this objection. First, fossilization is a very rare event.  Most organisms leave no trace of their time on earth.  Typically, to leave a fossil remnant, the body needs to be buried quickly in sediment, and the organism needs to have hard parts. In fact, only 250,000 fossil species have been unearthed. Compared to the ~10 million species alive today (which are perhaps 1% of species that have existed on earth), this is a very small fraction.9

But even with the rarity of fossilization, why do we not see more transitional forms, such as we would expect in a random sampling? One explanation may be that transitional species will often be found in small populations, where rapid changes in the environment may have provided a stronger evolutionary drive.10 Since fossilization is a rare event, fewer individuals from a small population will be fossilized.  And since this is where most of the transitional species are expected to have developed, this makes finding the fossils of transition species even less likely.

Given these constraints, the fact that transition species have been found at all (such as the examples above) is remarkable, and it is a strong indicator of gradual change. For years, people have argued against evolution because of the gaps in the fossil record. But these gaps continue to be filled, such as the recent finds confirming the lineage of whales. We must be careful not to confuse the unknown with the unknowable. We should, in fact, relish the unknown, because it shows an opportunity to learn something new about God’s work in the world.

Continue: Conclusion

Conclusion

The fossil record provides a fascinating picture of the history of life on earth. But what are the implications of this long history of life on earth and the idea of gradual change through time? Does it remove the need for God’s creative work? Falk holds that this picture of earth’s history by no means takes God out:

God creates by guiding and influencing a process that involves gradual change. Animals, plants, and other organisms really do share common ancestors, but through a process under the control of God’s Presence, the history of life has taken the course that it has. According to this view, God is not necessarily more active at one time than another. Rather 'the Spirit of God [is] hovering' over creation (Gen 1:2), always present and always in control as creation unfold accord to God’s will and God’s command.11

Next Page: DNA Sequences