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The Mechanism of Creation – The View from Science, Pt. 2

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This is the second part of a series of three posts dealing with the mechanism of creation from the point of view of science. These will be followed by a series of posts addressing questions and concerns that Christians might have about this scientific view.

Hominid transition fossils, showing increasing brain capacity over time. Note that gorillas and chimpanzees are our contemporaries, not our ancestors. Photo from Encylopedia Britannica.

In my previous post, I pointed out that evolution is a loaded word that has multiple meanings for people and that part of the conflict between Christianity and science in this area is due to misunderstandings about the meanings of the word. There are four basic meanings relevant to our discussion:

  1. change over time
  2. common descent
  3. a mechanism (natural selection)
  4. a justification for atheism.

The first three meanings are scientific conclusions while the fourth is a metaphysical interpretation of the scientific findings which I will talk about later in this series. In today’s post we’re going to consider the second scientific meaning of evolution, common descent.

Common descent, also known as descent with modification, is the idea that all living things including humans have descended through modification over time from a common ancestor. The most distant ancestor of all living things is believed to be a single cell organism, much like a bacteria, that lived more than 3 billion years ago.

I’m going to talk about four types of evidence which support the idea of common descent. They are

  1. the common cellular and molecular basis of life
  2. family relationships among living organisms
  3. transition forms in the traditional fossil record
  4. genetic fossils present in living organisms.
Figure 1 – Molecules of Life.

Common Cellular and Molecular Basis of Life. All organisms are made up of cells which serve as the basic building blocks of life. Additionally, all cells use the same basic molecules of life (see Fig. 1). Genes carry the information that is necessary for the normal functioning of all cells and are the basis of inheritance in all organisms. The chemical nature of genes is the same in all organisms. DNA, the molecule that carries genetic information, is a polymer made up of four types of nucleotide building blocks abbreviated as A, C, G and T. The information is carried through a genetic code by the order of the DNA building blocks in the polymer chain.

Figure 2: Carnivore Phylogenetic Tree.

Family Relationships among Living Organisms. The 18th century Swedish botanist Carolus Linnaeus developed a nested classification system for living things based on their anatomical similarities and differences. This system is still used today. In this system, species are grouped into increasingly general categories. For example, similar species are grouped into a genus and similar genera are grouped into families and so on. Based on these hierarchical anatomical relationships, one can construct a type of family tree called a phylogenetic tree. Figure 2 provides an example of such a tree showing the family relationships among carnivores (meat eating animals).

Transition Forms in the Traditional Fossil Record. As I mentioned in my last post, fossils are formed from the remains of dead animals and plants. Fossils in the geological layers (strata) provide a record of the history of life with the uppermost layers being most recent and deeper layers revealing progressively more ancient history.

In his book, Finding Darwin’s God: A Scientist’s Search for Common Ground between God and Evolution, Ken Miller says, “Just as human history reveals a succession of languages, civilizations, and empires, natural history reveals a succession of living organisms that are linked in a stunning pattern of relatedness.”

Figure 3: Transitions Between Major Vertebrate Groups.

This pattern has been especially well worked out in the major vertebrate groups (Fig. 3). There we see a series of transitions leading from fish to amphibians, from amphibians to reptiles and from reptiles to mammals and birds. In each case there are a series of transition forms in the fossil record that connect the major groups. Ken Miller again, “Within a particular series of transition forms the first members are loaded with characteristics that indicate their ancestry. . . .” For example, “The first amphibians looked more like fish than any amphibian species that would follow them in the next 380 million years.”

Figure 4: Whale Transitional Fossils.

A particularly interesting and well documented example of transition fossils is seen in the evolution of whales (Fig. 4). The series of transitional fossils begins with Sinonyx, a wolf-sized 4-legged land animal that was a predatory scavenger that lived by the sea shore. Over time in the fossil series the front legs became fins, back legs disappeared, there was a loss of fur and transition of the body form to the streamlined shape of modern whales. The fossils also reveal a gradual migration of nostrils to the top of the head, an adaptation which allowed breathing in the water. Here is a link (http://www.youtube.com/watch?v=I2C-3PjNGok) to an excellent video which documents the discovery and evidence for this series of transition fossils.

Genetic Fossils. Surprisingly the genomes of living organisms contain remnants of functional genes (pseudogenes) as well as two types of parasitic DNA (transposons and retroviruses) which provide a window into the history of the living creatures. These genetic fossils can be used as markers to trace the family history of organisms. Let me give you two examples, one involving a pseudogene the second involving a transposon.

Sailors on long ocean voyages used to suffer from a disease called scurvy. The disease is caused by a deficiency in Vitamin C. Humans are not able to make this important vitamin. We share this problem with other primates. In contrast rats and most other mammals are able to make their own vitamin C. The difference is the presence of a gene called gulo which is necessary for the synthesis of Vitamin C. Surprisingly humans and other primates have a remnant (pseudogene) of gulo but it has a single mutation that makes the gene non-functional.

Figure 5: Using a Pseudogene to Mammalian Track Ancestry.

The question is how to explain the presence of this pseudogene in humans and other primates. The simplest explanation is that they are descended from a common ancestor which at some point in the distant past this ancestor developed the mutation in the gulo gene.  This mutation was then passed on to all humans and other primates. The fact that rats and other mammals don’t have this pseudogene indicates that the common ancestor of humans and other primates was on an evolutionary branch that diverged from other mammals (Fig. 5).

The second type of genetic fossil we are going to consider are transposons, also known as jumping genes. Most transposons have no known function but are simply parasitic DNA that is reproduced with the rest of the genome during cell division and thus passed on to their ancestors. Amazingly transposable elements account for about ½ of the DNA in the human genome.

Figure 6: Using a Transposon to Track Mammalian Ancestry.

As the name jumping gene implies, transposable elements are able to jump in and out of the genome both within and between chromosomes. Occasionally they become damaged in the process and thus become fixed at a specific location on a chromosome. An example of this is a transposable element called Alu. It is found at the same specific location in gorillas, chimps and humans but not in orangutans. This is strong evidence that gorillas, chimps and humans are descended from a common ancestor which separated from the orangutan line sometime after insertion of Alu at some point in the distant past (Fig. 6).

Conclusions. In this post I have presented four lines of evidence that support the idea that all living creatures are descended from a common ancestor. These are

  1. the common cellular and molecular basis of life
  2. family relationships among living organisms
  3. transition forms in the traditional fossil record
  4. the use of genetic fossils as markers to trace the family history of organisms.

Looking ahead: The next post will be part 3 of The Mechanism of Creation – The View from Science. We will talk about the third scientific meaning of evolution, natural selection which is the mechanism that explains both the change over time and common descent.

Questions for further reflection:

  1. What tensions does the idea of common descent raise for you?
  2. What questions or concerns do you have about the evidence for common descent?
Finding Darwin’s God: A Scientist’s Search for Common Ground between God and Evolution  by  Kenneth R. Miller. Harper Collins, 2007.

Suggestions for further reading:

  1. Finding Darwin’s God: A Scientist’s Search for Common Ground between God and Evolution, Kenneth R. Miller. Harper Collins, 2007.
  2. Creation or Evolution: Do We Have to Choose?  Denis Alexander. Monarch, 2008.
  3. The Language of God: A Scientist Presents Evidence for Belief, Francis S. Collins. Free Press, 2007.
  4. Coming to Peace with Science: Bridging the Worlds between Faith and Biology, Darrel R. Falk. InterVarsity Press, 2004.
  5. The Bible, Rocks and Time: Geological Evidence for the Age of the Earth, Davis A. Young   and Ralph Stearley. InterVarsity Press, 2008.
  6. Evolution Basics: An Introductory Course on Evolutionary Biology. This is a multipart series from The BioLogos Forum written by BioLogos Fellow Dennis Venema. I particularly recommend the part of the course entitled Genomes as Ancient Texts which discusses genetic fossils in more depth.
  7. Talk Origins Archive, This Web site contains a collection of articles and essays about evolution. It is not always very Christian friendly but is a good source if you want to delve more deeply into the scientific evidence for evolution.
  8. Added by the editor:  PDF  with the titles and links to the posts in  Tom Ingebritsen‘s  Christianity and Science series. Yes, this was created to meet the requests of readers and will be updated. Your interest in and encouragement of this series is much appreciated.

Update: 2/19/2014, 8:18 PM.