This the second part of my discussion of Bruce Glass, Exploring Faith and Reason: The Reconciliation of Christianity with Biological Evolution (Houston: DBG Publishing, 2012).
While the chapters in Part 2 of Glass’s book (which I discussed in my last post) are helpful in dispelling many misunderstandings about Darwinian evolution, the chapters in Part 3: “The Evidence for Evolution” are even better.
Reviewers sometime say that a particular chapter was worth the price of the book. Sometimes, depending on the book’s price, that is pure hyperbole. In this case, I would make the “worth the price of the book” claim for chapter 7.
Chapter 7: “Clues All Around.” In this chapter Glass points to multiple lines of evidence of biological evolution in the natural world, citing example after example of actual changes that have been observed in the past century. If you want to understand what “natural selection” means, this is the best explanation I know of.
Glass first cites examples of humanly-guided selection (breeding) among both animals (fish, cats, dogs) and plants (corn, vegetables, flowers). But not all observable changes in organisms have been intentional. The reason we have shorter dandelions today is due to mowing of lawns (shorter dandelions have been “selected” for survival). He also points to the adaptive resistance of insects and other pests due to the use of pesticides in agriculture, antibiotic-resistant bacteria, and genetic drift in viruses. The discussion of the constant evolution of HIV strains and the avian flu is particularly illuminating for illustrating how natural selection works.
Most of the changes Glass discusses do not involve the transformation of one species into another (since this takes a lot longer than a century for complex animals). But bacteria and viruses (which have a much shorter generational life) demonstrate more significant evolution in a shorter time.
Glass also explains how genetic disorders (such as Down’s syndrome, cystic fibrosis, hemophilia, color blindness, sickle-cell anemia) are inherited. He notes that some of these genetic changes may have been adaptive measures to various diseases in the distant past (thus cystic fibrosis carriers seem to have increased resistance to cholera, while those with the sickle-cell gene are more resistant to malaria).
Beyond noting observable changes in organisms due to natural selection, Glass also points to the appearance and subsequent fading of ancestral structures in embryos. The fact that all reptile, bird, and mammal embryos have temporary gill slits, and that some whale embryos develop teeth (which are then reabsorbed into the tissue) is suggestive of evolutionary history.
Likewise, atavistic structures appear in some humans at birth (coccygeal tails in newborns) and in some animals (whales and dolphins born with legs, horses with extra toes).
Then there are the vestiges of the evolutionary past found in the normal anatomy of mature humans (wisdom teeth, tailbone, appendix). Other vestiges are consistently exhibited in certain animals (the dewclaw on dogs, hollow bones and wings on flightless birds, fingernails on the flippers of manatees, rudimentary leg bones inside the bodies of most pythons and some whales, and vestigial legs on some lizards that look more like snakes).
These structures are all consistent with the evolutionary history of the organisms involved.
What is particularly instructive about this chapter, besides the wide array of evidence Glass marshals, is that his many examples end up clarifying the meaning of “natural selection,” in contrast to the discredited Lamarckian notion of the “inheritance of acquired characteristics.” So this chapter is both great at explaining how evolution works and marshaling observational evidence for evolution that is consistent with what we know from paleontology and genetics.
Chapter 8: “The History of Life.” Having claimed that chapter 7 was worth the price of the book, I have to admit that I found chapter 8 (an overview of the evolution of life on earth) to be fascinating, especially the discussion of hominid evolution, which is a particular interest of mine.
Beginning with the formation of the earth (along with our solar system) some 4.6 billion years ago, Glass moves step-by-step through the development of simple single-celled organism (3.6 billion years ago), more complex single-celled organisms (1.4 billion years ago), the so-called “Cambrian explosion” (over 500 million years ago), the development and extinctions of more complex animals (first in the water, then on the land, including, of course, dinosaurs), right up to pre-human hominids (the oldest fossil hominid skull being about 6 million years old). While the chapter is clearly selective (it is a non-technical sketch for those not acquainted with the science), Glass gives us a bit more detail about the latest paleontological evidence for what seem to be twelve distinct types of humans known from the fossil record–the oldest dating back almost two million years, the latest being the relative newcomer, homo sapiens.
As Glass notes, the fossil record is certainly not complete. It’s been estimated that only one bone in a billion gets fossilized; others have estimated that only one in a hundred thousand species have been found. And yet existing fossils tells us a compelling tale of the history of life on earth.
Chapter 9: “The Tree of Life.” As a follow-up to chapter 8, Glass then explains (in somewhat brief compass) the basics of the classification system scientists use for living organisms, including the contribution of genetics to this understanding.
All in all, Parts 2 and 3 of this book are a superb overview for non-experts who want to understand the current state of the science on biological evolution. Glass has done us (especially Christians, who are his primary audience) a great service in this respect.
In my next two posts I’ll address the non-scientific aspects of the book, including Part 4: The Politics of Evolution (which was quite illuminating) and Part 1: Christianity and Evolution (which I didn’t find particularly satisfying). I’ll use the latter as a springboard to explore better ways to think theologically about evolution.