THE MAKING OF THE FITTEST, DNA AND THE ULTIMATE FORENSIC RECORD OF EVOLUTION by Sean B. Carroll. New York: W. W. Norton, 2006. $25.95 hardcover; 301 pp; 15 page index; 16 pages of sources for further reading. The book is illustrated throughout with black & white artwork, drawings and other illustrations. There are 8 pages of color plates.
Carroll has delivered an excellent follow-up to his 2005 book, Endless Forms Most Beautiful, The New Science of Evo Devo and the Making of the Animal Kingdom that I have reviewed here previously. Just to be clear, this is not a re-hash of the previous work. There is much new information presented in a less technical manner.
I couldn't help but be impressed with the title of the preface of The Making of the Fittest: "Beyond Any Reasonable Doubt." In the epigraph Carroll has appropriately quoted Aldous Huxley: "Facts do not cease to exist because they are ignored" (13). The preface title refers to Carroll's recount of DNA evidence freeing an innocent man after 16 years in prison for a crime he did not commit. In fact, this title as well as the Huxley quote are pointed at those who would deny the facts of evolution. Or as he aptly asserts: "The body of new evidence . . . clinches the case for biological evolution as the basis for life's diversity, beyond any reasonable doubt" (17).
Our first look at the evidence comes in the introduction wherein Carroll discusses the strange icefish of the Antarctic. This group of fishes has evolved some very unique features for survival including proteins that prevent their blood from freezing and the elimination of hemoglobin as a means of oxygen transport in the blood. In well documented examples Carroll explains the step-wise evolutionary changes in the DNA code that allowed these fish to survive the frigid water of the Antarctic. The important fact to note here is that these fish evolved from a warmer water group through alteration of DNA and the obsolescence of unused DNA. The time line presented shows that these change occurred over 25 to 30 million years and were triggered by environmental changes driven by plate tectonics (28). We are reminded by Carroll that, ". . .natural selection [Darwinian Evolution] acts only on what is useful for the moment. It cannot preserve what is no longer used, and it cannot predict what will be needed in the future" (38).
The Making of the Fittest contains a simple lesson in the logical probability of evolution in the second chapter: "The Everyday Math of Evolution." Carroll utilizes numerous examples including some actual mathematical proofs not unlike those from Endless Forms Most Beautiful. From a technical standpoint the treatment is not all that difficult. Some of the examples of probability are as common as lottery chances or the chances of being bitten by a dog.
Microbiologist Tom Brock's discovery of hyperthermophiles in the hot springs of Yellowstone led to a number of important discoveries about DNA and evolution according to Carroll. Originally classified as bacteria, the hyperthermophiles have since been re-classified as archaens, a third form of life in addition to the prokaryotes and eukaryotes. Most important to evolutionary biology was the discovery of immortal genes as Carroll terms them. These bits of genetic material were found in the hot springs archaens as well as all eukaryotes, including humans, thus making them ancestral to all other life forms. He goes on to explain the conservatism of evolution with this beginning. All genetic material is subject to random mutation. Mutations harmful to an organism are lost as the organism does not survive or reproduce. Genes that are essential to life are conserved through the success of the organism in reproduction. In this way, immortal genes have been conserved for over 2 billion years.
Carroll provides the reader with a lesson in reading DNA. This is not a difficult account and if more people understood it, there would be fewer misconceptions and falsehoods disseminated about evolution. In further explanation of the conservative nature of evolution, Carroll tells more about how DNA works in forming proteins. It is interesting to learn that mutations of genes can appear that are different from the original yet still encode for the production of the same amino acid within a protein. In this way the mutation will not harm the organism. These are termed synonymous mutations. On the other side are the nonsynonymous mutations that change the amino acid in the coded protein - potentially harmful changes. Carroll does a little math again to show that statistically over time, the ratio of nonsynonymous to synonymous mutations should be 3:1. In reality it is 1:3 meaning that the favorable or non-harmful changes are conserved over time. Carroll concludes that Natural Selection is the only process that can explain this purifying phenomena. He emphasizes, "Realize that an immortal letter [T, C, G, A of the DNA code] in a protein sequence has experienced mutation again and again, in uncountable numbers of individuals, in millions of species, over billions of years, but that all of these mutations have been purged by selection over and over again" (83).
Another bit of fascinating genetic matter pertains to LINES and SINES - long interspersed elements and short interspersed elements. These are sequences of junk DNA in an organism's genome that no longer have a function because of mutation and are not detrimental to survival. Because of this condition, these sequences do not get purged from the genome and thus become useful guides to mapping evolutionary descent. Carroll uses LINES and SINES to map the fascinating evolution of color vision in "Making the New from the Old."
Pursuing the genetics of color vision further in the next chapter we meet fossil genes. Carroll explains, "We have seen that shifts in lifestyles . . .involve the formation and fine-tuning of new genes. Here we will see that such shifts also leave their traces in the form of genes whose use and function have been abandoned" (119). He explains that human survival and its reliance on color vision has caused us to lose the heightened senses of smell and hearing that color-blind animals need to survive. Carroll points out that the quantity of fossilized genes normally associated with a highly developed sense of smell is much higher in animals with color vision. In summarizing the implications of his discussion of fossil genes Carroll emphasizes an important principle regarding evolution: "Because decaying genes [fossil genes, per se] generally accumulate multiple defects [over time], their inactivation cannot be easily reversed." And, "Once gone, these functions will not return" (132). The long range implication of this principle can be understood with the example of the icefish. A major rise in the water temperature of the Antarctic will doom the icefish to extinction as the genetic material is no longer available to re-evolve for warmer conditions. Carroll asserts that, "Gene fossilization and loss imposes constraints on the future direction of evolution in lineages" (132).
Further examples of evolution at work are presented to illustrate that similar environmental pressures can lead to the same evolutionary adaptation in different species. Carroll uses color vision in new world and old world monkeys to illustrate his point. Full color vision has evolved in new world howler monkeys that have similar habits to old world monkeys with color vision. The astounding fact that Carroll shares is that this adaptation occurred half a world apart and about 25 million years distant in time.
In the chapter "Seeing and Believing" Carroll delves into the importance of science to our world. In a fascinating recollection of Lysenkoism in the USSR Carroll skillfully shows the dangers of rejecting scientific methods for political or social reasons. Lysenko rejected genetics and the reality of DNA studies. A powerful political operative with minimal education, Lysenko set back Soviet science at least 25 years. His illogical directives to improve crop yields came close to destroying Soviet agriculture.
In further discussions along the same lines, chiropractors are introduced as an example of a group in denial of modern medical science. The discussion does not revolve around spinal cracking to cure back pain but rather the denial of the effectiveness of vaccines in preventing illness. Carroll lists "six of the common arguments or tactics used [by chiropractors] against vaccination" (231-232):
Carroll adds additional explanation to these which I have omitted for the sake of space.
But why bring these up? These are the same strategies and techniques used by creationists to refute evolution. In brief, Carroll's approach to the subject begins with a bit of the history of Intelligent Design with its roots in William Palley's concepts 200 years ago. This leads into examples of the modern movement which Carroll, like any competent scientist, easily refutes with scientific facts. Quotes are provided from Christian theologians in support of evolution who have no difficulty with its coexistence with Christianity.
The final chapter takes a slightly different look at future evolution than most books covering similar ground. Carroll presents specific examples of what he calls "Unnatural Selection" (254). Most of us understand the selective breeding programs used for hundreds of years to produce better or more desirable animals. This use of artificial selection includes purposes such as producing faster race horses, breeding dogs with more perfect form or cattle and pigs that are leaner or larger, etc. Breeders take the animals with the desired traits and breed them and then select the best of the offspring to continue the breeding program. Over time and repeated breeding the desired result is reached. This same principal is working against nature's ability to produce the fittest in some wild populations through natural selection. A number of examples are given but one should suffice here. Commercial fishing requires that only fish over a certain size be retained. Thus, humans are artificially culling the biggest most fit fish from wild breeding populations. The long term result is that the fish are evolving to smaller sizes through this unnatural selection process. Carroll provides a more detailed discussion of this regarding the Atlantic Cod. Further examples are also delivered. The final lesson illustrated here is that of the impact of humans on wild populations and the long term implications of this unnatural artificial selection.
Readability - College level readers, scientific background helpful but not necessary.
On the Upside - A worthy supplement to Carroll's 2005 book, Endless Forms Most Beautiful, The New Science of Evo Devo and the Making of the Animal Kingdom with additional examples in an even easier to understand presentation.
On the Downside - There is still a bit of technicality to some of the discussions but I do not think this book should be beyond the grasp of intelligent readers in the targeted audience.
Overall Rating - Highly recommended, especially to those with questions about the fact of evolution.