Endless Forms Most Beautiful

Title: Endless Forms Most Beautiful

Author: Sean B Carroll

Publisher: Quercus 2011 (First published 2006)

ISBN: 978-1-84916-048-3

Pages: 305

Sean B Carroll is a big popularizer of science, having the authorship of many extremely successful works to his credit. Two of them, Remarkable Creatures and The Making of the Fittest has already been reviewed in this blog earlier. Those books prove to be the cornerstones of how science could be brought in to the lives of ordinary people. Though this book is not as appealing as the above mentioned two, Carroll’s reputation and sincerety of expression places it in a special niche. This volume is owed more to the professional work of Carroll, being the subject matter of his own research, rather than to his superb communication skills. The title find its source in a fine sentence by Charles Darwin in his Origin of Species, asking his readers to see the grandeur in his new vision of nature, in how from so simple a beginning, endless forms most beautiful have been, and are being evolved. Carroll attempts to figure out the embryological development which attributes such an infinite variety to animals.

Though Darwin’s books, Origin of Species (1859) and Descent of Man (1871) put evolution firmly on the scientific mind, nobody was sure of how the evolutionary mechanism operated – how the changes actually came about. In 1900, the field split into embryology, heredity and evolution, each going their separate ways, denying an integrated approach for the world. Development of a fertilized egg to a full fledged animal required careful study, but it gained acceptance and recognition only in the 1970s. Since Watson and Crick’s discovery of the structure of DNA, microbiology gradually developed to full bloom in the 1980s when genes were studied and the machinery through which it affected development of body parts, using the ubiquitous fruit fly as the model. This overturned conventional wisdom that various animals proceed by different developmental mechanisms. The surprise was that the same genes which were responsible for body parts in various animals were also responsible for quite different body parts in some other animals or even in different regions of the same animal. This led to the growth of a new discipline, seeking comparison of developmental genes between species, named Evolutionary Developmental Biology, or Evo Devo for short.

The fruit fly and humans share 29000 genes, of which 1.5% codes for production of 25,000 proteins in the body. So where is the difference in form comes in? 3% of the DNA is regulatory in nature, which determines when and where a specific organ or trait is to be switched on. Animals share modular structures repeating in varying numbers and kinds. A basic pattern can be discerned in these serial homologs. An example is the vertebra in chordates, termed cervical (neck), thoracic and others, which is repeated in many species. There are hundreds of such links in snakes, while there is only 33 in humans. The fore- and hind-limbs also share the same prototype in a bewildering range of animals. The serial homologs tend toward reduction in number in later life forms, a law found by Samuel Williston. However, in biology, there is hardly any law which is not violated at least once by a little known organism.

Research on fruit flies generated exciting conclusions. Great similarity in the body building genes was noticed among them. Genes for specific functions like formation of eyes were found. The most exciting part was that the gene was exactly similar in mice, making eyes. When a mouse eye gene was transferred to fruit fly…..it created an eye, but not a mouse eye. A normal eye of the fruit fly was developed using the mouse gene. It showed that expression of a gene is strongly dependent on the context. Also, the same DNA is present in all cells (except reproductive organs), but the switching on of specific parts is different for a variety of organs. This action is controlled by a regulatory portion of DNA which contain switches (chemicals which attach to DNA) that manage the operation of genetic coding. These switches act singly or in digital combination for complex operations. Great bursts in animal diversity were shaped by evolutionary changes in genetic switches.

Carroll correlates the study of genes and genetic switching mechanisms to explain the surge in life forms observed around 500 million years ago in the Cambrian era. This sudden swell is termed the Cambrian Explosion. What was the cause of this? Not the development of new genes, as the genetic tool kit was almost assembled in its present form much before in pre-Cambrian life forms. However, we see shifting of proteins and switches in DNA during this period. This led to larger, complex life forms to evolve. Biologists were sometimes confused at the origin and evolution of similar looking, but different body parts or different looking but similar in origin body parts. This trouble is abundantly solved by Evo Devo, by pinpointing the genes responsible for development of the parts and thus obtaining hints about the origins.

Genes acquire new abilities over time depending on the selection pressure on the animal. The eye spots on butterfly wings provide a very good case in point. These are essential for the survival of the creature, as predators are either turned off by ferocious looking spots, or attracted to it, thereby the main body of the butterfly escaping unhurt. Analysis of genes forming these patterns imply that genes responsible for making limbs from the body trunk (termed distal-less) are also in charge of the formation of spots when expressed on the wings! When those genes are switched on by the regulatory machinery on wings, it produces a distinct colouration, rather than limbs. This logic is extendable to humans as well. Homo species began divergence from other hominids around 2.3 million years, marked by the higher brain sizes. Climate change is suggested as a cause, resulting in quick cooling of the planet. Rain forests in Africa shrunk, forcing the hominids to venture into expanding savannahs. Modern man was evolved around 200,000 years ago, but the Neanderthals separated much before. There are no mixing of the genes of these two human species. A curious observation of human genome is that it is 98.8% similar to a chimpanzee genome. The author puts this in clear perspective. There are about 3 billion base pairs in a human DNA, out of which 1.2% (the difference with chimps) constitutes about 36 million base pairs, which is huge! Two mutated genes between us and apes are MYH16, which reduces size of jaw musculature and FOXP2, helping in speech and language processing. It is to be remembered these genes are also found in other animals, but in mutated forms. Carroll specifically asserts that there is no single gene or change which resulted in the enormous differences between humans and apes.

The book is endowed with a great treasure of illustrations pointing out the finer nuances conveyed in text. The supremely knowledgable intellect of Carroll is apparent in every chapter, probing behind every single detail until it is clarified beyond an iota of vagueness. As the book includes subject matter of the author’s own research, a scholarly treatment is guaranteed and provided. There is also a good discussion about the religious concept of creation vis-à-vis evolution. The urgent need for modern society to implant the concepts of evolution to children, who are the promises of the future is very important. When the leaders of religious denominations are slowly veering around towards acceptance of evolution, at least in principle, time should not be lost in accepting it wholeheartedly. There are opponents on both sides of the divide, like the scientist Michael Behe opposing evolution (though with improper application of newly realized ideas) and theologians like John Haught, who are supporting it.

Unfortunately, the book is not enjoyable as the previous two titles from the same author mentioned above. This book uses complicated terminology and is unappealing to the ordinary reader. Sentences like “chordin is produced by cells around the dorsal lip of the blastopore” (p.99) does not help poor mortals like me. Regrettably, for once, Carroll seems to have rode in the path of scientific reporting instead of popular science. For biologists, or for those who have a background on the field, it may prove to be exceedingly worthwhile, but the targeted audience is not about to benefit from it. Even though the author claims that several ahas and wows are forthcoming as the readers move along the chapters, we can only surmise that the claim is a small embellishment on the actual state of being.

The book is strongly recommended for persons having a good background in biology and genetics.

Rating: 2 Star