The concept of a "selfish gene" has made its way into the popular and semi-popular press, and because of this has provoked many discussions in ethical circles as well as in the area known as evolutionary psychology. Some of these discussions attempt to set the record straight on just what biologists mean when they talk about selfish genes. This book could be considered part of these discussions, and offers the reader a fascinating account of the science behind what the authors call selfish genetic elements. The book however is not written for the popular audience, but instead assumes a strong background in genetics. However the authors have included a terminology section in the back of the book to assist non-experts in genetics (such as this reviewer). The authors are very careful to make distinctions between what is known about selfish genes and what constitutes speculation. For readers who still need more discussion over and above what the book gives, there is an extensive list of references included. In addition, the authors include a very detailed summary of the book in the last chapter.
Every page of this book is filled with interesting insights, and many questions are answered as well as raised. Some of the questions that this reviewer found interesting include:
1. What are the natures of genomic exclusion systems wherein chromosomes are discarded from one parent and transmit only those from the other parent?
2. Why did paternal genome loss (PGL) evolve? Was it because of bacterial endosymbionts manipulating the chromosomes of their hosts, and if so, what evidence is there for this? How common is PGL?
3. What is hybridogenesis and in what species does it occur? Why did it evolve?
4. Androgenesis is the loss of the maternal genome. How common is it and how risky is it for the species in which it occurs?
5. The chromosomal system of the fungus gnat is described in the book as the most complex of any organism. What is the nature of this complexity? And why do these gnats need such a complicated system?
6. Are there any species whose genome can benefit from outbreeding with closely related species?
7. How does a length of DNA distort its own transmission?
8. How fast do selfish genetic elements spread?
9. Can techniques from genetic engineering, such as transgenic strategies, suppress the spread of selfish genetic elements?
10. Can the spread of selfish genetic elements be suppressed by recombination?
11. What is the nature of segregation disorder? How did it evolve?
12. The t haplotype in mice spans one third of chromosome 17, making it very large. How is such a large section of DNA inherited? Why does it show drive in only one sex and what are the consequences of this?
13. What effects do selfish genetic elements have on the phenotype of the organism in which they occur?
14. What similarities are there between selfish genetic elements in terms of their genetic structure?
15. Can selfish genetic elements be created using techniques from genetic engineering?
16. What is the nature of maternal-effect dominant embryonic arrest (Medea)?
17. Why are maternal-effect killers more common than gamete killers?
18. Gametophyte factors are genes that act in the styles of plants in order to kill pollen in which they are absent. Why are they so prevalent?
19. Do killer X chromosomes ever cause species extinction?
20. In what species do killer Y-chromosomes occur?
21. Why is Y drive expected to cause more population extinction than X drive?
22. Why are killer sex chromosomes more prevalent in insects (dipterans) than mammals?
23. Why did meiotic sex chromosome inactivation evolve?
24. What is the nature of genomic imprinting? Why did it evolve?
25. Can genetic memory extend back for more than one generation?
26. Why do adult male chimeric mice possessing a large amount of parthenogenetic cells in their brains very aggressive towards other males?
27. Can imprinted genes affect brain function, and if so, what are the consequences of this for the organism?
28. Why do selfish mitochondrial genomes have a replication advantage over normal mitochondrial genomes in selection within organisms?
29. What evidence is there that uniparental inheritance evolved to prevent the spread of selfish mitochondria?
30. Why did doubly uniparental inheritance (DUI) evolve in freshwater mussels?
31. Does DUI lead to more recombination, and therefore to more effective evolution?
32. What is cytoplasmic male sterility (CMS) and how is it used in hybrid seed production in plants?
33. Homing endonuclease genes (HEG) can transfer between species. What advantages does this have for the persistence of these genes?
34. How are artificial HEGs used in genetic engineering?
35. Can selfish genetic elements be used to cure human diseases?
36. Transposable elements are described as being the most prevalent of the selfish genetic elements. What different types of transposable elements are there?
37. What are helitrons?
38. Why do DNA transposons persist for so long?
39. What evidence is there for the horizontal transmission of DNA transposons?
40. Are there any beneficial consequences of transposable element inserts?
41. About one-half of the mammalian genome is composed of transposable elements. What advantages does the genome have in possessing such a large number of transposable elements?
42. Large genomes have been shown to reduce the number of cells per unit brain size and the number of interconnections between them. What is the connection, if any, between selfish genetic elements and the intelligence of the organism?
43. Through more research of the type described in many parts of this book, will it be shown that every organism has some type of selfish genetic element? If some species lack selfish genetic elements, why do they have this property and what caused these elements to be suppressed in the course of evolution?
44. Do selfish genetic elements have any connection with determining sexual preferences in humans?
45. Can selfish genetic elements be induced by environmental or external pressures?
on May 27, 2007
Burt and Trivers have produced an encylopedic compilation of examples of selfish genetic elements. There is a wealth of information available in this book, but you have to work hard to wade through the authors' ambiguous wording, contradictory phrasing, utterly confusing tables and figures, and almost complete lack of follow-through on any of their ideas. This book is not for the general public. I read it with a group of professors and graduate students who focus on evolution, and we had a hard time getting through it.
Despite the problems with the book, I recommend it to anyone with a serious interest in this subject area. It's a great reference and source of ideas. It also provides a solid overview of what research has already been done and what remains to be conducted. Furthermore, it has some amazing examples of organisms with truly bizarre natural histories; those parts of the book are fascinating to read.
Overall, I'd say if you really think you'd be interested in this topic, buy the book. But be prepared to work hard while reading it, and expect to be frustrated with it on a regular basis.
on December 29, 2005
What a long strange trip it's been for Robert Trivers, who during the early 1970s was one of the most brilliant evolutionary theorists ever. Now, I'm happy to see he's back with a magisterial tome co-written with Austin Burt on "selfish genetic elements" that don't raise the Darwinian fitness of the organism as a whole, just of themselves, often at the expense of the overall life form.
As a crude analogy for what Trivers and Burt are describing, think of the Enron Corporation. Traditional economic theory, which bears many resemblances to traditional evolutionary theory, would conceive of that firm as an entity that competes against other firms for the good of its shareholders. Unfortunately, old fashioned economics did not prove an adequate guide to Enron's behavior because the firm was infested with "selfish managerial elements," executives who were looting the firm for their own selfish benefit.
Of course, developing a better understanding of Enron-like situations does not "refute" economics, just adds to its sophistication. Similarly, Trivers and Burt are adding to the explanatory power of Darwinism. Just as firms struggle to develop carrots such as stock options to to align individual managers' interests with the interests of the stockholders, and sticks to prevent embezzlement, organisms evolve responses to selfish genetic elements.
One quibble. I realize that this horse long ago left the barn, but Richard Dawkins' term "selfish gene" has caused a lot of misunderstanding among the public over the years. A better term might be "dynastic gene."
My Enron analogy can be misleading because what the "selfish genetic elements" are doing is not making themselves rich, per se, but contriving for copies of themselves to proliferate. The closest business analogy might be a firm damaged by nepotism, such as Wang Computer in the 1980s, where managers appoints their feckless relatives to important positions.
on December 4, 2007
I was EXTREMELY lucky to have taken an one-on-one course with Dr. Trivers and I must say that he's the first to both praise and point out pitfalls in this book.
While being the most definitive guide to the subject out there, it can at times be very technical and hard to understand. Especially the chapters on genomic imprinting, exclusion (for me). However, I feel that this complexity only arises from the fact that the chapters are written out with as much detail as possible (as you will be able to see from the pages and pages of references in the bibliography).
Each chapter comes with its relevant illustrations, with the figures for mechanisms of selfish drive being the most important ones. Figures showing data can be complicated and at times, he even CALLED the authors while I was in class to answer a question I had.
The book is very well organized with the authors laying out the background followed by each chapter dedicated to a specialized genetic element. Work on B chromosomes, genetic imprinting, sex chromosome and autosomal drive are particularly well written with implications and mechanisms detailed out with the latest (uptil time of publication) information.
The only think lacking that I thought from the book was a better and more thorough summary chapter at the end, but then again I'm just being picky. With so much detail on the each topic within the chapter, the summary is pretty well written out.
Finally, I want to add that this is a book on evolution and the evolution and role of selfish genetic elements in shaping the evolution of host genomes (if it happens at all). It can get technical but the subject is never introduced in any form of education that I have experienced so the concepts were relatively new to me. This book will be a difficult read for the average reader not well versed with some concepts in biology as kin-ship theory or "degrees of relatedness". But if you want a solid and detailed description of the world of selfish elements, this is the book !
When Richard Dawkins published "The Selfish Gene" two decades ago, today one wonders if he had any inkling then of what his idea launched. The din of protest over the concept was loud and vituperous. Yet, a generation of research has proven him more correct than anybody imagined then. In this work, researchers Trivers and Burt have summarized the wealth of information derived over the years. Genes do far more, it seems, than simply act to replicate themselves. They intrude, divert, even kill parts of the genome to provide themselves with any and every opportunity to endure down the generations. Some genes wish to protect the genome, while others seek to damage it - both for selfish ends. In this impressive and detailed overview, we learn which types of genes strive for dominance and why.
Your body is a mosaic of cell collections. These can be winnowed down to two basic types - somatic cells and sex cells. This is essentially the case for all plants and animals, down to such simple types as protozoa. The sex cells, the gametes, have the role of carrying the messages that will build the new body of somatic cells and containing new gametes. None of this process is as straightforward as was formerly thought. Within every body, conflicts rage as genes contend for favoured conditions. The genome, that fundamental instruction mechanism, is the arena where various genes, some with a long evolutionary history, insert themselves to provide a different recipe for life. The successful ones have what the authors describe as "drive". These genetic elements contrive to be transmitted to a disproportionate fraction of the organism's progeny" - a victory over the 50-50 Mendelian ratio taught in introductory biology classes.
The authors try to follow these actions from the molecular to the evolutionary, but as they accept, the full lines of evidence either have not, or cannot be tracked completely. They provide a brief history of research in selfish gene elements, then go on to expand on this with more recent work. Their account addresses such questions as how does the selfish element accomplish its ends, when and how did it likely originate, how far does it spread and how quickly, does it produce co-adaptations, and what does it do to the host and its lineage? The twists and turns of these elements vary from mundane parasitics who use the host only to replicate to killers which can modify sex ratios. The classifications they use permit the book to be read in any order, with the reader's interests easily covered by their chapter organisation.
Selfish genes may be readily identified in many cases by their tendency to locate on the centromeres of a chromosome. This is a critical area, hence protected from intrusion. Many of the groups, which may contain hundreds of genes, once found the means to enter this zone. Meiosis and cell division convey these groups through the process of reproduction and body construction, thus allowing them to proliferate easily. Of the ten topical areas, one of the more fascinating is that of gene imprinting. Unlike the "imprinting" of newborn creatures choosing the first moving object it sees as its parent, gene imprinting is parent-specific gene expression. Either the male or female parent may contain such genes, but in either circumstance, once established, a dominance will result that is passed to future generations. In many cases that imprinting will drive the sex of the embryo, usually favouring female progeny over male. Is it this sort of gene structure that contributed to the change from solitary insects such as the ancestral wasps to the social forms, including bees, that we see today? Is the formation of our own bodies, which are but groupings of specialised cells, the result of selfish genes that have learned to work together? How does it all hold together?
Clearly, as the authors point out, it is the sexual species where selfish gene elements have made their greatest successes. Some of them may find and invade the gamete cells and drive how the resulting union follows. In a few cases, the intruders have developed ways of ejecting unwanted segments from the gametes or the fertilised egg itself. With these methods available, they may even kill embryos of multiple-birth species, leaving only those individuals who carry their coding. With meticulous care, the authors describe those about which something is known, while pointing to areas needing dedicated research. Inevitably, the issue of stem cell research looms large in their proposals.
While the book is well-organised, effectively illustrated, and containing a useful glossary, it is the references that give it a firm underpinning. Burt and Trivers have made contributions of their own, but the nearly one hundred pages of source material are an invaluable resource. The authors have gone so far as to expand the subject areas in a special section to aid searching for topics. An unequalled work, this book will long endure - to be supplanted only by the ongoing investigations they call for. [stephen a. haines - Ottawa, Canada]