October 2009
How a Lancet Fluke Comes to Commandeer an Ant, Perhaps
This is an essay I wrote for a science course which describes a plausible natural selection scenario for how a parasitic lancet fluke evolves to be capable of a neurochemical 'mind control' of an ant host. I am not a professional scientist, so I claim no expertise on these subjects. The post to which I am responding was made by a fellow student, and was a response to an earlier post I made in a discussion of environment and responsibility. Here, I am countering a statement that my references to the lancet fluke (more info here: http://www.ted.com/talks/dan_dennett_on_dangerous_memes.html ) and the fish-tongue-eating-crustacean known as Cymothoa exigua (more info: http://www.youtube.com/watch?v=vAlEfrwr8aU ), which he refers to as "two horrifying examples", demonstrate that "nature [is] out of balance, or is a battle of Good-vs.-Evil? Perhaps even an unsettled balance of natural selection, due to our negligence of humans disrupting nature's preservation?." My rebuttal follows, edited for typos, and with off-topic text removed.
As to the 'two horrifying examples', I would argue that neither example is one of an out-of-balance nature nor a battle of good-vs-evil. Neither appears to be affected at all by human activity. The lancet fluke, for instance, is not alone in its ability to take over another creature in some useful way, there are literally countless examples like this one. Nature simply favors any ability which gives a member of the species an advantage over others of its species, and by extension, sees advantages in species which are generally better adapted than other species competing for the same resources -- which should not be confused with group selection, a concept which is controversial and outside the mainstream in biology, though there are absolutely well-respected biologists holding positions in favor of group selection, but I digress.
Let me create a hypothetical progression of lancet fluke behavior. This is purely a mind exercise with few details and backed only by my readings in biology and behavior, but I think it serves us well and presents a plausible pathway, even if incorrect and flawed in real details. Also note that when I use singular terms, such as 'fluke', I'm referring to a statistically signficant set of flukes acting in some way or possessing some characteristic, and am not suggesting that a single specific fluke was responsible for each stage.
The lancet fluke, like all parasites, requires a host, and we know that the first cycle in the fluke's existence takes place in the body of a snail ("Dicrocoelium dendriticum"). Originally, it is easy to imagine a life cycle that saw the fluke exist completely within the snail, and there are countless parasites for which this model is quite typical.
However, natural selection will favor any genetic change which gives an advantage over other members of the species, even if that edge is very small. Imagine, then that the snail spits up a slime ball which contains living lancet flukes. (Snails do in fact do this and theory holds that this is a likely vector taking the lancet fluke into the ant's body ("Dicrocoelium dendriticum")). The ant, which either physically contacts or otherwise ingests the slime ball, becomes a secondary host for any members of the fluke species which can survive and reproduce during this second stage. Initially, this was probably only a bare few, but enough flukes possessed the ability to live in the snail, survive in the slime ball, and then live in the ant's body that this ability was strongly favored by natural selection to the exclusion of the flukes which could not do so. ***
So, now we have a fluke which has evolved a survival trick which extends its life and offers it an advantage which allows it to reproduce and pass down genes which also tend to favor this trick. Again, this isn't anything inherently good or bad, and certainly didn't require human intervention, this is really the way natural selection works. It is cold, without emotion, and without forethought. It is simply a process which rewards (without intent) any advantage to survival possessed in the genes of a replicating entity. The fluke which survived the slime ball stage and took advantage of the ant-body stage was more likely to reproduce than one which died in the ant's body, and given that this survival had a large reliance on genetics, was also more likely to produce offspring which could likewise take advantage of the ant-body stage.
From there, you can imagine that ants are regularly eaten by ruminants such as cows and sheep. Ants crawl all over grass and other delicacies enjoyed by grazers, so it is inevitable that large numbers are swallowed by such beasts. Natural selection again gives pressure: if any fluke was capable of surviving in the gut of a cow, that fluke was again more likely to reproduce offspring capable of doing the same.
So at this point, we have a fluke which has gone from living solely in the belly of snail to a naturally-selected subset that was capable of surviving the snail coughing it up in a slime ball, being swallowed by an ant, and then being swallowed by a cow. We haven't yet gotten to the 'mind control' ability, but that comes next.
Given that this fluke has now a genetic advantage, however small, over other flukes and over other competing species, it may appear well off. But natural selection does not offer species many opportunities to rest. Likely, the snail, ant, and cow bodies have experienced pressure to be able to survive this invasion. Any fluke infestation which killed its host too soon probably didn't live long enough to reproduce (and likewise, neither did the host). This fatality-condition is shared by both fluke and host genes. Any combination which resulted in death for the pre-reproductive fluke or host whittled down the combination of fluke and host genes which were selected for, and only those flukes with genes which allowed the host to survive and reproduce while also allowing itself to suvive and reproduce enjoyed significant advantage over those which did not, in terms of leaving offspring.
Imagine, then, that the ant develops a set of defenses against the fluke. Perhaps natural selection favors ants which are less likely to position themselves somewhere they might be grazed upon. Perhaps behaviors which result in staying low to the ground or holding along the edge of fields (rather than in the middle of them) would find these ants less likely to be eaten. Naturally, this is bad news for the fluke which, by now, rather expects to get on with its third stage of life in the belly of the cow.
So here comes one of the amazing parts of natural selection: its ability to derive complex and apparently abstract behavior out of a few basic rules. Differential survival means that any advantage, no matter how small, is enough for the process of natural selection to reward these small advantages with the ability to leave more offspring. Imagine that a line of flukes possess a mutation which allows it to secrete a chemical trigger to the ant which prevents the (newly developed, in evolutionary time) behavior which has protected the ant from being eaten as often by cows. We don't need to posit that there was intent here, perhaps various mutations in the fluke had occurred which generated different chemical excretions. We only care hear about the one that actually affected the behavior of the ant in a way advantageous to the fluke.
Suddenly, the fluke has pressured the ant to change its behavior, and the ant is now more likely to return to its original behavior, or demonstrate a new behavior, which left it more likely to be eaten by a cow. This sort of chemical triggering is well-documented and I won't go into details here, except to mention that bacterial and viral infections use all manor of chemical triggers to affect a myriad of things. Again, there doesn't need to believe this is done with intent. For every thousand mutations which change the way chemicals are produced by a parasite, perhaps only one will ever have anything other than a neutral (or negative) effect on its host. This variety, between parasites which possess this one-in-a-thousand mutation and those which do not, is all natural selection needs to differentiate between them. If the chemical allowed its possessors to survive and reproduce more frequently, it is straightforward to see that this would be an advantage that future generations were more likely to possess. The fluke never needed to plan this devious trick, it was just along for the ride built by its own (marginally, but significantly) superior genes and subjected to pressure from natural selection.
The last step here is just an extension of the previous. Once a chemical trigger is in place which advantaged flukes being able to produce it, it is just a short distance to chemical triggers which directed the ant to repeatedly climb the blade of grass. The process is the same as above, so I won't repeat it here.
And so, we've looked at an entirely plausible explanation for how natural selection would deliver a lancet fluke capable of 'mind control' over an ant, living originally only in the belly of a snail, but evolving a complicated adaptation which saw it survive several stages of life in hosts from snail to ant to cow. I'll not go into the tongue-eating-crustacean situation since it too would have gone through a process mirroring this one.
Again, there is no need to posit intent or 'good vs bad', this is just the way natural selection works. Harsh, cold, or heartless, perhaps, but those really are human concepts which we anthropically apply to the world around us.
I'll not get into the 'reason for human existence' since that is a teleological subject probably best left alone here (and to avoid any heated emotions from all of us who have our beliefs or lack-there-of). I am, however, completely in agreement with you about reducing the toxins we dump, and I hope that rational and reasonable people, maybe even ourselves, can study and implement strategies which do just that.
References:
Wikipedia. (n.d.) Wikipedia - Dicrocoelium dendriticum. Retrieved on October 2, 2009 from http://en.wikipedia.org/wiki/Dicrocoelium_dendriticum
*** as a digression, natural selection doesn't necessarily produce an all or nothing differential survival, as Darwin himself explained in On the Origin of Species. The hypothetical situation described above might find that one species of lancet fluke, which evolved from the original species found only in snails, evolved adaptations which required life cycles in both snail and ant, while a second species evolved, also from the original species, which did not. This process works again at the point in which the fluke moved into a third stage in a ruminant body. Differential selection is a manner in which species are not only selected for, but the fuels the divergence of species from their common ancestry.
Book Review: The Greatest Show on Earth: The Evidence for Evolution by Richard Dawkins
(out of 5 stars)
There are few authors alive capable of weaving wonder and authority into popular science writing better than Richard Dawkins, and in his newest book The Greatest Show on Earth: The Evidence for Evolution, released in September, 2009, he has shown that he is still the master of popular biology. Following a narrative that works much as the one employed by Charles Darwin in On the Origin of Species (and frequently mentioning Darwin), Dawkins presents a comprehensive look at the modern state of evolutionary theory, and more specifically, the evidence which proves it is true beyond any serious doubt.
I had read many Dawkins books prior to Greatest Show, including his biology and science-oriented books The Selfish Gene, The Extended Phenotype, Unweaving the Rainbow, The Blind Watchmaker, and River Out of Eden. I have not yet read The Ancestors Tale (which I understand is Dawkins most comprehensive biological work, nor have I read Climbing Mount Improbable (which Dawkins has stated is his own favorite work), both of which I own but have yet to get to. So, my review is in light of these experiences (or lack thereof).
The first couple of chapters are for softening up any hesistant readers and convincing new learners that evolution is not only realistic, it can be observed around us in a myriad of ways, including the comparisons between natural selection and the artificial selection practiced by human animal and plant breeders.
Following this intro, Dawkins lays down the tool kit and shows how Neo-Darwinian theory knows how to trust estimated dates, looking at the various chemical clocks available.
The chapter titled "Before Our Very Eyes" was the most enjoyable and enlightening for me, personally, as the reader has described for him/her several fascinating experiments which have demonstrated the power of natural selection and mutation to drive complex genetic progression. The information on the Richard Lenski-led study of E. coli is worth the price of the book alone. Tremendously important and strong evidence for Dawkins' central thesis.
Dawkins follows this by moving into fossil records, showing the reader how scientists have studied and come to see the fossil record as important, but not the most important facts available to evolutionary theory. He shows that the 'gaps' in the fossil record are actually useful for taxonomic reasons, and posits that a complete fossil record would lead to immense confusion when trying to determine just where a new species begins from the old. Dawkins also knocks down the argument that talk of 'missing links' is useful, and pleads for the cessation of this term since its usefulness has long-since been destroyed. Like he says often, every fossil we find is a missing link, every one is a transitional fossil of some sort.
The chapter "You did it yourself in nine months" was my least favorite, though it was certainly necessary to present in a comprehensive view of evolution. The following chapter on biogeography returns to a superior narrative and offers strong evidence for geographic proof of evolution, again, just as Darwin did in describing the variety of species found strew across the Galapagos Islands. Following that are chapters on cousinship among life forms and the ability of DNA to provide a historical archive which begin to draw together a personal closeness that derives from the evidence of the preceding chapters.
The final couple of chapters move a bit more toward being meditative, though don't expect Dawkins to get too mushy. What begins as a discussion of arms races ends with a look at 'evolutionary theodicy', where Dawkins argues that we find suffering and pain exactly as we would expect from the emotionless processes of natural selection.
Finally, the book winds down with more reflection as Dawkins expounds upon the last paragraph of Darwin's Origin and draws together the book's conclusion by reinforcing that the fact of evolution does not depend on any statement about abiogenesis or origin of life concerns. Clearly, what the theory suggest, and has been proven by practically every bit of evidence uncovered, is that, however it started, evolution is the way in which living things grow, compete, reproduce, and change.
I haven't read a more comprehensive book on Evolution to date, and I think Dawkins has abolutely knocked it out of the park here. I admit to a strong Dawkins bias, so I wanted to like this book, but I also had very high hopes for it because it was the first Dawkins biology-centric book to be released since I started reading his work. I expected a ton. I got it and more.
For the beginning reader, I would still recommend the much-more streamlined arguments in Jerry Coyne's Why Evolution is True, but for the reader with some science experience, or for the curious reader who wants the full picture, this is as good as it gets. Five stars.
Book Review: Genome: The Autobiography of a Species In 23 Chapters by Matt Ridley
(out of 5 stars)
Matt Ridley's Genome is an exploration of human chromosomes heavy in biological and physiological science. Ridley, a journalist and science writer, looks at each chromosome per chapter, using a gene or two found on each to discuss a different aspect of physiology or behavior as affected by the gene, its alleles, or its mutated variations. A strong effort for any reader interested in biology and genetics, Genome is a treat from the very beginning.
Ridley manages to pack a lot of details into the book despite concentrating each chapter on one or two specific genes on the featured chromosome. He themes each chapter on concepts such as Love, Instinct, Conflict, and Free Will, using research on a gene to show how these concepts are affected by genetics.
This book is comprehensive and contains a lot of cutting-edge science from the time of publication (1999), but it remains approachable to the popular science reader. The examples Ridley chooses are fantastic and offer the reader information about research into molecular biology, physiology, psychology, behavior, neurochemistry, anthropology, and many other subjects.
All in all, a wonderful book filled with still-relevant scientific information. Any biology or popular science reader should enjoy Ridley's pace and presentation, and there is a great deal to learn about how genes affect a wide range of concepts. Four and one-half stars.
Book Review: Design for a Life: How Biology and Psychology Shape Human Behavior by Patrick Bateson and Paul Martin
(out of 5 stars)
In Design for a Life, Bateson and Martin look at how the interaction of nature and nurture affect human behavior. While the book does sample many bits of interesting research covering the subjects, it feels light on details and cursory in its explorations.
Design skips around quickly from subject to subject as the authors explore various points in the debate and research into how nature (genetics) and nurture (parenting and environment) determine human behavior. They look at numerous studies involved in isolating influences and discuss whether this points toward genetic or epigenetic sourcing.
While the book does stay on message and maintains a decent narrative, the manner in which the research and details were interjected felt muddled and off-the-mark. Often, the authors jump from one study to another to another without a solid narrative bridge to keep the reader interested. At times, the authors simply describe the basic results of a study without much analysis or integration into the larger argument. I feel a more streamlined and judicious selection of included research would have left more room for a proper presentation of the data without leaving the discussion feeling underwhelming on substance and detail.
Still, Design has many good points and provides a nice overview of the landscape of the nature / nurture argument as it stood at the time of publication in 2001. While not the best book I've read on the subject, it still holds value for the interested reader of biology, genetics, psychology, and behavior. Three stars.
Book Review: Java Man : How Two Geologists' Dramatic Discoveries Changed Our Understanding of the Evolutionary Path to Modern Humans by Carl Swisher, Garniss Curtis, and Roger Lewin
(out of 5 stars)
The discovery of the Java Man skeleton was one of the groundbreaking moments in paleontology and anthropology, providing a key piece of predicted but, until that point, largely absent evidence for near-human ancestors. Here, in a book written by Roger Lewin but credited as well to Carl Swisher and Garniss Curtis, the history of the discovery and related events is described. An interesting subject, the book nonetheless fails to thrive and instead is largely muddled and dull.
The first part of the book is by far the most interesting as the authors describe the finding of Java Man and the efforts required over the years to study the specimen. If the rest of the book had maintained the pace, level of detail, and science content, it would have been a recommended resource for popular anthropology and science readers.
However, the book takes a turn for the worse as the authors fall into a long section detailing the office politics which saw their research threatened from forces allied against them within their organization. While somewhat interesting, this digression from the story of Java Man breaks the narrative in a way which damages the reader's enjoyment and wonder.
The last section feels tacked on, as if the authors recognized that the book was not nearly long enough to warrant publication. So, a section on anthropology and human populations in general is presented which harbors very little information about Java Man or of the events which surrounded the fossils. A basic discussion of the subject, this section failed to produce any meaningful addition to the book itself or to the field of popular anthropology.
Java Man left me feeling unfulfilled, as if the story itself never warranted a book length treatment. The last two sections, which make up the majority of the work, are largely unnecessary for the reader and offer little on-topic information that wasn't already detailed in the opening chapters. Not specifically recommended for anyone, though it may be of interest to those who seek popular anthropological histories. Two and one-half stars.
Book Review: Adaptation and Natural Selection in Caves: The Evolution of Gammarus minus by David Culver
(out of 5 stars)
Adaptation is a highly-technical presentation by researchers Culver, Thomas Kane, and Daniel Fong on the study of a specific cave-dweller, the crustacean Gammarus minus. The first few chapters of the book, along with the last couple, are highly readable and interesting, but for the casual reader the rest of the book is not approachable as the authors present dozens of pages of data collected during their studies.
While I don't recommend this book to anyone who wants to sit and enjoy a read, there is an amazing amount of value and detail here for a reader needing highly-specific data in the field of evolutionary biology. As a pleasurable read, this book is not appropriate, but as a reference resource, it offers a fantastic presentation. Three stars.
Book Review: The Structure of Scientific Revolutions by Thomas Khun
(out of 5 stars)
Thomas Kuhn's foundational work The Structure of Scientific Revolutions lays out the concept of paradigm shifts as fundamental to the history of science. While the book is dense at times, and certainly scholarly-technical in many places, Structure still contains an enjoyable read for anyone with an interest in the ways in which significant changes occur in scientific theories.
Kuhn's argument concentrates on shifts in fundamental concepts in the fields of astronomy and physics, as well as a few other areas. He describes how the prevaling paradigm provides a set of facts and instruments which enable further progress in the field while still leaving holes in need of work. Demonstrating that paradigm shifts occur only after a crisis in the field, Kuhn argues that such crises predict a fundament shift in the underlying tenats of the paradigm. While these paradigm shifts can certainly be tremendously important and change many of the basic assumptions, Kuhn makes clear that these changes are not immediate and take place, typically, over decades of work and debate, and at times, are hindered by popular adherents to the old paradigm.
Structure is probably not a book for most popular science readers, but for anyone who is enthusiastic about the history of science, there are few books which offer the sort of discussion available here. Kuhn's look at the nature of paradigm shifts, despite being decades old, still offers a profound and engaging argument for the processes behind the shifting descriptions of the natural world. Four stars, but recommended only to those who really enjoy history of science and epistemological arguments.
Book Review: The Dirt on Clean: An Unsanitized History by Katherine Ashenburg
(out of 5 stars)
In The Dirt on Clean, Katherine Ashenburg presents a light history of baths, bathing, and the social implications of cleanliness in Western culture. A frank discussion light on science and technical detail, this pocket history is a quick read with many enjoyable historical anecdotes on the subject.
Ashenburg starts her exploration with the Ancient Greeks, a population which took bathing seriously and influenced the Romans to build technologically-advanced bath works. From there, she explores cleanliness throughout the centuries as attitudes shifted from a belief in the value of dirtiness and clogged pores to its opposite. The author reflects upon the various attitudes as told in diaries, letters, fiction, and other anecdotal writings available in each period. The modern day obsession with hygiene is put in perspective as Ashenburg demonstrates that this concept has not always held sway and that body odor was far more often expected and accepted than modern Western humans might believe.
An enjoyable romp through history, as people's shifting views in the value of being dirty or clean, as well as a light treatment of social influences surround the bathing cutlure are in store for the reader. Ashenburg is an excellent writer and weaves her stories together in a way which is quick-to-read and easy to digest. My only complaints are that I would like to have had much more information about the scientific and technical nature of the bath and its culture, as well as a more empirical, less anecdotal account. However, neither point really dampens the book's value and it need make no apology for offering the style it embraces. Fun and informative, don't take it too literally since so much appears to be anecdotal. Three and one-half stars.
Book Review: Symbiotic Planet: A New Look At Evolution by Lynn Margulis
(out of 5 stars)
Microbiologist Lynn Margulis presents an argument on behalf of symbiogenesis and Gaia Hypothesis in her book Symbiotic Planet. I had high expectations given Margulis's role in the establishment of the origins of mitochondria in cells. I was profoundly disappointed by the muddled, moody, and downright terrible treatment of her field of work found here.
Margulis starts the book with discussion of the nature of symbiosis and her own personal involvement in microbiological research. A few chapters in, it is difficult to determine if Margulis was trying to present a popular science book or an opinionated memoir. Neither was successfully presented.
Throughout the book, the author makes assertions about the nature of biology and symbiosis which are often described with 'my view' or 'in my opinion'. I'm not asking her to claim such hypothesis are indeed proven fact (although, at times, she does make such assertions), but the presentation, which only rarely includes descriptions of how such theories were validated through research, left me questioning whether Margulis had enough coffee on the morning she wrote the passage. Sometimes she just seems to lose interest in her current subject and changes course in mid-paragraph.
One telling moment in the book is when she is discussing Mendel's work. One sentence sums up the lack of professional presentation and effort that seems to have ruled her production of this book:
According to a brilliant unpublished manuscript by an amateur historian of science whose name I can't remember from Nassau Island in the Bahamas, Mendel saw no evidence at all that species change and evolve (20).
Seriously?!? Margulis is a widely-respected professional biologist who has contributed enormously to cutting-edge science, and she's quoting an unnamed amateur unpublished source to support her point? This appeared on page 20, at which point I was already questioning Margulis' ability to argue and present evidence. The rest of the book was not much better.
Highly disappointing treatment of a highly interesting subject by a well-respected key participant in 20th Century biology. I am really very suprised that this book was this bad. Maybe I just caught this read on a bad day (not likely), but I cannot recommend this book to anyone except the rare reader who has a personal interest in Margulis's theories and mindset. Two very generous stars.
Book Review: Microcosm: E. Coli and the New Science of Life by Carl Zimmer
(out of 5 stars)
The bacteria E. coli is among the most important living things in modern science, and as Carl Zimmer shows in this outstanding treatment, many huge discoveries owe a great deal to this very tiny "bug".
Zimmer packs a ton of information into these pages, highlighting a natural history of E. coli as well as discussing its physiology and evolutionary aspects. While I knew beforehand that this bacteria was very useful, I was still surprised and delighted to find out so much about something so little.
The best parts of the book for me were those which discussed key research utilizing the bacteria, including that of Richard Lenski's long-term evolutionary study, which was included in Richard Dawkins's book The Greatest Show on Earth. Zimmer brings the science to life and while this reads like a popular science book, it is densely packed with wonderful and enlightening science. Highly recommended to anyone with an interest in biology, microbiology, evolution, or just a great love of current science. Four and one-half stars.
