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Overview
Within a single captivating narrative, John Bonner combines an intensely personal memoir of scientific progress and an overview of what we now know about living things. Bonner, a major participant in the development of biology as an experimental science, draws on his life-long study of slime molds for an understanding of the life cycle-the foundation of all biology. In an age of increasing specialization and fragmentation among subfields of biology, this is a unique work of reflection and integration.
Originally published in 1993.
The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
Product Details
| ISBN-13: | 9781400872770 |
|---|---|
| Publisher: | Princeton University Press |
| Publication date: | 03/08/2015 |
| Series: | Princeton Legacy Library , #1769 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 222 |
| File size: | 19 MB |
| Note: | This product may take a few minutes to download. |
Read an Excerpt
Life Cycles
Reflections of an Evolutionary Biologist
By John Tyler Bonner
PRINCETON UNIVERSITY PRESS
Copyright © 1993 Princeton University PressAll rights reserved.
ISBN: 978-0-691-03319-8
CHAPTER 1
BEGINNINGS
I HAVE devoted my life to slime molds. This may seem a peculiar occupation — narrow at best, slightly revolting at its worst — but let me explain why they captivated me and how they opened my eyes so that I wanted to understand not only what made them tick, but how they fit into the general pattern of living things and what the principles are that integrate all of life.
Slime molds are an extremely common organism, widespread all over the world. Yet because they are microscopic and live mostly in the darkness of the soil, they are hard to see, and for that reason they have been little known until recent years. However, if one takes a small bit of topsoil or humus from almost anywhere and brings it into the laboratory, one can easily grow them on small Petri dishes containing transparent agar culture medium. There, through the low powers of a microscope, it is possible to follow their life cycle, which to me has always been a sight of great beauty (fig. 1).
The molds begin as encapsulated spores which split open, and out of each spore emerges a single amoeba. This amoeba immediately begins to feed on the bacteria that are supplied as food, and after about three hours of eating they divide in two. At this rate it does not take long for them to eat all the bacteria on the agar surface — usually about two days. Next comes the magic. After a few hours of starvation, these totally independent cells stream into aggregation centers to form sausage-shaped masses of cells, each of which now acts as an organized multicellular organism. It can crawl towards light, orient in heat gradients, and show an organized unity in various other ways. It looks like a small, translucent slug about a millimeter long (indeed, this migrating mass of amoebae is now commonly called a "slug"). It has clear front and hind ends, and its body is sheathed in a very delicate coating of slime which it leaves behind as it moves, looking like a microscopic, collapsed sausage casing.
After a period of migration whose length depends very much on the conditions of the slug's immediate environment, the slug stops, points up into the air, and slowly transforms itself into a fruiting body consisting of a delicately tapered stalk one or more millimeters high, with a terminal globe of spores at its tip. This wonderful metamorphosis is achieved first by the anterior cells of the slug, which will become the stalk cells. They form a small, internal cellulose cylinder that is continuously extended at the tip. As this is occurring, the anterior cells around the top of the newly created cylinder pour into the cylinder, like a fountain flowing in reverse. The result is that the tip of the cylinder (which is the stalk) rises up into the air. As it does, the mass of posterior cells, which are to become the spores, adheres to the rising tip, and in this way the spore mass is lifted upward. During this process each amoeba in the spore mass becomes a spore, imprisoned in a thick-walled, capsule-shaped coat, ready to begin the next generation. The stalk cells inside the thin, tapering cellulose cylinder become large with huge, internal vacuoles; during this process they die, using up their last supplies of energy to build thick cellulose walls. It is a remarkable fact that the anterior cells, on the other hand — the leaders in the crawling slug — die, while the laggard cells in the hind region turn into spores, any one of which can start a new generation. Slime molds seem to support the old army principle of never going out in front — never volunteer for anything.
This entire life cycle (which happens to be asexual) takes about four days in the laboratory. The organisms are very easy to grow, and in many ways ideal for experimental work. The species I have described is only one of about fifty species, making comparative studies possible. Today, in this modern, technical world, one can view one's experiments with extraordinary ease. For instance, I have in my laboratory a video camera on my microscope, and on the screen I can follow the results of any operation I might perform on the migrating slug. If I follow it for two hours, I can immediately play back the changes on time lapse, so the two hours can be speeded up to two minutes. The possibilities make going to the laboratory each day a delight of anticipation. The life of an experimental biologist is one of minute and often hum drum detail involving endless, frustrating experiments that do not work, b u t the rewards, albeit rare, are great. Suddenly — and how exciting it is when it happens — something will go right and give one a flash of in sight into how things work.
A few years ago an old friend who happened to be a veterinarian was sick in the hospital recovering from an operation. While I was visiting him, his surgeon came by and my friend introduced me as "Dr. Bonner." The surgeon asked me, "Are you a small animal or a large animal man?" Without thinking, and somewhat to his alarm, I replied that I was a "teensy-weensy animal man." I have often thought of this episode in the context of the many years I have helped students revive their sick cultures into healthy and thriving ones. One of my main roles in life, then, has been that of a slime mold veterinarian.
* * *
My interest in biology began with an interest in birds. My family was living in Europe when I was a child, and I can still remember my excitement at seeing the variety of ducks in St. James Park in London. (I have to be careful how I put this. Some years ago my university asked me to say something about my first interests in biology for a fund-raising pamphlet. Unfortunately I reported that "it all started watching the ducks in St. James Park." The roommates of one of my sons, who was then a freshman in college, found the quote and immediately taped it to his door.) I was going to boarding school in Switzerland at the time, and with the help of an old pair of binoculars (which my mother had used in her earlier days at the horse races) I began to spend more and more of my leisure time in the woods trying to spot birds and identify them in a rather quaint old bird guide.
My father was quick to see what was happening, and I think he worried at the time that his son, only about eleven or twelve at the time, would find it difficult to make a living as an ornithologist, which I firmly stated was to be my future. Very cleverly he gave me a copy of a wonderful book called The Science of Life, written by H. G. Wells, Julian Huxley, and Wells's son, G. P. Wells. H.G. Wells trained as a biologist under Thomas Henry Huxley (Julian's grandfather and the friend and defender of Charles Darwin) at Imperial College in London. Wells gives a splendid account of this in his Experiment in Autobiography. T.H. Huxley was the first to preach that there should be a unified biology, not a separate zoology and botany, which was the norm at the time, and for that reason he had an enormous influence on the teaching of "life sciences" in this century. The Science of Life is one such unified synthesis that came from this tradition. Wells was keen on bringing everything together under one cover as, for instance, he did in his now forgotten Outline of History, and with his two gifted collaborators he wrote a remarkably literate and cohesive biology. The only thing that today seems very odd is a section on mediums and how to communicate with the dead. As with an unpleasant illness, one tends to forget indiscretions of the past, but in the 1930s, when this book was published, many people believed that psychic phenomena of this sort might really exist. Even the great psychologist-philosopher William James left a fund to Harvard University for research on the sixth sense. Today we look upon séances and mediums, and even extrasensory perception, with either total disbelief or, in the latter case, terminal suspicions, but that apparently was not so when I was a boy. My most vivid memory of this section of the book was a photograph of a woman extruding "ectoplasm" from her nose — large, disgusting masses of it slithering over her shoulder. I think this one picture did much to make a standard biologist out of me; I wanted straightforward, clean animals and plants and stuck to the main part of the book.
My father's plan worked; I soon changed my ornithological aspirations and announced I wanted to become a plain biologist. Reading even part of that huge book was not easy for me, but the more I read, the more captivated I became. I was so inspired that I started to write an illustrated biology book, laboriously typed on a toy typewriter. The most interesting part is the grammar and the spelling (except, of course, for the sections lifted directly from Wells, Huxley, and Wells). A t one point my book describes the life cycle of Paramecium, the dilate protozoan, and says it has "two nucleus (sic), one for chemical business of every day, the other is responsible for sexual union and other rare reproductive occasions," whatever those might be.
In the years that followed, up through secondary school, I became increasingly involved in collecting everything I could find in the woods and ponds, keeping it alive or carefully preserving it. In this way, without realizing it, I slowly came to have an appreciation of the riches about me, so many of them unseen without the aid of a hand lens or a microscope. It was in no sense an intellectual exercise, b u t rather the simple enjoyment of poking about in my surroundings.
At the same time, I began reading about various naturalists — the biographies of biologists of the past. I remember being absolutely riveted by the life of Linnaeus, the eighteenth-century naturalist who classified all the known animals and plants, many of them discovered by him. He also devised the system of naming organisms by giving them a genus name followed by a species name, all in Latin (a matter of course at that time) — for instance, we hum an beings became Homo sapiens. Linnaeus lived w hat seemed to be a splendid life, constantly wandering off from his university in Uppsala, Sweden, and going on great collecting trips in northern Lapland. How I wanted to go to Lapland! In fact, I still want to go; the same old feeling comes over me as I write this sentence! In those early days I did not delve into the details of his taxonomy — I was far more interested in him as a person. However, I instinctively felt he held the golden key — and I was quite right. My reason, however, was not entirely reasonable: it was based on the fact that he called his great work on the classification of all animals and plants Systema Naturae. Anyone who could put system into nature was an automatic hero as far as I was concerned. From my puerile collecting I could see that without some system, nature could seem very chaotic indeed.
It was about that time that Paul de Kruif came o u t with a popular book called The Microbe Hunters. In it I learned about Antonie van Leeuwenhoek and Louis Pasteur and found them tremendously exciting. I was a bit put off by de Kruif's treatment of van Leeuwenhoek; he seemed to be more interested in his being a church janitor than in the extraordinary things he discovered with the microscope he invented. Pasteur is still everyone's hero. H e was a man of magic, for whatever he touched turned into scientific gold. At the same time I read Sinclair Lewis's Arrowsmith, a thinly disguised and highly romanticized account of the early days of biomedical research in what used to be called the Rockefeller Institute (now University) in New York City. All of this was what I needed in the way of inspiration to carry me through a lifetime of laboratory research. (I reread Arrowsmith a few years ago and could n o t imagine what I found so riviting about it in my teens. Certain books have to be read at just the right age, although I doubt if a teenager today would be magnetized by Sinclair Lewis's old book the way I was. It is very dated.)
Perhaps the greatest of my discoveries in the biographies of scientists was my encounter with Charles Darwin. As is true for Pasteur, there are many biographies of Darwin and the drama behind his revolutionary ideas about evolution in the middle of the nineteenth century. Some of the recent ones are far superior to the ones I was reading, but nevertheless I was totally captivated. Darwin, like Linnaeus, spent a long time collecting and observing in the wild — not in Lapland, but in South America, Australia, and various islands. This led to his famous Voyage of the Beagle, which he published a few years after he returned from his expedition, and a wonderful book it is. He went as a very young man in his twenties and the voyage took five years, but with his extraordinary mind he gathered riches that lasted him a lifetime. He began working on his theory of natural selection a few years after his return, but he did not publish his great book, On the Origin of Species, until 1859. He perhaps would not even have done so then, for he was so worried about its reception by the world at large, had not Alfred Wallace sent him a manuscript with the very same idea suggesting natural selection as the mechanism for evolutionary change. Wallace, another gifted naturalist, had the idea while collecting in the Malay Archipelago, and wrote to Darwin about it. Wallace's paper — and a companion one of Darwin's — was published in the Proceedings of the Linneaen Society, but the two articles caused little stir. It was Darwin's book that created the explosion. Wallace and Darwin became friends, and Wallace was most generous in deferring to Darwin, who had spent so many years working out the evidence for natural selection. As the ultimate expression of generosity, Wallace even wrote a book he called Darwinism.
One of the books I read at an early age was Darwin's Autobiography, which he wrote primarily for his children. It is an unpretentious account of his life and work in which he emphasized his inability to do well in school and his difficulty in deciding on a suitable vocation. He manages to give the impression that he is an average person with average gifts. Today he is generally regarded as one of the great geniuses of the nineteenth century, although he has always had his detractors who cite, among other things, his autobiography as evidence for his mediocrity. Unknown to me or the rest of the world, the autobiography I read had been greatly censored by his wife, and it was not until the 1950s that his granddaughter, Lady Nora Barlow, published the unexpurgated version. What had been suppressed were Darwin's views on religion: he had, over the course of years, become a nonbeliever. It is particularly fascinating that, in the complete version, he writes that his father, a very successful medical practitioner, was also an agnostic. According to Charles, his father told him that should he ever have doubts, he should not communicate them to his wife for it would make her very unhappy, as then there would be no hope of meeting him again in the next world!
Due to a chronic illness Darwin remained a recluse at his house in Down, Kent. No one really knows what ailed him, but there has been an enormous amount of speculation on the subject. One popular theory is that he contracted Chagas' disease in the Andes. There he was bitten by "the great bug of the Pampas," which through the much later work of Chagas is known to carry the disease. There are also a number of explanations involving his psychological difficulties, and it has even been suggested that he feigned the illness so that he could work without interruption. One result of his isolation was a vast correspondence with others on scientific subjects, only now being edited and published in many volumes. Another is that all the lecturing and debating that necessarily followed the publication of On the Origin of Species was done by others, and by far his most eloquent advocate was Thomas Henry Huxley, whom I mentioned a few pages ago. As a teenager I admired Huxley as much as Darwin. In time I came to realize that although Huxley was a superb teacher and an exceptionally gifted essayist as well as a first-rate biologist, Darwin was the one with the really great and profound mind. It is because of the profundity of his thought that his ideas on evolution "by means of natural selection" have such a firm grip on every aspect of biology today and form a principal theme of this book. He provided the intellectual cement to bind all things living that has given us a genuine understanding of the problems of life.
(Continues...)
Excerpted from Life Cycles by John Tyler Bonner. Copyright © 1993 Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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Table of Contents
Preface
The Background 1
Ch. 1 Beginnings 3
Ch. 2 The Life Cycle 15
The Period of Size Increase 37
Ch. 3 Becoming Larger by Becoming Multicellular 39
Ch. 4 Becoming Larger by Developing 68
Ch. 5 Becoming Larger during Evolution 93
The Adult Period 121
Ch. 6 Becoming Aware 123
Ch. 7 Becoming Social 158
Ch. 8 Becoming Cultural 179
Selected Reading 201
Index 205