The Origin Then and Now: An Interpretive Guide to the Origin of Species - Softcover

Reznick, David N.

Softcover

ISBN 10: 0691152578 ISBN 13: 9780691152578

Publisher: Princeton University Press, 2011

Synopsis

An accessible modern guide to Darwin's masterwork

Charles Darwin's Origin of Species is one of the most widely cited books in modern science. Yet tackling this classic can be daunting for students and general readers alike because of Darwin's Victorian prose and the complexity and scope of his ideas. The "Origin" Then and Now is a unique guide to Darwin's masterwork, making it accessible to a much wider audience by deconstructing and reorganizing the Origin in a way that allows for a clear explanation of its key concepts. The Origin is examined within the historical context in which it was written, and modern examples are used to reveal how this work remains a relevant and living document for today.

In this eye-opening and accessible guide, David Reznick shows how many peculiarities of the Origin can be explained by the state of science in 1859, helping readers to grasp the true scope of Darwin's departure from the mainstream thinking of his day. He reconciles Darwin's concept of species with our current concept, which has advanced in important ways since Darwin first wrote the Origin, and he demonstrates why Darwin's theory unifies the biological sciences under a single conceptual framework much as Newton did for physics. Drawing liberally from the facsimile of the first edition of the Origin, Reznick enables readers to follow along as Darwin develops his ideas.

The "Origin" Then and Now is an indispensable primer for anyone seeking to understand Darwin's Origin of Species and the ways it has shaped the modern study of evolution.

About this title

About the Author

David N. Reznick is professor of biology at the University of California, Riverside.

From the Back Cover

"For those about to read the Origin of Species for the first time, or for those about to read it yet again, David Reznick has provided a marvelous guide. He looks to the past so that readers can understand the history of Darwin's great book, but he also looks to the future, showing how, chapter by chapter, the Origin set the ground rules for modern biology."--Carl Zimmer, author of The Tangled Bank: An Introduction to Evolution and A Planet of Viruses

"This is a beautiful book--the best book I have ever read dealing with the Origin. It will move many people, experts and lay readers alike."--Lee Alan Dugatkin, author of Principles of Animal Behavior

"The "Origin" Then and Now has made the wealth of information held within Darwin's opus many times more accessible. This book is unquestionably essential reading for students and others approaching the Origin for the first time. It should be terrifically useful to anyone with an interest in understanding one of the most important books in intellectual history."--Kurt Schwenk, University of Connecticut

"David Reznick's elegantly written introduction to evolution is magnificent. It should be highly recommended reading for any course on evolution or Darwin, and I will recommend it to scientists and nonscientists alike."--Francisco J. Ayala, University of California, Irvine, author of Darwin's Gift to Science and Religion

"While most treatments of the Origin of Species set the book in the context of its time, this elegant account sets the book in the context of its science. By explaining Victorian science and showing how modern scientific discoveries illuminate Darwin's ideas, Reznick demonstrates just how revolutionary and brilliant the Origin was. Engaging, scholarly, and insightful, this is the essential companion to the Origin."--Joseph Travis, Florida State University

"Reznick masterfully highlights one of the most important, but commonly overlooked, aspects of the Origin--its scholarly approach to the theory of evolution, encompassing expertise from geology and natural history to embryology. Exceptionally well-written and comprehensive, and full of fascinating historical and cultural accounts of major biological discoveries, Reznick's book is itself a perfect illustration of the timeless qualities of scientific rigor and scholarship that were so crucial to Darwin's theory."--Alexander V. Badyaev, University of Arizona

"Reznick cogently argues that Darwin's seminal book holds more than historical interest; it is as relevant today as it was in 1859. The 'Origin' Then and Now provides an accessible way to enjoy the totality of Darwin's thesis."--Kenneth Dial, University of Montana

Excerpt. © Reprinted by permission. All rights reserved.

The Origin Then and Now

An Interpretive Guide to the Origin of SpeciesBy David N. Reznick

PRINCETON UNIVERSITY PRESS

Copyright © 2010 Princeton University Press
All right reserved.
ISBN: 978-0-691-15257-8

Contents

Preface................................................................................................ixCorrespondence between Chapters........................................................................xivAcknowledgments........................................................................................xvIntroduction: Charles Darwin and the Origin of Species MICHAEL RUSE...................................31 Preamble to Natural selection........................................................................292 Variation under Domestication........................................................................383 Variation under Nature I.............................................................................564 The struggle for existence...........................................................................665 Natural selection I..................................................................................776 Laws of Variation....................................................................................1027 evolution today: A Modern Perspective on Natural selection...........................................1198 Preamble to speciation...............................................................................1379 Variation under Nature II............................................................................15210 Natural selection II................................................................................16411 Hybridism...........................................................................................19012 evolution today: The Mosquitoes of the London Underground...........................................20513 Preamble: What Is a Theory?.........................................................................21914 Difficulties on Theory..............................................................................22715 Instinct............................................................................................25016 Geology I: Background...............................................................................26417 Geology II: on the Imperfection of the Geological Record............................................27518 Geology III: on the Geological succession of organic Beings.........................................28819 Geology IV: evolution today.........................................................................30120 Geographical Distribution...........................................................................31421 Geographical Distribution, Continued................................................................33122 Mutual Affinities of organic Beings: Morphology: embryology: Rudimentary organs.....................34623 Recapitulation and Conclusion.......................................................................38124 evolution today: The Witness Has Been Found, Again and Again........................................401Illustration Credits...................................................................................417Index..................................................................................................419

Chapter One

Preamble to Natural selection

In the opening chapters of the Origin, Darwin intertwined the processes of natural selection and speciation. You will see why he did so later. His not separating the two has been a source of confusion. Some readers concluded that the Origin of Species is all about natural selection and not really about the origin of species. Others concluded that speciation and evolution are equivalents, so that we only see evolution when we see the origin of new species. Neither of these inferences is true. As a first step in making the Origin accessible, I have separated Darwin's proposal of natural selection as the mechanism of evolutionary change from speciation, which is a possible consequence of natural selection. One virtue of separating natural selection from speciation is that natural selection, and the resulting evolution that it causes, does not necessarily cause speciation. Natural selection is a process that is constantly in action within all species and has important consequences in its own right. Today, many scientists study natural selection without any reference to speciation. In part 1, I describe Darwin's presentation of natural selection. I consider speciation separately in part 2. This presentation is consistent with Darwin's message, since he was explicit in addressing the importance of natural selection to evolution within a species and in stating that speciation is only an occasional outcome of evolution by natural selection.

Darwin was not the first to propose a theory of evolution. His distinction, shared by A. R. Wallace, is that he proposed natural selection as the cause of evolution. The full title for Darwin's theory is thus the "theory of evolution by natural selection." I will often abbreviate this title to just "Darwin's theory." It is important to realize that evolution and evolution by natural selection are separable. Darwin was very successful in convincing the world that evolution is a fact, but his success in promoting natural selection as the cause of evolution was delayed until the modern synthesis era (1920s–1950s). As biologists' appreciation for natural selection was rekindled, they also realized that there are other causes of evolution, to be described later. Since this book is about Darwin and the Origin, I will focus on natural selection.

Darwin presented the concept of natural selection over the first five chapters of the Origin. Because of the length and complexity of his argument, it is good to know the premises and some of the properties of evolution by natural selection at the outset. To present these, I begin in the Galapagos Islands, where Darwin gained some of his key insights about natural selection and speciation.

The Galapagos archipelago straddles the equator and lies 500–600 miles off the west coast of south America. These are "oceanic" islands, meaning that they have never had contact with other landmasses. They were formed by volcanoes that erupted under the ocean, then grew to the surface and emerged as lifeless, dry land. Prevailing winds and ocean currents control their climate. Trade winds blow persistently from east to west and drive the surface water of the ocean in their path. As the water on the surface is driven west, an upwelling of deep, cold, nutrient-rich water along the coast of south America replaces it. These wind-driven currents create the continuous stream of cold water that surrounds the islands. The water in turn cools the winds. Because the islands are on the equator, the sun continuously heats them. This combination of warm land and cool winds causes the islands to be dry. The cool sea winds warm up and absorb moisture as they pass over the land, just as the dew on a lawn dries as the sun rises and heats the air. When el Niño events occur, this flow of cold water ceases, and the waters and winds around the islands warm up. As they do, their drying effects wane, and rainfall can increase dramatically. El Niño events occur at irregular intervals, ranging from two to seven years. They are often interspersed with droughts, so, over time, the amount of rainfall fluctuates widely and irregularly.

The same ocean currents and trade winds that dictate the climate today were the conveyors of most of the plants and animals that colonized the islands. Charles Darwin surmised this when he visited these islands. His visit came after he had spent nearly four years exploring south America, so he was very familiar with the plants and animals found on the mainland. He was impressed by the plants and animals on the Galapagos because so many proved to be new species, yet they were often similar to those found on the mainland. The wildlife was also remarkable because the animals had no fear of humans, since they had lived without human contact until the Spanish landed there in the seventeenth century. Collecting birds and lizards proved as easy as picking apples from trees.

Darwin made large collections of plants, insects, mollusks, and birds from the Galapagos. Some of his shipmates made collections as well. It was only years later, after Darwin's return to England, that the eminent ornithologist John Gould discovered the diversity of bird species that were present on the islands and fully described how they differed from one another. It was telling that Darwin did not always record the island from which he collected his birds, because he did not imagine that there could be any differences between species found on islands that were sometimes within sight of one another. This was an unusual lapse in Darwin's otherwise meticulous record keeping. Luckily, Captain FitzRoy had made collections as well and kept track of the island of origin. FitzRoy's diligence enabled Gould to determine not only that many of the birds in the collection were unique to the Galapagos, but also that some were unique to individual islands.

Darwin enlisted the help of Joseph Hooker to identify the plants. Of the 193 species that Darwin collected, Hooker determined that 109 were unique to the Galapagos. Of these, 85 were found on only one island.

At this point, Darwin had important pieces of information that drove him to the idea that speciation is an ongoing process. He knew that the islands were of volcanic origin, that they were younger than south America, and that many of the species living there were found only on the islands, but had close relatives in south America.

Modern geological methods allow us to provide specificity to Darwin's observations. For example, we can now estimate the age of the lava that is the bedrock of the islands, and know that the islands range from 700,000 to 3.5 million years old. We also know that the bird fauna includes thirteen species of finches that are found only on the islands. Investigators have shown, with the use of molecular genetic methods, that all thirteen Galapagos species share a single species of finch from the mainland of south America as their common ancestor. This combination of island endemism, molecular evidence, and islands of known age provides a basis for estimating the time required for these species to have evolved, which is actually a few million years more than the oldest extant island. This is possible because some older volcanoes in the archipelago that were once islands have since eroded away, leaving behind submerged sea mounts: the speciation must have started on those older islands before they eroded away.

These thirteen species of finch are an example of an "adaptive radiation," or the diversification of a single ancestor species into an array of separate species that fill a diversity of ecological niches. Their common ancestor arrived at a habitat already colonized by plants, insects, and other organisms, but with few birds. The islands gave the original colonizing individuals and their descendants diverse, unexploited sources of food. As the finch populations expanded onto all the islands, they diversified into separate species, each of which adapted to exploit different sources of food and different types of habitat. Diet differences are reflected in the beak structure of each species. The ground finches, one group of species, specialized in eating seeds. The species in this group now have beaks of various sizes that differ in their ability to crack seeds. Shorter, narrower beaks make birds more agile in picking up and shelling small seeds, while longer, wider beaks enable them to crack the shells of larger, tougher seeds. Other species instead specialized to live in trees and feed on insects, or to exploit other combinations of habitat and diet.

One species, the medium ground finch (Geospiza fortis), has become a model for the study of natural selection because of the work done by Peter and Rosemary Grant and their colleagues on the small Island of Daphne Major. It and the other islands in the Galapagos are especially good natural laboratories for studying evolution because they have few species of plants and animals relative to the mainland, making it easier to characterize them all and to study their interactions.

The Grants' remarkable long-term study has provided detailed documentation of the process of natural selection. Their detailed methodology, the properties of their study site, and propitious timing came together to turn evolution by natural selection into a visible process. First, the island—an emergent tip of a volcano shaped like a cone with a hollow interior—is manageably small, with bird habitat concentrated on the slopes and plane that fill the interior of the cone. The Grants came to know almost every bird on the island as an individual. They caught adult birds with fine mist nets, then measured and recorded various dimensions of their bodies such as wing or leg length, plus the dimensions of the beak, and then gave each bird a leg band that uniquely identified it.

There was considerable variation among individual finches in the shape and size of bodies and beaks. Birds had beaks that ranged from short, narrow, and shallow to long, wide, and deep. This is the same sort of variation found among different species of ground finch, although differences between individuals within this species were smaller than differences between species. During the breeding season, the investigators visited the nests and measured and marked all the nestlings. Because they knew who the parents were, they also knew how many surviving offspring were produced by each parent. Because they measured both parents and offspring, they could evaluate how similar they were in appearance. Offspring tended to look like their parents.

The Grants also studied food availability. Most fresh seeds were produced during periods of rainfall. During the dry season, the birds mined the "seed bank," or seeds that had accumulated in the soil. The Grants cataloged all the seed-bearing plants on the island and characterized each type of seed by its hardness, or the amount of force required to crack it. They regularly sifted samples of soil to see how many and what types of seeds were available. They also quantified how effective individual finches were in harvesting the different types of seeds and found that differences in beak dimensions were associated with differences in harvesting ability.

Then in 1977, during this study of the island's finch population and food supply, the island experienced a year-long drought—an accident of timing that gave the investigators an opportunity to observe and record the process of natural selection. There was little plant growth or seed production, forcing the birds to rely entirely on the seed bank for food. Food was so scarce that none of them produced young that year. They depleted the supply of small seeds as the drought progressed, leaving just the large, thick-shelled seeds as the more abundant food source. As the seed supply dwindled, birds began to die. Only 15% of the adults had survived to reproduce by the time the drought finally ended. Those that survived were different, on average, from those that had died. Because small seeds were harder to come by, the survivors tended to be birds that were larger overall and had longer, wider, deeper beaks than those that had died. They survived because they were better able to harvest the more abundant larger seeds in the seed bank. When the rains returned and the birds were once again able to reproduce, they gave birth to babies that looked like them. The average postdrought finch was a bit larger and had a larger beak than the average predrought finch.

Because the amount of rainfall can vary so dramatically from year to year, the nature of the seed supply also varies. During the winter of 1982–3, there was an el Niño event and a surfeit of rain that was as dramatic as the scarcity of rain in 1977–8. Grasses carpeted the inside of the volcanic cone and produced an abundance of small seeds. Whereas the finches did not reproduce at all during the drought, some of them produced multiple sets of offspring during this especially wet season. Those individuals with short, narrow beaks were better at harvesting the available seeds and were much more likely to survive and reproduce. Once again, offspring tended to look like their parents, so the average bird in the population after the el Niño was smaller and had a shorter, narrower beak than seen the year before, thus reversing the change that had occurred during the drought. This reversal is telling because it says that there is not a universal "best" bird. Whether or not a given feature of an individual gives it an advantage over another depends entirely on the circumstances. As circumstances change, so do the sorts of traits that favor one individual over another.

These changes that the Grants observed in the finch population from one year to the next, and the sequence of events that caused them, are a model for the process that Darwin called "natural selection." Darwin's first goal in the Origin was to define this mechanism. He named it "natural selection" because he saw it as an analogy to "artificial selection." The breeding of plants and animals for desired properties was widely practiced in the England of his time, so it was a process that was well known to his intended readership. The goals of this artificial selection ranged from developing improved domesticated plants and animals as sources of food and fiber to attaining aesthetic goals, such as developing a prizewinning rose or pigeon.

Darwin's mechanism consisted of four parts. First, all organisms make many more offspring than are required to replace themselves in the next generation. If all offspring lived, they would quickly fill the world many times over. This does not happen because something intervenes to control their abundance. They may be eaten by predators, killed by disease or parasites, succumb to competition, or, like the finches, starve during a time of scarcity.

Second, individuals are almost always different from one another in how they look or how they work on the inside. Some differences are obvious. In the finch study, individual variation was quantified by measuring beaks and the size of different parts of the body and wings. Consider the variation that we see in humans. There are differences between us in hair color, skin color, eye color, and height. There are "shape" differences, such as the relative length of the legs or trunk of the body, and a host of internal differences, such as blood type. Among other organisms, the differences may not be so apparent, but they are always there if you know how to look for them.

Third, at least some of these differences between individuals are heritable, meaning that they are transmitted from parents to offspring. The Grants were able to quantify this similarity by measuring parents and off-spring. We know this from practical experience as well, since children tend to look like their parents.

Finally, these differences between individuals can influence who survives and reproduces and who dies or fails to reproduce. In finches, the difference between life and death during a drought came down to the dimensions of their beaks and their ability to harvest large seeds. Life is not as harsh for humans, so the life-and-death aspects of our variations may be hard to appreciate. But for organisms exposed to the rigors of nature, factors such as height, shape, and color can make a big difference in speed, agility, endurance, or the extent to which an individual blends into its background. Such variation really can spell the difference between life and death.

(Continues...)

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Edition details

• Publisher: Princeton University Press
• Publication date: 2011
• Language: English
• ISBN 10: 0691152578
• ISBN 13: 9780691152578
• Binding: Paperback
• Number of pages: 448