On the Origins of New Forms of Life: A New Theory PDF
Preview On the Origins of New Forms of Life: A New Theory
On the Origins of New Forms of Life A New Theory ________________________________________ EUGENE M. McCARTHY By doubting we come to questioning, and by questioning we perceive the truth. —PIERRE ABELARD1 ii Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. iii Once again, for Rebecca, Clara, and Margaret ____________________________________________________________________ Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. iv And such things as are not commonly known, and lie scattered here and there in other men’s writings, or are found among the old monuments and archives, I shall endeavor to bring together. —PLUTARCH, Nicias (1st century A.D.) They who have presumed to dogmatize on nature, as on some well investigated subject either from self-conceit or arrogance, and in the professorial style, have inflicted the greatest injury on philosophy and learning. —FRANCIS BACON, Novum Organum (1620) The conclusion reached by a process of thought is also not infrequently the conclusion of the process of thought. —ARTHUR O. LOVEJOY, The Great Chain of Being (1936). Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. v Preface _________________________________________ At one time, before I had become a geneticist and an expert on hybrids, it would never have occurred to me that hybridization might play a direct and frequent role in the production of new types of organisms, one of the primary claims made in this book. In fact, until I read the Origin of Species, I had never given hybrids much thought at all. I knew hybridization was a technique used in plant breeding and that a mule is a hybrid of a horse and an ass. But beyond these facts, my knowledge of hybrids was minimal. And yet I still made certain general assumptions about hybrids. For example, I had always believed organisms could interbreed only if they closely resembled each other and that some rule allowed biologists to predict with certainty whether a given cross was possible. I had also assumed hybrids were always sterile. I was surprised, then, when I first encountered Darwin's observation that "No one has been able to point out what kind, or what amount, of difference in any recognizable character is sufficient to prevent two species crossing"2 and that "the facility of making a first cross between any two species is not always governed by their systematic affinity [that is, by how closely they are related] or degree of resemblance to one another."3 It was difficult for me to believe biologists lacked a firm predictive rule. I also balked when Darwin pointed out that hybrids are not always sterile: Finally, looking to all the ascertained facts on the intercrossing of plants and animals, it may be concluded that some degree of sterility, both in first crosses and in hybrids, is an extremely general result; but that it cannot, under our present state of knowledge, be considered as absolutely universal.4 Darwin's comments made me wonder: How often are hybrids fertile? Do they occur naturally? What is their evolutionary significance? I decided to investigate reported Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. vi accounts of hybrids. As I read, it became clear that thousands of different crosses produce fertile hybrids. Eventually, in completing a book on bird hybrids (Handbook of Avian Hybrids of the World, 2006), I found that the majority of avian crosses, at least the majority of those for which data on fertility is available, actually do produce hybrids that are themselves capable of having offspring. Moreover, about half (i.e., about 1,800) of the crosses listed in my book occur in a natural setting. Many of these crosses occur on an ongoing basis and have produced permanent hybrid populations. I am currently working on a survey of hybridization among mammals. There, too, I have found that many crosses produce fertile hybrids and that many such crosses occur in a natural setting. In other categories of organisms, other workers have reported similar findings. Among fish and plants, such hybrids are even more numerous than among mammals or birds. Hybrids among invertebrates seem innumerable. After looking at so much data, I began to wonder: what becomes of these myriad hybrids that, from the standpoint of geological time, are being produced in such vast numbers? If many kinds of natural hybrids can produce offspring, which is clearly the case, what is the role of hybridization in the evolutionary process? Over the years, I have accumulated information bearing on these issues and have made a particular study of genetic mechanisms known to produce new types of organisms, many of which involve hybridization. In the process, I have come to believe that certain important flaws in standard evolutionary theory have passed unnoticed, primarily because most people are unfamiliar with the actual facts of hybridization as revealed by observation. Indeed, in comparing modern attitudes toward hybrids with the statements of naturalists of past eras, I have come to the realization that we have retained certain potent presuppositions derived from ancient systems of thought without change and without substantiation. Some of these unfounded claims are axiomatic in the modern scientific account of the natural world. In particular, a stereotypic conception of hybrids as sterile evolutionary nonentities has remained largely in force. Even many biologists think this way. In this book I have tried to replace this stereotype with a new image that better corresponds with available data. I also offer a different theory of evolution that, I am convinced, is more consistent with observation than is Darwin's. I hope the reader will be convinced as well. Of course, I expect no one to accept such a radical assertion on faith. The validity of any theory can be assessed only by sifting through the evidence, point by point, fact by fact. I have therefore done my best to construct this book with what James Boswell once described as "that diligence which alone can collect those scattered facts that genius, however acute, penetrating and luminous, cannot discover by its own force." I want to thank the many friends and colleagues who in some way helped with this book. They are too numerous to name individually, but I would like to express my special appreciation to Stuart Katz and my wife Rebecca. Their endless Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. vii enthusiasm and support for this project kept me going when I would otherwise surely have set it aside. Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. viii Contents _________________________________________ Introduction 1 Chapter 1: On Species 6 Chapter 2: On Hybridization 34 Chapter 3: Karyotypes, Variation, and Stasis 67 Chapter 4: Stabilization Processes: Examples 85 Chapter 5: Stabilization Processes: Prevalence 117 Chapter 6: The Fossil Record 145 Chapter 7: The Unknown Force 164 Chapter 8: On Diversification 206 Chapter 9: On the Origin of Mammals 233 Chapter 10: Concluding Remarks 273 Appendices 283 Bibliography 313 Notes 376 Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. ix On the Origins of New Forms of Life: A New Theory ________________________________________ Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy. x Extracts _________________________________________ This book is concerned more with the actual characteristics of hybrids than with their reputation. However, given the theoretical nature of this work, and given that hybridization plays an important role in the theory presented, it will be worthwhile to consider not only what hybrids are, but also how they have been perceived. The peculiar, often unfounded, impressions people have had of hybrids have contributed greatly to the position allotted them in theory — perhaps as much, or even more than, the facts. The following extracts, then, are intended merely to place hybrids within the context of human opinion. From a factual standpoint, many of the statements quoted in this section are false. More is conveyed here of connotation than of fact. Indeed, those who wish merely to learn the facts about hybrids might just as well pass over this section and proceed straight to page 1. But, for the curious reader who wants to understand more of human attitudes toward hybrids, these quotations may prove informative. ------------------- You speak words of love, but when have you been true? In your youth, you wed Tammuz, but then soon left him. Now our autumns are sodden with his tears. And the Allala bird, when he wooed you, you embraced him as your mate. Then you struck him, broke his wing. Now he moans in the forest, alone. The lion you made your lover, then ensnared. With wild groans he died writhing, dangling by a paw. You seduced the stallion, then harnessed him – rode him raw. Even Silili, his dam, knew the strokes of your crop … The Spurning Of Ishtar (from the Epic of Gilgamesh)5 There was a time in which there existed nothing but darkness and an abyss of waters, wherein resided most hideous beings, which were produced of a two-fold principle. There appeared men, some of whom were furnished with two wings, others with Copyright © 2008 by Eugene M. McCarthy, Macroevolution.net. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission of Eugene M. McCarthy.
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