We must not treat the unknown as known and too readily accept it. And he who wishes to avoid this error (as all should do) will devote both time and attention to the weighing of evidence.
—Cicero, De Officiis, I, 6
This book is a reference listing reports about mammalian hybrids. As such, it might be of interest to a scientist. But I did not write it for scientists alone. In fact, this book lacks an inherent quality of a scientific work because the intent here is to be strictly factual. Scientists almost never attempt to limit themselves to fact. Instead, they constantly make inferences about reality based on their theories about the nature of reality. In other words, scientific writings are permeated with beliefs. They are theory laden. The idea behind this book, however, is that I would proceed as would a neutral journalist. I would simply report what others have said and done without introducing my own beliefs into those reports.
For when it comes to hybrids, most people believe either too much or too little. That is, they tend to either accept too many fanciful hybrids as real, or to reject too many factual hybrids as false. Of course, if one actually had to adhere to one of these two states of mind, it might be wise to choose the latter. For there are, in fact, many hoaxes and false reports about hybrids, so believing everything you hear would be naive. But indiscriminate disbelief — even in the face of contradictory evidence — is also bad, perhaps even worse than a simple gullibility, because an unwillingness to alter one’s beliefs reflects just that sort of narrow-minded bias that precludes any valid investigation and real learning. It’s exactly the attitude that centuries ago prevented Galileo’s conservative colleagues from looking through his telescope.
So when I considered my own approach to the construction of this book, I decided I would try to avoid expressing my own beliefs and instead do my best to stick to the things I know. Instead of saying “such and such a hybrid exists,” I would say “so and so reported such and such a hybrid.” I know, of course, that there are many false reports of hybrids, but I cannot say with certainty, in every case, which of them is correct. So here I record reports about hybrids and say what others believed about them, but I try not to judge their beliefs or to state my own opinions. I feel this distinction is important because it means I will be better able to avoid false statements, which is always the result when one presents the mistaken claims of others as fact. And yet, it also allows me more fully to communicate what others have said about the various strange, and often dubious hybrids that appear in the literature. For, though it is often questionable whether a hybrid has been correctly reported to exist, it is never in doubt, so long as a definite citation can be given, whether or not the report itself exists. Obviously, such a policy will mean that a certain number of nonexistent hybrids will be listed in this book. But hybrid crosses seem to fall into the same category as do accused men on trial: It’s better to acquit a hundred criminals than to convict a single innocent man. In the same way, I would rather list a hundred falsely reported hybrids than omit a single reported cross that’s real. After all, anyone interested in any given cross will be able to look at the evidence cited and decide whether the report is worthy of belief.
In the opening paragraph of his Lives of the Noble Greeks and Romans, the historian Plutarch (46-120 A.D.) explains to his friend, the Roman politician Quintus Sosius Senecio, that his task in attempting to give an account of long-dead or even mythical individuals, was much like that of the mapmakers of his day:
And Plutarch, who clearly does consider Romulus mythical, goes on to give a detailed account of his life.
This book, too, contains elements of both history and myth, for the student of hybridization today is placed in much the same position as Plutarch and his geographers. Reports of hybrids range from the well-documented and mundane, to the poorly documented but plausible, to the hearsay and improbable, to the seemingly impossible and mythical. However, at exactly what point along this spectrum it might be that reality and feasibility pass over into imagination and impossibility is unclear. We are faced with Plutarch’s boundary problem. No one knows just how different two animals can be if they are to produce hybrid offspring together. And reports of hybrids sometimes do pass well “beyond the earliest times that reason can reach and real history embrace.” But even untrustworthy accounts of extreme antiquity can be of interest. After all, some crosses are very hard to obtain, and the only report of a very rare type of hybrid might well date back hundreds of years, and we might have to wait centuries more to see one again. To hear of such organisms, we would of course have to look back into the early literature, in the same way that astronomers do to learn of a supernova or some comet observed in times gone by. Such reports can be bizarre, but there is really no other source of information. And some readers may choose to believe them. As I say, this book is not just for scientists, it’s also for people who wish to believe things that many scientists would consider impossible. There are, of course, many intelligent people, even geniuses, who have accepted reports about hybrids that modern science would deny, for example, Voltaire (1768, p. 121):
Moreover, even false reports, which tell us of hybrids that have never occurred, can be informative. If nothing else, they indicate something about the beliefs people have held about hybrids. For example, it’s interesting that many people (including such acknowledged geniuses as John Locke and Voltaire) have expressed the belief that humans can hybridize with animals, whether or not reliable evidence exists to support such a notion.
The parallel between hybrid crosses and Plutarch’s historical personages can perhaps be made clearer with an example. Take Jesus Christ. There are many people who do not believe that Jesus ever existed, let alone that he was divine. And yet, even an atheist would admit that there are historical references to a person of that name. Thus, while not believing in the real existence of Jesus, a fair-minded atheist might admit that such references do exist. He or she might even read, list or quote them. Both the honest believer and the honest unbeliever would be justified in collecting every shred of evidence relating to the existence or nonexistence of Jesus. The former might gather it with the intention of bolstering Christianity’s case. The latter might wish to show that available historical data is entirely insufficient to justify belief. A third type of person, however, a neutral historian, might simply wish to assemble all the information bearing upon the topic. It is this third motive that has guided the creation of this book. In the case of every cross, I have endeavored not to express my own beliefs as to whether it might occur. My intention, instead, has been to collect reports bearing on the phenomenon of mammalian hybridization and to record each such piece of information under the headings of the various crosses to which it relates. Viewed in this light, each separate type of cross is a distinct historical entity to be investigated. The crosses “dog × cat” and “gorilla × chimpanzee” are topics that can be researched, just as Jesus and Mohammed can, whether you believe in them or not. With this approach, which brings a strong historical element to the study of natural history, belief can be largely set aside. So I try to take the same attitude as many defense attorneys take with respect to the alleged crimes of their clients: I say, “It’s not my job to believe anything.”
This perspective has directly influenced the construction of this book. Previous references listing hybrid crosses have set a conservative policy. In general, the authors of such works have either not listed poorly documented crosses or, when they did, have expressed opinions dismissing their possibility. But anyone who wishes to encourage further investigation of the phenomenon of hybridization cannot afford such an approach. After all, much is unknown about hybridization, and if an author dismisses the possibility of a given type of cross, or fails to mention allegations that it has occurred, then the readers of the resulting book, all of whom are potential researchers, will see no reason to look into the matter further. So the expected consequence of such a policy is stagnation of both knowledge and thought.
For example, if we wish to make any real progress in understanding how different two animals can be if they are still to produce hybrids, we can do so only by investigating distant crosses. Such crosses, if they do occur, must be rarer than ones between nearer relations, and therefore must also be more poorly documented. But whatever evidence does exist to attest the existence of a given type of hybrid cross must be brought together under the heading of that cross so that we can better judge whether such a cross does in fact occur. So in the spirit of Plutarch, “I thought I might reasonably venture” to include in this book reported crosses that others have described as impossible. Many of these, I am sure, are in fact mere cases of error, fable or hoax. But my plan is to list, as fully as possible the evidence attesting each reported cross, and then to leave it at that. The reader then can judge. Because, again, not to list reported crosses on the simple basis of my own opinion would be to introduce a systematic bias into this work, which is meant to be as full an account as possible of the phenomenon of mammalian hybridization. No doubt, certain types of hybrids that are poorly documented at present will one day be either better substantiated or firmly ruled out as false. It’s my hope that those who make this progress in human knowledge will first read about some of those crosses in this book.
Human Origins: Are we hybrids?
On the Origins of New Forms of Life
Cat-rabbit Hybrids: Fact or fiction?
Georges Cuvier: A Biography
Prothero: A Rebuttal
Branches of Biology