The Origin of Specious : SHADOWS OF FORGOTTEN ANCESTORS: A Search for Who We Are, <i> By Carl Sagan and Ann Druyan (Random House: $23; 505 pp.)</i>

This is the first in what the authors intend to be a multivolume series in which the true nature of human beings will be set forth so that we can get ourselves out of the “mess” we find ourselves in. The mess that provided the original motivation for the series was the nuclear-arms race, but that doesn’t affect its timeliness--indeed, there has probably never been a time when human beings haven’t been in one sort of mess or another.

This first volume is devoted to establishing the proposition that human beings are part of the animal kingdom and therefore share both our chemistry and some behavior patterns with other animals, particularly other primates.

The authors start with a couple of chapters describing the formation of the earth, the appearance of life, and the workings of the genetic code. This is as good a description of this material as you’ll find anywhere. The book then goes into a long description of some carefully selected studies and experiments in primate behavior, highlighting examples that the authors believe will illuminate the way people act. The last few chapters argue that any differences between human beings and other animals are differences in degree, rather than differences in kind. There is, they tell us, no soul, nothing that distinguishes humanity from the rest of creation. The thread of this argument, we are promised, will be taken up in future volumes.

It’s difficult to form a judgment on a series of books when you’ve only seen the first volume, but “Shadows” is 397 pages long and is being marketed as a free-standing work, so I think it’s fair to take what the authors and publisher offer at face value. On these grounds, I am sad to report that I found the book falls far short of the (admittedly high) standards set by Sagan’s earlier books.

At the most trivial level, it is full of diversions that add little to the text, serving only to distract the reader. One minute you’re reading about the formation of multicellular colonies in the primeval oceans; in the next paragraph the subject has switched for no apparent reason to experiments on the cognitive abilities of cats. A discussion of baboon behavior in zoos is interrupted by a description of primatologist Solly Zuckerman’s career as a postwar science adviser in Britain, after which we are invited to “Consider the gibbon.” I hope future volumes will be edited a bit more aggressively.

If these were the only problems in the book, they could easily be ignored and we could all have a good read. It seems to me, however, that there are serious flaws in the author’s arguments--flaws that are likely to prove fatal to their entire project if they persist in later volumes. The most serious of these involves what I like to call the Fallacy of the Continuum.

Here’s an example of the fallacy: You can’t define the income that separates the rich from the poor, since someone earning a dollar more than any amount you name will be no better off than someone earning a dollar less. Therefore, there is no difference between the rich and the poor.

We all recognize this as a ridiculous conclusion--Ross Perot is clearly rich and the homeless man sleeping on the downtown grate is poor, even if you can’t give a precise quantitative definition of poverty, and even though they both may have some dollars in their pockets. Yet this is precisely the kind of argument the authors use to establish that humans are no different from other animals. Chimpanzees use sticks as tools to pull termites from mounds, they say, and humans build tools like airplanes and interstate highways. We’re both toolmakers, and there is no real difference between us. I don’t know about you, but it seems to me that anyone who dismisses the difference between a stick and a 747 as a mere “difference in degree” is being willfully obtuse.

I am particularly disturbed that Sagan, who has had a distinguished career as a theoretical astrophysicist and is a man of no mean mathematical ability, has ignored or remained ignorant of more than a decade of research on the nature of complexity. When you deal with highly interconnected systems like the brains of primates and human brains, you reach a point where adding a bit more of the same stuff produces completely new forms of behavior--where differences in degree become differences in kind.

I would argue that the development of a large cerebral cortex during human evolution was the equivalent of adding a hard drive to a computer--it’s still a computer when you’re done, but it has a whole suite of new capabilities. There is plenty of room in this new science of complexity to accommodate fundamental properties like self-awareness in the human cortex but deny them to other existing primates (although not necessarily to our now extinct ancestors and relatives).

We do, indeed, share much with our animal relatives, but we’re different as well. The authors aren’t going to get anywhere unless they are willing to recognize both of these central truths abut the human condition.

And then there’s the problem of anthropomorphism--the tendency to assign human motives and emotions inappropriately to non-humans. This book is full of anthropomorphisms. At first I thought it was just being used for literary effect, then I thought it was one more of those glib oversimplifications that make Sagan’s books so accessible to the general reader and so infuriating to specialists. But no--from spiders to chimpanzees, the authors talk about the imagined thoughts and feelings of all sorts of beings. This reaches its zenith (or nadir) in a disastrous chapter titled “Gangland,” in which the authors treat us to what they fondly imagine various chimpanzees in a troupe led by “Big Guy” are thinking. In what will probably be the most quoted line in the book, one female comments that “The Big Guy, he’d as soon (go to bed with) me as look at me.”

This is the stuff of Saturday morning cartoons, not PBS specials. Although they offer a few paragraphs of flabby defense (“It is possible to carry the fear of anthropomorphism too far”), the authors have clearly gone overboard on this issue. They rightly point out how ridiculous it was for Victorians to consider monkeys “immoral and lascivious” because of their sexual behavior. Why, then, do they turn around and do the same thing by using the terminology of our politically correct modern Victorians and talk about “sexual oppression” among chimpanzees? Even if “Big Guy” and his followers were as conscious as the authors imagine, I doubt if they’d know what to make of this concept.

In responding to one writer who claimed that animals could neither remember nor anticipate events, the authors express their (justifiable) disagreement by exploding, “How could he know that?” I hope they will apply this criterion more rigorously to themselves in the rest of this ambitious work.