The Ancestor's Tale
by Richard Dawkins
Pedigrees tell you a lot. Somebody once said every family includes a railroad man, a drunk and a clown; by process of elimination you may discover you have one of those roles in your own future. Or you may learn, as my wife did from an eccentric great-uncle's research, that your forebears were the rightful Kings of Scotland. [1] A typical family tree has the customer at the root. Or you can do it the other way, from one ancestor in the remote past to many descendants today, showing for example that you (a twig) are a distant half-cousin to President Cheney, both tracing back to a Crusader's venturesome wife. Stephen Jay Gould taught that a family tree of life on Earth takes this shrub shape: one ancestral species at the bottom giving rise, through untold generations of natural selection, to a million or so present-day ones at the top.
When you look at such a shrub, your first impulse is probably to locate Homo sapiens [2] and follow the branchings from your single-celled ancestor up to your own twig. (To be fair, a beetle or a kangaroo would do the same if they made a habit of scanning charts. But in practice it's probably a uniquely human failing.) You learn this way, too: We are just as much descended from gorillas as we are from gillyflowers.
Richard Dawkins--this is not the first time we have noticed him doing this--takes a fresh look at the scheme. He says tracing the path through the tree of life to get to ourselves means treating our twig as a goal, but evolution doesn't care about goals. A hiccup in history some 6 million years ago produced a chatty bipedal ape, but it didn't have to happen that way. Another hiccup farther back in time could have left dinosaurs around to suppress [3] our ancestors and evolve into a chart-making species themselves. Looking still deeper into the fog, I suppose some ancient colony of one-celled biochemistry geniuses could have had descendants capable of inventing philosophy and the buddy flick. In fact, it's hard to insist that the "Crown of Creation" has to be a considering species in the first place; a different set of hiccups could just as well have led to a world won by big teeth or horrible toxins. Reading the diagram of our ancestry as pointing to our kind, and our gifts, not only distorts the history of life but also deprives the reader of useful perspective.
What if, instead, we begin where we now are and go down the shrub, allowing rabbits and sawgrass to do the same whenever they get around to it? We use the same diagram, but we have no illusion of choice when we get to a place where it branches: All the splits in the chart, reading up, were "either A or B but not both"; when we read down it's always "keep straight on." This way of tracing history works with knowledge rather than speculation, and at each junction we can note some things about the branch that is joining itself to our path. Even more to the point, if we stop immediately after each such event, we can draw inferences about the being that must occupy that perch in the shrub.
Take for example the most recent fork, just a few million years ago: Human beings arrive, coming down our twig, and the chimpanzees join us. Now it's a pretty good rule that whatever we have in common with chimps is quite likely to be a characteristic of the ancestor we share with them. So we take stock and conclude that our "concestor" was a pretty clever type who lived socially, ate a mixed diet, traveled mostly on the ground, and made a wide variety of vocal sounds.
Wait a minute. Who says we have a common ancestor with chimpanzees? After all, there was no one there to earmark one of its offspring This one leads to people and another This one leads to chimps. In other words, no history of a familiar sort. But we have a growing wealth of data instead that tells us not only who our sisters are but when our lines forked. The last umpty-ump million years are "documented" by fossil finds, and labs around the world are busy with DNA analyses that reveal kinships going back literally millions of generations. Paleontologists sometimes reach a near-consensus (T. rex lived in such-and-such a time and belonged to a group ancestral to birds) and sometimes not (elephants and manatees are/aren't more closely related than elephants and hyraxes), but molecular evidence goes a long way to resolve conflicts. And molecular evidence says chimps are nearest to us. The group comprising chimps and us is then nearest to gorillas, meaning the (chimps + us) line and the (gorillas) line have a common ancestor a few more million years ago.
(I should say here that scientists do their DNA sequencing on living species, not extinct ones. They don't try to analyze genetic material from our ancestors, because there isn't any. [4] In looking at DNA from us and other apes, they connect chimps and H. sapiens first on the strength of matches between our DNA and that of today's chimpanzees. The methods are complicated and occasionally inconclusive, but the author sets forth enough detail to give the reader a degree of confidence in the results.)
Dawkins throws out the shrub and adopts a literary conceit: We form a band to go on pilgrimage to Canterbury (sans martyr), and from time to time we are joined by other troops bound there too. So after the gorillas have added themselves to our company, the orangutans join next, then gibbons and so forth. The "rendezvous" are numbered from 1 (the chimps joining us) to 39 (the eubacteria joining all other beings), although details and even simple counts get blurred as we approach the end of the journey. Some of the travelers get to relate a tale, like another set of Canterbury pilgrims. The layout of the book has the contradictory virtues that it allows for our focus on ourselves but it doesn't make our twig in any way a destination.
As far as the big picture is concerned, I have to say the plan surpasses the product. You just can't read The Ancestor's Tale as a collection of pilgrim stories, because all the relations come out in the narrator's voice. Well, you reply, what voice would a cichlid fish speak in? You argue acutely, yes, but it doesn't save the Canterbury conceit.
That isn't to say that the structure of the book fails. Far from it: "Us" being joined by band after band of species is a strong image, time organization is just as clear reversed as forward, and the back-and-forth between the narrator's account of the journey and short theme pieces (tales) helps the reader stay attentive. The flow of the book is not just easy to follow but really compelling--it even has suspense, "What's holding up them fungi?"--and the charts are more understandable than shrubs.
I'll tell you what I mean by that last remark, then I'll stop. [5] The shrub diagram is so full of information that you really have no hope of gathering what it says. If it has detail down to, say, the level of orders, then it includes way too many twigs (thousands, probably) to take in; reduce it to 10 or 100 twigs and you have to strain to recall the wide variety of creatures each one represents. Dawkins' one-page graphics, on the other hand, show "already joined" species in one line--the children we know because they boarded the bus at previous stops, so to speak--and give a moderate level of detail about the ones now joining the pilgrimage. At Rendezvous 1 he has human beings on the one hand and, on the other, the line comprising chimps and bonobos. That's a simple example; the picture's more complicated when the monkeys appear, but still elegantly concise. The fine presentation of data makes it all the more impressive when the plants join our progress after their own billion years of backward history.
The Ancestor's Tale will repay the time you spend reading it. Good book.
[1] The Stuarts were Charlie-come-latelies.
[2] It just galls me when people cut the S off the ends of words. I knew a woman in Texas who would describe your specs as having a left len and a right len. Thinking back, I wonder if she would have named a wall-mounted candleholder a scon.
[3] E.g., eat.
[4] Amber, schmamber.
[5] As I write these notes I find a recurring temptation to put in more paragraphs and even footnotes, which is not what's needed.
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The Ancestor's Tale