One day, every kind of living thing on our planet decided to travel back in time to find its first and original ancestor. Humans, ferns, lobsters, sparrows, porpoises, roses, earthworms, bacteria, redwood trees, kangaroos, to name only a few, started out on their various evolutionary routes in reverse.

Each route led a species—including humans—in stages back to the ancestors that they shared with other living species. There, at the rendezvous with a common ancestor or ‘concestor,’ the cousins would travel together like pilgrims on the next segment of the reversed journey to the next concestor, where more cousins—sometimes a few, sometimes thousands—joined the group.

At each rendezvous, transformations took place. As the calendar spun us humans backwards through millions and then billions of years, our old “pre-human” traits became new again. We gained a tail, then night vision, then we were hatched instead of born, and we breathed under water. We lost our bones, then our bodies. The greater the number of cousins together, the farther back we all went, the more our reverse-evolutions became one story. At our fortieth rendezvous, about 3.8 billion years ago, all of today’s 8 million species found ourselves in the presence of the concestor of us all.

The stories of each stage of this grand evolutionary-tour-in-reverse are the work of Richard Dawkins in his The Ancestor’s Tale: The Dawn of Evolution (2004; revised with Yan Wong, 2016). Dawkins adopted the device of stories-told-during-a-pilgrimage from Chaucer’s Canterbury Tales, written in the 1300s. Instead of “The Miller’s Tale” and “The Knight’s Tale,” Dawkins gives us “The Gorilla’s Tale,” “The Peacock’s Tale,” and others, detailing the evolutionary changes along with the scientific innovations that made our understanding of them possible.

The Ancestor’s Tale is a story of coming together, of merging and then merging again. It grew, Dawkins explains, from his frustration with popular misperceptions of evolution as a march of “progress” that has produced humans as its “most evolved” result thus far. We tend to view too many species around us as beautiful or impressive but of course “less evolved” than we are. Today’s eagles and ferns, we think, reached an evolutionary dead-end some time ago and then somehow managed to hang on as species.

But Dawkins shows us vividly that over time, all species change. Every organism alive has the fullness of evolution behind it. The pilgrimage back in time reminds us of that. “Go backwards and, no matter where you start, you end up celebrating the unity of life. Go forwards and you extol diversity” (6).

Along the way, the milestones are the concestors.

What is a concestor? A moment in history when there were two animals in the same species, one of whom became the ancestor of [for example] all humans and no wombats, while the other became the ancestor of all wombats and no humans. They may well have met, and may even have been brothers. (27)

To guide us through Dawkins’ 700 imposing pages, we have the work of Connie Barlow, teacher and science writer. Her 34-page text Greet the Concestors is available for free on the Internet. In 2005 Barlow adapted Dawkins’ book to make it usable as an outline for a ritual celebrating nature and even for an elementary science class. (See http://www.thegreatstory.org.) Her work is a valuable counterbalance to Dawkins’ erudition.

Here is Barlow’s description of the first Rendezvous for humans, followed by highlights of four others. Keep in mind that the concestors, though some have familiar names, did not look the same back then as they do today, any more than we do.

The likely Concestor of humans and chimps about 6 million years ago. Meet Sahelanthropus tchadensis. (Smithsonian)

#1 Rendezvous: Greet your CHIMPANZEE cousins!
TIME: 6 million years ago, during the late part of the Miocene epoch of our Cenozoic Era.
WHERE: a forest clearing in Africa
WHO JOINS? Chimpanzees and Bonobos (pygmy chimps), which are the 2 living species of genus Pan.
CONCESTOR 1 is your 250 thousandths great-grandparent.
FORM: This concestor looks more like a chimp than a human; it probably makes and uses tools. Although we spend a lot of time on the ground, we feel safest in trees and certainly sleep there.
TOTAL # LIVING SPECIES ON THE PILGRIMAGE NOW: 3 [humans, Chimps, and Bonobos]

Rendezvous #5, 25 million years ago. “Nearly 100 species of colobus and langur monkeys and baboons” join the pilgrims, who now number 118 living species. With Concestor #5, we now “have a tail for the first time!”

Our distant present-day cousin the Salamander, descended from our 175 millionth great-grandparent. (wikimedia)

Rendezvous #17, 340 million years ago. Greet your Amphibian cousins. “5,000 species of living frogs, toads, and salamanders” join the pilgrimage, for a total of 27,000 species. “We spend our early youth as a fishlike tadpole! This is the first time we can breathe underwater…and we still have lungs to breathe on land.”

Rendezvous #36, time unknown. Our plant cousins. This concestor, the shared ancestor of plants and animals, is a primitive single cell some of whose descendants will absorb photosynthetic bacteria to become the 30,000 species of all living land plants, even the giant redwoods. The pilgrims now number 2.7 million species.

Finally, #40, 3.8 billion years ago, is not actually a Rendezvous, for every species living today is already present. Barlow writes that we witness the “first semblance of life – whatever that might have been. …Praise LIFE! And praise our Planet Earth and the vast and creative Cosmos which, together, are capable of manifesting Life!”

Dawkins himself concludes his book and the story of his own ‘pilgrimage’ more severely. He explains why he scorns beliefs in the supernatural.

‘Pilgrimage’ implies piety and reverence. I have not had occasion here to mention my impatience with traditional piety, and my disdain for reverence where the object is anything supernatural. But I make no secret of them.… My objection to supernatural beliefs is precisely that they miserably fail to do justice to the sublime grandeur of the real world. They represent a narrowing down from reality, an impoverishment of what the real world has to offer. (700)

For me, the story of the pilgrimage weaves my connection to the life around me more closely. I like imagining that the shrubs and birds and dogs and squirrels I see every day have all returned from their pilgrimage to the past, as I have. We look at each other knowing what a long way we have all come.