Our walk through time begins on a country lane in the village of Kingston Saint Mary, in southwestern England. This is a pilgrimage of sorts, a hike that is also a metaphorical voyage backward through 3.5 billion years of evolution. As we head down the road, a small brass band sees us off, making a joyful noise unto anyone listening—presumably not the Lord, since it’s Sunday morning and He probably thinks we should be in church instead.
But this is an unbelievers’ pilgrimage inspired by the biologist and polemical atheist Richard Dawkins. Specifically, we are re-enacting the imaginary walk through time described in Dawkins’ book The Ancestor’s Tale, a history of life that takes the usual metaphor of evolution, a tree with roots in the Precambrian and branches for all the major phyla, and turns it upside down. Dawkins begins his account in the present and traces the human lineage back to the hypothesized single cell that set the whole process in motion by dividing in two.
Our leader, Chris Jenord, has taken Dawkins’ timeline and overlaid it on the literal map of the Quantock Hills, a popular hiking area in Somerset. In homage to Dawkins, he calls it the “Ancestor’s Trail.” The branch we’ll follow is about 14 miles, ending at the cobblestone, fossil-rich beach at Kilve. The 40 or so who start here are Humans. Along the way we’ll meet groups of hikers starting from other points, representing other species.
Most of the interesting events in evolution—interesting to us vertebrates, anyway—are crowded into the last half-billion or so years, leaving around three billion years during which evolutionary changes happened relatively slowly. Accordingly, Jenord has drawn up a sliding scale relating the distance we’ll cover to evolutionary time. At the end of our walk, a single step will stand for a million years, but as we set out, one step corresponds to 10,000 years. This timeline has no relation to the actual history—geologic or biologic—of the Quantocks, which are mainly sandstone and limestone hills dating from roughly 350 million years ago. The place last played a significant role on the world stage during the Monmouth Rebellion against James II, 328 years ago. On our hike’s time scale, that’s a fraction of an inch.
With our very first step we cover all of recorded human history.
Six Million Years Ago: We have been walking for less than 10 minutes, along a path that winds gently uphill through sparse woods. We pause at the edge of a field, where a muddy track comes in from one side, and after a few minutes a half-dozen “Chimpanzees” emerge from the trees. This is the first of a number of rendezvous that we Humans will have with other hikers, many wearing masks or costumes depicting their place in the great panoply of species. The hikers wearing chimp masks lend the event a kind of determined whimsy, like a cross between Stephen Jay Gould and Monty Python.
Yet here we stand, metaphorically, at a sacred moment, the origin of the human species (or, more accurately, genus), when our lineage diverged from that of the other apes six to eight million years ago. Of course nothing special marked the moment: An ape gave birth in the forest, surrendering her offspring to the relentless winnowing of natural selection. Two lines of descent diverged and led, over some 300,000 generations, to chimpanzees inhabiting human zoos, instead of (among an infinite number of evolutionary possibilities) the other way around.
We toast the event with water, and continue walking.
140 Million Years Ago: According to Jenord’s plan we are now on an intermediate scale, in which a single step is equivalent to 100,000 years. Even at that rate, we must take 10,000 steps, roughly five miles, to cover a billion years. We emerge onto a landscape of rolling hills and gently sloping, intensely green pastures. This countryside has been inhabited and cultivated for millennia, but apart from the occasional farmhouse there is nothing to suggest that we are in one of the most densely populated nations in the world. Cattle and sheep (real four-legged ones) eye us languidly while we step fastidiously over and between the plentiful evidence of their outstanding diet. At one point our column of walkers somehow gets between a ewe and her lamb, who runs alongside us, bleating, until an opening in our ranks allows her to cross.
August days in the Quantocks can be hot, or so we’ve been warned, but today isn’t one of them, certainly not to anyone who has hiked in the American West. But as we enter a copse, a ruddy-faced Englishman walking with me sighs, expressing relief to be out of the sun—or, as we would call it in the States, the “overcast.”
On a low ridge we find ourselves at a hedge of blackberry bushes. Trisha Rogers, one of those ageless and indefatigable Englishwomen who are always solving murders on public television, reaches for a few, but finds them sour. The path turns downhill and, as it bottoms out, the berries ripen, and she pops a few into her mouth. “I guess this makes me a hunter-gatherer,” she says cheerfully.
On our timeline we have passed through one of the most consequential events in the history of life, the Cretaceous extinction, about 65 million years ago, which wiped out the dinosaurs and opened up an ecological niche for large mammals to evolve. Our designated minstrel, a science buff named Jonny Berliner, describes it this way in a song called “The Evolution of Man”:
One day a mighty meteor came down from out the sky,
And killed those nasty dinosaurs so the micey things could thrive,
Everything mammalian, grew bigger almost daily and...
Soon our furry ancestors were swinging in the trees...
We pause here to wait for the Marsupials. According to Dawkins we share a common ancestor with kangaroos, opossums and other pouched mammals approximately 80 million generations back. Presumably this relation was a small and unimpressive quadruped that rooted around in the dirt for insects—a seemingly unlikely candidate to supplant the giant reptiles that dominated the Triassic. But, Dawkins notes, those are often the species whose descendants inherit the earth. “It seems to be a rule,” he writes, “that large and specialised animals...don’t have a long term evolutionary future but belong to the 99 per cent of species destined for extinction.” Left unsaid is that “large and specialized animal” is a pretty good start on a description of Homo sapiens.