The story of evolution recounts the ways that plants and animals have changed over time as small bodily variations have improved their odds for survival. But what about those species that fitted so successfully early on into stable environments that they have altered little or not at all? Are any such ancient species (besides the microbes) still around today?
Yes. In Survivors: The Animals and Plants that Time Has Left Behind (2011), Richard Fortey tracks down present-day plants and creatures that look much like their fossilized ancestors. Oddly, their stories of sameness impress me with as strong a sense of evolution’s power as stories of modification; natural selection goes with what works, whether it’s new or old.
Horseshoe crabs, after half a billion years, still crowd the beach.
In the opening chapter, Fortey is on a beach in Delaware on the night of the annual horseshoe crab orgy, when thousands of male horseshoe crabs come ashore to clamber on top of the females. Horseshoe crabs have been scrambling up beaches for 500 million years.
In the darkness along Delaware Bay the scratching percussion of the crabs provides an unmusical accompaniment on an imaginary journey backwards in time: to an era well before mammals and flowering plants; a time before the acme of giant reptiles, long before Tyrannosaurus; backwards again through an extinction event 250,000,000 years ago that wiped nine-tenths of life from the earth; and then back still further, before a time of lush coal forests to a stage in the earth’s history when the land was stark and life was cradled in the sea.
Four hundred mya, plants like this Norwegian Huperzia moved from the water to land and were among the first to acquire the crucial, stiffened water-conducting tubes–today we know them as stalks–that enabled them to stand upright and compete for light.
In the other chapters, Fortey describes the velvet worm in New Zealand, the lovely Norwegian fir moss, the not-so-lovely lungfish. The photo captions here mention their keys to long-running adaptive success.
It helps that their environments have changed very little. “Survival is about endurance of habitat.” One habitat that endures is the tidal flat, where the shallow sea meets the muddy shore. Organisms here can burrow, find oxygen in the water and air, find food through filtering or scavenging. Here are horseshoe crabs, snails, small fish, many plants. “This habitat does seem like a good place to be for an organism with conservative tendencies. If its own place survives, then so will the beast. It is the right place to weather mass extinctions that affect many other environments more severely.…Stick-in-the-muds last longest.”
As for the durable species themselves, a few characteristics recur. “Many…seem to have long life spans.” Horseshoe crabs take a decade to mature. And some enduring animals invest more resources in fewer progeny by producing “relatively large eggs or few offspring.” But there are no fool-proof formulae. “[T]he luck for old timers will eventually run out. It always does.”
In Australia, Fortey finds the lungfish that dates back 400 mya, “the great survivor among the vertebrates, the animals with backbones.” With lungs, these sea creatures, in transitioning to the land, can gulp air whenever the river runs low on oxygen.
What about humans? When will our time run out? Fortey doesn’t make guesses, but he has a hard label for us.
[Early man] may have hunted edible mammals and birds to the point of obliteration even in his earliest days; he was the first species that deserves to be called the Terminator….The extinction event that is happening right now is the first one in history that is the responsibility of a single species. There’s no meteorite this time, no exceptional volcanic eruptions, no ‘snowball earth,’ just us, prospering at the expense of other species.
He is confident about the survival of only one kind of organism. “I am not worried about the survival of bacteria. They will be there to rot down the last bodies of the last humans, and then the wheel of life will have turned full circle.” So ends the book.