Over the long reaches of earthly time, species change, of course; some do so drastically, many become extinct, some have appeared as distinct species only recently. But what about the opposite case, species that have changed very little, that have survived so successfully in their niches that adaptations have been few? Are any of these creatures, often preserved in fossils, still wandering the forests or swimming the seas?
Yes. In a wonderful book, Survivors, Richard Fortey tracks down some of them, organisms that are not only long-term survivors but were here in only slightly different form when life took its momentous steps from the sea to the land, from lacking any bones to hanging from backbones. For most of us the last half billion years is an abstraction, but the picture springs to life when we are close up to the living descendants of its pioneers.
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 date back 500 million years, bringing their skeletons of armor from the water onto land long before the dinosaurs and throughout the mass extinctions.
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 that enabled them to stand upright and compete for light.
Over the succeeding chapters, Fortey introduces us to the velvet worm in New Zealand, the colorful archaea microbes in Yellowstone National Park, the lovely Norwegian fir moss, the not-so-lovely lungfish. He values all their stories. “I would like to use the term biography if the word had not already been hijacked for humans.”
How did these survivors endure? “Survival is about endurance of habitat. Every organism has a place where it fits in, earns a living, reproduces—a niche in nature.” One common habitat that endures is the tidal flat, where the shallow sea meets the muddy shore. Organisms 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.”
And as for species themselves, “there are particular properties of the organism itself that may have helped with endurance.” “Many… seem to have long life spans.” Horseshoe crabs, for example, 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 for long-term survival. “We must never forget about being in the right place at the right time. The inescapable truth is that the 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 the transition to the land, can gulp air when the river runs low on oxygen.
Even for humans? The unanswered question hangs over the final pages. Will humans be counted among the million-year survivors in the future? Certainly, Fortey does not go easy on 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 worries about the survival of all species except for one, and it is not us. “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.” And so ends the book.
Colorful microbial archaea thrive in the hot springs of Yellowstone National Park. “Imagine being adapted to sitting in nearly boiling acid.” Life may have begun in such cauldrons. (theglobalpanorama.com)
While the close of the book is apocalyptic, its substance is uplifting. Religious believers may feel dwarfed by the vastness of their deity and yet empowered by their own awareness of it. Similarly, for non-theists who follow science, learning of these ancient lives still present today after long eons is also both humbling and exhilerating.