Survivors and the Terminator

The story of biological evolution recounts the ways that most plants and animals have changed over time as small bodily variations improved their odds of survival. But what about those species, fitted successfully to stable environments early on, that have changed very little? Are any such ancient species (besides the microbes) still around today?

Yes. In Survivors: The Animals and Plants that Time Has Left Behind, Richard Fortey tracks down some present-day creatures that look much like their fossilizeds ancestors from millions of years ago. Oddly, their stories of sameness impress me with as strong a sense of evolution’s power as the stories of other species, including ours., that have changed to adapt.

Horseshoe crabs, after half a billion years, still crowd the beach. (delaware-surf-fishing.com)

Horseshoe crabs, after half a billion years, still crowd the beach.
(delaware-surf-fishing.com)

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.

firmoss (newfs.s3.amazonaws.com)

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.
(newfs.s3.amazonaws.com)

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 particular keys to 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.”

lungfish (media-web.britannica.com)

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.
(media-web.britannica.com)

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 type 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.

 

Feeling Old? Envy the Lobster

The certainty of death is hard enough. But aging as a prelude—the wrinkling, weakening, deteriorating and the rest of the assault—can feel downright demeaning! Is there a benefit here for survival of the species, or for any species, that no one told me about before I reached 73?

lobster (anvilcloud.blogspot.com)

(anvilcloud.blogspot.com)

Not all species go through their version of this. The paths that organisms follow after maturity vary enormously. Some plants live for one year only, others come back every season. Bacteria clone themselves and don’t die from age at all but from hostile organisms and conditions in their environment. Seabirds age very slowly; as long as they can fly, they can stay ahead of most predators.  Lobsters don’t age; they can continue to grow and remain fertile for 45 years or more in the wild, dying only when they can no longer molt and grow a larger shell.

How and why the declines of aging are included in the final phases of some species’ lives is complex. Wikipedia’s “Senescence” introduces the range of theories and uncertainties. Here are three insights from the evolutionary perspective that make sense to me.

One is that certain harmful genetic mutations switch on later in life after an organism’s reproductive period has ended. Many cancers in humans do, for example. Because they don’t impact the number or health of the offspring, such genes do no harm to the persistence of the species and so they are unlikely to be lost over the generations. The diseases of the elderly get passed along by the young.

Even more unfortunately, some mechanisms in our bodies boost our health when we’re young and then come back to bite us when we get older. Digesting calcium, for instance, builds strong bones early on but helps clog and stiffen arteries decades later. As long as such a function improves our fitness to make and raise babies, whatever damage it does later on doesn’t matter much in the very long run.

A third way in which selection seems indifferent to the pains of aging is statistical: even if natural selection did reduce the ravages of aging and prolong the fertile period, the population of such organisms would still decline with age as accidents and predators took their inevitable toll. The body invests its resources where they are the most effective for the future, in youth and early reproduction, not in a comfortable old age.

In these ways and others, aging is linked to the importance of reproduction and the dangers of predators and other external forces. For primates, including me, we reproduce early because the big cats—leopards, jaguars, cougars, tigers—stalked us for millions of years in the forests and grass lands. And for most other species as well, the safest bet for species continuity is simple: reproduce early. Still, the exceptions are fascinating. Lobsters in their suit of armor run little risk from ancient predators, so they can reproduce throughout their lives without ever aging into genetic irrelevance.

So, armed with such insights, do I experience my weakening muscles, declining sexuality, distracted thinking,  and dulled senses with any less resentment? Yes, a little. Knowing that the decline has its place, even though it’s a melancholy one, in the evolution that brought me to being in the first place is some consolation.

 

Is DNA Alive?

No, it’s not alive…mostly. The only sense in which a DNA molecule is a living thing is that it makes copies of itself, although it can’t even do that on its own. Otherwise, DNA fails all the tests: it doesn’t process any kind of fuel in order to maintain its state, it doesn’t grow and develop, so it has no energized activity that starts or ends—in other words, it’s not born and it doesn’t die.

Somewhere along the line in reading general science I picked up the impression, even though I think I knew differently, that DNA strands are alive. They are such vital keys to living organisms, and I’d read so many descriptions of what DNA does and of “selfish” genes, that although I knew they were blueprints of a sort, they came to seem like living blueprints.

DNA and seed (kew.org)

DNA and seed
(kew.org)

One image that took shape in the back of my mind was that DNA was a kind of seed, and seeds, I thought, are alive. But no, seeds are not fully alive either. They are not active and, until they germinate, they don’t change or develop. (Another familiar item that may seem alive but that doesn’t meet all the criteria are viruses. Viruses are bundles of DNA that become active only when they are inside a cell, at which point they take over the cell and give us the flu.)

It shouldn’t be surprising that some familiar biological components do not, by themselves, meet all the criteria for the complex condition we call “being alive.” Still, surprised I was about DNA. Perhaps because we humans are so fully aware that we are alive, it is easy to think that there must be a fully living seed or even a soul at the root. It is almost more than we can imagine that the liveliness we feel is the product of a complexity of non-living parts. It’s an astounding thing.