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.

 

Walk, Run, Eat: The Evolution of Our Body

It can be difficult to visualize the stages that led from our chimp ancestors to the body that we see in the mirror. But Daniel E. Lieberman’s The Story of the Human Body: Evolution, Health, and Disease is a fine time machine. It took me back six million years to changes in feet, legs, arms and torso, all molded as our ancestors searched for food.

Reconstruction of sahelanthropus tchadens, who lived six to seven million years ago. (smithsonianscience.org)

Reconstruction of sahelanthropus tchadens, who lived six to seven million years ago. Not your average chimp. (smithsonianscience.org)

Human evolution can be said to have begun when one of our ancestors developed a feature that has been unique to us: We walk on two legs. That ability separated us from our cousin chimps between six and seven million years ago. We remain the only two-footed walking animal that doesn’t carry the feathers of a bird or the tail of a kangaroo.

Why walk? We began walking when the fruit that we ate became sparser; the African continent was cooling and the forests were shrinking. (I’ve conflated the species that Lieberman names to “us.”) Those who could stand upright and walk distances on two feet found not only more fruit but also edible stems and leaves. We were chimp-size, but as bi-pedal walkers our arms and hands became free for new uses.

intermediate human

A reconstruction of australopithicus bosei, “Nutcracker Man,” who lived two million years ago, discovered by Mary and Louis Leakey in 1959. Our intermediate stage. (Wikipedia)

The transition continued. By four million years ago, our anatomy had changed again. Foraging over distances fostered “more habitual and efficient long-distance walking.” Our feet acquired an arch that put a spring in our step and pushed the body forward. For stronger chewing, molars and jaws became much larger than ours today. These ancestors are nicknamed “Nutcracker Man.” We were still small but more upright, and still with relatively long arms and short legs.

The next stage was the Ice Age, two and a half million years ago. Foraging over larger areas required more calories, calories that meat could provide. Our ability to throw accurately brought down animals. Sharp stone tools cut up their flesh and made it chewable and digestible. We became taller, with arms and legs close to today’s proportions. We developed external noses to humidify the air that we inhaled during long walks. We began to run—far—with Achilles tendons for more spring and unique sweat glands and finer fur to stay cool.  As teeth and snouts shrank and brains grew, heads became rounder. Organized hunting and gathering became necessities. Generally, females gathered while males hunted. Unlike chimps, we shared food readily with extended families. Cooperation, coordination, and communication were means of survival. We—Homo erectus—became “significantly human.” 

homo erectus

Homo erectus reconstructed.
“Significantly human,” writes Lieberman. (Wikipedia)

Lieberman continues the story of our evolution into the present and discusses its relevance to disease. After millions of years of seeking food and storing its energy in our bodies whenever we could find it, today we eat more calories than we need while we burn off fewer calories than ever before. As a result, we suffer from “mismatch diseases” such as diabetes and other conditions like hardening of the arteries that our ancestors had no need to adapt to. We may treat the symptoms successfully, but we ignore the reality that, given evolution’s slow clock, we won’t be adapting to resist them any time soon.

march of progress

The original version of the “March of Progress,” from Time magazine in 1965. The details are out of date now and the notion of linear, progressive development has been criticized. But the image remains indelible.
(Wikipedia)