Perpetual Summer Species - Summer World: A Season of Bounty - Bernd Heinrich

Summer World: A Season of Bounty - Bernd Heinrich (2009)

Chapter 18. Perpetual Summer Species

12 August 2006. THE STUNTED SWAMP MAPLES ARE starting to turn red and are dropping leaves. The crickets’ monotonous chirping refrain—before they mate, lay their eggs, and die—is constant. In contrast, the birds are almost silent. But they may be more restless and on the move through new territory—two ovenbirds (common warblers living in deep shady woods) just hit the windows and were killed. I am also already switching modes, but downward. I curl up in bed a little earlier, sleep later, and eat more. The farmers have harvested their second crop of hay. I’ve finished the woodpile, and we’re canning tomatoes and string beans. Signals indicating the end of summer are all around.

TWO VERY DIFFERENT GROUPS OF ANIMALS LIVE IN A PERPETUAL summer, or nearly perpetual summer, in the far north and deep into the south. The first are birds that migrate from one summer in the north to the other one at the other end of the globe. They can always live in a summer world, thanks to energy-rich berries and heroic sustained exercise. We have come close to imitating them. We manage the same trick of living in perpetual summer, although not by strenuous biannual migrations but by creating and retreating into “climate bubbles.” Temperatures outside may be minus 50°F and the outdoors can be dark with howling wind and swirling snow, but we can be experiencing a comfortable 65°F and fourteen hours of light per day while we feast on fresh tropical fruit. The trouble is that a population of hundreds of millions living in a virtual summer while eating bananas from Central America and drinking coffee from Africa probably can’t sustain wresting summer from winter indefinitely.

For now and the immediate future, each household that I know of, every single one and for every day throughout six months of winter, consumes vast quantities of fuel imported from thousands of miles away to keep the occupants warm and for cooking, lighting, transportation, and—directly or indirectly—for almost everything we do and own. For six months we can’t grow any food. And we insist on building more homes here all the time; almost weekly there are new patches of monstrous new houses that arise like mushrooms up out of the ground in our neighborhood, and each and every one of them requires more and more of the same fossil fuels. Without them vast stretches of the North American continent would virtually overnight be depopulated. And with agrofuels to build and sustain them, vast stretches of the Earth’s most beautiful southern ecosystems would have to be sacrificed, creating biological deserts to sustain our northern perpetual summer.

It is at this point tempting to spout personal and political views. But factual scenarios are scarcely either. There is the necessity of maintaining sound natural ecosystems—those that sustain the life of all animals that evolved in them and that live there in a complex unity.

I am an optimist. There is a way. As Thoreau wrote, “Men think it is essential that the Nations have commerce, and export ice, and talk through the telephone, and ride thirty miles an hour.” He meant they are mistaken. I believe Thoreau was a happy man. People have lived happily in a small cabin in the woods where they had none of the amenities such as refrigerators, oil furnaces, electric toasters, cars, telephones, television, running water, etc. Some who have experienced it even think with nostalgia of such a presumably deprived existence.

It is unlikely that we will, or even can, change our lifestyles radically enough to make much difference. It is madness to suppose we would make a significant difference by using more energy-efficient lightbulbs and using agrofuels rather than oil, or that city dwellers can or would take up a rural farming or a hunter-gatherer lifestyle: given our numbers, there is no land. There is only one thing to do that will have an almost immediate effect (say, in a century or two): radical reductions of population. Ironically, if we do take that route then we can have everything—cars, jetliners, televisions, and all the rest, even perpetual summer. With a low population we could subsist and get by, in perpetuity, with the most efficient method yet devised for capturing solar energy—trees.

We can cut down some of the most beautiful creations imaginable, but out of forests. That requires having more forests rather than creating tree plantations. We need two things: clear vision and also a spiritual imperative so that we will focus on the ultimate ecology, not the proximate economy. The increase in human happiness of future generations that this simple solution would create staggers the imagination, and the vast misery that would result if we do not adopt it is almost too horrendous to contemplate. Those are the “knowns.” The solution is obvious. The treating of symptoms is opinion and hype.

I ask here instead how we got to where we are now. To start simply, I think we can learn a lot from—yes—hair. If one accepts the almost universally applied premise that we evolved from furred apelike ancestors, then our present insufficient amount of insulating body hair indicates that we evolved while being subjected to more overheating than was experienced by them while other (furred) lines became present-day apes. (An alternative hypothesis, which needs scarce consideration, is that we became naked to shed lice. If that were true, then any number of other primates would also be naked.) That is, not only did we not need insulation; it was a liability in terms of survival. We were, therefore, spawned by a perpetual summer world.

When Homo sapiens first spread out of Africa about 150,000 years ago (plus or minus a few tens of thousands of years), we were, as now, already defurred or nearly so. However, by then we were also clever enough to co-opt the fur of other animals who had already adapted to a cold environment. We don’t know precisely when that happened, but thanks to lice, DNA technology, and clever sleuthing by the geneticist Mark Stoneking at the Max Planck Institute of Evolutionary Anthropology, it looks as though we became clothed about 115,000 years ago. The remarkable closeness in the two dates—spreading out of Africa and becoming clothed—is probably not coincidental.

Lice are ectoparasites (parasites living on our skin rather than under it), and ectoparasites are remarkably species-specific; each kind of bird or mammal has its very own louse and flea species living on it because each is an island with regard to the others. However, even though any one nonhuman mammal species has the dubious honor of hosting only one of each louse or flea species, humans are unique: we have three species of lice. They are head lice (Pediculus humanus capitis); body lice (Pediculus humanus corporis), which live primarily in clothing; and pubic lice (Pthirus pubis).

Thanks to the logic of evolution and DNA technology, we know that DNA accumulates gene changes, generally at a steady rate. Therefore, by comparing the number of gene changes between two animals, we can use DNA to determine relatedness, and we can use the changes as a “clock” that tells us when the divergence occurred. The data indicate that head and body (Pediculus) lice had a common ancestor about 114,000 years ago. Logically, these lice would not have diverged to become two species unless they had two different habitats to adapt to. The choice pubic spot had already been taken much earlier by a more distant relative, Pthirus pubis. Stoneking deduced that when we were still fully furry—long before we were human—we had only one other louse habitat, the fur covering the rest of our body. We became naked under the heat in the tropical African savanna, and only the head hair (which has special significance, as I will discuss later) remained as the second ecologically suitable louse habitat. When we came out of Africa about 150,000 years ago, we were probably still naked, but we would not have progressed very far north without wearing clothes. The lice took up residence in those clothes, and they needed different behavior to prosper in that new and different habitat, next to our warm body rather than on the head. A population of the original colonists stayed in our head hair, but the clothes-loving lice diverged and perfected to live in their new habitat. As they adapted, their offspring would have been disadvantaged by being saddled with the lifestyle of their old haunts. Similarly, the head lice would also be disadvantaged by inappropriate lifestyles, so isolating mechanisms evolved, and eventually the two lice could no longer interbreed and the line split into the two species.

More interesting, perhaps, is the obvious question: why were we naked in the first place? If we came out of Africa naked or nearly so, and if the apes’ and our common ancestor was probably hairy, as all apes still are, then why did we become naked? I think the best hypothesis to account for our nakedness is that we derived from a very special ape-man, an endurance predator who depended on rapid and prolonged locomotion in the heat in order to compete with other predators, primarily sprint specialists. We can still compete with cheetahs, lions, and leopards in running down antelope, but we can do it only in the midday heat. And the reason is that we have the mental capacity to pursue a goal that we can neither see nor smell but that we can imagine. Additionally we have a unique suite of adaptations to deal with internally generated body heat under the blazing sun. They include our nakedness, our ability to route blood to the surface of our extremities so that our veins bulge at the surface of exposed skin, and our ability to sweat profusely over the skin. These are capacities needed by hunters who get their edge through endurance in the heat.

A recent review article (Rantala 2007) argues that the cooling hypothesis “does not bear close scrutiny.” Perhaps, if one discounts the zoological perspective: that the predecessors of H. sapiens differed from other hominids in being erect and needing to hunt at noon under the direct overhead sun in order to compete with the large carnivores who rest then. Although feathers and hair on the dorsal surface insulate other desert animals from direct solar radiation, most have “thermal windows”—areas of very thin hair or no hair, as on the bare bellies and flanks of desert antelope, the areas less exposed to the direct rays of the sun. Other examples include the naked thighs and necks of ostriches and the large, heavily vascularized ears of desert jackrabbits and elephants.

We are the hominid analogue of the Cataglyphis ant, except that we had a significant internal as well as external heat load and we not only scavenged dead animals as these ants do—but eventually also incapacitated and hunted down our prey.

Mobility generates body heat, and that requires sweat to continue the chase, but you can be profligate with sweat only if you have lots of water. Out of view of the eland or kudu we killed, there was undoubtedly a lake, a stream, or some other water.

Several years ago an issue of Geo magazine contained a photograph that is indelibly imprinted on my mind. It shows the bloody mass of a dead elephant whose trunk has been hacked off. Around it swarm more than a dozen armed men who are cutting into the animal with knives and spear blades. The scene is in open bush country, under bright sunshine. African elephants are as naked as men—unlike the woolly mammoths, mastodons, and rhinoceroses, former residents of the northern ice age steppes. Along with those images I also see a petroglyph in a small rock shelter in East Africa showing running hunters chasing a wildebeest, just as the present-day Bushmen chase kudu and run them into submission.

We are not exempt from the physical and biological laws of necessity and constraint that govern all organisms. But this generalization applies especially to our exterior. The remarkable similarity of the DNA signatures of human groups living today suggests that our external differences are trivial; we are all derived from a small founder population, which lived as recently as about 89,000 years ago. We were arguably modest agents promoting species diversity by being responsible for splitting off a second species of louse, where two had sufficed previously and one fewer might suffice even now. However, we were never much “into” tolerance or promotion of diversity. Indeed, there is a puzzling if not disturbing record of disappearance of other human as well as other animal species whenever Homo sapiens arrived on the scene.

IN THE NORTH, THE HUMANS COMING OUT OF AFRICA encroached on the domain of the Neanderthal people, who had lived there for perhaps 250,000 years, over three ice ages. And by 30,000 years before the present we had replaced Homo neanderthalensis. This northern species was physiologically and behaviorally superbly adapted to a cold climate. Neanderthals had a brain as large as, or possibly slightly larger than, ours. We now consider them not to have been as innovative as Homo sapiens, by our standards (which include imagining supernatural beings, drawing pictures, etc.), but there is evidence that they did use fire, decorate their dead with flowers, and perhaps blow on bone flutes. They probably sang, talked, and played. As I will shortly suggest, they were probably also as hairy as bears. They didn’t succumb to the weather. They succumbed to something else.

The reason for the Neanderthals’ demise is extremely murky, and perhaps that is just as well for our collective ego. But there has been no lack of speculation about what they looked like and how they lived. Primarily, it is thought that since they did not change their stone implements, they were less imaginative than the invaders and would therefore have been outcompeted or killed off or both. I will here add my own two cents’ worth, which is not contrary to what has been found and said before, but it adds a zoological twist to the more common paleontological and anthropological perspectives.

First, I will return once more to body hair. If there is one thing which almost everyone agrees on (but for which there is not a stitch of direct evidence), I think it is that Neanderthals were furry. If even some Homo sapiens coming north possibly started to become furry (my speculation, from a limited sample of specimens) despite having invented clothes, then the Neanderthals living in the north for 200,000 years or more would have been furry. It might even be a fairly solid inference that they were more furry than any of us are now. Could they have been as furry as other northern mammals? Could they have been as furry as the macaques that have adapted to the cold climate of northern Japan? Fur like that of the northern-adapted macaque or a bear should have made a huge difference to their survival throughout three ice ages, in both males and females. Fur could also have had other implications besides insulation: sexual selection, hybridization or lack thereof, tactical aspects of conflict, and species extinction.

One of the major selective pressures operating on the behavior, physiology, and appearance of vertebrate animals is sexual selection. Sexually selected traits vary enormously, yet they almost always signal something about the bearer that is correlated with survival value and the ability to produce or rear offspring. Survival and fertility markers, or features that can become correlated with strength and vigor—antlers, long tails, and so on—almost by definition become marks of “beauty.” The relevant features vary enormously from one species to the next, and what may be very attractive to one should and would probably be repugnant to another. For example, we don’t perceive the pale blue scrotum in the background of a bright red penis in the vervet and patas monkeys as a turn-on. The swollen red buttocks of a female chimp seem rather ugly to us, but to male chimps they are a sexual turn-on. If a solid, sleek coat of body hair in Neanderthals had, versus a thin, scraggly coat, survival value, then it would probably become a mark of beauty to them and it would have become more entrenched in their genome as a selected trait. It would be like the lack of body fur in warm-adapted Homo sapiens hunters. It would be like clothes to us, since clothes have become a necessity for our survival. As a matter of record, we do find body hair a turn-on, or else we would not fuss with it so much. I am talking of course, of head hair, which was probably of great survival value long ago at “crunch” times such as chasing down an antelope in the noonday heat. It may be selected for still, though not for the same reasons.


Fig. 35. Japanese macaques from the northern part of the island are densely furred, unlike any other living primates.

Large differences in sexual selection signals are especially important in closely related species, where interbreeding is a possibility. The songs and showy feather displays of birds are markers of fitness, but the males of the song sparrow sing entirely different notes and an entirely different repertoire from the white-throated; and the males of one finch species are bright yellow whereas other species are purple or indigo or green. We assume too much when we say that the Neanderthals valued the same things as we did and thus looked like us. External appearance relating to body fur or facial features, or clothes or lack of them, might have accounted for DNA evidence that now indicates there was no interbreeding between us and the Neanderthals. There is reason to believe there might have been outright aggression between the two species.

Neanderthals were probably low-tech survivors, or else more artifacts than crude campfires and scrapers would have been found. Would low technology then perhaps have been compensated for by some other attributes: fur and hibernation? If the Neanderthals hibernated in caves as the northern bears did (and if not, why not?), then we, the summer-adapted human hunters who invaded their territory, would probably have killed a Neanderthal as readily as we would kill a bear. But even if there was resemblance between us and the Neanderthals that could have inhibited our seeing them as prey, that would not have been an absolute deterrent. We are superbly adapted for making “us versus them” distinctions, on the basis of incredibly slight real differences and even on the basis of imagined or created stereotypes. This highlighting of differences is a psychological mechanism that divides, but the capacity to apply it to others probably evolved because it functions within the group to strengthen cohesion for “better” (more efficient) competition against other groups.

I believe the Neanderthals would have been more distinct from us than they seem now from the structure of their bones. They were not inferior. Their apparently more simple lifestyle was probably, given the 200 millennia or more in which it was tested, sustainable and in tune with their environment. In perhaps another century or less we may find out if we can do as well. We will learn if it is possible to live happily and be healthy in mind, body, and spirit surrounded by a devastated fauna, as a perpetual summer species in the north, sustained there by food and energy imported from distant continents.