The primacy of reproduction, the sense that the next generation is all, or nearly all, that matters, is made most clear in those many species that promptly die, both sexes, in huge numbers, immediately after conception has occurred and precautions have been taken to safeguard the fertilized eggs. In other species, including our own, the parents play a vital role in protecting and educating the young, and so for them there is life after copulation. Otherwise, the parental generation would have served its purpose, and been hustled off before it came into competition for scarce resources with its own progeny.
The adaptive value of getting DNA strands together has been so substantial that vast changes have been worked in anatomy, physiology, and behavior to accommodate the needs of these molecules. While cooperation was present long before sex—in stromatolite colonies, say, or in the symbiotic relationships of chloroplasts and mitochondria with the cell—sex has introduced a new kind of cooperation, common endeavor, and self-sacrifice into the world. In the differing sexual strategies of male and female, sex has also introduced a novel creative tension—one that cries out for reconciliation and compromise—as well as a potent new motive for competition. Our own species is as good an example as any of the nearly determining role of sex—not just the sex act itself, but all the attendant preparation, consequences, associations, and obsessions—in establishing much of the personality, character, agenda, and drama of life on Earth.
ON IMPERMANENCE
Only
for sleep we come,
for dreams.
Lie! It is a lie.
We come to live on Earth.
As a weed we become
each springtime,
swell green, our hearts
open,
the body makes a few flowers
and drops away withered somewhere.
Poems of the Aztec Peoples14
* In vitro fertilization is of course still sex.* Although strands from two different dead bacteria might, on rare occasions, be incorporated by a live bacterium
Chapter 9
WHAT THIN PARTITIONS …
How instinct varies in the grovelling swine,
Compar’d, half-reasoning elephant, with thine!
’Twixt that, and reason, what a nice barrier,
Forever sep’rate, yet forever near!
Remembrance and reflection how ally’d!
What thin partitions sense from thought divide!
ALEXANDER POPE,
Essay on Man1
Most people would rather be alive than dead. But why? It’s hard to give a coherent answer. An enigmatic “will to live” or “life force” is often cited. But what does that explain? Even victims of atrocious brutality and intractable pain may retain a longing, sometimes even a zest, for life. Why, in the cosmic scheme of things, one individual should be alive and not another is a difficult question, an impossible question, perhaps even a meaningless question. Life is a gift that, of the immense number of possible but unrealized beings, only the tiniest fraction are privileged to experience. Except in the most hopeless of circumstances, hardly anyone is willing to give it up voluntarily—at least until very old age is reached
A similar puzzlement attaches to sex. Very few, at least today, have sex for the conscious purpose of propagating the species or even their own personal DNA; and such a decision for such a purpose, coolly and rationally entered into, is exceedingly rare in adolescents. (For most of the tenure of humans on Earth, the average person did not live much beyond adolescence.) Sex is its own reward.
Passions for life and sex are built into us, hardwired, pre-programmed. Between them, they go a long way toward arranging for many offspring with slightly differing genetic characteristics, the essential first step for natural selection to do its work. So we are the mostly unconscious tools of natural selection, indeed its willing instruments. As deeply as we can go in assessing our own feelings, we do not recognize any underlying purpose. All that is added later. All the social and political and theological justifications are attempts to rationalize, after the fact, human feelings that are at the same time utterly obvious and profoundly mysterious.
Now imagine us with no interest at all in “explaining” such matters, no weakness for reason and contemplation. Suppose you unquestioningly accepted these predispositions for surviving and reproducing, and spent your time solely in fulfilling them. Might that be something like the state of mind of most beings? Every one of us can recognize these two modes coexisting within us. A moment of introspection is often all it takes. Religious writers have described them as our animal and spiritual states. In everyday speech, the distinction is between feeling and thought. Inside our heads there seem to be two different ways of dealing with the world, the second, in the sweep of evolutionary time, arisen in earnest only lately.
——
Consider the world of the tick.2 Plumbing aside, what must it do to reproduce its kind? Ticks often have no eyes. Males and females find each other by aroma, olfactory cues called sex pheromones. For many ticks the pheromone is a molecule called 2,6-dichlorophenol. If C stands for a carbon atom, H for hydrogen, O for oxygen, and Cl for chlorine, this ring-shaped molecule can be written C6H3OHCl2 A little 2,6-dichlorophenol in the air and ticks go wild with passion.3
After mating, the female climbs up a bush or shrub and out onto a twig or leaf. How does she know which way is up? Her skin can sense the direction from which light is coming, even if she cannot generate an optical image of her surroundings. Poised out on the leaf or twig, exposed to the elements, she waits. Conception has not yet occurred. The sperm cells within her are neatly encapsulated; they’ve been put in long-term storage. She may wait for months or even years without eating. She is very patient.
What she’s waiting for is a smell, a whiff of another specific molecule, perhaps butyric acid, which can be written C3H7COOH. Many mammals, including humans, give off butyric acid from their skin and sexual parts. A small cloud of the stuff follows them around like cheap perfume. It’s a sex attractant for mammals. But ticks use it to find food for prospective mothers. Smelling the butyric acid wafting up from below, the tick lets go. She drops from her perch and falls through the air, legs akimbo. If she’s lucky, she lands on the passing mammal. (If not, she falls to the ground, shakes herself off, and tries to find another bush to climb.)
Clinging to the fur of her unsuspecting host, she works her way through the thicket to find a less hairy spot, a patch of nice warm bare skin. There, she punctures the epidermis and drinks her fill of blood.*
The mammal may feel a sting and rub the tick off, or intently comb through its hair and pick it off. Rats may spend as much as one-third their waking hours grooming themselves. Ticks can draw a great deal of blood, they secrete neurotoxins, they carry disease microbes. They’re dangerous. Too many of them on a mammal at the same time can lead to anemia, loss of appetite, and death. Monkeys and apes meticulously search through each other’s fur; this is one of their principal cultural idioms. When they find a tick, they remove it with their precision grip and eat it. As a result, they are remarkably free from such parasites in the wild.
If the tick has avoided the hazards of grooming, and has become engorged with blood, she drops heavily to the ground. Thus fortified, she unseals the chamber with the stored sperm cells, lays the fertilized eggs in the soil (perhaps ten thousand of them) and dies—her descendants left to continue the cycle.