Who Are We?
You might be surprised by what's in charge of your body



The Caterpillar and Alice looked at each other for some time in silence: at last the Caterpillar took the hookah out of its mouth, and addressed her in a languid, sleepy voice.

'Who are YOU?' said the Caterpillar.

This was not an encouraging opening for a conversation. Alice replied, rather shyly, 'I — I hardly know, sir, just at present.'

— Lewis Carroll

The answer might seem simple, even trivial: name, rank, serial number, family connections, occupation, and so forth. But there is more to the caterpillar's contemptuous question than meets the eye, for biologists no less than for a philosophically inclined insect.

Who are we?

It turns out that the business of being a "self" is more fraught than cultural tradition and subjective experience tell us. John Donne be damned: Each person, most of us assume, is indeed an island, entire of him or herself, everyone his own man or woman — separate, distinct, independent, and in charge. An army of one, a skin-encapsulated ego whose identity is beyond dispute. But wait a moment. Where, exactly, does that "us" reside? Whereas "self psychology" is widely attributed to the work of the psychoanalyst Heinz Kohut and often appears murky enough, "self biology" is even more so.

The deepest, most private recesses of our genome might seem, if not sacrosanct, at least the inner sanctum of our "selves." But consider this: More than four times as much space in the human genome is occupied by "endogenous retroviruses" than by all the genes that code for the enzymes and other proteins used to create and run our bodies. These viruses long ago incorporated themselves into our ancestors, apparently by using reverse-transcriptase enzymes of the sort employed by such malefactors as HIV to pry their way these days into the DNA of the immune cells they exploit. The silent viral debris we all carry is "foreign" in nearly every way, yet it must be seen as a large part of "us." (Some of these fossil bits of hitchhiking nucleic acid have even been resurrected in the laboratory, whereupon they can infect mice and act like the perfectly independent viruses they once were.)

Add to that the saga of mitochondria, fabled "powerhouses" of our cells, the sites of metabolic energy production. It is now generally agreed that these fundamental subcellular organelles are actually derived from primitive bacteria that, long ago, became incorporated into the genome of nucleated organisms. From our DNA to our ATP, the biological alphabet soup of selfhood is not so easily identified.

Think of the morgue scene in the movie Men in Black, when what appears to be a human corpse is dissected and revealed to be a highly realistic robot, its skull inhabited by a little green man from outer space. Or for a less fanciful example, turn to the disconcerting fact that there are many more parasitic creatures alive today than free-living counterparts. Endogenous retroviruses and mitochondria are either benign or downright beneficent, but pretty much every multicellular animal is also home to numerous additional fellow travelers, and — this is especially noteworthy — each of these creatures may have its own agenda. Considering just one group of worms, the biologist N.A. Cobb suggested, "If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable. ... Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites." Put another way, if a biologist were to answer Frank Zappa's question, "Suzy Creamcheese, honey, what's got into you?" the response might well be: "A whole lot of other living things."

What difference does this make? For many of us supposedly free-living creatures, quite a lot. Providing room and board to other life-forms not only compromises one's nutritional status (not to mention peace of mind), it often reduces freedom of action, too. The technical phrase is "host manipulation." For example, the tapeworm Echinococcus multilocularis causes its mouse host to become obese and sluggish, making it easy pickings for predators, notably foxes, which — not coincidentally — constitute the next phase in the tapeworm's life cycle. Those the gods intend to bring low, according to the Greeks, they first make proud; those tapeworms intending to migrate from mouse to fox do so by first making their mouse fat, sluggish, and thus, fox food.

Sometimes the process is more bizarre. For example, the life cycle of a trematode worm, known as Dicrocoelium dentriticum, involves doing time inside an ant, followed by a sheep. Getting from its insect host to its mammalian one is a bit of a stretch, but the resourceful worm has found a way: Ensconced within an ant, some of the worms migrate to its formicine brain, whereupon they manage to rewire their host's neurons and hijack its behavior. The manipulated ant, acting with zombielike fidelity to Dicrocoelium's demands, climbs to the top of a blade of grass and clamps down with its jaws, whereupon it waits patiently and conspicuously until it is consumed by a grazing sheep. Thus transported to its desired happy breeding ground deep inside sheep bowels, the worm turns, or rather, releases its eggs, which depart with a healthy helping of sheep poop, only to be consumed once more, by ants. It's a distressingly familiar story ... distressing, at least, to those committed to bodily "autonomy."

A final example, as unappetizing as it is important: Plague, the notorious Black Death, is caused by bacteria carried by fleas, which, in turn, live mostly on rats. Rat fleas sup cheerfully on rat blood, but will happily nibble people, too, and when they are infected with the plague bacillus, they spread the illness from rat to human. The important point for our purposes is that once they are infected with plague, disease-ridden fleas are especially enthusiastic diners because the plague bacillus multiplies within flea stomachs, diabolically rendering the tiny insects incapable of satisfying their growing hunger. Not only are these fleas especially voracious in their frustration; because bacteria are cramming its own belly, an infected flea vomits blood back into the wound it has just made, introducing plague bacilli into yet another victim. A desperately hungry, frustrated, plague-promoting flea, if asked, might well claim that "the devil made me do it," but in fact, it was the handiwork of Pasteurella pestis. ("So, naturalists observe, a flea/ Has smaller fleas that on him prey,/ And these have smaller still to bite 'em,/ And so proceed ad infinitum," observed Jonathan Swift.)

Not that a plague bacterium — any more than a mouse-dwelling tapeworm or ant-hijacking brainworm — knows what it is doing when it reorders the inclinations of its host. Rather, a long evolutionary history has arranged things so that the manipulators have inherited the earth.

Once again, however, things aren't quite so simple. The ways of natural selection are devious and deep, embracing not only would-be manipulators but also their intended victims. Hosts needn't meekly follow just because others seek to lead. In Shakespeare's Henry IV, Part I, Owen Glendower boasts, "I can call spirits from the vasty deep," to which Hotspur responds, "Why, so can I, or so can any man; But will they come when you do call for them?" Sometimes it is unclear whether our spirits, no less than those of Glendower, might seek to enlist others, act at another's behest, or suit themselves. Take coughing, or sneezing, or even — since we have already broached some indelicate matters — diarrhea.

When people get sick, they often cough and sneeze. Indeed, aside from making you feel crummy or possibly run a fever, coughing and sneezing are important ways we identify illness in the first place. It may be beneficial for an infected person to cough up and sneeze out some of her tiny organismic invaders, although to be sure, it isn't so beneficial for others nearby. That, in turn, leads to an interesting possibility: What if coughing and sneezing aren't merely symptoms of disease, but also — even primarily — a manipulation of us, the host, by, say, the influenza virus? Shades of fattened mice and grass-blade-besotted ants. As to diarrhea, consider that it is a major (and potentially deadly) consequence of cholera. To be sure, as with a flu victim's sneezing and coughing, perhaps it helps a cholera sufferer to expel the cholera-causing critter, Vibrio cholerae. But it also benefits Vibrio cholerae. Just as Lenin urged us to ask "Who, whom?" with regard to socioeconomic interactions — who benefits at the expense of whom? — an evolutionary perspective urges upon us the wisdom of asking a similar question. Who benefits when a cholera sufferer dies from unremitting diarrhea? Answer: the cholera bacillus.

That dramatic symptom of cholera is caused by a toxin produced by the bacillus, making the host's intestines permeable to water, which generates a colonic flood that washes out much of the native bacterial intestinal flora, leaving a comparatively competitor-free environment in which Vibrio cholerae can flourish. A big part of that flourishing, moreover, occurs when more than 100 billion V. cholerae per liter of effluent sluices out of the victim's body, whereupon, if conditions are less than hygienic, they can infect new victims. Diarrhea, then, isn't just a symptom of cholera, it is a successful manipulation of Homo sapiens, by the bacteria and for the bacteria.

Troublesome as such tales of alien invasion and pathologic manipulation may be, it is easy to shrug them off when it comes to the daily, undiseased lives most of us experience. Things feel pretty straightforward when we are "doing our own thing," if only because then — we like to insist — we are acting on our volition and not for the benefit of some parasitic or pathogenic occupying army. When we fall in love, we do so for ourselves, not at the behest of a romance-addled tapeworm. When we help a friend, we aren't being manipulated by an altruistic bacterium or a long-pacified retrovirus. If we eat when hungry, sleep when tired, scratch an itch, or write a poem, we aren't knuckling under to the needs of our nematodes or anything else. Or are we?

As modern evolutionary biologists increasingly recognize, bodies are our genes' way of projecting themselves into the future. Bodies are temporary, ephemeral, short-lived apparatuses for those genes, which are the only entities that persist over evolutionary time. No matter how much money, time, or effort is lavished on bodies, regardless of how much they are exercised, pampered, or monitored for bad cholesterol, they don't have much of a future. In the scheme of things, they are as ephemeral as a spring day, a flower's petal, a gust of wind. What does persist are genes. Bodies go the way of all flesh: ashes to ashes, and atom to atom. Genes, on the other hand, are potentially immortal.

In his poem "Heredity," Thomas Hardy had a premonition of modern evolutionary biology and the endurance of genes: "I am the family face;/ Flesh perishes, I live on."

More troublesome than the fact that our genes — at least in theory — are eternal, whereas our bodies are ephemeral, is the caterpillar's question to Alice: Who are we? Or, rephrasing Lenin by way of Glendower, Who's calling and who's heeding?

The biologically informed answer is that we're not all that different from those alarming rat/tapeworm, ant/trematode, flea/bacteria relationships, only this time it's genes/body. Unlike the cases of parasites or pathogens, when it comes to genes manipulating bodies, the situation seems less dire to contemplate, if only because it is less a matter of demonic possession than of our genes, ourselves. The problem, however, is that those presumably personal genes aren't any more hesitant about manipulating us than a brainworm is about hijacking an ant.

Consider a seemingly more benign behavior, indeed, one that is highly esteemed: altruism. This is a favorite of evolutionary biologists because, superficially, every altruistic act is a paradox. Natural selection should squash any genetically mediated tendency to confer benefits on someone else while disadvantaging the altruist. Such genes should disappear from the gene pool, to be replaced by their more selfish counterparts. To a large extent, however, the paradox of altruism has been resolved by the recognition that "selfish genes" — per Richard Dawkins and others — can promote themselves (rather, identical copies of themselves) by conferring benefits on genetic relatives, who are likely to carry copies of the genes in question. By that process, known as "kin selection," behavior that appears altruistic at the level of bodies is revealed to be selfish at the level of genes. When someone favors a genetic relative, who, then, is doing the favoring: the nepotist, or the nepotist's genes?

Just as sneezing may well be a successful manipulation of "us" (Homo sapiens) by "them" (viruses), what about altruism as another successful manipulation of "us," this time by our own "altruism genes"? Admirable as altruism may be, it is therefore, in a sense, yet another form of manipulation. After all, just as the brainworm gains by orchestrating the actions of an ant, altruism genes stand to gain when we are nice to Cousin Sarah, never mind that such niceness is costly to that entity we unthinkingly call "ourselves."

All this may seem a bit naïve, since biologists know that genes don't order their bodies around. No characteristic of any living thing emerges full-grown from the coils of DNA, like Athena leaping out of the forehead of Zeus. Every trait — including behavior — results from a complex interaction of genetic potential and experience, learning as well as instinct, nurture inextricably combined with nature. Life is a matter of genetic influence, not determinism.

But does that really resolve the problem? Let's say that a brainworm-bearing ant still possesses some free will. And that a trematode-carrying mouse has even a bit more. So what if their behaviors were influenced, but not determined? Wouldn't even "influence" be enough to cast doubt on their agency, their independence of action? And (here comes the Big Question) why should human agency or free will be any less suspect? Even if we are manipulated just a teensy-weensy bit by our genes, isn't that enough to raise once again that disconcerting question: Who R we? Or, more to the point, who's in charge?

Maybe it doesn't matter. Or, put differently, maybe there is no "one" home, nobody minding the store. If so, that is because the "environment" is no more outside us than inside, part tapeworm, part bacterium, part genes, part hitchhiking retroviruses, collaborating mitochondria, and no independent, self-serving, order-issuing homunculus. Purveyors of Buddhist wisdom note that our skin doesn't separate our organismic selves from the environment; it joins us, just as purveyors of biological wisdom know that we are manipulated by, no less than manipulators of, the rest of life. Who R we? Well, that depends on what the meaning of "who" is. Who's left after the parasites and pathogens and other fellow travelers are removed? And after "you" are separated from your genes?

"That what we call mind," wrote David Hume, "is nothing but a heap or collection of different perceptions, united together by certain relations, and supposed, though falsely, to be endowed with a perfect simplicity and identity." The question of whether human consciousness reflects a single, coherent identity is fraught enough to have occupied battalions of philosophers and, these days, more than a few neurobiologists as well (even without the vexed question of free will). Add to that the identity-challenging insights of evolutionary genetics and ecology, and the caterpillar's question takes on even greater weight. One thing we know, however, is that no one can issue a bona fide Declaration of Independence.

Accordingly, let's leave the last words to a modern icon of organic, oceanic wisdom: SpongeBob SquarePants. Mr. SquarePants, a cheerful, talkative — although admittedly, somewhat cartoonish — fellow of the phylum Porifera, "lives in a pineapple under the sea/ Absorbent and yellow and porous is he!" I don't know about the pineapple or the yellow, but absorbent and porous are we, too.

David P. Barash is a professor of psychology at the University of Washington and a frequent Chronicle contributor. His most recent book, Natural Selections: Selfish Altruists, Honest Liars, and Other Realities of Evolution (Bellevue Literary Press), is based on his recent Chronicle articles.