Yes friends, the molecular biologists have concluded that humanity 's basic genetic blueprint - our DNA - differs from that of Pan troglodytes by a mere 2 percent. Charles Darwin would have loved it.

Edward T. Hall watched people line up for a bus. Each person who arrived in line tended first to crowd the one in front a little but, in time, moved away until everyone in the line was was exactly equidistant from each other. This, he noted, is exactly how seagulls behave as they land on a roof. Virtually all animals insist on personal space, including (however unconsciously) humans.

Or take the human smile. All human babies, including blind ones, smile, proving that the smile is not learned by imitation. Where did the smile come from?

Apes.

An angry chimp pushes its lips forward and lowers its brows. If it's about to attack, it bares its front (biting) teeth. But if it's alarmed or wants to appease, it pulls its lips all the way back, exposing its molars as well. In essence, a smile.

Such visual clues to our state of mind as grins and smiles, nods as well, also probably helped avoid a lot of unnecessary club fights between hominoidal strangers back in our earliest days. So smiling came to be wired into the human animal by virtue of the facts that charming your mother aids survival an that getting in a fight disrupts your reproductive success.

the findings of Eugene Moriton of the National Zoo are powerful: he discovered that all mammals and all birds share a universal mode of vocal communication. When angry or hostile, they lower their voice into a raspy growl. This makes them seem bigger When fearful, submissive or hoping to appease someone, they raise their voice into a whine, a babyish noise suggests smaller size.

In fact, in terms of mentality, science has confirmed that feelings are essentially all that nonhuman animals have. What humans have beyond that is reason, the capacity to think symbolically, to think (and talk about) things are neither present nor material -- such as the past or the future, or morals; to make sentences and to tell lies.

In this regard, it has been possible to train some chimpanzees to use sign language (a kind of symbolic communication) to make what appear to be sentences. Dolphins and even a parrot have similarly trained, and this suggests that the ability to "think" symbolically is latent in others besides ourselves. Exactly what all signifies, if anything, remains a matter of debate among scientists but what is not debated is that such behavior is a matter of training only. In the wild, chimps, dolphins and parrots do not make sentences. Just us.

But in sifting through the traits that distinguish us from other animals, what about the stuff that really preoccupies us? Like war. For a time, gloomy commentators upon human nature could say that we humans were the only species that engaged in out-right war, the organized killing of one's own kind. But alas, the dubious distinction has been clouded.

In her years of patient observation of chimpanzees, Jane Goodall found that on several occasions males from one band simply got together and roamed out of their own territory into another, expressly searching out other males to destroy. Maybe ethnic hostility is wired into us in some way.

Even more of a human preoccupation than killing is procreation. Sex. What about love? Mating? Monogamy? Divorce? What does the human animal really do about all that if left to its own devices? Which is to say, what does it do regardless of whatever culture and societal customs it is born into? Here the findings of anthropologist Helen E. Fisher, recounted in her book The Anatomy of Love, are provocative. To begin with, she dismissed that old wives' tale about the seven-year itch.

It's a four-year itch.

All around the world, Fisher discovered from United Nations censuses kept since 1949, whether it is in Finland, England or the Kalahari Desert, and whether society promotes polygamy or monogamy, and whether divorce is frowned upon or not, or is common or rare, divorce peaks around four years after marriage. The innate human pattern appears to be this: to get infatuated, court and marry a person (one at a time - even in societies that permit polygamy). Then, most often with a single child, the person divorces and a few years later remarries.

Many factors serve to prolong marriage: for example, the more children a couple has the less likely it is to divorce. The more dependent the wife is on the man for sustenance (as in pre-industrial Europe and other peasant societies dependent on the plow), the less common divorce is. Outright forbidding of divorce tends to decrease it too. But the four-year peak in divorce appears to be another human constant, something built in to the human animal . . . and maybe even built in biochemically.

Virtually everyone at one time or another experiences the wild, tidal ecstasy of romantic love, or infatuation. Whatever it is about a person that triggers it, you feel overwhelmed with both euphoria and apprehension. And indeed, the emotional center of your brain (called the limbic system, which we share with all mammals) is in fact overwhelmed - awash with natural amphetamines produced in the brain, especially one called phenylethyline or PEA.

The chemical high can last up to three years, when it begins to trail off. PEA production wanes and the brain begins to produce another chemical bath--endorphins, which are related to morphine, natural opiates that provide a sense of tranquility. The high of passion tends to turn to the comfort of attachment - or it doesn't and the quest for another PEA high begins.

But by the time a human child reaches the age of 3, it can run around a good bit, even be part of a play group watched over, say, by an old granny. The mother no longer needs the father around all the time, unless he has sired another child with her. So they could, and probably often did (according to Fisher) separate - both partners going off with others and getting that big high again. This way, the female wouldn't be stuck with old Grog's genes but could scout out someone a bit more dashing who might make an even better contribution to her progeny.

Of course, we owe a lot of that success to the cerebral cortex that lies between our skulls and our mammalian limbic systems and reconciles what we call thinking with the tidal chemistry of emotion. But that old troglodyte does demand its due.