Apes appear regularly in ads for the computers of Digital Equipment Corporation  except that the cute chimpanzee is labeled a monkey,' as part of suggesting that you shouldn't monkey around by buying a competitor's computer. Personally, I tend to run in the other direction when elementary errors are proudly paraded via full-page ads. The apes have quite enough problems without being confused with the more prosaic and prolific monkeys  people cutting down the apes' rain forests, for example. There are only seven ape species left: in Africa, there's the gorilla -- and the chimpanzee and its near relative, the bonobo. In southeast Asia, there's the orangutan -- and the gibbon and its near relative, the siamang. Those are the usual six apes. Homo sapiens is the seventh ape species; we're basically the third of the chimpanzee lineage.
      Apes evolved from the Old World Monkeys about 30 million years ago; besides losing the monkey's tail and improving their shoulders, apes enlarged their brains. A chimpanzee brain is more than twice the size of a monkey brain. The surface of the brain, a sheet of cells where all the interesting creative stuff happens, is wrinkled like a crumpled-up wad of paper. If you flatten it out on a cookie sheet, it's about the thickness of two dimes  and that's true in all mammalian species. What differs is the amount of it; a rat's might cover a postage-stamp-sized area while a monkey's neocortex covers an area about the size of a postcard. A chimp's neocortex would cover a whole sheet of typing paper  and that of a human brain would cover four sheets.
      We'd like to understand why the monkey's brain doubled to become an ape, and why the ape's brain recently quadrupled to become human in size. Now, the apes are amazingly humanlike in many ways that the monkeys are not (just read any of the books by Frans de Waal such as Bonobo, Good Natured, Peacemaking Among Primates, and Chimpanzee Politics).
      The bonobos, so-called pygmy chimpanzees,' are particularly humanlike -- the way they stand or walk, their facial expressions, their gestures -- all have strong human overtones. The more we study their social interactions, the more we see hugs and kisses, reassuring touches, arms around shoulders, peacemakers that promote reconciliation between antagonists, and so forth. We last shared a common ancestor with them and the common chimpanzees about five million years ago.
     And in the common chimp, you can similarly see a number of the foundations of group aggression and warfare; they have distressingly humanlike tendencies to raid their neighbors, ganging up and beating to death isolated individuals of a neighboring troop. This isn't because the neighbors look different or act different; it happens even though genetically the neighboring group is very closely related, just as close as we see today in the Balkans or Northern Ireland. For this other set of ancestral prehuman behaviors, you'll want to read Richard Wrangham's recent book, Demonic Males.
      We'd also like to understand where our higher intellectual abilities came from  those abilities like language, planning ahead, logical trains of reasoning, games with rules, and music which the apes mostly lack. Apes really don't plan for tomorrow -- if they did, chimps would not only raid their neighbors but stockpile food and weapons for protracted wars.
      It's not that apes are totally incapable of some of the higher intellectual functions  some bonobos like Kanzi can be laboriously taught enough protolanguage skills so he can guess the meaning of never-heard-before sentences about as well as a two-and-a-half year old child can do. But the bonobos are not acquisitive of words and word patterns, not the way that a preschool child soaks up six new words every day, just from listening to others, discovers syntax before the age of three, and demands a proper ending to a bedtime story in another year or two. All that inborn acquisitiveness for larger-and-larger patterns in the environment appears to be something that has come along during hominid evolution. The child is looking for orderly patterns amidst the seeming chaos of sensations, and discovering one after another. Someone once asked me after one of my brain lectures what I thought the child's first thought was  and I replied, "Eureka! Another pattern!"
      We're the Third Chimpanzee, as Jared Diamond likes to call us, and we're into large patterns  like these long sentences I'm speaking, which you can understand because we both know about how long strings of words can be structured using phrases and clauses. No one taught us how to do this  What parent can describe the rules well enough to teach syntax? There really are things we know but of which we cannot speak.

The big questions in science tend to be variants on What, and How, and Why? So far, I've been addressing some of the big What issues: brain size, social behaviors, and higher intellectual functions. I can tell you a little about how the brain generates language, the mechanistic process that happens in your brain in the seconds before the words pop out of your mouth, but our understanding is incomplete unless we can also say something about why  the process of coming into being' on the evolutionary time scale, why an ape brain was transformed into a human brain, four times larger and reorganized for emphasizing the higher intellectual functions.
      The big questions what-how-why all illuminate one another, even though we sometimes attempt to treat them in isolation. For example, most of the people in contemporary linguistics aren't really interested in the evolutionary why or the physiological how questions, just the linguistic what's. Most neurophysiologists are how specialists and have little patience with coming-into-being why questions. Whenever we try to juggle all three big questions at once, we usually call it philosophy.' This morning, I'm going to briefly tackle one aspect of the why. Back in the early 1980s, it was becoming apparent that the four-fold enlargement of the ape-sized brain in that third chimp lineage started to happen about 2.5 million years ago. That's when the Homo line split off from the Australopithecines, when the chimps and bonobos last shared a common ancestor, when the gibbon and siamang split too. That's also when the archaeologists say that stone toolmaking really took off.
      Two and a half million years ago is also when the ice ages started, and I've always wondered what ice ages had to do with brain size -- given that there wasn't much ice in Africa where all the action was in hominid evolution. So figuring out brain enlargement has meant, for me, paying a lot of attention to what the climate researchers and oceanographers have been saying.

Our usual idea of past climates are the ice ages, when big mountains of ice slowly formed over Scandinavia and Canada, sea level slowly dropped, and even the ice-free regions of the tropics became about [50C] ten degrees colder than at present. About every hundred thousand years, much of this accumulated ice melts off and sea level rises enough to cover any forty story beachfront hotels there might have been built during an ice age. For a while, we have a warm period like today and, after maybe ten or fifteen thousand years, the cold comes back for a long time.
      Climate change was thought to happen very slowly, due to slow changes in the earth's orbit around the sun and the tilt of the earth's axis  and so the temperature changes and the sea level changes were thought to be slow too. A glacial' pace.
      That's the old story  and it's still true. Sort of. But it's misleading, like talking about average traffic and never mentioning rush hours or gridlock. What we now know is that, superimposed on those slow stately rhythms that the astronomers have explained, there are also some breathtaking abrupt climate changes. The temperature can change very quickly, just in a matter of ten to twenty years, between warm temperatures like today and the cold temperatures of an ice age. The ice takes a long time to form, however, and so the sea level takes a long time to change. Before then, the temperature has usually flipped back, just as suddenly. These whiplash changes in climate often last a few centuries, though the last big one lasted 1,300 years.
      Now, because the media have done a very poor job of reporting on this branch of science, the only abrupt climate change that you've probably heard about is the abrupt cooling associated with an volcanic eruption (or a nuclear winter). But most of the abrupt climate changes seem to be due to something else. You can guess that because you can see both abrupt coolings and abrupt warmings in the ancient temperature records. The temperature is rather like an old fluorescent light tube, suddenly on and then suddenly off, flickering back and forth. Something in our climate has two stable states  it's bistable  and the earth's average temperature flips back and forth between them.
      While one of these stepwise flips hasn't happened for about twelve thousand years, one was happening every several thousand years before that. We've been living in an unusually stable period of the earth's history, and there is no reason to assume it will continue. There is every reason to assume that, some decade in the next few centuries, there will be an abrupt, catastrophic cooling. It won't be the end of Homo sapiens but it might well be the end of our civilization. Yet we might be able to head it off, natural' though it is. We humans have amazing abilities to guess the future, and sometimes we can head off trouble in the making.

All that cold dry arctic air from Canada comes wafting across the warm water of the North Atlantic Current, aka Gulf Stream  and naturally evaporates quite a lot of it, picking up its heat. From Labrador all the way across to Ireland, the air picks up heat. That's why Europe isn't like Canada. Canada doesn't get warmed from the Pacific in a similar way. The North Atlantic Current has unique circuit that it follows, rather like a roller-coaster with a vertical drop. The problem, however, is that this heat pump can fail  and Europe can revert to a Canadian climate. It not only can fail, but it looks like it does fail, and has been doing so every few thousand years for most of the last 125,000 years. And that the rest of the world cools at the same time, all within 10-20 years.

If this failure were to happen gradually over a number of centuries, and we could see it coming and act effectively to head off trouble, then you can imagine re-engineering agriculture and decreasing population numbers in such a way as to track the decline. It might be miserable, but not catastrophic, not the apocalyptic Four Horsemen featuring famine, plague, and warfare.
      But abrupt climate change doesn't happen gradually. The full change in temperature happens in just twenty years, and there is big trouble already in just three to five years. Yes, we can always eat the corn ourselves rather than feeding it to the pigs and chickens first, and feed the U.S. population on half the food  but two- or three-fold improvements in efficiency aren't enough, and they're not possible in countries where meat is a smaller part of the present diet. If my back-of-the-envelope calculation comparing Europe with Canada is even remotely correct, then most Europeans will starve.
      And they won't die quietly, either. Armies, unpaid and unfed, will go marauding in the country next door and a series of wars will break out, trying to grab what resources remain -- and eliminate competitors for them. The human population crash would feature famine, plague, and genocidal warfare.
      These abrupt coolings happen every few thousand years. Unlike greenhouse warmings, these abrupt coolings have quite a track record that we may be able to discover and understand  and perhaps utilize, to head off another episode. One of the things I've learned in thirty years on a medical school faculty is that, when you understand what's going on, you can often head off trouble  and cheaply, too. Vaccines and antibiotics are products of our understanding of the underlying cellular mechanisms. And even when our understanding isn't that powerful, we can often "buy time," muddling through long enough to allow the search to continue for something better. I spell this out in some detail in my article in the January 1998 issue of The Atlantic Monthly.

Let me finish by telling you why I'm reasonably optimistic, despite what would appear to be a pretty depressing prospect, given the natural course of things. I'm fatalistic about some things  I doubt that I'll still be writing books fifty years from now, even in the unlikely event that I'm still alive at 108. I'm sort of fatalistic about some aspects of climate  I can't see any way that we could intervene in El Niqo, for example. But since I can see ways in which we might be able to effectively intervene to stabilize our flip-flop climate in its present warm mode, I think that fatalism about another climate flip is needless -- perhaps even foolish.
      Medieval cathedral builders learned from their design mistakes over the centuries, and their undertakings were a far larger drain on the economic resources and people power of their day than anything yet discussed for stabilizing the climate in the twenty-first century. We may not have centuries to spare, but any economy in which two percent of the population produces all the food has many options for reordering its priorities.
      We cannot avoid trouble by merely cutting down on our present warming trend, though that's an excellent place to start. Paleoclimatic records reveal that any notion we may once have had that the climate will remain the same unless pollution changes it is wishful thinking. Judging from the duration of the last warm period, we are probably near the end of the current one. Our goal must be to stabilize the climate in its favorable mode and ensure that enough equatorial heat continues to flow into the waters around Greenland and Norway.
      The stabilized climate must have a wide "comfort zone," and be able to survive the El Niqos of the short term. We can design for that in computer models of climate, just as architects design earthquake-resistant sky scrapers, and I think that understanding and intervening in the abrupt aspects of climate change is well within the capability of our science and technology -- and the economic base that supports them. This isn't science-fiction terraforming we're talking about. Stabilizing abrupt climate mechanisms might cost no more, in relative terms, than building a medieval cathedral. But we may not have centuries for acquiring wisdom, and it would be wise to compress our learning into the years immediately ahead. We have to discover what has made the climate of the past 8,000 years relatively stable, and then figure out how to prop it up.
      There's an irony in this, too. The same centuries-long climate flips between warm and cold -- the ones that made our brains grow four times larger and capable of foresight and planning ahead  those same climate flips now provide a "use it or lose it" challenge to our civilization.