Humans: the party animal

Daedalus, Summer 2009 by Gazzaniga, Michael S

By definition, the species Homo sapiens is unique. Over a time course of approximately seven million years, humans have evolved into quite a different animal from what was the last common ancestor we share with our closest surviving relative, the chimpanzee. Trying to figure out how we came to be what we are, and identifying what aspects, both physical and behavioral, we share with other animals, most especially the chimpanzee, and those that are uniquely human has been of ongoing interest.1

Take a minute the next time you go to a dinner party, barbecue, wedding reception, or baby shower - run-of-themill events for us Homo sapiens - to ponder the fact that such events are completely unheard of in any other species. What other animal would plan an event, provide food to unrelated others, and sit together and share it without a food fight, all while laughing about stories of the past and hopes and dreams of the future ? There is none. No matter how smart your family dog may be, he would not divvy up a prime rib roast and pass it out to the other dogs of the neighborhood with a happy little bark; neither would our closest relatives, the chimps. Humans are social beings, and although there are other animal and insect species that are social, our species takes sociability to a previously unknown level. We are party animals, and on our way to becoming such we have evolved a whole host of unique features - features so unique that we humans are playing in another ballpark.

Although many may suggest that humans act "like a bunch of animals," and the daily news intimates that we are endlessly fighting with one another, it is by cooperating with and helping unrelated others that we are unparalleled among animal species. Something is markedly different in our brains : we are "wired" differently. The results of this altered wiring allow humans to read books, or to go to the symphony, school, or jail. That is not to say humans are 100 percent different. In fact, most of our automatic processing is much the same as in other animals.

Although all species are unique unto themselves, all have a common origin and are made up of the same materials. It isn't surprising that when Charles Darwin first proposed that humans were descended from the great apes, he thought that the difference between us and our closest relatives, the chimpanzees, was a quantitative difference, not a qualitative one. We were just fancier apes with bigger brains, Darwin reasoned. In the mid-1960s, however, Ralph Holloway added to Darwin's theory, concluding that brain reorganization, rather than brain size alone, resulted in the evolutionary changes in cognitive capacity. Evidence for Holloway's insight is accumulating.

What exactly is brain reorganization, and how has it affected brain computations and the human mind? Cognitive scientists Derek Penn, Keith Holyoak, and Dan Povinelli, "happy to be the hostage [ s ] of empirical fortune, "2 claim :

The profound biological continuity between human and nonhuman animals masks an equally profound functional discontinuity between the human and nonhuman mind. . . . [That discontinuity] pervades nearly every domain of cognition - from reasoning about spatial relations to deceiving conspecifics - and runs much deeper than even the spectacular scaffolding provided by language or culture alone can explain.

This "discontinuity of human cognition," they propose, was a watershed change that occurred after the hominid line diverged from our last common ancestor with the chimp, and it resulted in our exceptional relational ability. We far exceed other species in our ability to grasp analogies and to combine relations into higher-order structures. Mindful that there are no "unbridgeable gaps" in evolution, figuring out how this came to be is the question. Regardless of whether or not our ability to form higher-order relations is the basis for our cognitive differences, something very different is going on in the human brain.

There is no question that the human brain is big. After the hominid line diverged from the last common ancestor we share with the chimps, the brain underwent a huge growth spurt. In comparison to a chimp's brain, which weighs about 400 grams, an average human brain weighs about 1,300 grams. Homo neanderthalensis, however, had a bigger brain than modern-day humans, and although it is clear through fossil evidence that their culture was more advanced than that of the chimp, they were not in the same league as H. sapiens. Thus brain size is not the only variable in human uniqueness.

In non-primate mammals, the brain's prefrontal cortex has two major regions that work together to contribute to the "emotional" aspects of decision-making. We do, of course, make many of our decisions quickly and based on our emotions, and so still utilize these two evolutionarily older regions. However, some decisions are based on rational thinking. Only primates possess a third, evolutionarily newer region, the lateral prefrontal cortex, where the intriguing Brodmann Area 10 is located. One hundred years ago, German neurologist Korbinian Brodmann identified fifty-two distinct regions of the human cerebral cortex, based on the underlying cytoarchitectonics. Area 10 in humans is disproportionately larger compared to the rest of the great ape brains, and is densely interconnected with other still larger regions in human brains. Area 10 is concerned mainly with the "rational" aspects of decision-making and is involved with all sorts of abilities in which humans excel : memory and planning, cognitive flexibility, abstract thinking, initiating appropriate behavior and inhibiting inappropriate behavior, learning rules, and picking out relevant information that is perceived through the senses.