Tuesday, July 25, 2006

Making the mind: Why are our brains so big?

The author of The Origin of Mind describes human brain development and a meta-theory of evolution

By Brint Montgomery

The Origin of Mind: Evolution of Brain, Cognition, and General Intelligence
David C. Geary
Washington, D.C. American Psychological Association, 2005.
459 pages. $59.95 hardcover

Seven million years ago, there was a small group of lock-kneed primates walking around with brains that measured 350 cubic centimeters. Seven seconds ago, there was a large group of lock-kneed primates walking around with brains that measured 1,350 cubic centimeters. How did we get from there to here?

In The Origin of Mind, David C. Geary offers his answer in the meta-theory of evolution. The development of the brain, cognition and general intelligence of the human mind differ from that of other mammalian species only as a matter of degree, not kind, he says. A professor of psychological sciences at the University of Missouri-Columbia, Geary offers the working assumption that motivational, feeling-emotive, behavioral and cognitive systems have evolved to process social and ecological information patterns — such as facial expressions — that correlated with survival or reproductive options during human evolution. Specifically, he proposes that all of these are ultimately and proximately focused on supporting individuals’ attempts to gain access to and control of the social (mates), biological (food), and physical (demarcation of territory) resources that supported survival and improved reproductive prospects during human evolutionary history.

If that last paragraph seemed a bit ponderous, get used to it. Geary’s prose is flamethrower-on, full-bore, scorched-earth academic writing — which is to say it’s dry. Nevertheless, it’s all about us because the whole thrust of the work is to explain the rise and success of the human race as we know it. The story being about us, then, lends a continuing and ultimately satisfying intrigue to the overall book as the explanation of our origin and cognitive skills unfolds.

Brain takes center stage

Although the book’s nine chapter divisions move roughly from hominid history to brain modularity and function to general intelligence, the real story of the biological arms race that fed human brain development actually has only two acts.

In the first act, humans achieve “superpredator” status, probably around 800,000 years ago at the latest, with Homo erectus’ mastery of fire. That, along with the ever-developing use of tools, allows humans to become masters of their ecological domain. This has enormous survival and reproductive consequences. Once ecological mastery was achieved, “an evolutionary Rubicon was crossed.” After that point, the effects of extrinsic forces of natural selection diminished, and within-species competition became the principal hostile force of nature, guiding the long-term evolution of behavior capacities, traits and tendencies.

In the second act, the natural, cyclical contractions of ecological resources force social competition among small human bands for diminishing resources. In such a situation where social competition intensifies, the stage is set for a form of runaway selection, whereby the more cognitively, socially and behaviorally sophisticated individuals are able to outmaneuver and manipulate other individuals to gain control of resources in the local ecology and to dominate of the behavior of other people.

The 17th-century British philosopher Thomas Hobbes would be proud of himself, no doubt, for guessing something not too different from this. To the extent that access to these resources correlates with survival and reproductive outcomes — and trust me, Geary cites all the studies that do indeed show such correlation — the associated socio-cognitive competencies and supporting brain systems will necessarily evolve. To boil it all down: Ecological pressures were salient earlier in hominid evolution, and social pressures were salient later in hominid evolution.

ID: Not just today’s debate

Upon considering brain expansion during the social pressure phase of human evolution, Geary moves to explicate which particular modules support survival and reproductive success. As a setup to this explanation, Geary recounts an important but rancorous squabble — as eerily familiar as this morning’s news — between Charles Darwin and natural selection codiscoverer Alfred Russel Wallace.

In 1871, Darwin argued that the mental faculties of the human brain, such as language, had evolved by means of natural and sexual selection. And although qualitatively different in some ways, the human brain showed much continuity with the faculties of mind and brain in other species. Wallace just couldn’t buy it and was unable to countenance that the mental faculties of the human brain — with its sensitivity to moral values and its rational powers — could be the result of mindless, purely organic evolution. As Geary duly notes, one of the first places in which Wallace’s argument was articulated was at the conclusion of a review of geologist Charles Lyell’s 1867 edition of Principles of Geology. It is worth recounting outright:

“But let us not shut our eyes to the evidence that an Overruling Intelligence has watched over the action of those laws [natural selection] so directing variations and so determining the accumulation [of favored traits], as finally to produce an organization sufficiently perfect to admit of, and even to aid in, the indefinite advancement of our mental and moral nature.”

Sound familiar? It should, for much of the haggling over intelligent design issues is associated with people who seem to have the same intuitions about other biological structures that Wallace had over the astounding powers of the human brain. But Geary is explicit in his ultimate goal: To develop a theory that not only is consistent with Darwin’s idea of evolved faculties but also integrates contemporary theory and research on modularity with the competencies that define general intelligence. On the Darwin-Wallace squabble, Geary concludes that “contemporary debates have a less theological flavor.”

Hunt directors and lie detectors

Rejecting Wallace’s position that the brain/mind of humans is fundamentally different from those of other species, Geary shows how the pattern emerging from current research suggests that the basic architecture and some of the specialized functions of the mammalian neocortex and subcortical regions are conserved across many species, including humans. Geary argues that in both stages of human brain evolution — the ecological and the social — specialized modules within the brain form a means of processing information. As a coordinated grouping, I will dub them “hunt directors” and “lie detectors.” I extend my apologies to Geary for abridging his multiple and more subtle module classifications.

Hunt directors are concerned with what Geary and others have called “folk biology” and “folk physics.” Specialized brain processing areas for identifying flora and fauna as well as other kinds of natural features in the world, fall under the rubric of folk biology. Specialized brain areas for identifying human faces, hands and other structural patterns in the environment fall under the rubric of folk physics. Finally, the ability to isolate and/or discount various combinations of modules for specialized attention and learning falls to the master command and control center of consciousness, in particular the “executive module.”

Lie detectors are specialized processing areas for understanding beliefs and intentions, predicting behaviors and recognizing minded entities. These all fall under the rubric of “folk psychology.” Naturally, lie detectors play into survival and reproduction rates for mastery of social competition, cooperation and control.

With the growing evolutionary efficiency of hunt director module groupings and lie detector module groupings, growth in the overall volume and increased connectivity of the human brain is a natural consequence. In the end you have the “big brain” — or, more accurately, a brain with a more favorable ratio of size to body weight. Elephants’ brains, for example, are much bigger than ours, but when one factors in their body weight, they do not make it into the big-brain club.

Consciousness and self-awareness

With Geary’s position being so carefully nuanced and documented, it might appear to present few opportunities for counterargument. But let me suggest at least two ways to place the king in check, even if checkmate is hardly in the offing.

Geary holds that even though there is a vigorous debate, one finds no definitive evidence that great apes have a sense of self or can make inferences about inferences — the latter sometimes called “second-order thought.” There are certainly issues to worry over here, and some cut to the heart — or perhaps to the head — of Geary’s theories on the origin of the human mind.

First, as Geary well knows, there’s little truly definitive evidence on anything pertaining to that most difficult of difficult issues concerning mind — to wit, “consciousness.” Even determining what counts as evidence is controversial. The 17th-century philosopher René Descartes, for example, argued that because animals don’t use language, they don’t have minds. In contrast, advocates for the idea that animals are indeed minded — often defended as prelude to establishing some ethical argument for our accountability to them — think that language use is neither helpful nor decisive concerning their mental status.

Second, the central issues of self and second-order thinking are pivotal for evaluating when consciousness arises in the evolutionary chain of human development. One might make the argument that only humans are conscious because all normally functioning humans are self-aware, while no other mammals outside of our seven-million-year common primate heritage definitively exhibit this trait. However, both of these premises are open to debate.

After all, not all humans have an “awareness of self.” Children under the age of 2, in fact, seem not to be self-aware. Self-awareness is commonly tested by surreptitiously marking an animal’s skin or fur, then placing the animal in front of a mirror. If the animal recognizes the mirror image as itself, it will usually examine or try to clean the marking on its body, prompting scientists to dub it “self-aware.”

Nevertheless, infants are certainly perceived as conscious by people who shuffle that term around. Indeed, there are some powerful empirical studies to this effect. So why think that children under age 2 lack a concept of self? Because one can have a concept of the self only if one has a concept of what a mind is. But experiments with young children indicate that they do not recognize the very concept of other minds. Hence, they have no recognition of the concept of a self. Eventually, of course, virtually all do come to such recognition of other minds, though some children, such as acute autistics, never come to gain this power.

And, to debunk the notion that no animals outside of our primate heritage are self-aware, there are intriguing results from studies with another group of mammals, ones that were alive and well 43 million to 63 million years before our primate heritage sees a positive trend in brain size, and ones that have developed along a different evolutionary trajectory — namely, bottlenose dolphins. Bottlenose dolphins have brain sizes about 250 cubic centimeters greater than human adults. Moreover, they have a favorable brain-size to bodyweight ratio. And, most importantly, they can recognize artificially imposed body markings in the mirror-exposure studies, as do chimps and humans. But whatever developmental pressures evolved self-aware brains of such great size and abilities in bottlenose dolphins must be different from the kinds of ecologically and socially induced developmental pressures posited by Geary for the self-aware big brains in us.

Recall that Geary holds that evolutionary pressures first resulted in our superpreditory status, and subsequently resulted in our social competitor status. But bottlenose dolphins are neither superpreditors nor cutthroat social competitors. Thus, the exclusive development of self-aware creatures need not have necessarily followed the trends identified by Geary. Granted, Geary never claims this need be so, but it significantly weakens what is interesting about his thesis — that evolutionary pressures for predation and social competition ultimately are the basis for the development of conscious creatures. Maybe in a few million years the octopus, another highly complex creature with an up-and-coming favorable brain-size ratio, will offer a more objective opinion on this matter.

Even so — and with the earlier cautions about writing style still on the table — I recommend this book as a thought-provoking, tour-de-force overview of recent findings in cognitive science and neuroscience as well as in primatology, anthropology and sociology.

Brint Montgomery is professor of philosophy at Southern Nazarene University in Oklahoma City, Okla. A version of this review appeared in Science and Theology News.


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