If someone showed you a caricature of Richard Nixon—a man’s face with oversize shaggy eyebrows, a bulbous nose and pronounced jowls—you would probably recognize the former president immediately, even though the drawing is not true to life. A cartoonist creates such a sketch by taking the average of many male faces and subtracting it from Nixon’s face, then amplifying those distinctive differences. To an observer, the result looks more like Nixon than Nixon himself. Why is it that our brains respond so intensely to extremes?
When the cartoon’s “Nixon-ness” jumps out at you, you are experiencing what scientists call “peak shift.” To understand the concept, imagine, for argument’s sake, that you want to teach a rat to distinguish a rectangle from a square. It’s quite easy to do. Simply give the animal cheese every time it picks the rectangle, and it will soon learn to select the rectangle every time. Once the rat has developed this preference, let’s say you show it a longer, skinnier rectangle. Inevitably, you will find that the rat prefers the exaggerated one to the original. What the rat has learned to recognize is not a particular rectangle but rather rectangularity itself: the more rectangular the better. The savvy rodent looks at the longer, skinnier quadrilateral and goes, “Wow, what a rectangle!” In scientific parlance, the rat’s “peak response”—its strongest reaction—has shifted away from the original—hence the term “peak shift.”
The sway that exaggerated characteristics hold over us is a special kind of illusion—and a powerful one, we believe. In the five years that we have been writing about perception for this magazine, we have described a range of illusions, from geometric patterns that seem to move because they activate our motion perception systems to optical tricks that arise because each of our eyes sees the world from a slightly different position.
Now we would like to make a daring suggestion: that illusions are not merely fascinating windows into our minds and the way we perceive the world. They help to drive the most powerful force that shapes life on earth: evolution.
The standard theory of evolution is that animals that randomly inherited genes that produced beneficial traits—in the case of the giraffe, a longer neck, which made it easier to reach tall acacia trees—ate better, reproduced more often and passed these gene variants to their offspring. Hence the progressive lengthening of the giraffe’s neck across successive generations.
What we are proposing is yet another mechanism of evolution. Our hypothesis involves the unintended consequences of aesthetic and perceptual laws that evolved to help creatures quickly identify what in their surroundings is useful (food and potential mates) and what constitutes a threat (environmental dangers and predators). We believe that these laws indirectly drive many aspects of the evolution of animals’ shape, size and coloration.
Let’s return to the giraffe. Giraffes need to recognize and mate with others of their own kind—and not, say, with antelopes or okapi. Wired into the animals’ visual centers is a recognition system that automatically prefers mates that have more “giraffelike” characteristics. In this formulation, the longer necks were selected not because of any functional
reason but simply because in scanning for desired traits, the visual system lights upon exaggerated ones first. They stand out, like Nixon’s prominent brows. Across successive generations, the long neck would have become an ever more reliable species marker for giraffeness, thereby enabling a partner to be spotted even from a great distance.
Our theory is not intended to replace Charles Darwin’s but to point out that other powerful forces besides the natural selection of fitness-conferring genes may be involved. Darwin, of course, acknowledged as much when he observed that mating behavior—so-called sexual selection—can exert its own, often maladaptive, impact on evolution. Because female peacocks prefer males with large tails, big-tail genes multiply in the population, eventually culminating in modern peacocks’ magnificent but absurdly impractical tails.
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3 Comments
Add CommentI believe that the Ramachandrans hypothesis proposed in Carried to Extremes also has ramifications in the development of extreme behavior in cults. Leaders like Jim Jones do not usually start out being as bizarre as we later find them. The group selects a behavior that is deemed to represent the ideal of the cult. Those who demonstrate higher levels of dedication to that behavior are elevated to leadership. As they struggle to retain their influence they will tend to exhibit extreme degrees of said behavior to the continued admiration of their followers. As the trend continues more and more bizarre behavior is seen until the situation becomes untenable and comes crashing down.
Reply | Report Abuse | Link to thisThe red spot doesn't just identify the mother, it tells the mother there's a chick there that's hungry. The mother's job is to keep the dot near the chick so it doesn't go picking at a different beaklike structure or beak of some predatory species, etc. I can see a lot of other things wrong with this article's analysis, but I'll pass on them for now.
Reply | Report Abuse | Link to thisOk, I'll bite. Very interesting article. At first I thought they were attempting to counter the influence of natural selection, as if this was a rival theory, and then I read that they were suggesting it was just an additional force influencing the origin of species. I think they may be right, however this theory may be difficult to apply or prove for several reasons. Application of this theory may be limited to those animals, such as mammals, with visual systems like that of our species. If they use the strict criteria of animals noticing visual differences in a way similar to we, humans, do, then I think they could be extrapolating human thought patterns to the reaons for behavior of other quite different life forms. But of course, they say they are not. But even if they were to enlarge the criteria and not limit it to just visual differences, but rather those of smell, chemical stimuli, etc, it would still be limited to certain life forms, namely those who reproduce sexually. Obviously an ant may not be subject to this influence, a jellyfish even less likely, a plant even less likely, and a bacterium probably not likely at all. Nonetheless, among species where the theory does apply, it probably does input some influence. However, proving it would be difficult. Using the giraffe example in the article, there could be evolutionary forces based on those in the article, distinct from classic natural selection based on ability to reach for food supply. However, these two forces cannot be realistically looked at independently, because the other force is always present, filtering the gene pool. But then I thought, maybe the two are not mutually exclusive. Maybe the two forces could be part of the same process for survival. For example, if there were two species of antelope who looked quite similar, but were genetically distinct enough to be unable to reproduce if they were to mate, then the theory in this article may be applicable, but when you think about it, it may be only a means of selection itself. If the two antelope species couldn't tell themselves apart, then every time one were to court or mate with the opposite species, it would be a wasted effort. Even males sparring off against males in the other species could happen and would be a further waste of effort. The species that can distinguish apart in one or more distinct ways would be more efficient at breeding, and passing along its genes. Hence, the genes that conferred the ability to differentiate based on exaggerated recognition of others' traits would find themselves more commonplace over time, and would dominate in a gene pool. So, the theory in the article may not be a force in its right, but may be a further criterion around which individuals must compete for natural selection. Our abilities to do this peak-shifting visually may have evolved long ago in the earliest mammals or even before. And before that, perhaps it was exaggerating the chemical differences between one worm and another. But far enough back, when we were non-sexually reproducing "species", the entire environment, whether competing rivals from within the same species, others outside the species trying to compete within the same niche, or non-living hazards, were a danger to the individual. Recognition of which type of hazard would have been useful, but not in the same manner as it would be among sexually reproducing species. So, all in all, this article's theory seems to me actually a criterion for selection within the classical theory of natural selection, rather than a new independent force co-acting upon species.
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