The aesthetic theory of evolution that we are proposing also revolves around mating behavior, but it differs from sexual selection. For one thing, sexual selection only explains why secondary sexual characteristics in males (the peacock’s tail, the rooster’s wattle, the unwieldy antlers of the Irish elk) become exaggerated. The peak-shift effect, in contrast, helps to explain extreme traits and behaviors that pertain to all members of a species (both male and female giraffes must identify potential mates, which helps to explain why both genders have long necks).
Because humans (taxonomists included) are diurnal and hence visual creatures, we tend to place a strong emphasis on appearances. But the principle of peak shift can apply as easily to nonvisual signals. For nocturnal critters such as rodents that use smells to find mates and interpret their world, attractions to strong scents could drive evolutionary change. These changes would be hard to see but just as real. If dogs were taxonomists, the evolutionary trees in their textbooks would look very different from ours.
The Gull Chick Principle
Other rules of aesthetics besides peak shift can also be invoked to explain the astonishing diversity of species. One is what we call the “gull chick principle.”
Niko Tinbergen, a pioneering investigator of animal behavior, experimented with herring gulls 50 years ago, but the relevance of his work to evolutionary theory has not been widely appreciated. The adult herring gull has a long, yellow beak with a red spot near the tip. As soon as a chick hatches, it starts pecking at this spot, which triggers the parent to regurgitate food into the chick’s mouth. How does the chick recognize its mother? Tinbergen found that it doesn’t: chicks will peck as intently at a disembodied beak.
Why is a beak sufficient? The purpose of vision is to identify and interpret objects and events while expending the least amount of mental processing power. Through millions of years of evolution, the chick’s brain has acquired the wisdom that this long thing with a red spot always has a mother, not an inquisitive ethologist, attached to it, and it makes an interpretive shortcut.
Tinbergen next found that a beak is not even required. He held out a long, yellow stick with three red stripes on it, and the chicks pecked it—more, in fact, than they would have pecked at a real beak. Tinbergen had stumbled on a superbeak!
Why does this happen? Clearly, there are neural circuits in the visual pathways of the chick’s brain that are specialized to detect the red spot on a beak as soon as the chick hatches. Perhaps the neurons’ receptive field embodies a rule such as “the more red contours the better.” So even though the stick does not look like a beak—maybe not even to the chick—this strange object is more effective than a real beak at activating the bird’s beak-detection system. Hence, we predict that a species of gull will emerge that has two or even three red beak stripes instead of just a bigger red splotch. Another, even more striking example of the gull chick principle is the idiosyncratic preference (demonstrated in the lab) that guppies show for potential mates that have been painted blue—even though in nature guppies are not blue. Again, we anticipate the emergence of a new species: the blue guppy. It’s not often in evolutionary theory that one can make such specific predictions.
The gull chick principle may apply widely, because the visual system of every animal is wired to use specific characteristics to identify others of its species. If a potential mate diverges from the standard in a way that more optimally excites “species-identifying” brain circuits, the genes that promote such supertraits will flood the population. Unlike the peak-shift principle, no obvious parameter is being exaggerated (such as a long neck); the changes in appearance are selected because of idiosyncratic aspects of neural wiring. Even the florid, almost comical, exaggeration of dance rituals in some bird species may be influenced by this principle.
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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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