September 13, 2010 | David F. Coppedge

Archer Fish See Like People

An archer fish can spit out a man’s cigarette.  That’s actually a humorous scene at the end of a video clip on The Scientist that talks about the amazing eyes of this underwater sharpshooter.  New research shows that these freshwater fish, known for their ability to spit bugs off bushes, have a mammal-like ability to pick out their targets against various backgrounds.
    A paper in PNAS describes the experiments that proved archer fish possess “orientation saliency,” a “fundamental building block of vision” that allows the brain to discern a target from its background.1  The Scientist said,

Up till now, researchers believed that the ability to see objects positioned out of line with their backgrounds, known as orientation saliency, was only found in mammals, which have specialized neurons in their brain that allow the animal to perceive these off-kilter objects.  But recent anecdotal evidence suggested that archer fish are also capable of picking out askew objects, such as insect prey, from complex visual backgrounds.

The first video clip in the article shows some of the experimental setup scientists at Ben Gurion University used to test the orientation saliency of the fish.  The second video clip explains other physiological abilities that allow these fish to compensate for refraction and gravity as they shoot out bugs (or cigarettes) up to two meters above the water.
    Both The Scientist and PNAS were baffled by how such a complex trait could have evolved.  Why?  The authors of the paper explain, “Given the enormous evolutionary distance between humans and archer fish, our findings suggest that orientation-based saliency constitutes a fundamental building block for efficient visual information processing.”  But if so, they did not demonstrate that all fish have this ability, to say nothing of the all animals in the evolutionary branch leading to mammals.  The Scientist quoted a German researcher (not involved in the study) with a different evolutionary suggestion: “Obviously evolution manages to bring out phenomena when they are useful for a species.”
    The authors, however, noted that fish do not have a visual cortex where orientation saliency is located.  “If fish, who don't have a visual cortex, can exhibit the same behavior, then researchers need to reestablish their understanding of how these processes work,” the article ended.  But in the paper, the German suggestion appeared again: “These observations demonstrate how evolutionary pressures for efficient visual processing bring distant evolutionary paths to express similar functional solutions,” the authors said.  Somehow, some way, the call for survival introduced “an evolutionary pressure toward orientation-based visual saliency processing.”
    At the end of their paper, the authors hedged their bets.  They tried to argue that either way, whether the trait evolved by homology (common descent) or analogy (convergent evolution), Darwin can’t lose:

Another intriguing question raised by our findings is the implications of the evolutionary relationship between orientation saliency in the two species investigated.  If orientation saliency mechanisms in archer fish and humans are homologous (i.e., derived from common ancestry), then the fact that this functionality has been preserved for so long implies that these mechanisms are of high functional importance and that no better alternatives have been found during the course of evolution.  This further suggests orientation saliency as a fundamental building block for visual representations and efficient visual processing.  Similarly, if orientation saliency mechanisms in archer fish are analogous to those of humans (i.e., reflect independently convergent evolutionary processes), it would strongly support the notion that orientation saliency has computational optimality in a wide variety of contexts.  Hence, both evolutionary alternatives suggest that orientation-based saliency constitutes a universal building block for efficient visual information processing.

1.  Alik Mokeichev, Ronen Segev, and Ohad Ben-Shahar, “Orientation saliency without visual cortex and target selection in archer fish,” Proceedings of the National Academy of Sciences, published online before print September 13, 2010, doi: 10.1073/pnas.1005446107.

Evolution dogmatists are funny sometimes.  The most embarrassing facts fail to dislodge their beliefs.  They’re like bugs wrapping themselves with velcro around a twig, lest the facts, like the spit-cannons of an archer fish from the observable world below, knock their feet out from under them.
    Consider how silly both evolutionary explanations are.  If the trait “arose” in some common ancestor of fish and humans (perhaps some acorn worm), what ancestor was it, and why did the worm need orientation saliency?  Why doesn’t every animal from the ancestor up have it?  Without a natural law demonstrating a path from need to function, it’s an appeal to a miracle anyway.
    If, on the other hand, evolution “gave rise” to the trait independently by “convergence,” is that not an appeal to two miracles?  A miracle can be defined in the materialist world as any improbable situation that requires a leap of faith to accept the evolutionary explanation.  It’s a corollary of the Stuff Happens Law (SHL) that says, “Sometimes amazing stuff happens.”  (The SHL, in philosophy of science, represents the absence of scientific explanation.)
    The more amazing things that happen – e.g., flight six times (insects, birds, mammals, reptiles, humans with their flying machines, and flying fish, 09/11/2010), the more the miracles like human-like sight in archer fish, the more evolutionary theory is lacking in explanation, the more they reach ecstasy.  It gives the Darwiniacs even more reason to sing their praises to Evolution, that miracle worker from which, and to which, and for which, are all things.
    Now go watch the video clips on The Scientist and think like a rational human being.

(Visited 126 times, 1 visits today)

Leave a Reply