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In a Tadpole’s Eye: Another Case of Darwinism’s Plasticity Problem

David Klinghoffer


Once you get over the slightly disturbing aspects of some recent experiments at Tufts University, you realize it’s just another fine demonstration of Darwinism’s plasticity problem that James Barham has repeatedly emphasized.
Plasticity refers to the ability of animal bodies to remarkably adapt themselves to challenges that otherwise you might expect to be catastrophic. Tufts biologists have now succeeded in granting something close to vision to tadpoles by planting an ectopic eye in their tail. The eye has no connection to the brain, only to the spinal cord, yet somehow visual data is being effectively gathered and analyzed.
The researchers did this: They removed eye primordia from “donor” tadpole embryos and installed them in “recipients,” in the tail, with the recipients having been surgically relieved of their own natural eyes — resulting in what should have been a blind tadpole. But no, incredibly, it turned out through a series of tests involving differently colored lights and electric shocks that some of the tadpoles could see well enough to maneuver away from the light that signaled “mild” electrocution. (I warned you this was little bit upsetting if you’re sensitive to tadpoles.)
Science Daily summarizes the original report in Journal of Experimental Biology (“Ectopic eyes outside the head in Xenopus tadpoles provide sensory data for light-mediated learning“):

Just over 19 percent of the animals with optic nerves that connected to the spine demonstrated learned responses to the lights. They swam away from the red light while the blue light stimulated natural movement.
Their response to the lights elicited during the experiments was no different from that of a control group of tadpoles with natural eyes intact. Furthermore, this response was not demonstrated by eyeless tadpoles or tadpoles that did not receive any electrical shock.
“This has never been shown before,” says [Professor Michael] Levin. “No one would have guessed that eyes on the flank of a tadpole could see, especially when wired only to the spinal cord and not the brain.” The findings suggest a remarkable plasticity in the brain’s ability to incorporate signals from various body regions into behavioral programs that had evolved with a specific and different body plan.

Here and at his own blog, Barham has pointed out that such plasticity cannot be accounted for in Darwinian terms: no animal in the history of life was previously rewarded by natural selection for being able to survive with visual information being somehow assimilated via the spinal cord (a serious enigma in itself) after its were eyes extracted and a friend’s eye surgically emplaced in its tail.
This is one of many amazing instances of similar phenomena. Barham has written:

Moreover, it would be absurd, in terms of the relative significance of cause and effect.
To say that the massive reorganization exhibited by the brain in the first three experiments is a side effect of selection for some specific neural trait like vision would be like saying that binocular vision in all its complexity is a side effect of selection for the retina or selection for the lens. It would be to confuse the tail with the dog.
Another strategy that the desperate Darwinist might adopt would be to posit selection for an entirely general capacity for intelligent, goal-directed plasticity.
That is certainly a more promising way to go. However, such a strategy would still be tantamount to admitting defeat.
Why? Because it would be to acknowledge the existence of a fundamental, inherent, and quite general biological principle of what we might call “adaptivity.”
Why would that matter? Because the main task of Darwinian theory is to “reduce” teleology and normativity to mechanism.
Therefore, as soon as the Darwinist admits the reality of a general capacity for adaptivity extending throughout all of the living world, he has already given away the whole ballgame.

As ever, you are kindly requested to go over there, and over here, to read the rest.
Image credit: D. Blackiston and M. Levin.