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Heads or tails? The actual, factual tale of brainy gecko tails
Life is too short to regret one's inadequacies; nobody can be good at everything. (I sometimes wonder if I'm good at anything.) Though I have a digital camera and a book on digital photography I haven't yet found the time to do the necessary grunt work to rise above the level of utter novice. I wish, I wish! You see, it's the time of year when the local skinks are rousing themselves from their winter dormancy and invade my office to bask on its sun-soaked carpet. I'm about to tell you about lizards that drop their tails and just moments ago a tailless specimen scurried across the floor only feet away - a great photo-op for anyone a notch above novice in competence.
Everybody has heard about skinks and geckos that drop their tails when sorely set upon by some villain intent on satiating a basic lust - hunger. Who hasn't heard how such tails thrash around for a while afterwards, giving their owners a narrow window of opportunity to escape while the predator is distracted by the thrashing and twitching worm? But did you know that serious fans of severed tails are highly intrigued and impressed by the complex behavioral repertoire of such mortal remains? True, experts in muscle coordination would not expect a severed tail to just lie there like a head with its chicken chopped off, but they are hard pressed to explain the "flips, flops and cartwheels" that severed tails execute without the benefit of a brain to coordinate the sophisticated movements.
I tell the truth, not a fabulous tale, when I say that even the twitches and lunges of detached tails had to be carefully planned. The Creator of heaven and earth, the Father of Jesus Christ, devoted serious thought to the challenge of making disengaged lizard tails perform "highly complex movements, including acrobatic flips up to three centimeters in height". In a recent article, Timothy Higham and Anthony Russell report that, "Whereas the energetic, ecological and functional ramifications of tail loss for many lizards have been extensively documented, little is known about the behavior and neuromuscular control of the autotomized tail", which, they tell us, "In addition to rhythmic swinging. exhibits extremely complex movement patterns for up to 30 min following autotomy". 1 Those who recognize the truth of divine creation find entertainment, a lifting of the spirits, and insights into the powerhouse mind of God in phenomena as seemingly unimportant and unrelated to daily life as twitching tails. Jesus died to atone for mankind's sins. He also considered designing fragile tails worthy of His consideration.
An intricate repertoire of feats such as this doesn't just happen; the muscular movements must be systematically
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coordinated by nerve impulses emanating from somewhere. Furthermore, the tail has to decide which of its various movements would be the most effective under the circumstances of the moment; in at least some cases, the evidence suggests that the tail crafts its response to environmental conditions! No physiologist worth his salt is going to propose some kind of spooky spiritual connection between cut-off tail and brain. A scientific explanation must be forthcoming.
Physiologists have long understood that a limited degree of coordination of muscular movements in the extremities is carried out by clusters of nerves, known as "neural networks" or "neural circuits", found in the spinal cord. Loosely speaking, one can say that the brain extends from the head all the way to the tip of the backbone. Obviously, the circuits governing tail movements in severed lizard tails must be in the tail. Also long understood is the interconnectedness between the circuits and the muscles they control, with constant feedback from the muscles to the circuits; nerves and muscles "act together to generate controlled but complex outputs". Environmental conditions provide stimuli that activate sensory cells in the skin that help the nerve-muscle system to decide which specific behavior - pivot, leap, lunge, twitch, swing, flip - it should perform. But Higham and Russell were surprised to discover that,
. the signals responsible for movements of the shed tail begin at the very far end of the tail, indicating that there is a control centre located there that is likely overridden by higher centers until the tail is shed, at which point its potential is realized.
Now is that amazing or is that amazing? These tail-tip circuits have been designed to be activated only when they become independent of the brain. As long as the tail is connected to the body, signals from the brain keep repressing them. What staggering contingency planning.
Now here's another fascinating tidbit in this story. The movements are so mystifying to the predator that oftentimes it gives up the chase:
This would allow a lizard to return to the site of autotomy and ingest the severed tail, as observed in the lab and field by Clark. This would potentially compensate for the loss of high levels of lipids that are typically stored in the tails of geckos (Higham and Russell).
Unless you wish to see a grown man cry or put on a tantrum, please don't tell me that this system was crafted over millions of years by chance mutations and competition between lizards with and lizards without this clever design. All praise must go to the Infinitely Intelligent Designer.
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