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Of Polydactyls, Polypods & Polycephalics
|by Gaurang Bhatt, MD|
Certain things seem so obvious and routine to us that we often falsely assume that they are the universal norm. We are accustomed to seeing animals and mostly all humans with four limbs and five digits on each limb. These form the basis of our counting in tens and twenties. While India invented decimal system is barely 1600 years old and counting by twenties (vingt) common in the French language and also in English as in Lincoln’s Gettysburg address - Four score and seven years ago -.
Winston Churchill remarked that the US will ultimately do the right thing, but only after it has tried all other alternatives first. I want to draw my readers’ attention to the comparable stubborn obstinacy of evolution and its blind tinkering. We begin with the phylum Cnidaria which includes many creatures called jellyfish. They have variable numbers of tentacles. Sea anemones also have varying numbers of tentacles (corresponding to primitive limbs). Starfish or Echinoderms have a five fold symmetry but rare species may have many more arms. Primitive insects have a repetitive segmental body plan and may have a leg on each side of every segment as in centipedes and millipedes. Marine arthropods like Shrimps and lobsters have this kind of limb distribution on each thoracic segment, but they also have maxillipeds or jaw arms and grasping claws. Another appendage below the one destined to become a leg develops into a gill and in the flying insects, change development to become a wing or stabilizing haltere. In spiders (Arachnoidea) there are eight legs in all and the same in octopuses. Squid have ten appendages, two tentacles and eight arms. Most other insects have three pairs of legs, all on the thorax. (See Marlene Zuk’s book “Sex On Six Legs”)
On the other hand, snakes have no legs or at most two small rudimentary ones as in some pythons. They have all their body segments develop as thoracic ones with a pair of ribs, but no legs. Whales also do not develop hind legs. All this becomes possible in different animals as do the wing designs of all butterflies by activation or inactivation of genetic switches in different body segments. This allows endless variations in body plans while preserving viability, without the risk of severely faulty development and body plan destined for extinction or inability to mate and reproduce and allows opportunity to seek out an unexplored or unexploited niche for survival. This is the new science of evolutionary development described in Sean B. Carroll’s book “Endless Forms Most Beautiful” and Kirschner & Gerhart’s book, “The Plausibility Of Life”.
The above story shows how evolution varied the number of limbs. In Sanskrit, the word for leg is “Pada” from which we get pug and paadukaa. In Greek and Latin, the word is pod or even pus, hence octo (eight) + pus (feet). Thus also Orthopod, orthopedics and even Oedipus from Oedema (swollen) +pus (feet). Oedipus was cursed from birth to kill his father and marry his mother, so his parents tied up his feet tightly (they swelled) and set him adrift in the river, where they hoped he would drown. See the connection to the story of Moses and Karna with precisely opposite benign intentions.
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