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Polydactyls, Polypods & Polycephalics - II
|by Gaurang Bhatt, MD|
In the first part, I emphasized that the number of limbs has not always been four (two forelimbs and two hind limbs). There are creatures with no limbs and worms with two limbs on each body segment. Let us now consider digits (called dactylos in Greek and referring to fingers and toes).
Such creatures capable of living in water and on land are called amphibians (ambi - amphi is an Indo-European prefix implying both as in ambidextrous and amphitheater). They found the fossil in the Canadian Arctic and named it Tiktaalik for the local Inuit language. The animal had a forelimb with one proximal and two distal bones (like our humerus and the ulna and radius) and wrist bones as well as digits. The number of fingers was not five but more and in another amphibian link called Acanthostega, there were eight fingers. Horses have a prominent single digit, Cows have two digits, Cranes and chickens have three and dogs have four, while we and sea turtles have five.
An embryologist named John Saunders discovered a zone of polarizing activity (ZPA) in the posterior part of a growing chicken limb bud and transplanted it on the anterior side of the growing limb bud. Chickens have only three digits in their forelimb which correspond to our fingers 2,3 and 4. The transplant grew two extra digits with a mirror image order 4-3-2-3-4. Identical results can be obtained by applying retinoic acid or vitamin A derivatives. They activate a gene called Sonic Hedgehog after the video game. That gene is responsible for differentiating of finger morphology and function. If it is defective persons and animals are born with undifferentiated extra fingers (from six or more) or polydactyly.
The hand and foot in us and the hind limb in birds are initially shaped like paddles and for the fingers and toes to be separated, the tissue cells between the fingers and toes has to die. Those cells during development are ordered to die like Al Qaeda recruits, Japanese Kamikaze or Harakiri and the order is signal transduction by another gene product belonging to the Bone Morphogenic Protein family. If the order is ignored because of a mutation in the web space genetic switches, we have webbed fingers and webbed toes, called Syndactyly. Guess what, such webbed toes are a distinct advantage if you live in the water and paddle with your hind limbs and that is the switch mutation in ducks, which has bestowed them with an advantage. A wonderful experiment was performed by a scientist named Randy on the embryos of skates (cartilaginous fish like sharks). He injected mouse hedgehog bead implants in the developing limb of the skate embryo skeletal rods and observed differentiation of the rods just like our fingers or chicken wings instead of their normal monotonous similarity.
Similar results have been obtained by implanting mouse Pax-6 (gene for eyes) on the wing bud of a fruit fly, which goes on to develop a compound insect eye ectopically on the wing, even though the mouse gene in its normal habitat leads to the development of a mammalian camera eye and not an insect eye. There is a gene called Tinman (from the Wizard Of Oz) which is responsible for developing the heart in animals from insects to us. Evo Devo, the new science has put the final nail in the coffin of creationists, except for the Republican contenders for the US presidency, who are retarded ineducable like their voters or psychopathologically inclined like the Ayn Rand cultist Greenspans, rabid libertarians and Tea Partiers. No wonder Hilary Clinton of the cattle futures fortune fame and her rent-a-white house husband and his Oval office shenanigans are trying to activate the oncogene Ras in Putin to transform him into a Rasputin, while they pursue regime change under the guise of R2P, spread Stuxnet viruses and use NGOs for spying and overthrowing regimes under our Nobel War Prize winner Phoney Audacious Hopeless Smarmy O’Blarney president.
Finally Hans Spemann transplanted the dorsal lip of the blastopore of one newt embryo on to another newt embryo and it developed into a two headed monster. It is not because of the natural proclivity of Newts transforming into monsters, as those of you politically astute may think. The Hindus are unique in making their gods mutiheaded and chimeras. The Greeks did the opposite and their chimeras were monsters, gorgons or centaurs. The non-evolutionary message I wish to convey is about the unity and commonality of life forms, promote secular humanism and put an end to the shameless pandering and race to the bottom in US and Indian politics and religion.
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