Polydactyls, Polypods & Polycephalics - II by Gaurang Bhatt, MD SignUp
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Polydactyls, Polypods & Polycephalics - II
by Gaurang Bhatt, MD Bookmark and Share
 

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).

About 365 million years ago, all living creatures lived in water and to avoid predation by bigger fishes of smaller fishes (Matsyanyaya of Hindu philosophy comparable to a Hobbesian hell), some fish tried to eke out a living on land. This required breathing air by lungs and not oxygen from water through the gills. Some fish had developed a buoyant air bladder and this was modified to breathe. Lungfish are a current species which do that. Neil Shubin and his colleagues looked for fish fossils with flat heads, powerful shoulder bones and limbs instead of fins. 

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.
 

10-Mar-2012
More by :  Gaurang Bhatt, MD
 
Views: 1181
Article Comment Prof Bhutt, I've been reading your columns for a quite a few years now and always found them to be informative as well as entertaining. They always seem to be thoroughly researched. I also love the way you co-relate facts and myths from different spheres.

As to your complaint about 'human beings in general and Indians in particular', wonder, how many establishments (governments and business) reflect the beliefs or principles of the actual people. Are only Indians to be blamed of this double standard?

Sorry, didn't mean to criticise, just wanted to point out that at some level, may be the nature of human life sets us up as hypocritical creatures.
Shilpa
04/10/2012
Article Comment Andy, you can't spell, write a coherent sentence or put forth an argument. You represent the majority of this world and people like me are up a creek against your kind who cannot think, are unwilling to learn and are ruled by religion like Santorum, prejudice like Gingrich, and unprincipled self interest like Romney and Obama's popularity prove. I bet that your claim to US citizenship must rest entirely on your stupidity. I am not fazed by your kind. What is disheartening is that not one of the few, if any readers who possibly appreciates my efforts, has the time, interest or energy to come to my defense. It makes me wonder whether it is even worth my efforts to write my weekly columns. I certainly don't do it for money. There is an element of ego, which I cannot deny. It is not critical for me, because I get my kicks out of just learning, knowing and connecting. It certainly reinforces my extremely low opinion of human beings in general and Indians, in particular, who will not stand up for anything, have no beliefs or principles and are obsessed with making money and personal financial security, while professing to be religious and espousing Tyaaga and Aparigrahana and pontificating about Dharma.

Gaurang Bhatt
gaurang bhatt
03/14/2012
Article Comment Well, the author most certainly publishes lot of crapy science articles, as is the case here, some fantastic theory to support evolution like his many articles. Basic questions are the missing link from monkey to human are still in question.
Nature does provides the same building blocks in every spicies but it does not mean that the mutation have happened and evolution have taken place.

I challange the author to postulate whats the next pattern/frontier in evolution of any single spicies leave alone of humans. Its useless to have a very simplestic in the approach or formulation to what is universally visible.

Give ur facts, let science create a new species (which are different or evolved) to supports ur theries.

Andy
03/13/2012
 
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