Why can't Chinu shed his finger off like a lizard's tail?

 It was a hot summer afternoon, and Chinu was happily slurping ice gola with Shweta. They were so busy enjoying their icy sweet that they didn't notice their pet dog Joy was chasing a lizard in the same room. After a good chase and entertainment, Joy finally jumps on the poor lizard, but something happens that makes Chinu jump out of disbelief. The lizard escaped, dropping its tail that was still wriggling!

Chinu goes to the dead tail and calls Shweta to see the bizarre behaviour of the lizard. Chinu, with his eyes widened and mouth open, showing his crooked teeth, asks Shweta, "Didi, how? How can this happen? How can the lizard just run and forget to take its tail? How can its tail fall off and still move?"

Chinu started bombarding Shweta with all sorts of questions all at once. Shweta calms him down and tells him, "Chinu, baby, it is normal in many families of lizards, as much as 13 out of 20, to show such behaviour of self-amputation of an external body part that protrudes out. And you might be surprised, not just lizards, even octopuses, bees, spiders, some crustaceans, and even two species of African spiny rats exhibit this phenomenon. It is scientifically called AUTOTOMY. This signifies the behaviour of an organism where it sheds or discards its appendage to defend itself either by avoidance or protection behaviour."

Chinu wonders how it would help them to protect themselves. To which Shweta explains, "When lizards shed their tail and they keep on wriggling, this distracts the predator, providing a chance to them to escape by providing a deceptive sense of the continued struggle. Also, do you know Chinu, some lizards have elaborately coloured tails like vibrant blue, which diverts the predatory attack towards the tail, away from the body and head?" 

Chinu was highly surprised by this phenomenon. He asks Shweta further, "But, how can a lizard drop off its tail and run away? If we cut off any part of the human body, it keeps on bleeding for so long. Why doesn't happen to the lizards?"

Shweta replies, "Chinu, I like your thought process. This type of autotomy where the organism self-amputees its tail is called CAUDAL AUTOTOMY. And it can happen in two ways. Either the lizard can drop off its tail between the two vertebrae, or the lizard contracts a muscle to fracture a vertebra. The previous one is called INTERVERTEBRAL AUTOTOMY. And the second process is called INTRAVERTEBRAL AUTOTOMY."

Chinu interrupts Shweta midway and says, "But the bones are too strong. Aren't they? Then how can they fracture by contracting a muscle?" 

Shweta explains the presence of zones of weakness, fracture planes across each vertebrae in the mid-part of tail. Which makes it easier for lizard to autotomize its tail. And further she continues to tell him about how the presence of circular muscles called Sphincter, normally maintaining the constriction of a natural body passage, in tail contract around artery present in tail to minimise bleeding. 

Chinu and Shweta were talking, and suddenly Sachin, friend of Chinu, comes to call him to play. He also joins the discussion and asks Shweta, "I've heard that the lizards are able to regrow their shed tail. Is that true?"

Shweta replies, "Yes, it is true. Some animals can fully regenerate their autotomized body parts, whereas some can't. Some have different colour and texture in the regrown appendage, whereas some can have it identical to the original."

Chinu was mesmerised that an organism can shed its body part and run off and still get a new one. How lucky? He asks Shweta, "Then initially, why was the lizard trying to run away from Joy? Why did it not shed its tail off and then go away? it would have been able to distract Joy and escape nicely." 

Shweta throws some light on the part that autotomy is a very costly response for any organism. She tells him that the tails are essential for locomotion and energy storage of fat deposits. If that's been lost, a lizard might have to manage a period of being weak and this might make it loose the societal status that it can have in its colony and its reproductive fitness. 

Chinu and Sachin looks at each other and laughs. Sachin asks, "Do lizards also have societal status?"

Shweta  nods, laughing and says, "They have it based on strength. The weak ones come last."

Chinu, being a naughty kid, tries to pull Sachin's finger and now starts to twist it. Sachin cries of pain and tells Chinu to stop. Chinu says, "I was trying to see if you could also shed off your finger like that lizard." and laughs.

Sachin replies, "We don't have the ability to do so. Do we Shweta didi?"

Shweta tells him, "No Sachin, we can't regrow body parts. Whenever any body part is lost, two responses are induced in the body, the formation of scar tissue and REGENERATION. Humans form scar tissue but there might be a way to regenerate body parts too, but scientists are still midway in discovery."

Chinu tells both, "I'm really looking forward to a time, when i can grow a body part if i loose it."

Shweta replies, "We all do!"

Chinu says, "Then Sachin will be able to grow his head as he lacks one already!"

Sachin laughs and runs after him. Boys start playing and a random incident again becomes so educative. 

Also, isn't it like that in our lives too? We need to learn to be stronger after every setback. Every push that might make us leave behind something, makes us lighter to fly even higher.