Head binding now and the past

[brewer]

WTF?

You don't cut the tail off, you breed shorter tails thru successive generations. It's about genetics, not what you do to the animal after.

That depends what you are affecting via chemical or mechanical means before the rat procreates and how many successive generations you cut the tail and say keep breeding the rats with the closest to average tail size. Simply cutting the tail off over successive generations may not have any real effect however there will be some biological workings. you may have to damage the high stem cell areas with enough damage to cause an effect over enough generations. There may well be a good method in biology to maintain stability across generations of a creature but some effects will have a generational impact beyond breeding choice including dietary changes. 
With artificial cranial deformation this was done for 10's of 1000's of years over countless generations. they may have even breed more with those best afflicted by the practice just to confuse issues.
so less than 30 generations of elephant is enough for tuskless elephants to come and you say this had nothing to do with the dna being effected by constant damage to the populations tusks and instead is purely down to breeding and survival.
I think the real answer is more messy and biologically complicated myself.

You do not understand evolution or genetics at all. You're referring to selective breeding, whether through environment or outside (manipulated) forces.

If outside vectors (tusk hunters) leave only the aberrant (those without tusks) to reproduce (within a small breeding herds) then this will result aberrant's (do some research in fruit flies . That's forced environmental change, which can happen but over many, many generations, and not do to the short tern human effect. How many outside forces breed tail -less rats? Only tails-less rats will become dominant if the environment supports that rats without tails are more successful.

Don't think I'm right? Look at dog breeding. Genetics can be manipulated in a species.

High stem cell? You need to provide more explanation-documentation. Also explain these chemical effects? What the fuck is either of those?

Artificial cranial deformation is a process applied after birth, not genetic breeding for deformation.