See: https://en.wikipedia.org/wiki/Polydactyly
so 1) likely a mutation (or one of your parent was having a 6th finger and had it removed and for some reason chose not to tell or ignore it)
2) 50% chance of them having it
3) It would be stupid to do it by yourself, but if you are not satisfied by your first surgery, go see a doctor to see what could be done (plastic surgeon?)

It’s not necessarily a mutation – fingers develop in a fetus as a response to secreted chemicals, and that can be affected by certain allele combinations, but also by environmental interactions (womb chemistry, for instance).

My professor was just talking about Polydactyly (Dominant disorder) today and said that the many children that are born with an extra piece of skin that does not have a bone inside is NOT considered Polydactyly and thus is not an inherited, dominant mutation. Apparently, sometimes extra skin, with or without a nail, just forms on the hands and feet resembling a finger or toe and the doctors remove it at birth for cosmetic purposes. People who have Polydactyly have muscle and nerve function in the sixth digit as well as a bone. You will need to ask your parents if there was an X-ray performed to determine whether or not there was a bone in there and that will let you know if you carry the dominant gene. My professor is a Geneticist and I would believe her over anything read on Wikipedia. I just checked out the link and it has inaccurate information listed. But then again, my professor could make a mistake, but being her small lecture on Polydactyly centered upon distinguishing it from extra skin that may form, I tend to believe her.

You should never perform your own surgery because you can risk serious infection and uncontrolled bleeding, or worse. You have a lot of bacteria on your skin and no matter how well you think you clean it, it’s never clean enough. The tools you use would also not be sterile and you also do not know how to perform surgery (that’s why doctors go to school for many years so that they can learn properly). You could cut a vein or an artery and then you would be in big trouble…not to mention that doctors don’t just cut off parts like that. There is a fine technique that utilizes lasers, sutures and sometimes even skin grafting, something you are incapable of performing in your own home. If the skin is bothersome and causing pain or getting in the way, you could see if your insurance will cover the removal. Otherwise, you would have to pay a plastic surgeon to remove it.

The presence of an extra sixth finger or toe, a very common congenital malformation (birth defect).

This condition is called hexadactyly. The word hexadactyly literally means six digits. In medical usage, hexadactyly does not specify whether the six digits are fingers or toes (although in Greek "dactylos" is without equivocation a finger).

The 6th digit can be located in three different locations: on either side of the extremity or somewhere in between. With the hand for example, the extra finger can be out beyond the little finger (which is called ulnar hexadactyly) or out beyond the thumb (radial hexadactyly) or, finally, between two of the normally expected fingers (intercalary hexadactyly).

Far and away the most frequent form of hexadactyly is ulnar (postaxial) hexadactyly. Next comes radial (preaxial) hexadactyly. And far and away the rarest form of hexadactyly is intercalary hexadactyly.

Hexadactyly in itself can be innocuous, absolutely harmless and very easily remedied, when the hexadactyly is an isolated finding and the baby is otherwise entirely normal. Ulnar hexadactyly with just a rudimentary tag of a sixth digit, for instance, can be very simply treated by tying it off with one suture.

However, according to Plastic Surgeon Dallas hexadactyly can also be one of a number of congenital malformations affecting the baby. These cases are more complicated and require further evaluation.

Hexadactyly can be seen on some prenatal ultrasound scans. To present a real case, an ultrasound scan showed "a rudimentary 6th digit on both hands." A more detailed ultrasound confirmed "a 6th digit on ulnar side of each hand" and showed that 6th digit "is small and just a floppy skin tag." No other morphological (physical) abnormalities of the fetus were visible. Another ultrasound with even greater resolution revealed "a rudimentary digit/skin tag on the palmar surface of the hand lying between the 4th and 5th digits." Again, no abnormality was seen elsewhere on the baby.

The differential diagnostic list of disorders causing hexadactyly is pretty long. But many were excluded by the absence of other malformations. It also seemed a particular type of hexadactyly. If it were an intercalated extra digit (with the extra finger situated between the other fingers), the list would be much smaller and only a very few entities such as the Pallister-Hall syndrome and Greig syndrome (but there would usually be other things to see in either of these 2 syndromes). The final diagnosis in this case has not yet been made. We have present the case to convey the quandary that can occur when hexadactyly is discovered antenatally (before birth) today.

Hexadactyly is the most frequent form of polydactyly, a diagnosis that encompasses all cases of extra digits, irrespective of the number of extra digits in a particular case.

Yes it is quite clearly and well defined on wikipedia also.

Wiki is a very powerful tool.

Polydactyly in cats is not considered a deformity but having "extra genes". I never really looked into the topic beyond that but now I am interested. I think this is the case of if it continues to happen more and more, maybe it will become "normal".

Is it disadvantageous to have a sixth finger on our hands in our current stage of evolution? Just curious.