Strictly Speaking, Identical Twins are Not Identical
Identical twins are identical by definition only. The definition however does not completely hold up. It is not 100 per cent correct. Friends and family can sometimes tell these twins apart, where strangers cannot. That however often has more to do with their mannerisms than their appearance. Even their mannerisms will be quite similar in many cases.
If one twin gets a tattoo and the other does not, there will of course be an observable difference between the two, but they are still identical. Getting a tattoo doesn’t change the DNA of one of the twins, which still should be identical to that of the other twin, or should it? More about that later.
There Is No Such Thing as a Pair of Identical Twins
If by identical, you mean exactly the same with no ifs, ands, or buts, there is no such things as a pair of identical twins. Personality doesn’t count. These twins don’t need to have identical personalities to be identical, although many of them do. Personalities can be shaped by the environment. The truth is, many of these twins have differing personalities. It’s the environment however that accounts for many of the small, subtle differences that exist between twins. The most telling difference is in the fingerprints. Even inside the womb the environment the twins share is not exactly the same for both. Imagine if the lining of the womb consisted of a very hard material, and that one of the twins happened to be squeezed up against it more often than the other. At birth, that twin might exhibit some subtle or not-so-subtle differences.
The lining of the womb isn’t at all hard however. It is soft and forgiving. The differences in the environments the two babies experience, no matter how small, do have an effect however, and that difference is an important one. As far as anyone has been able to determine, even identical twins do not have the same fingerprints. It has been fairly well established the fingerprints a person has are established by the conditions in the womb. No two people have ever been found to have exactly the same fingerprints, and that appears to count for these twins as well.
Fingerprints Differ – But What About the DNA?
Since the DNA is the same, it would appear that the only way to tell the difference between these twins would be by their fingerprints. Their DNA is not the same however, despite the fact that there has been a long-held belief that it is. Every person’s DNA is unique as far as anyone knows. That doesn’t mean that the differences jump out at you. It takes a little investigating to note these differences. The DNA of a human being matches up pretty close to that of a dog or a horse, and isn’t all that different from the DNA of a butterfly. There is a readily observable difference however. Between 80 and 90 percent of a human’s DNA closely corresponds to the DNA of most other animals. It’s the 10 to 20 per cent that makes us so very different. Individual humans have DNA that is nearly identical to that of all other humans, which is to say it varies from person to person by less that one-tenth of one per cent. That’s more than enough however to tell one person from another, and more than enough to allow every human being to have a unique DNA code.
DNA Appears to Differ – But Barely
What about twins that are exactly alike? It has recently been discovered that their DNA is very close to 100 per cent the same, but ‘very close’ is not quite the same as ‘exactly.’ The difference is much less that a tenth of one percent and may even be much less than one hundredth of one percent, but there is a measurable difference. That is at least the case with those twins who have been tested. Most twins of course have not been tested and quite possibly never will be.
Where It All Starts
These somewhat special types of twins result from a fertilized egg splitting into two separate embryos. No one known why or quite how this happens, but this is where the whole business of being identical gets its start. About 1 in every 250 births produces these types of twins. Heredity in not involved. There does not appear to be any evidence of identical twins running in families. It’s something that just happens.
It’s worth mentioning that many of these twins continue to look like two peas in a pod for most of their lives. As they age however, both genetic and environmentally induced changes can sometimes create noticeable differences. Older twins are often easier to tell apart. The scars of time can make a difference too, but like tattoos, those scars don’t make the twins any less identical. The fact remains, if one commits a crime, and is seen doing so but leaves no fingerprints behind, it can sometimes be quite impossible to tell which of the two is the guilty party, unless their DNA can be traced to the scene of the crime.