More anatomy changes

People are claiming the two holes seen in the human chin were never there, and it's a Mandela Effect. They are placed either side of the jaw, at the front, and are seen today in most skull images and representations. It's been pointed out by doctors they are for nerves and blood vessels, and even that Neanderthals had them but were covered by bone, so there is evidence of the structure being evolutionary, although there is no suggestion homo sapiens humans evolved from them, of course.

One explanation for this comes down to the practicalities of teaching. When in school, the fake skulls made to illustrate anatomy may well have not shown them due to the complexities of their manufacture, so children would first learn of the skull without them.

They are called the "Mental foramina"

It's been pointed out that if these holes are truly new, there must have been a way for the nerves and blood vessels which pass through them to perform their function some other way. They are found to form differently in children, where it changes direction as the child grows older in line with the way teeth act differently at this stage in their growth too. There's also a marked differences between males and females in this regard, which has allowed skilled forensic pathologists to quickly determine the sex of a victim from the skull alone, since this is one of the indicators they can look for.

There are actually two main holes on either side of the jaw, the mandibular foramen through which the mandibular nerve and various blood vessels run, and the mental foramen carrying the inferior alveolar nerve.

As well as the explanation regarding simplifying model skulls mentioned earlier, there is something else which would contribute to this. Most of the time a skull appears, it will have been hand drawn or rendered otherwise as a work of art. The two holes in the jaw would be a detail the creator of the work was either unaware of or just deemed an unnecessary detail. This in turn means those familiar with the bulk of the depictions just wouldn't be aware of them because they weren't shown.

Next time you see a skull, on anything from a heavy metal album cover to a skeleton discovered in a horror movie, look out for them and the chances are they'll still be missing.