Wild boar are the wild ancestors of the modern pig. This is why pigs and boar can interbreed – The domestication occurred in Europe, but started about 9,000 years ago, about 3000 years after we started farming crops. It appears to have happened slowly over time, not all at once as some other domestication moves have been. It is thought that this process started in Turkey, and a couple of millennia later in China. There is some evidence that it also occurred elsewhere in Europe.
The modern pig appears to be descended from a variety of different species of wild boar, suggesting a certain amount of mixing of the different domesticated pigs. It is also clear that human preference had a great impact, as very similar pig like animals appeared in several different parts of the world independently.
In the UK, wild boar populations have accidently been created. These have grown fast, and are currently requiring big culls most years. I would like to see some of these boar moved rather than being killed. Forests with wild boar in, are far more healthy with more young saplings naturally sprouting. I believe that we should accept that the boar is back and reintroduce it into every significant area of woodland in existence.
It is true, that they can be dangerous however so can deer. As with all wild animals, provided you do not get too close you should be fine. Now I would argue that natural predators would be the best control on numbers, but I think in the UK we are not there yet.